You searched for subject:(Drag Reduction).
Showing records 1 – 30 of
167 total matches.
◁ [1] [2] [3] [4] [5] [6] ▶
Texas A&M University
1.
Gawloski, Nicholas Adam.
Experimental Investigation of Pulsed Electrical Discharge Energy Deposition in Supersonic Flows.
Degree: MS, Mechanical Engineering, 2017, Texas A&M University
URL: http://hdl.handle.net/1969.1/161614 
► Energy deposition in the form of a direct current spark discharge in Mach 2.2 flow is experimentally investigated, to measure the conversion efficiency of electrical…
(more)
▼ Energy deposition in the form of a direct current spark discharge in Mach 2.2 flow is experimentally investigated, to measure the conversion efficiency of electrical energy into thermal energy. The energy is impulsively deposited into to the flow. This impulsive deposition occurs much faster than the flow can react, creating a strong blast wave and a high temperature, high pressure region in the flow. The plasma discharge is created between two sharpened tungsten electrodes inclined into the flow, powered by a pulsing high voltage RC circuit. Schlieren imagery was utilized to track the expansion of the blast wave and the expansion of the high temperature, high pressure region created by the spark discharge into a low density region.
To estimate the conversion efficiency of electrical energy into the thermal energy in the flow, a high temperature thermodynamic heating and expansion model was developed to simulate the deposition process. The model consisted of two portions. First, the thermodynamic properties of N2, O2, N, O, Ar, were calculated from the NASA PAC database, valid for temperatures 200-20,000K. A high temperature air mixture was then constructed from the five species assuming chemical equilibrium for temperature from 200-20,000K. Second, a heating and expansion model was developed utilizing the high temperature air properties. The energy deposition was modeled as a constant volume heating process to simulate its impulsive nature. The initial volume of the plasma is calculated from direct imaging of the discharge at delays ranging from 80-120ns. The resulting high temperature, high pressure region is then mixed with varying amounts of ambient air to simulate heat transfer. The high temperature region is then expanded isentropically back to ambient pressure, where the final volume was compared to the experimental Schlieren images to estimate the conversion efficiency.
Three different capacitors were used during experimentation to vary the input electrical energy three orders of magnitude; specifically, the energies were calculated to be: 3.4, 20.8 and 203mJ per pulse. The range of possible efficiencies for the three cases was found to be: 70-90%, 14-30%, and 5-12%. The lower energy case was found to be the most efficient with regards to energy conversion. However, the largest energy case was found to be more effective because it resulted in the region with the highest expanded temperature (4150K) and lowest expanded density (0.017 [kg m^-3]) in its final expanded state.
Advisors/Committee Members: Staack, David (advisor), Kulatilaka, Waruna (committee member), Tichenor, Nathan (committee member).
Subjects/Keywords: Energy Deposition; Drag Reduction
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Gawloski, N. A. (2017). Experimental Investigation of Pulsed Electrical Discharge Energy Deposition in Supersonic Flows. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/161614
Chicago Manual of Style (16th Edition):
Gawloski, Nicholas Adam. “Experimental Investigation of Pulsed Electrical Discharge Energy Deposition in Supersonic Flows.” 2017. Masters Thesis, Texas A&M University. Accessed March 07, 2021.
http://hdl.handle.net/1969.1/161614.
MLA Handbook (7th Edition):
Gawloski, Nicholas Adam. “Experimental Investigation of Pulsed Electrical Discharge Energy Deposition in Supersonic Flows.” 2017. Web. 07 Mar 2021.
Vancouver:
Gawloski NA. Experimental Investigation of Pulsed Electrical Discharge Energy Deposition in Supersonic Flows. [Internet] [Masters thesis]. Texas A&M University; 2017. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/1969.1/161614.
Council of Science Editors:
Gawloski NA. Experimental Investigation of Pulsed Electrical Discharge Energy Deposition in Supersonic Flows. [Masters Thesis]. Texas A&M University; 2017. Available from: http://hdl.handle.net/1969.1/161614
2.
Silvestri, Anton.
The attenuation of sweep events within the turbulent boundary layer over a flat plate using a micro-cavity array.
Degree: 2018, University of Adelaide
URL: http://hdl.handle.net/2440/118055
► For most aeronautical applications skin friction drag is a significant issue for efficient operation. It is estimated that 49% of the total drag an aircraft…
(more)
▼ For most aeronautical applications skin friction
drag is a significant issue for efficient operation. It is estimated that 49% of the total
drag an aircraft experiences is due to skin friction
drag and a small
reduction of 5% would currently result in an annual saving of $3.3 billion US dollars. The large Reynolds number at which aerospace applications typically operate results in a turbulent boundary layer, which causes a large increase in shear stresses and a subsequent increase in skin friction
drag. The key culprits for the large shear stresses are the turbulent boundary layer structures that form once the boundary layer transitions from the initial laminar state, the most influential of which are the coherent structures. These structures pump fluid into (sweep) and away (ejection) from the near wall region and generate the shear stresses. Hence the aim of this research is to manipulate the turbulent boundary layer to reduce the effect of the aforementioned coherent structures. Specific attention has been applied to the passive application of a micro-cavity array as a potential control technique to attenuate the coherent structures. The micro-cavity array consists of a cavity arranged flush with the surface, underneath of which is a backing cavity similar to the design of a Helmholtz resonator. As a passive control technique, this device aims to have the advantages of an easy implementation and the absence of an external power source, with targeted control of the coherent structures commonly achieved by active systems. The micro-cavity array aims to capture and dampen the sweep events, therefore reducing the strength of both the ejection and sweep events due to their high dependence on one another. As such the present work assesses the ability of an array of micro-cavities to reduce the turbulent properties of a fully developed boundary layer. Previous results from the flow excited Helmholtz resonator and a two-dimensional square cavity on a flat plate have confirmed the potential of the micro-cavity array. Both techniques achieved successful control of the boundary layer and attenuation of the coherent structures. However these applications had limitations at higher Reynolds numbers and as a result a smaller device such as the micro-cavity is proposed and forms the basis of this thesis. Being of smaller size, the shear layer is hypothesised not to break apart while traversing the small orifices of the micro-cavity, which occurs for the larger flow excited Helmholtz resonator and results in an adverse pressure gradient and an undesirable increase in the disturbances and viscous
drag in the boundary layer. To investigate the potential of the proposed micro-cavity array, the device has been thoroughly examined experimentally at a range of Reynolds numbers (1195 < Reθ < 3771). Experiments were predominately focused on identifying the potential of the micro-cavity, whilst evaluating the impact of the orifice distribution along the cavity array and the effect of other geometric parameters, including the length of the…
Advisors/Committee Members: Arjomandi, Maziar (advisor), Chin, Rey (advisor), Cazzolato, Benjamin (advisor), Zander, Anthony (advisor), School of Mechanical Engineering (school).
Subjects/Keywords: Fluid mechanics; turbulence; drag reduction
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Silvestri, A. (2018). The attenuation of sweep events within the turbulent boundary layer over a flat plate using a micro-cavity array. (Thesis). University of Adelaide. Retrieved from http://hdl.handle.net/2440/118055
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Silvestri, Anton. “The attenuation of sweep events within the turbulent boundary layer over a flat plate using a micro-cavity array.” 2018. Thesis, University of Adelaide. Accessed March 07, 2021.
http://hdl.handle.net/2440/118055.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Silvestri, Anton. “The attenuation of sweep events within the turbulent boundary layer over a flat plate using a micro-cavity array.” 2018. Web. 07 Mar 2021.
Vancouver:
Silvestri A. The attenuation of sweep events within the turbulent boundary layer over a flat plate using a micro-cavity array. [Internet] [Thesis]. University of Adelaide; 2018. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/2440/118055.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Silvestri A. The attenuation of sweep events within the turbulent boundary layer over a flat plate using a micro-cavity array. [Thesis]. University of Adelaide; 2018. Available from: http://hdl.handle.net/2440/118055
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
3.
Huang, Weicong.
Drag Reduction in Pipeline by Polymer-Surfactant and Polymer-Polymer Mixtures.
Degree: 2015, University of Waterloo
URL: http://hdl.handle.net/10012/9853
► Extensive researches have been conducted to investigate into the drag reduction behavior of the polymer-surfactant mixture and the polymer-polymer mixture. The drag reduction effect of…
(more)
▼ Extensive researches have been conducted to investigate into the drag reduction behavior of the polymer-surfactant mixture and the polymer-polymer mixture. The drag reduction effect of PAM (polyacrylamide), PEO (polyethylene oxide) and CMC (carboxymethyl cellulose) has already been studied respectively. However, the drag reduction effects of the combination of these polymers have not been studied before. It is interesting to investigate into these combinations because the synergy between different polymers can enhance the drag reduction effect under the right condition.
SDS (sodium dodecyl sulfate) is a surfactant widely used in many commercially available detergents. When dissolved in water and circulated in the flow loop, the drag reduction effect of SDS has also been observed. Therefore, the combination of PAM and SDS is also worth exploring. The synergy between the polymer and the surfactant may strengthen the drag reduction effect.
In this thesis, the drag reduction effects are investigated for the following combinations: the PAM-SDS system, the PAM-CMC system and the PEO-CMC system. The mixed solutions are circulated in the flow loop, where the pressure drop over a certain distance and the flow rate are recorded in order to plot the friction factor against the Reynolds number. In addition, the viscosity, conductivity and surface tension of the mixed solutions are studied at bench-scale to look for the synergy in the mixed system.
Subjects/Keywords: Drag reduction polymer surfactant mixture
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Huang, W. (2015). Drag Reduction in Pipeline by Polymer-Surfactant and Polymer-Polymer Mixtures. (Thesis). University of Waterloo. Retrieved from http://hdl.handle.net/10012/9853
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Huang, Weicong. “Drag Reduction in Pipeline by Polymer-Surfactant and Polymer-Polymer Mixtures.” 2015. Thesis, University of Waterloo. Accessed March 07, 2021.
http://hdl.handle.net/10012/9853.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Huang, Weicong. “Drag Reduction in Pipeline by Polymer-Surfactant and Polymer-Polymer Mixtures.” 2015. Web. 07 Mar 2021.
Vancouver:
Huang W. Drag Reduction in Pipeline by Polymer-Surfactant and Polymer-Polymer Mixtures. [Internet] [Thesis]. University of Waterloo; 2015. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/10012/9853.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Huang W. Drag Reduction in Pipeline by Polymer-Surfactant and Polymer-Polymer Mixtures. [Thesis]. University of Waterloo; 2015. Available from: http://hdl.handle.net/10012/9853
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Delft University of Technology
4.
Martinez de la Cruz, Roberto (author).
Underwater Drag Reduction: Air Layer Stability over SuperHydrophobic Surface under Turbulent Conditions: A thesis submitted for the degree of MSc Aerospace Engineering at TU Deflt.
Degree: 2019, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:b401d3a9-4800-4340-8c78-50a3fbae299b
► Framed in the current trend of global energetic efficiency, active drag reduction techniques in water vehicles have regained popularity in the last decades thanks to…
(more)
▼ Framed in the current trend of global energetic efficiency, active
drag reduction techniques in water vehicles have regained popularity in the last decades thanks to the intense research in the air lubrication approach. Within the last decade, bubbly
drag reduction has yielded its place to air layer
drag reduction, in which a thin, continuous air layer is produced under the ship’s hull. Reductions in friction
drag have shown to be between the 80 and 99% and net energy savings of around 8-12 % have been predicted, which is however probably not enough to compensate the complexity of the system. Nevertheless, by coating the lower part of the hull with a superhydrophobic coating, C. Peifer et al. (2019) showed that air flow requirements to obtain a stable air layer diminished by a factor of three. Thereportpresented here is a first study of the mechanisms that enhance the air layer stability when combined with a superhydrophobic surface. Water impact dynamics and free surface - turbulence interaction are studied experimentally and numerically respectively. Water behaviour upon impact has been investigated through an ascending jet impacting on the underside of four different surfaces with contact angles ranging from 45 to 150 degrees, obtaining the plate forces and top and side views of the water spread on the surface. Interesting results regarding the collapse of the spread area when a modified Weber number is used has been obtained. Two characteristic dewetting mechanisms for surfaces with low and high contact angle have been identified and explained by a simple theoretical model. Furthermore, possible independence of the friction coefficient on the surface wettability characteristic has been found. When plotted against the streamwise Reynolds number all surfaces collapse in the theoretical Blasius laminar friction coefficient, which suggests that once the surface is fully wetted (Wenzel state), the lower dimensional
drag seen in (super)hydrophobic surfaces is due solely to their smaller contact area. To the best of our knowledge, these comprise the first experiments in which area and force were measured in a scenario in which viscosity, inertia, surface tension and gravity shape the water flow characteristics. On the other hand, a numerical model based on the classic elastic membrane concept has been employed to represent the deformations due to turbulence pounding in an air-water interface. Although further adjustments are needed, the model has been able to predict the tow tank experiments in C. Peifer et al. (2019) by using the surface-dependent water spread obtained in the water impact experiment. The dependence of the critical air flux to form a stable air layer on the surface wettability characteristics can therefore be predicted.
Advisors/Committee Members: Delft University of Technology (degree granting institution).
Subjects/Keywords: Superhydrophobic Surfaces; Air Layer Drag Reduction; Drag Reduction; Multiphase Flow
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Martinez de la Cruz, R. (. (2019). Underwater Drag Reduction: Air Layer Stability over SuperHydrophobic Surface under Turbulent Conditions: A thesis submitted for the degree of MSc Aerospace Engineering at TU Deflt. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:b401d3a9-4800-4340-8c78-50a3fbae299b
Chicago Manual of Style (16th Edition):
Martinez de la Cruz, Roberto (author). “Underwater Drag Reduction: Air Layer Stability over SuperHydrophobic Surface under Turbulent Conditions: A thesis submitted for the degree of MSc Aerospace Engineering at TU Deflt.” 2019. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:b401d3a9-4800-4340-8c78-50a3fbae299b.
MLA Handbook (7th Edition):
Martinez de la Cruz, Roberto (author). “Underwater Drag Reduction: Air Layer Stability over SuperHydrophobic Surface under Turbulent Conditions: A thesis submitted for the degree of MSc Aerospace Engineering at TU Deflt.” 2019. Web. 07 Mar 2021.
Vancouver:
Martinez de la Cruz R(. Underwater Drag Reduction: Air Layer Stability over SuperHydrophobic Surface under Turbulent Conditions: A thesis submitted for the degree of MSc Aerospace Engineering at TU Deflt. [Internet] [Masters thesis]. Delft University of Technology; 2019. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:b401d3a9-4800-4340-8c78-50a3fbae299b.
Council of Science Editors:
Martinez de la Cruz R(. Underwater Drag Reduction: Air Layer Stability over SuperHydrophobic Surface under Turbulent Conditions: A thesis submitted for the degree of MSc Aerospace Engineering at TU Deflt. [Masters Thesis]. Delft University of Technology; 2019. Available from: http://resolver.tudelft.nl/uuid:b401d3a9-4800-4340-8c78-50a3fbae299b
Delft University of Technology
5.
Hoogendoorn, Marijn (author).
Base Drag Reduction of Heavy Duty Vehicles by Combining a Tail and Guide Vanes: A Numerical and Experimental Analysis.
Degree: 2018, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:bd10a9ef-54df-47fd-b8c2-5a9d5d9afa03
► To limit the threat posed by global climate change it is vital to reduce the emissions of the transport sector in the short term. Two…
(more)
▼ To limit the threat posed by global climate change it is vital to reduce the emissions of the transport sector in the short term. Two existing aerodynamic add-on devices for the rear-end of a heavy duty vehicle, a tail and guide vanes, are combined in an attempt to achieve a larger
drag reduction. A research is performed using numerical simulations and a wind tunnel experiment in the Open Jet Facility to gain insight in the interaction between the tail and the guide vane. It was found that the guide vane is able to further increase the base pressure of the vehicle, but that the
drag reduction is sensitive to the
drag of the vane. Due to the interaction between the tail and the guide vane the largest
drag reduction is achieved when the guide vane is operating at its minimum
drag condition.
Advisors/Committee Members: van Raemdonck, Gandert (mentor), Timmer, Nando (mentor), Delft University of Technology (degree granting institution).
Subjects/Keywords: bluff body; Aerodynamic drag; drag reduction; heavy duty vehicle
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Hoogendoorn, M. (. (2018). Base Drag Reduction of Heavy Duty Vehicles by Combining a Tail and Guide Vanes: A Numerical and Experimental Analysis. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:bd10a9ef-54df-47fd-b8c2-5a9d5d9afa03
Chicago Manual of Style (16th Edition):
Hoogendoorn, Marijn (author). “Base Drag Reduction of Heavy Duty Vehicles by Combining a Tail and Guide Vanes: A Numerical and Experimental Analysis.” 2018. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:bd10a9ef-54df-47fd-b8c2-5a9d5d9afa03.
MLA Handbook (7th Edition):
Hoogendoorn, Marijn (author). “Base Drag Reduction of Heavy Duty Vehicles by Combining a Tail and Guide Vanes: A Numerical and Experimental Analysis.” 2018. Web. 07 Mar 2021.
Vancouver:
Hoogendoorn M(. Base Drag Reduction of Heavy Duty Vehicles by Combining a Tail and Guide Vanes: A Numerical and Experimental Analysis. [Internet] [Masters thesis]. Delft University of Technology; 2018. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:bd10a9ef-54df-47fd-b8c2-5a9d5d9afa03.
Council of Science Editors:
Hoogendoorn M(. Base Drag Reduction of Heavy Duty Vehicles by Combining a Tail and Guide Vanes: A Numerical and Experimental Analysis. [Masters Thesis]. Delft University of Technology; 2018. Available from: http://resolver.tudelft.nl/uuid:bd10a9ef-54df-47fd-b8c2-5a9d5d9afa03
Loughborough University
6.
Varney, Max.
Base drag reduction for squareback road vehicles.
Degree: PhD, 2019, Loughborough University
URL: https://doi.org/10.26174/thesis.lboro.11823759.v1
;
https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.799187
► As we are in the throes of a climate crisis, we need to scrutinise how our everyday activity impacts it. A significant portion of the…
(more)
▼ As we are in the throes of a climate crisis, we need to scrutinise how our everyday activity impacts it. A significant portion of the global CO 2 emissions are a result of passenger vehicles (16%) with a significant portion of these being sports utility vehicle geometries (37.5%). The squareback nature of sports utility vehicles is desired by some manufacturers to maintain brand identity, but these geometries are not typically aerodynamic. On top of this, the emissions regulations do not take into account realistic conditions that a vehicle will operate in, resulting in an underestimation of their impact on the global CO2 emissions. This thesis implements cavities and small trailing edge side edge tapers on a quarter scale Windsor model (with and without wheels) at more realistic flow conditions to generalise drag reduction techniques. These generalisations focus on the base of the model as this region generates a significant portion of the overall drag. As the geometries are unlikely to be implemented on a full-scale vehicle, the generalisations provide a goal for a lower drag vehicle which can be applied to any baseline geometry. Irrespective of the device used it was found that a way to reduce drag generally was to force the wake into a balanced, symmetric condition. The lateral symmetry is shown to reduce the instantaneous base drag at yaw on the baseline geometry, but also the mean base drag with a cavity or side edge tapering at yaw. The vertical symmetry is shown to improve the mean base drag on the Windsor model with wheels, both with a cavity and with the side edge tapering at all yaw angles tested. A symmetric, balanced wake was shown not to be the only route to low drag. The cavities showed a reduction in base drag due to the reduced flow velocity in the wake with flow field measurements inside the cavity, while presenting an asymmetric wake. The tapering generated base drag reductions with slower velocities parallel to the base, higher velocities perpendicular to the base and shorter wakes that were upwash or downwash dominated.
Subjects/Keywords: Base drag; bluff body; drag reduction; suv; cavities; tapers; fundamental flow
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Varney, M. (2019). Base drag reduction for squareback road vehicles. (Doctoral Dissertation). Loughborough University. Retrieved from https://doi.org/10.26174/thesis.lboro.11823759.v1 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.799187
Chicago Manual of Style (16th Edition):
Varney, Max. “Base drag reduction for squareback road vehicles.” 2019. Doctoral Dissertation, Loughborough University. Accessed March 07, 2021.
https://doi.org/10.26174/thesis.lboro.11823759.v1 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.799187.
MLA Handbook (7th Edition):
Varney, Max. “Base drag reduction for squareback road vehicles.” 2019. Web. 07 Mar 2021.
Vancouver:
Varney M. Base drag reduction for squareback road vehicles. [Internet] [Doctoral dissertation]. Loughborough University; 2019. [cited 2021 Mar 07].
Available from: https://doi.org/10.26174/thesis.lboro.11823759.v1 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.799187.
Council of Science Editors:
Varney M. Base drag reduction for squareback road vehicles. [Doctoral Dissertation]. Loughborough University; 2019. Available from: https://doi.org/10.26174/thesis.lboro.11823759.v1 ; https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.799187
Delft University of Technology
7.
Claro Dittrich, Eric (author).
Transonic Dimples: An experimental study of the flow structures formed at transonic speeds over dimpled surfaces.
Degree: 2021, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:661ddb37-f84c-404e-b471-cdf925297fd7
► Dimples are shallow surface indentations that have been recently considered as a passive viscous drag reducing technique for turbulent boundary layers. Studies so far were…
(more)
▼ Dimples are shallow surface indentations that have been recently considered as a passive viscous
drag reducing technique for turbulent boundary layers. Studies so far were limited to incompressible low-Re flows and display little consensus on whether dimples can actually produce net improvements in total
drag. Conversely, dimple geometry can be regarded as the inverse of transonic bumps, a matured wave
drag reduction. In light of this, this thesis sets off to analyse the flow structures that arise over dimples at transonic speeds provide, serving as an initial assessment of their wave
drag reducing potential. A transonic flow was reproduced experimentally using an asymmetric nozzle. Then, the performance of five dimple designs was evaluated against the criteria adopted for transonic bumps. Measurements included Schlieren, surface pressure and PIV. Results reveal that small spherical dents seem to produce spanwise excitations that subdue the detrimental effects of expansion fans formed at their edges, and ultimately allow for a higher momentum retention across the interaction.
Advisors/Committee Members: van Oudheusden, B.W. (mentor), Schrijer, F.F.J. (graduation committee), van Campenhout, O.W.G. (graduation committee), Delft University of Technology (degree granting institution).
Subjects/Keywords: wave drag; shock wave; dimples; drag reduction; transonic flow
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Claro Dittrich, E. (. (2021). Transonic Dimples: An experimental study of the flow structures formed at transonic speeds over dimpled surfaces. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:661ddb37-f84c-404e-b471-cdf925297fd7
Chicago Manual of Style (16th Edition):
Claro Dittrich, Eric (author). “Transonic Dimples: An experimental study of the flow structures formed at transonic speeds over dimpled surfaces.” 2021. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:661ddb37-f84c-404e-b471-cdf925297fd7.
MLA Handbook (7th Edition):
Claro Dittrich, Eric (author). “Transonic Dimples: An experimental study of the flow structures formed at transonic speeds over dimpled surfaces.” 2021. Web. 07 Mar 2021.
Vancouver:
Claro Dittrich E(. Transonic Dimples: An experimental study of the flow structures formed at transonic speeds over dimpled surfaces. [Internet] [Masters thesis]. Delft University of Technology; 2021. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:661ddb37-f84c-404e-b471-cdf925297fd7.
Council of Science Editors:
Claro Dittrich E(. Transonic Dimples: An experimental study of the flow structures formed at transonic speeds over dimpled surfaces. [Masters Thesis]. Delft University of Technology; 2021. Available from: http://resolver.tudelft.nl/uuid:661ddb37-f84c-404e-b471-cdf925297fd7
UCLA
8.
Xu, Muchen.
Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows.
Degree: Mechanical Engineering, 2016, UCLA
URL: http://www.escholarship.org/uc/item/29r7038c
► Sustaining a gas layer on them in liquid, superhydrophobic (SHPo) surfaces have attracted enormous attention due to the possibility of reducing friction drag in numerous…
(more)
▼ Sustaining a gas layer on them in liquid, superhydrophobic (SHPo) surfaces have attracted enormous attention due to the possibility of reducing friction drag in numerous flow applications. Although many SHPo surfaces proved to reduce drag significantly (e.g., > 10%) in microchannel flows and certain SHPo surfaces proved to have an unprecedentedly large slip length (e.g., > 100 microns), a significant drag reduction is still elusive in turbulent flows that reflect most applications, such as watercraft in marine environment. Recognizing the gas layer (called plastron) as the key and studying its robustness under water of varying depths, we first conclude that the SHPo surfaces capable of a significant drag reduction cannot maintain the plastron indefinitely if submerged deeper than a few centimeters. By developing a high-resolution shear sensor for centimeters-size sample surfaces and using silicon SHPo surfaces that keep plastron more robust than others, we obtain up to ~25% drag reduction in turbulent boundary layer flows at Reynolds numbers up to 1.1x107. Obtained at a high-speed water tunnel and a high-speed tow tank, the results also indicate that the drag reduces more with increasing Reynolds number, corroborating the numerical studies in the literature. Moreover, we develop and conduct SHPo drag experiments using a real boat in marine conditions for the first time, achieving ~20% drag reduction. Finally, a scalable fabrication process is developed for scale-up manufacturing of both passive and semi-active SHPo surfaces. For the semi-active SHPo surfaces, i.e., SHPo surfaces with self-regulating gas restoration capability, we propose and demonstrate a gas generation mechanism that does not require any external power input.
Subjects/Keywords: Mechanical engineering; drag reduction; superhydrophobic; turbulent
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Xu, M. (2016). Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows. (Thesis). UCLA. Retrieved from http://www.escholarship.org/uc/item/29r7038c
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Xu, Muchen. “Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows.” 2016. Thesis, UCLA. Accessed March 07, 2021.
http://www.escholarship.org/uc/item/29r7038c.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Xu, Muchen. “Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows.” 2016. Web. 07 Mar 2021.
Vancouver:
Xu M. Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows. [Internet] [Thesis]. UCLA; 2016. [cited 2021 Mar 07].
Available from: http://www.escholarship.org/uc/item/29r7038c.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Xu M. Design, Fabrication, and Evaluation of Superhydrophobic (SHPo) Surfaces for Drag Reduction in Turbulent Boundary Layer Flows. [Thesis]. UCLA; 2016. Available from: http://www.escholarship.org/uc/item/29r7038c
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
McMaster University
9.
ZHU, LU.
Inertia- and elasticity-driven turbulence in viscoelastic fluids with high levels of drag reduction.
Degree: PhD, 2019, McMaster University
URL: http://hdl.handle.net/11375/24887
► In dilute polymer solution, polymers are able to change the flow structures and suppress the intensity of turbulence, resulting in a considerable friction drag reduction…
(more)
▼ In dilute polymer solution, polymers are able to change the flow structures and suppress the intensity of turbulence, resulting in a considerable friction
drag reduction (DR). Despite the extraordinary progress made in the past few decades, some critical questions remain unanswered. This dissertation will try to address two fundamental questions in dilute polymeric turbulence: (I) interactions between polymers and turbulent motions during the qualitative low-extent to high-extent
drag reduction (LDR and HDR) transition in inertia-driven turbulence, (II) roles of the inertia- and elasticity-driven turbulent motions in the dynamics of high elasticity polymeric flows.
Many studies in the area of DR turbulence have been focused on the onset of DR and the maximum
drag rection (MDR) asymptote. Between these two distinct stages, polymeric turbulent flows can also be classified into the qualitative LDR and HDR stages. Understanding the polymer-turbulence interactions during the drastic LDR-HDR transition is of vital importance for the development of efficient flow control technology. However, knowledge regarding this qualitative transition is still limited. In our DNS (direct numerical simulation) study, differences between the LDR and HDR stages are presented by a number of sharp changes in flow structures and statistics.
Drag reduction in the flows is thus governed by two different mechanisms. The first is introduced at the onset of DR, which has been well explained by the indiscriminate suppression of turbulent fluctuations during the coil-stretch transition of polymers. The second mechanism starts at the LDR-HDR transition but its physical origin is not clear. Based on instantaneous observations and indirect statistical evidence, we proposed that polymers, after the LDR-HDR transition, could suppress the lift-up process of the near-wall vortices and modify the turbulent regeneration cycles. However, direct evidence to support this hypothesis is not available without a statistical analysis of the vortex configurations. Therefore, a new vortex tracking algorithm – VATIP (vortex axis tracking by iterative propagation) – is developed to analyze statistically the configurations and distribution of vortices. Implementing this method in the polymeric turbulence demonstrates that the lift-up process of streamwise vortices in the buffer layer is restrained at HDR, while the generation of hairpins and other three-dimensional vortices is suppressed. In addition, the characteristic lifting angle of conditional eddies extracted by a conditional sampling method is found to be larger in HDR than in the Newtonian turbulence. These observations all support our hypothesis about the mechanism of LDR-HDR transition.
Research on the low elasticity turbulence usually considered the flow motions to be Newtonian-like. Turbulence here is driven by the inertial force (and hence called ``inertia-driven'' turbulence (IDT)) while polymers are responsible for dissipating turbulent kinetic energy. In the high elasticity turbulence, recent…
Advisors/Committee Members: Xi, Li, Chemical Engineering.
Subjects/Keywords: Turbulent Flows; Vortex Dynamics; Viscoelasticity; Drag Reduction
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
ZHU, L. (2019). Inertia- and elasticity-driven turbulence in viscoelastic fluids with high levels of drag reduction. (Doctoral Dissertation). McMaster University. Retrieved from http://hdl.handle.net/11375/24887
Chicago Manual of Style (16th Edition):
ZHU, LU. “Inertia- and elasticity-driven turbulence in viscoelastic fluids with high levels of drag reduction.” 2019. Doctoral Dissertation, McMaster University. Accessed March 07, 2021.
http://hdl.handle.net/11375/24887.
MLA Handbook (7th Edition):
ZHU, LU. “Inertia- and elasticity-driven turbulence in viscoelastic fluids with high levels of drag reduction.” 2019. Web. 07 Mar 2021.
Vancouver:
ZHU L. Inertia- and elasticity-driven turbulence in viscoelastic fluids with high levels of drag reduction. [Internet] [Doctoral dissertation]. McMaster University; 2019. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/11375/24887.
Council of Science Editors:
ZHU L. Inertia- and elasticity-driven turbulence in viscoelastic fluids with high levels of drag reduction. [Doctoral Dissertation]. McMaster University; 2019. Available from: http://hdl.handle.net/11375/24887
10.
Fairhall, Christopher Terry.
The influence of superhydrophobic surfaces on near-wall turbulence.
Degree: PhD, 2019, University of Cambridge
URL: https://www.repository.cam.ac.uk/handle/1810/290211
► Superhydrophobic surfaces are able to entrap gas pockets in-between surface roughness elements when submerged in water. These entrapped gas pockets give these surfaces the potential…
(more)
▼ Superhydrophobic surfaces are able to entrap gas pockets in-between surface roughness elements when submerged in water. These entrapped gas pockets give these surfaces the potential to reduce drag due to the overlying flow being able to locally slip over the gas pockets, resulting in a mean slip at the surface. This thesis investigates the different effects that slip and the texturing of the surface have on turbulence over superhydrophobic surfaces. It is shown that, after filtering out the texture-induced flow, the background, overlying turbulence experiences the surface as a homogeneous slip boundary condition. For texture sizes, expressed in wall units, up to L+ ≤ sssim 20 the only effect of the surface texture on the overlying flow is through this surface slip. The direct effect of slip does not modify the dynamics of the overlying turbulence, which remains canonical and smooth-wall-like. In these cases the flow is governed by the difference between two virtual origins, the virtual origin of the mean flow and the virtual origin experienced by the overlying turbulence. Streamwise slip deepens the virtual origin of the mean flow, while spanwise slip acts to deepen the virtual origin perceived by the overlying turbulence. The drag reduction is then proportional to the difference between the two virtual origins, reminiscent of drag reduction using riblets. The validity of slip-length models to represent textured superhydrophobic surfaces can resultantly be extended up to L+ ≤ sssim 20. However, for L+ \gtrsim 25 a non-linear interaction with the texture-coherent flow alters the dynamics of the background turbulence, with a reduction in coherence of large streamwise lengthscales. This non-linear interaction causes an increase in Reynolds stress up to y+ ≤ sssim 25, and decreases the obtained drag reduction compared to that predicted from homogeneous slip-length models.
Subjects/Keywords: wall-bounded turbulence; drag reduction; superhydrophobic surfaces
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Fairhall, C. T. (2019). The influence of superhydrophobic surfaces on near-wall turbulence. (Doctoral Dissertation). University of Cambridge. Retrieved from https://www.repository.cam.ac.uk/handle/1810/290211
Chicago Manual of Style (16th Edition):
Fairhall, Christopher Terry. “The influence of superhydrophobic surfaces on near-wall turbulence.” 2019. Doctoral Dissertation, University of Cambridge. Accessed March 07, 2021.
https://www.repository.cam.ac.uk/handle/1810/290211.
MLA Handbook (7th Edition):
Fairhall, Christopher Terry. “The influence of superhydrophobic surfaces on near-wall turbulence.” 2019. Web. 07 Mar 2021.
Vancouver:
Fairhall CT. The influence of superhydrophobic surfaces on near-wall turbulence. [Internet] [Doctoral dissertation]. University of Cambridge; 2019. [cited 2021 Mar 07].
Available from: https://www.repository.cam.ac.uk/handle/1810/290211.
Council of Science Editors:
Fairhall CT. The influence of superhydrophobic surfaces on near-wall turbulence. [Doctoral Dissertation]. University of Cambridge; 2019. Available from: https://www.repository.cam.ac.uk/handle/1810/290211
11.
Sayad Saravi, Samira.
An investigation on design and analysis of micro-structured surfaces with application to friction reduction.
Degree: PhD, 2014, Brunel University
URL: http://bura.brunel.ac.uk/handle/2438/8559
;
http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607544
► Drag reduction in wall-bounded flows can be achieved by the passive flow control technique using riblets and surface grooves aligned in the mean direction of…
(more)
▼ Drag reduction in wall-bounded flows can be achieved by the passive flow control technique using riblets and surface grooves aligned in the mean direction of an overlying turbulent flow. They were inspired by the skin of fast sharks covered with small longitudinal ribs on their skin surfaces. Although it was found that the drag reduction depends on the riblets’ geometrical characteristics, their physical mechanisms have not yet been fully understood in the scientific terms. Regarding riblets sizing, it has been critically explained in the literature how riblets with vanishing size interact with the turbulent flow and produce a change in the drag proportional to their size. Their shapes are focused upon because these are most significant from a technological perspective, and also less well understood. Different riblet shapes have been designed, some with complicated geometries, but except for the simple ones, such as U and V grooves, there has not been enough study regarding shape features. Therefore, special effort is undertaken to the design of an innovative type of ribleted surface, e.g. the Serrate-Semi-Circular shape, and its effect on the skin friction and drag reduction. In this work, the possible physical mechanisms of riblets for turbulent drag reduction have been explored. The modelling and experiments concerning the relationship between the riblets features and the turbulent boundary layer structure have also been reviewed. Moreover, numerical simulations on riblets with different shapes and sizes are presented and studied in detail. An accurate treatment based on k-ε turbulence model was adopted to investigate the flow alteration and the consequent drag reduction on ribleted surfaces. The interaction of the overlying turbulent flow with riblets and its impact on their drag reduction properties are further investigated. In addition, the experimental facilities, instrumentation (e.g. hotwires) and measurement techniques (e.g. time-averaged turbulence structure) have been employed to experimentally investigate the boundary layer velocity profiles and skin friction for smooth and micro-structured surfaces (the proposed riblet shape, respectively and the presented new design of riblets with serration inside provides 7% drag reduction. The results do not show significant reduction in momentum transfer near the surface by riblets, in particular, around the outer region of the turbulent boundary layer. Conclusions with respect to the holistic investigation on the drag reduction with Serrate-Semi-Circular riblets have been drawn based on the research objectives as achieved. Recommendations for future work have been put forward particularly for further future research in the research area.
Subjects/Keywords: 621; Drag reduction; Riblets; CFD modelling
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Sayad Saravi, S. (2014). An investigation on design and analysis of micro-structured surfaces with application to friction reduction. (Doctoral Dissertation). Brunel University. Retrieved from http://bura.brunel.ac.uk/handle/2438/8559 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607544
Chicago Manual of Style (16th Edition):
Sayad Saravi, Samira. “An investigation on design and analysis of micro-structured surfaces with application to friction reduction.” 2014. Doctoral Dissertation, Brunel University. Accessed March 07, 2021.
http://bura.brunel.ac.uk/handle/2438/8559 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607544.
MLA Handbook (7th Edition):
Sayad Saravi, Samira. “An investigation on design and analysis of micro-structured surfaces with application to friction reduction.” 2014. Web. 07 Mar 2021.
Vancouver:
Sayad Saravi S. An investigation on design and analysis of micro-structured surfaces with application to friction reduction. [Internet] [Doctoral dissertation]. Brunel University; 2014. [cited 2021 Mar 07].
Available from: http://bura.brunel.ac.uk/handle/2438/8559 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607544.
Council of Science Editors:
Sayad Saravi S. An investigation on design and analysis of micro-structured surfaces with application to friction reduction. [Doctoral Dissertation]. Brunel University; 2014. Available from: http://bura.brunel.ac.uk/handle/2438/8559 ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607544
Delft University of Technology
12.
Raghunathan Srikumar, Sampath Kumar (author).
LES of a novel wing/body junction : Anti-fairing.
Degree: 2019, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:86621aa3-90a6-4929-9534-97459ef11f87
► Large Eddy Simulations (LES) of a novel type of wing/body junction called the anti-fairing are performed in the current thesis to study the complex turbulent…
(more)
▼ Large Eddy Simulations (LES) of a novel type of wing/body junction called the anti-fairing are performed in the current thesis to study the complex turbulent flow physics involved in the junction area and also to obtain a clear understanding of the
drag reduction capabilities of the anti-fairing. In regards to that, two separate LES are performed: one for the baseline case with a Rood wing/flat plate combination and another with the Rood wing/anti-fairing combination. A detailed comparative study is performed between the two cases to observe important differences in junction flow characteristics. Both the simulations are performed on a 25 million immersed boundary Cartesian mesh by solving the incompressible Navier-Stokes equations using the in-house finite volume LES solver called INCA. Results from the LES study confirms the existence of the propulsive pressure mechanism of
drag reduction for the anti-fairing case, previously proposed by Belligoli et al. However, the results also show that there exists a secondary
drag reduction mechanism caused by a combination of increase in approach boundary layer momentum thickness and dampening of the turbulence associated with the horseshoe vortex (HSV) upstream of the wing. This secondary mechanism has been found to be caused by the convex dent present at the start of the anti-fairing geometry. The total
drag reduction for the anti-fairing case comes out to be 1.8%. A new parameter called junction
drag is defined which accounts for the
drag only due to the presence of a junction. The
reduction in junction
drag obtained for the anti-fairing case is about 6.8%. Apart from the LES analysis, a RANS analysis has also been performed to further investigate the
drag reduction capabilities of anti-fairing for different approach boundary layer thicknesses and anti-fairing depths. All the RANS analysis have been performed on a 5 million body-fitted mesh by solving the incompressible Navier-Stokes using the open source finite-volume solver OpenFOAM. Results from the RANS analysis indicate that there exists an optimum depth for the anti-fairing which corresponds to the least
drag. Furthermore, it is found that the effect of approach boundary layer thickness is mostly on changing the base
drag of the case where no anti-fairing is present, rather than actually affecting the performance of the anti-fairing at different depths.
Advisors/Committee Members: Dwight, Richard (mentor), Belligoli, Zeno (mentor), Eitelberg, Georg (graduation committee), Hickel, Stefan (graduation committee), Delft University of Technology (degree granting institution).
Subjects/Keywords: Anti-fairing; LES; INCA; Drag Reduction; CFD
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Raghunathan Srikumar, S. K. (. (2019). LES of a novel wing/body junction : Anti-fairing. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:86621aa3-90a6-4929-9534-97459ef11f87
Chicago Manual of Style (16th Edition):
Raghunathan Srikumar, Sampath Kumar (author). “LES of a novel wing/body junction : Anti-fairing.” 2019. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:86621aa3-90a6-4929-9534-97459ef11f87.
MLA Handbook (7th Edition):
Raghunathan Srikumar, Sampath Kumar (author). “LES of a novel wing/body junction : Anti-fairing.” 2019. Web. 07 Mar 2021.
Vancouver:
Raghunathan Srikumar SK(. LES of a novel wing/body junction : Anti-fairing. [Internet] [Masters thesis]. Delft University of Technology; 2019. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:86621aa3-90a6-4929-9534-97459ef11f87.
Council of Science Editors:
Raghunathan Srikumar SK(. LES of a novel wing/body junction : Anti-fairing. [Masters Thesis]. Delft University of Technology; 2019. Available from: http://resolver.tudelft.nl/uuid:86621aa3-90a6-4929-9534-97459ef11f87
Delft University of Technology
13.
Hensbergen, J. (author).
Drag reduction.
Degree: 1972, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:00e0356e-01f7-434d-9ef2-eaa7a0742622
Literatuurstudie over methoden om de buisweerstand te verkleinen.
Hydraulic Engineering
Civil Engineering and Geosciences
Subjects/Keywords: drag reduction; buisweerstand
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Hensbergen, J. (. (1972). Drag reduction. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:00e0356e-01f7-434d-9ef2-eaa7a0742622
Chicago Manual of Style (16th Edition):
Hensbergen, J (author). “Drag reduction.” 1972. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:00e0356e-01f7-434d-9ef2-eaa7a0742622.
MLA Handbook (7th Edition):
Hensbergen, J (author). “Drag reduction.” 1972. Web. 07 Mar 2021.
Vancouver:
Hensbergen J(. Drag reduction. [Internet] [Masters thesis]. Delft University of Technology; 1972. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:00e0356e-01f7-434d-9ef2-eaa7a0742622.
Council of Science Editors:
Hensbergen J(. Drag reduction. [Masters Thesis]. Delft University of Technology; 1972. Available from: http://resolver.tudelft.nl/uuid:00e0356e-01f7-434d-9ef2-eaa7a0742622
Delft University of Technology
14.
Toutouh, Azeddine (author).
Drag Reduction in Turbulent Flows by Polymers and Surfactants: An Experimental Study Into the Mechanisms of Drag Reduction by Additives.
Degree: 2018, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:1094e6c1-d1c8-4440-af31-f6a972b94d48
► In 1949, Toms (Toms B.A., (1949, 1977)) observed that small amounts of a drag reducing agent (DRA) could cause a considerable drag reduction in turbulent…
(more)
▼ In 1949, Toms (Toms B.A., (1949, 1977)) observed that small amounts of a
drag reducing agent (DRA) could cause a considerable
drag reduction in turbulent pipe flow. In application of polymer enhanced oil recovery, degradation of polymers in the supply lead could cause clogging. It was, however observed that surfactants at sufficiently high concentration also showed
drag reduction without the problem clogging. A DRA reduces the energy loss by friction and unstable flow, thus improving injection throughput with the same pressure pump and thereby reducing the exergetic pumping costs. This study investigates experimentally the
drag reducing capacity of surfactants and compares it to the
drag reducing capacity of polymers. For the experiment, a set-up consisting of a pump, a coiled test tube with a length of 1.48 m and an inner diameter of 0.5 mm and pressure gauges is built. The diameter of the coil is 12.5 cm. We use a pump capable of injection up to 200 ml/min. The pressure drop is measured between the entrance and end of the tube. The injection rate is varied between 1 and 200 ml/min, roughly corresponding to Reynolds numbers between 50 and 10,000. The additives are dissolved in brine with a 33,000 ppm salt concentration. The viscosity of the solution is dependent on the concentration of the DRA. The ratio of the measured pressure drop with only brine and the pressure drop with the DRA solution was used to calculate the
drag reduction (DR) factor, as from a technical point of view we are only interested whether adding DRA reduces the
drag with respect to the original brine solution. From an academic point of view, we remark that for low concentrations the viscosity enhancement due to the presence of the DRA is negligible. As polymers we use xanthan (a biopolymer), and a synthetic emulsion polymer based on polyacrylamide. Maximum DR factors are 23% for xanthan at 90ppm and 32% at 90ppm for the synthetic emulsion polymer. DR only occurs at turbulent conditions. Three types of surfactants, each from a different branch of surfactants are used in this study. The surfactants used are AOS {훼-Olefin Sulfonate}, CTAB {hexadeCylTrimethylAmmonium Bromide} and APG {Alkyl PolyGlucoside} which are a cationic, anionic and a nonionic surfactant respectively. The surfactants did not show any DR at (for DRA applications) high concentrations up to 20.000ppm. Addition of Sodium Salicylate (NaSaL) to CTAB with a 1:1 ratio led to a maximum DR of 33% at 2500 ppm concentration. Several pressure gauges have been installed along the test tube in order to observe how the pressure drops along the tube, how the DRAs affect these pressure drops and at what location of the test tube the DR factor is the highest. It is found that xanthan has the same DR factor at each location of the test tube, the emulsion polymer has a decreasing DR factor as the distance from the inlet of the test tube increases and the CTAB+NaSaL DRA has an increasing DR factor as the distance from the inlet increases. The DRAs are sheared using a constriction in…
Advisors/Committee Members: Bruining, Hans (mentor), Fadili, Ali (mentor), Vincent-Bonnieu, Sebastien (mentor), Jones, Sian (mentor), Zitha, Pacelli (mentor), Delft University of Technology (degree granting institution).
Subjects/Keywords: Drag Reduction; Polymers; Surfactants; Turbulence; Turbulent Flow
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Toutouh, A. (. (2018). Drag Reduction in Turbulent Flows by Polymers and Surfactants: An Experimental Study Into the Mechanisms of Drag Reduction by Additives. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:1094e6c1-d1c8-4440-af31-f6a972b94d48
Chicago Manual of Style (16th Edition):
Toutouh, Azeddine (author). “Drag Reduction in Turbulent Flows by Polymers and Surfactants: An Experimental Study Into the Mechanisms of Drag Reduction by Additives.” 2018. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:1094e6c1-d1c8-4440-af31-f6a972b94d48.
MLA Handbook (7th Edition):
Toutouh, Azeddine (author). “Drag Reduction in Turbulent Flows by Polymers and Surfactants: An Experimental Study Into the Mechanisms of Drag Reduction by Additives.” 2018. Web. 07 Mar 2021.
Vancouver:
Toutouh A(. Drag Reduction in Turbulent Flows by Polymers and Surfactants: An Experimental Study Into the Mechanisms of Drag Reduction by Additives. [Internet] [Masters thesis]. Delft University of Technology; 2018. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:1094e6c1-d1c8-4440-af31-f6a972b94d48.
Council of Science Editors:
Toutouh A(. Drag Reduction in Turbulent Flows by Polymers and Surfactants: An Experimental Study Into the Mechanisms of Drag Reduction by Additives. [Masters Thesis]. Delft University of Technology; 2018. Available from: http://resolver.tudelft.nl/uuid:1094e6c1-d1c8-4440-af31-f6a972b94d48
Delft University of Technology
15.
Fokker, A.D. (author).
Investigating the drag sensitivity parameters and lateral dynamic response of a road vehicle in cross-wind flow.
Degree: 2015, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:bb871e9d-2596-49a4-9bf2-cbed4c6a9446
► Recent trends in the automobile industry focus towards enhancing the operating efficiency of the road vehicle. One can achieve this by a combination of increasing…
(more)
▼ Recent trends in the automobile industry focus towards enhancing the operating efficiency of the road vehicle. One can achieve this by a combination of increasing the powertrain efficiency, reducing the weight and increasing the aerodynamic performance. The scope of this study is on the latter, i. e. enhancing the aerodynamic performance. Most cars are optimized for minimum
drag in idealized conditions, driving engineers to design for the test rather than for to optimize for actual flow encountered in real world conditions. These realistic conditions include (un)steady cross-wind flows encountered by the vehicle, rather than a perfectly aligned flow as is the case in an idealized situation. Different researchers studied the effect of these real world conditions on the performance of a vehicle. Many of these studies focussed upon the vehicle stability rather than the potential to reduce aerodynamic
drag. This is because typical
drag reducing means (such as radiused edges) tend to have a detrimental effect on the cross-wind stability and comfort of the vehicle. \ The introduction of the fully electric Tesla Model S created new opportunities within this conception. This 2500 {kg vehicle has an 800 {kg battery underneath the car, which results in a different - relatively flexible - position of the center of gravity, total mass and corresponding mass moments of inertia. As a result it is questioned if this difference in vehicle specifications allow for
drag reducing shape modifications on a vehicle which is then still stable during cross-wind flows. After a careful trade-off it was chosen to use the recently launched open-source CFD software suite SU2 in order to find an answer to the following research objective: What design modifications reduce the
drag coefficient of a simplified vehicle model which experiences a cross-wind flow, and how does this affect the lateral dynamic performance? An interesting follow-up question on this would be to identify which design variables are (most) sensitive to
drag increments in realistic crosswind flows. This document describes the process of solving the research objective within the framework of a Master of Science thesis. A thorough vehicle dynamics study was performed in order to assess the most influential parameters which affect the lateral deviation of a vehicle. Within this study it was found that the cross-wind induced lateral deviation with a longitudinal velocity of 30m/s and a cross-wind flow of 3.15m/s or 6 degrees is roughly similar to the situation where the steering wheel angle is set to 1 degree. This implies that the lateral deviation during cross-wind flows is not much of an issue during steady cross-wind flows of up to 6 degrees. Experiments were designed for three different cross-wind flows; 0 degrees, 3 degrees and 6 degrees cross-wind flow for both conventional and electric vehicles. Here the effects of the following shape modifications have been studied: arrowing the front of the vehicle, tapering the aft of the vehicle, applying a side-window tumblehome…
Advisors/Committee Members: Van Zuijlen, A.H. (mentor), Veldhuis, L.L.M. (mentor).
Subjects/Keywords: vehicle aerodynamics drag reduction vehicle dynamics
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Fokker, A. D. (. (2015). Investigating the drag sensitivity parameters and lateral dynamic response of a road vehicle in cross-wind flow. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:bb871e9d-2596-49a4-9bf2-cbed4c6a9446
Chicago Manual of Style (16th Edition):
Fokker, A D (author). “Investigating the drag sensitivity parameters and lateral dynamic response of a road vehicle in cross-wind flow.” 2015. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:bb871e9d-2596-49a4-9bf2-cbed4c6a9446.
MLA Handbook (7th Edition):
Fokker, A D (author). “Investigating the drag sensitivity parameters and lateral dynamic response of a road vehicle in cross-wind flow.” 2015. Web. 07 Mar 2021.
Vancouver:
Fokker AD(. Investigating the drag sensitivity parameters and lateral dynamic response of a road vehicle in cross-wind flow. [Internet] [Masters thesis]. Delft University of Technology; 2015. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:bb871e9d-2596-49a4-9bf2-cbed4c6a9446.
Council of Science Editors:
Fokker AD(. Investigating the drag sensitivity parameters and lateral dynamic response of a road vehicle in cross-wind flow. [Masters Thesis]. Delft University of Technology; 2015. Available from: http://resolver.tudelft.nl/uuid:bb871e9d-2596-49a4-9bf2-cbed4c6a9446
University of Minnesota
16.
Li, Yixuan.
A numerical and theoretical study of drag reduction using superhydrophobic surfaces.
Degree: PhD, Aerospace Engineering and Mechanics, 2018, University of Minnesota
URL: http://hdl.handle.net/11299/201149
► Motivated by the potential drag reduction benefits of superhydrophobic surfaces (SHS), direct numerical simulation (DNS) and theoretical analyses are used to explore the interaction between…
(more)
▼ Motivated by the potential drag reduction benefits of superhydrophobic surfaces (SHS), direct numerical simulation (DNS) and theoretical analyses are used to explore the interaction between SHS and turbulent channel flow. First, DNS is used to study the drag reduction by SHS in laminar channel flow. Resolved multi-phase simulations using the volume of fluid (VOF) methodology are performed to study the effects of groove geometry, interface shear rate and meniscus penetration independently. An analytical solution for the flow in a laminar channel with grooved surface with gas-pocket within is obtained. The solution accounts for both the groove geometry and the trapped fluid properties, and shows good agreement with simulation results. The solution is used to propose a scaling law that collapses data across fully wetted to fully gas-filled regimes. The trapped gas is simulated as both flat and meniscal interfaces. The drag reduction initially increases with interface deflection into the groove and then decreases for large deflections as the interface velocity approaches zero due to the proximity to the bottom of the groove. Next, the geometric effect of SHS in turbulent flow is studied by performing DNS at friction Reynolds number \Rey_τ = 400 over longitudinal grooves whose size is comparable to the viscous sublayer thickness. It is found that despite the bulk flow being close to that of a flat-wall channel, the slip effect of the grooves causes some differences within the viscous sublayer. Spectral analysis of the velocity transfer function between the interior and the exterior regions of the grooves shows that the grooves suppress the energy at low frequencies. The DNS reveals negligible Reynolds shear stress near the grooves, which motivates an unsteady Stokes flow model. It is assumed that the flow in the vicinity of the grooves is governed by the unsteady Stokes equations, forced by an oscillating external flow. The effects of streamwise, spanwise and vertical velocity, freestream wavenumber and the height of freestream perturbation above the groove are studied. The non-dimensional parameter ω L2/ν obtained from this model problem (L is half of the groove span, ω is the frequency of the external turbulent signal and ν is the kinematic viscosity) is used to relate the model to the current DNS. Good agreement is seen with DNS at low frequencies. It is suggested that higher frequency disturbances are produced by smaller spanwise structures near the wall, and when this effect is accounted for, good agreement is also observed at higher frequencies. Finally, we study multiphase flow within grooved textures exposed to external unsteadiness. We derive analytical expressions for multiphase unsteady Stokes flow within periodic grooves driven by oscillating streamwise/spanwise freestream velocity. Good agreement is obtained between the analytical solution and DNS performed with the VOF method. The effect of oscillation frequency, Reynolds number, and the multiphase interface location on the…
Subjects/Keywords: drag reduction; multiphase; simulation; superhydrophobic; theoretical; turbulent
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Li, Y. (2018). A numerical and theoretical study of drag reduction using superhydrophobic surfaces. (Doctoral Dissertation). University of Minnesota. Retrieved from http://hdl.handle.net/11299/201149
Chicago Manual of Style (16th Edition):
Li, Yixuan. “A numerical and theoretical study of drag reduction using superhydrophobic surfaces.” 2018. Doctoral Dissertation, University of Minnesota. Accessed March 07, 2021.
http://hdl.handle.net/11299/201149.
MLA Handbook (7th Edition):
Li, Yixuan. “A numerical and theoretical study of drag reduction using superhydrophobic surfaces.” 2018. Web. 07 Mar 2021.
Vancouver:
Li Y. A numerical and theoretical study of drag reduction using superhydrophobic surfaces. [Internet] [Doctoral dissertation]. University of Minnesota; 2018. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/11299/201149.
Council of Science Editors:
Li Y. A numerical and theoretical study of drag reduction using superhydrophobic surfaces. [Doctoral Dissertation]. University of Minnesota; 2018. Available from: http://hdl.handle.net/11299/201149
University of Melbourne
17.
Woodcock, James D.
Convective methods of pumping and drag reduction.
Degree: 2013, University of Melbourne
URL: http://hdl.handle.net/11343/38330
► It is the convection of the velocity field by itself that renders many fluid mechanics problems mathematically challenging, and produces complicated, and often non-intuitive flow…
(more)
▼ It is the convection of the velocity field by itself that renders many fluid mechanics problems mathematically challenging, and produces complicated, and often non-intuitive flow phenomena. Pumping and drag reduction are effectively related concepts, in that they both involve increasing the volume flux of the fluid. In this work, we consider three different methods of pumping and drag reduction, all of which result, partially or entirely, from the effect of convection.
The first of these methods is the drag reduction obtained by the addition of elastic polymers to a turbulently flowing liquid. This effect is not well understood, and a complete physical explanation of the phenomenon remains to be made. However, it is clear that the polymer has the capacity to transport energy and momentum within the fluid, and energy may also dissipate within the polymer itself. In this work, it is proved that the addition of elastic polymers to a turbulent flow cannot reduce the drag to a level below that of the equivalent laminar flow. This proof can also be applied to similar methods of drag reduction, such as the presence of surfactant micelles within a turbulently flowing liquid and the presence of sand particles within high winds and water droplets within cyclones.
The second method is known as "transpiration", and consists of a dynamic regime of blowing and suction at the wall of the pipe or channel which imparts no net volume flux upon the flow. Using a perturbation analysis, the pumping effect of transpiration has been quantified in this work. It is shown that this pumping results from convection, and relies on the presence of large velocity gradients within the flow.
The third method consists of oscillating waves in the wall of the pipe or channel. This has particular relevance to the valveless impedance pump, which consists of a thin tube, one section of which is elastic and is subjected to rhythmic pinching at some point offset from its centre. This pinching induces oscillating waves within the wall of the tube, which in turn induce a flow. The flow induced by small-amplitude oscillations, in the wall, has been derived through a perturbation analysis. In this way, we are able to separate the effect of convection from the more readily intuitive dragging effect that the wave has upon the fluid, and thereby quantify the importance of convection in such systems. It is found that even within small tubes, the effect of convection remains generally of the same order of magnitude as the dragging effect, and that no effective model of the valveless impedance pump could safely neglect the effect of convection.
Subjects/Keywords: fluid mechanics; flow control; drag reduction; turbulence
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Woodcock, J. D. (2013). Convective methods of pumping and drag reduction. (Doctoral Dissertation). University of Melbourne. Retrieved from http://hdl.handle.net/11343/38330
Chicago Manual of Style (16th Edition):
Woodcock, James D. “Convective methods of pumping and drag reduction.” 2013. Doctoral Dissertation, University of Melbourne. Accessed March 07, 2021.
http://hdl.handle.net/11343/38330.
MLA Handbook (7th Edition):
Woodcock, James D. “Convective methods of pumping and drag reduction.” 2013. Web. 07 Mar 2021.
Vancouver:
Woodcock JD. Convective methods of pumping and drag reduction. [Internet] [Doctoral dissertation]. University of Melbourne; 2013. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/11343/38330.
Council of Science Editors:
Woodcock JD. Convective methods of pumping and drag reduction. [Doctoral Dissertation]. University of Melbourne; 2013. Available from: http://hdl.handle.net/11343/38330
Virginia Tech
18.
Dominic, Justin.
Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel.
Degree: MS, Mechanical Engineering, 2011, Virginia Tech
URL: http://hdl.handle.net/10919/76796
► Presented in this paper are experiments to test the hypothesis that drag reduction is possible over hydrophobic surfaces in the Wenzel state during laminar and…
(more)
▼ Presented in this paper are experiments to test the hypothesis that
drag reduction is possible over hydrophobic surfaces in the Wenzel state during laminar and turbulent flows. Quantification of surface
drag reduction in rectangular channel flow over walls with specific hydrophobic or hydrophilic properties was obtained with pressure drop measurements along the channel for a range of Reynolds numbers between 350 and 5900. Several commercially available materials and coatings were chosen in order to span a range of contact angles between 30° and 135°. The results are within the bounds of the theoretical values calculated with the Colebrook equation, and do not show any
reduction in wall shear stress as a function of material properties or surface chemistry. The differences between this experiment and others measuring pressure drop over hydrophobic surfaces is the macro-scale conditions and the hydrophobic surfaces being fully wetted. These experiments are further proof of the importance of a liquid-vapor interface for increasing the shear free area to produce
drag reduction.
Advisors/Committee Members: Vlachos, Pavlos P. (committeechair), Diller, Thomas E. (committee member), Charonko, John J. (committeecochair).
Subjects/Keywords: boundary layer; drag reduction; hydrophobicity; wetting
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Dominic, J. (2011). Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/76796
Chicago Manual of Style (16th Edition):
Dominic, Justin. “Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel.” 2011. Masters Thesis, Virginia Tech. Accessed March 07, 2021.
http://hdl.handle.net/10919/76796.
MLA Handbook (7th Edition):
Dominic, Justin. “Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel.” 2011. Web. 07 Mar 2021.
Vancouver:
Dominic J. Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel. [Internet] [Masters thesis]. Virginia Tech; 2011. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/10919/76796.
Council of Science Editors:
Dominic J. Experimental Study of Wall Shear Stress Modification by Surface Coating: Pressure Drop Measurements in a Rectangular Channel. [Masters Thesis]. Virginia Tech; 2011. Available from: http://hdl.handle.net/10919/76796
Delft University of Technology
19.
van der Voort Maarschalk, Joost (author).
Dimpled channel flows: An experimental investigation into the drag performance of dimpled surfaces in turbulent channel flows.
Degree: 2021, Delft University of Technology
URL: http://resolver.tudelft.nl/uuid:5a227ee5-0bfb-4591-b983-3c3a59adf31e
► Drag in pipelines is composed almost solely of skin friction drag. The most common technique to achieve drag reduction (DR) is by adding drag-reducing agents.…
(more)
▼ Drag in pipelines is composed almost solely of skin friction
drag. The most common technique to achieve
drag reduction (DR) is by adding
drag-reducing agents. However, in the aerospace industry, various impressive passive
drag-reducing techniques have been suggested to reduce skin friction
drag in the past decades. Among these techniques, dimpled surfaces form a relatively unexplored terrain. Research into reducing skin friction
drag in the turbulent regime by using dimples has been performed in the aviation industry since the '80s. The excessive amount of skin friction
drag in pipelines forms an intriguing challenge to break new grounds. Several researchers investigated the potential of DR of turbulent flows using dimpled channels. Even though most of these studies that found DR are disputed, studies published at the National University of Singapore (NUS) obtained positive results time and again. NUS's exact test setup was reconstructed at Delft University of Technology, which has not been done yet as far as the author of this report is aware. Identical pressure measurements were performed, yielding an absolute DR of ≈ 5%, which is slightly less than what was obtained at NUS (>7%). Flat plates return a DR between 8-15%, dimpled test plates returned at DR between 12-20%. The test plates were covered for 99.5% with diamond-shaped dimples of 100 mm long and 50 mm wide. In total, 29 pressure taps were used to determine the change in
drag in an 8 m long channel of 20 mm in height. Tests were done at Reynolds numbers, based on half channel width and centerline velocity, between 6,000 and 40,000. Accurate results were perceived up to a Reynolds number of 21,000, likely due to test-setup limitations. Multiple verifications such as two-dimensionality of the ow, comparison of theoretical and experimental skin friction coefficients, and instantaneous pressure tests were used to allow for an objective analysis. The pressure measurements were also supported by 1D hotwire anemometry (HWA) tests and surface oil ow visualizations (SOFV). The majority of the investigated boundary layers were absent of anomalies. It should be mentioned that the viscous sublayer could not be captured, neither a quantitative momentum analysis was performed. However, a shift in the velocity profile, acquired at the same test location, for different test plates was observed. Furthermore, an increased velocity near the wall was observed for dimpled test plates. Surface oil ow measurements did show similar ow patterns to what was recorded at NUS. However, the actual behavior is not investigated through HWA. Hence, it cannot be confirmed nor denied if the change in
drag is a consequence of these near-wall ow mechanisms. SOFV did not show irregular ow structures such as ow reversal. Finally, tests were performed with a correction for test volume increase caused by the dimples. After this correction, the
drag over dimpled plates increased instead of reduced. Considering other studies on dimpled surfaces that also found an increase in
drag, it is strongly…
Advisors/Committee Members: Broere, W. (graduation committee), van Rhee, C. (graduation committee), Schrijer, F.F.J. (graduation committee), van Campenhout, O.W.G. (mentor), Delft University of Technology (degree granting institution).
Subjects/Keywords: Dimples; Channel; Drag Reduction; turbulent boundary layer
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
van der Voort Maarschalk, J. (. (2021). Dimpled channel flows: An experimental investigation into the drag performance of dimpled surfaces in turbulent channel flows. (Masters Thesis). Delft University of Technology. Retrieved from http://resolver.tudelft.nl/uuid:5a227ee5-0bfb-4591-b983-3c3a59adf31e
Chicago Manual of Style (16th Edition):
van der Voort Maarschalk, Joost (author). “Dimpled channel flows: An experimental investigation into the drag performance of dimpled surfaces in turbulent channel flows.” 2021. Masters Thesis, Delft University of Technology. Accessed March 07, 2021.
http://resolver.tudelft.nl/uuid:5a227ee5-0bfb-4591-b983-3c3a59adf31e.
MLA Handbook (7th Edition):
van der Voort Maarschalk, Joost (author). “Dimpled channel flows: An experimental investigation into the drag performance of dimpled surfaces in turbulent channel flows.” 2021. Web. 07 Mar 2021.
Vancouver:
van der Voort Maarschalk J(. Dimpled channel flows: An experimental investigation into the drag performance of dimpled surfaces in turbulent channel flows. [Internet] [Masters thesis]. Delft University of Technology; 2021. [cited 2021 Mar 07].
Available from: http://resolver.tudelft.nl/uuid:5a227ee5-0bfb-4591-b983-3c3a59adf31e.
Council of Science Editors:
van der Voort Maarschalk J(. Dimpled channel flows: An experimental investigation into the drag performance of dimpled surfaces in turbulent channel flows. [Masters Thesis]. Delft University of Technology; 2021. Available from: http://resolver.tudelft.nl/uuid:5a227ee5-0bfb-4591-b983-3c3a59adf31e
King Abdullah University of Science and Technology
20.
Jetly, Aditya.
Drag reduction by gas layers and streamlined air cavities attached to free-falling spheres.
Degree: Physical Science and Engineering (PSE) Division, 2019, King Abdullah University of Science and Technology
URL: http://hdl.handle.net/10754/660292
► The general objective of this thesis is to conduct experiments on sphere free-falling in liquid that advance our understanding of the drag reduction on solids…
(more)
▼ The general objective of this thesis is to conduct experiments on sphere free-falling in liquid that advance our understanding of the
drag reduction on solids moving in liquid by means of lubricating gas layers and attached streamlined air cavities.
Part I of the thesis investigates the effect of thin air layers, naturally sustained on superhydrophobic surfaces, on the terminal velocity and
drag force of metallic spheres free- falling in water. The surface of 20 mm to 60 mm steel or tungsten-carbide spheres is rendered superhydrophobic by a simple coating process that uses a commercially available hydrophobic agent. By comparing the free-fall of unmodified spheres and superhydrophobic spheres, in a 2.5 meters tall water tank, it is demonstrated that even a very thin air layer (~ 1 – 2 μm) that covers the freshly dipped superhydrophobic sphere, can reduce the
drag force on the spheres by up to 80 %, at Reynolds numbers 105 to 3×105, owing to an early
drag crisis transition.
Part II of the thesis investigates the
drag reduction by means of the dynamic Leidenfrost vapor-layer sustained on the surface of heated metallic spheres free-falling in a fluorocarbon liquid, FC-72 (perfluorohexane). In these experiments we employed two tall liquid tanks: a 3 meter tall 14 cm wide tank and a 2 meter tall 20 × 20 cm cross-section tank with a heater device. These tanks are significantly larger than the tanks used in prior studies and allow us to track the extended fall trajectories and to compare the
drag on room-temperature no-vapor-layer spheres to that of heated Leidenfrost vapor-layer spheres. Analysis of the extended free-fall trajectories and acceleration, based on the sphere dynamic equation of motion, enables the accurate evaluation of the vapor-layer-induced
drag reduction, without the need for extrapolation. We demonstrate that the
drag on the Leidenfrost sphere in FC-72, can be as low as CD = 0.04 ± 0.01, or an order of magnitude lower than the values for the no-vapor-layer spheres in the subcritical Reynolds number range. This
drag reduction extends into the supercritical Reynolds number range. The analysis method developed herein, to describe the sphere trajectories, can be applied in other related studies.
Part III of the thesis examines a recently demonstrated phenomenon of the formation of stable-streamlined gas cavity following the impact of a heated Leidenfrost sphere on a liquid surface or a superhydrophobic sphere on water. The sphere encapsulated in a teardrop-shaped gas cavity was found to have near-zero hydrodynamic
drag due to the self-adjusting streamlined shape and the free-slip boundary condition on the cavity interface. Here it is shown that such cavities can be formed following the water impact from a sufficient height of non-superhydrophobic spheres with water contact angles between 30° and 120°. In this case the streamlined cavity is attached just above the sphere’s equator, instead of entirely wrapping the sphere. Nevertheless, this sphere with attached cavity has near-zero
drag and predetermined…
Advisors/Committee Members: Thoroddsen, Sigurdur T (advisor), Roberts, William Lafayette (committee member), Ghaffour, NorEddine (committee member), Vakarelski, Ivan Uriev (committee member), McHale, Glen (committee member).
Subjects/Keywords: drag reduction; Superhydrophobic Coatings; Leindenfrost; Air cavities
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Jetly, A. (2019). Drag reduction by gas layers and streamlined air cavities attached to free-falling spheres. (Thesis). King Abdullah University of Science and Technology. Retrieved from http://hdl.handle.net/10754/660292
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Jetly, Aditya. “Drag reduction by gas layers and streamlined air cavities attached to free-falling spheres.” 2019. Thesis, King Abdullah University of Science and Technology. Accessed March 07, 2021.
http://hdl.handle.net/10754/660292.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Jetly, Aditya. “Drag reduction by gas layers and streamlined air cavities attached to free-falling spheres.” 2019. Web. 07 Mar 2021.
Vancouver:
Jetly A. Drag reduction by gas layers and streamlined air cavities attached to free-falling spheres. [Internet] [Thesis]. King Abdullah University of Science and Technology; 2019. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/10754/660292.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Jetly A. Drag reduction by gas layers and streamlined air cavities attached to free-falling spheres. [Thesis]. King Abdullah University of Science and Technology; 2019. Available from: http://hdl.handle.net/10754/660292
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
21.
Camello Barros, Diogo.
Wake and Drag Manipulation of a Bluff Body Using Fluidic Forcing : Manipulation du sillage et de la traînée d'un corps épais par forçage fluidique.
Degree: Docteur es, Mécanique des milieux fluides, 2015, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique
URL: http://www.theses.fr/2015ESMA0019
► La réduction de la trainée aérodynamique des véhicules terrestres est un défi actuel dans l’industrie automobile. La région de basse pression du sillage à l’arrière…
(more)
▼ La réduction de la trainée aérodynamique des véhicules terrestres est un défi actuel dans l’industrie automobile. La région de basse pression du sillage à l’arrière des voitures est responsable d’une part importante de la résistance à l’avancement. Cette étude porte sur le développement de nouvelles stratégies de manipulation de l’écoulement autour de ces géométries dans le but de réduire la traînée. Afin d’atteindre ces objectifs, nous explorons expérimentalement les effets d’un forçage fluidique sur le sillage et la traînée d’un corps au culot droit. Des jets périodiques émis aux bords de fuite du modèle, tangentiellement à l’écoulement principal et avec des fréquences et amplitudes variables sont utilisés pour forcer le sillage. Selon les conditions du contrôle, trois phénomènes sont principalement observés. Premièrement, sur la plage des fréquences comprenant celle du lâcher tourbillonnaire, les jets pulsés sont convectés et modifient l’entrainement de fluide vers la région de recirculation ainsi que l’évolution des instabilités de la couche cisaillée. Cette dynamique complexe a comme conséquence l’augmentation de la trainée du corps. De plus, une résonance subharmonique apparait quand les jets pulsés sont émis avec des fréquences voisines de deux fois la fréquence du mode global. Une importante augmentation de la trainée est alors mesurée et corrélée à une forte amplification des mouvements du sillage. Une augmentation de la fréquence de pulsation se traduit par un effet de vectorisation des couches cisaillées. En outre, une diminution de l’intensité turbulente du sillage proche ainsi qu’une réduction de l’entrainement de fluide le long des couches cisaillées sont mesurés, correspondant à une réduction globale de l’énergie cinétique turbulente de l’écoulement. Le couplage de ces effets est responsable d’une augmentation de la pression au culot et de la réduction de la traînée. Il est important de noter que ces trois régimes d’actuation sont indépendants des modes de brisure de symétrie existant dans ces écoulements, qui sont analysés ici par des études paramétriques de sensibilité aux perturbations. Les aspects physiques de ces phénomènes sont discutés par des mesures de la traînée, de la pression pariétale et de la vitesse avec différentes conditions de l’écoulement et du contrôle. L’addition d’une surface courbée au voisinage du jet pulsé permet de profiter d’un effet Coanda et augmente les réductions de traînée jusqu'à 20%dans le régime instationnaires. De façon générale, l’effet Coanda amplifie non seulement la récupération de la traînée mais préserve aussi les effets de la pulsation haute fréquence sur l’écoulement turbulent. Ces résultats encouragent le développent des actionneurs fluidique pour l’utilisation en aérodynamique des véhicules et fournissent un complément pour notre compréhension sur la traînée des corps non profilés et sa manipulation.
Aerodynamic drag reduction of bluff bodies has become a major challenge for transport vehicles. The massive flowseparation occurring behind cars, buses or…
Advisors/Committee Members: Borée, Jacques (thesis director), Noack, Bernd R. (thesis director).
Subjects/Keywords: Réduction de traînée; Contrôle des écoulements; Drag reduction; Flow control
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Camello Barros, D. (2015). Wake and Drag Manipulation of a Bluff Body Using Fluidic Forcing : Manipulation du sillage et de la traînée d'un corps épais par forçage fluidique. (Doctoral Dissertation). Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique. Retrieved from http://www.theses.fr/2015ESMA0019
Chicago Manual of Style (16th Edition):
Camello Barros, Diogo. “Wake and Drag Manipulation of a Bluff Body Using Fluidic Forcing : Manipulation du sillage et de la traînée d'un corps épais par forçage fluidique.” 2015. Doctoral Dissertation, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique. Accessed March 07, 2021.
http://www.theses.fr/2015ESMA0019.
MLA Handbook (7th Edition):
Camello Barros, Diogo. “Wake and Drag Manipulation of a Bluff Body Using Fluidic Forcing : Manipulation du sillage et de la traînée d'un corps épais par forçage fluidique.” 2015. Web. 07 Mar 2021.
Vancouver:
Camello Barros D. Wake and Drag Manipulation of a Bluff Body Using Fluidic Forcing : Manipulation du sillage et de la traînée d'un corps épais par forçage fluidique. [Internet] [Doctoral dissertation]. Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique; 2015. [cited 2021 Mar 07].
Available from: http://www.theses.fr/2015ESMA0019.
Council of Science Editors:
Camello Barros D. Wake and Drag Manipulation of a Bluff Body Using Fluidic Forcing : Manipulation du sillage et de la traînée d'un corps épais par forçage fluidique. [Doctoral Dissertation]. Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique; 2015. Available from: http://www.theses.fr/2015ESMA0019
UCLA
22.
Park, Hyunwook.
A Numerical Study of the Effects of Superhydrophobic Surfaces on Skin-Friction Drag Reduction in Wall-Bounded Shear Flows.
Degree: Mechanical Engineering, 2015, UCLA
URL: http://www.escholarship.org/uc/item/4vz7m8hb
► Recent developments of superhydrophobic surfaces (SHSs) have attracted much attention because of the possibility of achieving substantial skin-friction drag reduction at high Reynolds number turbulent…
(more)
▼ Recent developments of superhydrophobic surfaces (SHSs) have attracted much attention because of the possibility of achieving substantial skin-friction drag reduction at high Reynolds number turbulent flows. An SHS, consisting of a hydrophobic surface combined with micro- or nano-scaled topological features, can yield an effective slip length on the order of several hundred microns. In this numerical study, direct numerical simulations of turbulent channel flows and turbulent boundary layers (TBLs) developing over SHSs were performed. An SHS was modeled through the shear-free boundary condition, assuming the sustainable gas-liquid interface remained as a flat surface. For the considered Reynolds number ranges and SHS geometries, it was found that the effective slip length normalized by viscous wall units was the key parameter and the effective slip length should be on the order of the buffer layer in order to have the maximum benefit of drag reduction. The effective surface slip length can be interpreted as a depth of influence into which SHSs affect the flow in the wall-normal direction. This result demonstrates that an SHS achieves its drag reduction by affecting the turbulence structures within the buffer layer of wall-bounded turbulent flow. It was also found that the width of an SHS, relative to the spanwise width of near-wall turbulence structures, was also a key parameter to the total amount of drag reduction. Significant suppression of near-wall turbulence structures were observed, which resulted in large skin-friction drag reduction due to the lack of the shear over SHSs. A comparison between TBLs and turbulent channel flows over SHSs were also examined. In contrast to fully developed turbulent channel flows, the effective slip velocity and hence the effective slip length varied in the streamwise direction of TBL, implying that total drag reduction of TBL would depend on the streamwise length of a given SHS. The present numerical study was compared with recent experimental results and showed good agreement. In addition to flow and SHS geometry conditions, the streamwise length of SHSs was also a key factor to understand the underlying physics of wall-bounded shear flows. Finally, it was found that the amount of drag reduction was theoretically estimated as a function of the effective slip length normalized by viscous wall units.
Subjects/Keywords: Mechanical engineering; Direct Numerical Simulation; Drag Reduction; Superhydrophobic Surfaces
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Park, H. (2015). A Numerical Study of the Effects of Superhydrophobic Surfaces on Skin-Friction Drag Reduction in Wall-Bounded Shear Flows. (Thesis). UCLA. Retrieved from http://www.escholarship.org/uc/item/4vz7m8hb
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Park, Hyunwook. “A Numerical Study of the Effects of Superhydrophobic Surfaces on Skin-Friction Drag Reduction in Wall-Bounded Shear Flows.” 2015. Thesis, UCLA. Accessed March 07, 2021.
http://www.escholarship.org/uc/item/4vz7m8hb.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Park, Hyunwook. “A Numerical Study of the Effects of Superhydrophobic Surfaces on Skin-Friction Drag Reduction in Wall-Bounded Shear Flows.” 2015. Web. 07 Mar 2021.
Vancouver:
Park H. A Numerical Study of the Effects of Superhydrophobic Surfaces on Skin-Friction Drag Reduction in Wall-Bounded Shear Flows. [Internet] [Thesis]. UCLA; 2015. [cited 2021 Mar 07].
Available from: http://www.escholarship.org/uc/item/4vz7m8hb.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Park H. A Numerical Study of the Effects of Superhydrophobic Surfaces on Skin-Friction Drag Reduction in Wall-Bounded Shear Flows. [Thesis]. UCLA; 2015. Available from: http://www.escholarship.org/uc/item/4vz7m8hb
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
University of Alberta
23.
Hou, Jianfeng.
Particle image velocimetry/ tracking in turbulent flow over
riblet surfaces with superhydrophobic coating.
Degree: MS, Department of Mechanical Engineering, 2016, University of Alberta
URL: https://era.library.ualberta.ca/files/cv405s969r
► Riblet surfaces have been introduced as of one successful technique to reduce skin-friction. Advanced particle image velocimetry (PIV) and particle tracking velocimetry (PTV) are employed…
(more)
▼ Riblet surfaces have been introduced as of one
successful technique to reduce skin-friction. Advanced particle
image velocimetry (PIV) and particle tracking velocimetry (PTV) are
employed to investigate turbulent structures over riblet surfaces
by several researchers including Suzuki and Kasagi (1994), Lee and
Lee (2001) and Sasamori et al. (2014). However, a complete
characterization of turbulent statistics including mean velocity,
and three components of turbulence intensities and vorticities over
riblet surfaces is still missing due to difficulties in measurement
of small-scale near-wall turbulence. The capabilities of the planar
and volumetric PIV and PTV in capturing three dimensional
structures of the turbulent flow over a riblet surface with the
groove spacing of 750 μm (s+ = 11) has been investigated at Reτ =
147. The two-dimensional measurements are carried out using the
planar PIV and high-magnification long-range micro-PTV. The
three-dimensional techniques include tomographic-PIV (tomo-PIV) and
3D-PTV which were carried out at high tracer density of 0.02
particle per pixel (ppp). Measurements over the riblet surface are
evaluated in comparison with the measurements over a smooth
surface, direct numerical simulation (DNS) of the turbulent flow in
a smooth channel at Reτ = 150, and previous investigations of
turbulent statistics over riblet surfaces. Reduction of
skin-friction is calculated to be 6.1% and 7.5% from the velocity
profiles in the linear viscous sublayer from 2D-PTV and profiles of
the Reynolds stress from 2D-PIV, respectively. Reductions of the
maximum streamwise, wall-normal and spanwise turbulence intensity
are characterized to be 5.9%, 9.4% and 9.4%, respectively, over the
riblet surface from 2D-PIV and 3D-PTV compared to those on the
smooth surface. Three components of the fluctuating vorticity over
the riblet surface measured by a tomo-PIV are first shown in
experimental riblet study but no changes are spotted compared to
the vorticities in the smooth surface case. As a relatively new
skin-friction reduction (SFR) technique, superhydrphobic surfaces
(SHSs) are capable of reducing skin-friction by entrainment of air
pockets in the surface. Improvement of SFR over riblet surfaces are
expected when the surfaces with riblets are coated with
superhydrophobic layers. However, with only two studies by Barbier,
Jenner, and D’Urso (2012) and Prince, Maynes, and Crockett (2014)
in the area, it needs more detailed investigation if the SHSs are
able to help riblets achieve additional SFR. The effect of riblets
combined with superhydrophobic coating on skin-friction is studied
by means of a planar PIV at Reτ = 141. The evaluation was acquired
by comparing results between riblet surfaces with and without
superhydrophobic coatings. The wall-normal turbulence intensities
and the Reynolds shear stress over the coated smooth surface are
both reduced by about 5% compared to the smooth surface, indicating
the SFR. The analysis of the longevity of the SHS over the smooth
surface reveals the loss of SHS in…
Subjects/Keywords: Drag reduction; Riblet; Superhydrophobic surface; Particle image velocimetry; Particle tracking velocimetry
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Hou, J. (2016). Particle image velocimetry/ tracking in turbulent flow over
riblet surfaces with superhydrophobic coating. (Masters Thesis). University of Alberta. Retrieved from https://era.library.ualberta.ca/files/cv405s969r
Chicago Manual of Style (16th Edition):
Hou, Jianfeng. “Particle image velocimetry/ tracking in turbulent flow over
riblet surfaces with superhydrophobic coating.” 2016. Masters Thesis, University of Alberta. Accessed March 07, 2021.
https://era.library.ualberta.ca/files/cv405s969r.
MLA Handbook (7th Edition):
Hou, Jianfeng. “Particle image velocimetry/ tracking in turbulent flow over
riblet surfaces with superhydrophobic coating.” 2016. Web. 07 Mar 2021.
Vancouver:
Hou J. Particle image velocimetry/ tracking in turbulent flow over
riblet surfaces with superhydrophobic coating. [Internet] [Masters thesis]. University of Alberta; 2016. [cited 2021 Mar 07].
Available from: https://era.library.ualberta.ca/files/cv405s969r.
Council of Science Editors:
Hou J. Particle image velocimetry/ tracking in turbulent flow over
riblet surfaces with superhydrophobic coating. [Masters Thesis]. University of Alberta; 2016. Available from: https://era.library.ualberta.ca/files/cv405s969r
University of Alberta
24.
Bhambri, Pallavi.
Drag reduction using additives in a Taylor-Couette
Flow.
Degree: MS, Department of Mechanical Engineering, 2016, University of Alberta
URL: https://era.library.ualberta.ca/files/cn583xv03c
► The current study investigates the drag reduction (DR) using high molecular weight polymers such as commercial polyacrylamide, polysaccharides and thermo-responsive polymers. A Taylor-Couette (TC) setup…
(more)
▼ The current study investigates the drag reduction (DR)
using high molecular weight polymers such as commercial
polyacrylamide, polysaccharides and thermo-responsive polymers. A
Taylor-Couette (TC) setup was designed and fabricated to examine
the abovementioned polymers for drag reduction, and to demonstrate
that turbulent Taylor-Couette testing is a convenient and cost
effective analogue for pipe flow drag reduction. Initial
experiments were conducted with water as a working fluid and the
dimensionless torque was used to scale the torque which compared
well with the previous TC studies. Further, the results obtained
were found to scale well with the turbulent drag in wall bounded
shear flows (such as pipe/channel flow). Using TC flow, commercial
polyacrylamide along with polysaccharides such as aloe vera,
pineapple fibers, tamarind powder and cellulose nano crystals (CNC)
were studied for DR. The effect of Reynolds number (Re) and
concentration of these high molecular weight polymers was observed.
Polysaccharides are environmentally friendly and offer a huge
advantage over commercial polymers due to their biodegradable
nature. Furthermore, the high molecular weight polymers are also
used extensively in oil recovery during hydraulic fracturing for
DR. However, due to their long chain length, these polymers get
adsorbed on the surface of reservoir, diminishing the effectiveness
of fracking. Hence, this study was then extended to
Poly-(N-isopropylacrylamide) (PNIPAM), a thermoresponsive polymer.
PNIPAM collapses reversibly beyond 33°C known as Lower Critical
Solution Temperature (LCST), thereby preventing it from getting
adsorbed beyond this temperature. In the current study, PNIPAM was
synthesized using free radical polymerization and then examined for
DR. The effect of concentration of this thermo-responsive polymer,
Reynolds number (Re) and temperature on DR was studied. In summary,
the current study exploits several polymers such as a commercial
drag reducing agent (Polyacrylamide), biodegradable polymers such
as polysaccharides, and smart polymers like thermo-responsive
polymer for drag reduction. Taylor-Couette flow is utilized as a
tool for testing these polymers for DR.
Subjects/Keywords: Polymers; Polysaccharides; Taylor-Couette Flow; Thermo-resposive polymers; Drag reduction
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Bhambri, P. (2016). Drag reduction using additives in a Taylor-Couette
Flow. (Masters Thesis). University of Alberta. Retrieved from https://era.library.ualberta.ca/files/cn583xv03c
Chicago Manual of Style (16th Edition):
Bhambri, Pallavi. “Drag reduction using additives in a Taylor-Couette
Flow.” 2016. Masters Thesis, University of Alberta. Accessed March 07, 2021.
https://era.library.ualberta.ca/files/cn583xv03c.
MLA Handbook (7th Edition):
Bhambri, Pallavi. “Drag reduction using additives in a Taylor-Couette
Flow.” 2016. Web. 07 Mar 2021.
Vancouver:
Bhambri P. Drag reduction using additives in a Taylor-Couette
Flow. [Internet] [Masters thesis]. University of Alberta; 2016. [cited 2021 Mar 07].
Available from: https://era.library.ualberta.ca/files/cn583xv03c.
Council of Science Editors:
Bhambri P. Drag reduction using additives in a Taylor-Couette
Flow. [Masters Thesis]. University of Alberta; 2016. Available from: https://era.library.ualberta.ca/files/cn583xv03c
University of Alberta
25.
Luk, Jason.
Pipeline Transport of Wheat Straw Biomass.
Degree: MS, Department of Mechanical Engineering, 2010, University of Alberta
URL: https://era.library.ualberta.ca/files/79407x56x
► This study experimentally evaluated wheat straw slurry pipelines. Tests were conducted to determine the particle properties of the biomass mixed in water over time. The…
(more)
▼ This study experimentally evaluated wheat straw slurry
pipelines. Tests were conducted to determine the particle
properties of the biomass mixed in water over time. The saturated
particle density of 1,060kg/m3 was reached after 24 hours, while
the saturated moisture contents of 78.5% and 79.5% were later
reached for particle sizes of 1/8” and 3/4" respectively. A
pipeline loop was redesigned to operate with 1/8”, 1/4", and 3/4"
straw particle slurries at up to 30% wet basis concentrations. The
modifications allowed measurements of pressure loss through a
length of pipe. These measurements which show the influences of
drag reducing fibre suspension. Straw particles added to water
lowered the pressure loss, by suppressing turbulence at lower
concentrations or higher velocities. Additional straw further
improved the result, until the maximum concentration was reached.
High concentrations create plugs, increasing the pressure loss.
Longer straw particles can further reduce losses, but have lower
maximum concentrations.
Subjects/Keywords: Drag Reduction; Transport; Biomass; Fiber Suspension; Slurry; Biofuel; Pipeline; Wheat Straw
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Luk, J. (2010). Pipeline Transport of Wheat Straw Biomass. (Masters Thesis). University of Alberta. Retrieved from https://era.library.ualberta.ca/files/79407x56x
Chicago Manual of Style (16th Edition):
Luk, Jason. “Pipeline Transport of Wheat Straw Biomass.” 2010. Masters Thesis, University of Alberta. Accessed March 07, 2021.
https://era.library.ualberta.ca/files/79407x56x.
MLA Handbook (7th Edition):
Luk, Jason. “Pipeline Transport of Wheat Straw Biomass.” 2010. Web. 07 Mar 2021.
Vancouver:
Luk J. Pipeline Transport of Wheat Straw Biomass. [Internet] [Masters thesis]. University of Alberta; 2010. [cited 2021 Mar 07].
Available from: https://era.library.ualberta.ca/files/79407x56x.
Council of Science Editors:
Luk J. Pipeline Transport of Wheat Straw Biomass. [Masters Thesis]. University of Alberta; 2010. Available from: https://era.library.ualberta.ca/files/79407x56x
Texas A&M University
26.
Gutierrez Torres, Claudia del Carmen.
Modification of turbulent structure in channel flows by microbubble injection close to the wall.
Degree: PhD, Mechanical Engineering, 2005, Texas A&M University
URL: http://hdl.handle.net/1969.1/2783
► An investigation of turbulent structure modification of a boundary layer for a fully developed channel flow by microbubble injection close to the upper wall was…
(more)
▼ An investigation of turbulent structure modification of a boundary layer for a fully developed channel flow by microbubble injection close to the upper wall was carried out using Particle Image Velocimetry (PIV). Two-dimensional velocity components in an x-y plane at Reynolds number of 5128 based on the half height of the channel and bulk velocity were measured. Microbubbles, with an average diameter of 30 ??m were produced by electrolysis and injected in the buffer layer. Different values of the void fraction were attained and used to evaluate the effects of the presence of microbubbles and their concentration within the boundary layer.
A
reduction in
drag was observed due to the injection of microbubbles.
Drag reduction augments as the value of the void fraction increases. Furthermore, increases in both the non-dimensional values of streamwise and normal turbulent intensities, normalized by the friction velocity were observed with the void fraction growth.
A gradual decrease in the Reynolds shear stresses was achieved as the void fraction increases. This effect is due to a ??decorrelation?? or ??decoupling?? between the streamwise and normal fluctuating velocities.
Modifications in the length and time scales due to the presence of microbubbles were detected by calculating two-point correlation coefficients in one and two dimensions and the autocorrelation coefficient at various locations within the measurement zone. Streamline length and time scales were increased. On the contrary, the normal length and time scales were decreased.
The vorticity and strain rate values decreased with the injection of microbubbles. Turbulent energy production was also decreased within the boundary layer.
Quadrant analysis was used to find out the contribution of the u?? and v?? fluctuating velocity components to the Reynolds stress. The presence of microbubbles reduces the contribution to the Reynolds stresses by Q4 events (sweeps), which are responsible for the production of skin friction. Vortical structure detection in the measurement area was pursued. The structure with and without the microbubble injection is compared.
In this study the presence of microbubbles within the boundary layer has produced several modifications in the flow structure as well as
reduction in the
drag.
Advisors/Committee Members: Anand, Nagamangala K. (advisor), Hassan, Yassin A. (advisor), Phares, Denis (committee member), Scott, Stuart L. (committee member).
Subjects/Keywords: PIV; microbubbles; drag reduction
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Gutierrez Torres, C. d. C. (2005). Modification of turbulent structure in channel flows by microbubble injection close to the wall. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/2783
Chicago Manual of Style (16th Edition):
Gutierrez Torres, Claudia del Carmen. “Modification of turbulent structure in channel flows by microbubble injection close to the wall.” 2005. Doctoral Dissertation, Texas A&M University. Accessed March 07, 2021.
http://hdl.handle.net/1969.1/2783.
MLA Handbook (7th Edition):
Gutierrez Torres, Claudia del Carmen. “Modification of turbulent structure in channel flows by microbubble injection close to the wall.” 2005. Web. 07 Mar 2021.
Vancouver:
Gutierrez Torres CdC. Modification of turbulent structure in channel flows by microbubble injection close to the wall. [Internet] [Doctoral dissertation]. Texas A&M University; 2005. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/1969.1/2783.
Council of Science Editors:
Gutierrez Torres CdC. Modification of turbulent structure in channel flows by microbubble injection close to the wall. [Doctoral Dissertation]. Texas A&M University; 2005. Available from: http://hdl.handle.net/1969.1/2783
McMaster University
27.
Bai, Xue.
EFFECTS OF DRAG-REDUCING POLYMERS ON TURBULENCE GROWTH AND BURSTING IN NEAR MINIMAL CHANNELS AND EXTENDED DOMAINS.
Degree: MASc, 2017, McMaster University
URL: http://hdl.handle.net/11375/21348
► Two major problems in viscoelastic turbulence, the effects of polymers on the laminar-turbulent transition dynamics and the origin of the maximum drag reduction asymptote, can…
(more)
▼ Two major problems in viscoelastic turbulence, the effects of polymers on the laminar-turbulent transition dynamics and the origin of the maximum drag reduction asymptote, can be both better understood in the regime near the margin of turbulence. In the first part of this thesis, direct numerical simulation trajectories initiated from the edge state are used to follow its unstable manifold into the turbulent basin. In Newtonian flow, the growth of turbulence starts with the intensification of velocity streaks and a sharp rise in the Reynolds shear stress. It is followed by a quick breakdown into high-intensity small-scale fluctuations before entering the core of turbulence. Adding drag-reducing polymers does not affect the initial growth of turbulence but stabilizes the primary streak-vortex structure, which help the flow circumvent the breakdown stage. Throughout the process, polymers act in reaction to the growing turbulence and do not drive the instability. This part not only reveals the transition dynamics into turbulence but also presents a comprehensive view of the bursting stage observed in the near-wall self-sustaining cycle, which starts as the flow leaves hibernating turbulence and is redirected towards the turbulent basin by the unstable manifold of the edge state.
On the other hand, this thesis also discusses the effects of polymer addition on the laminar-turbulent transition in extended domains. Localized turbulent spot can be clearly observed in the large box, and this turbulent region will spread as well as tend to “split” but finally fill up the whole domain before it is separated. Polymers do not affect the flow dynamics until the burst. Similarly, vortex structures rapidly break down into small scales after the first bursting of Reynolds shear stress, but polymer additives depress this process.
The thesis offers a clear and comprehensive overview of the transition into turbulence in the presence of drag-reducing polymers. Future work remains in two major directions. The first is to pinpoint the flow states responsible for the quantitative origin of the universal upper limit of drag reduction observed in experiments. The second is to determine the role, if any, of elasticity-driven instabilities in the transition.
Thesis
Master of Applied Science (MASc)
Turbulence exists everywhere and can be observed in most fluid flows occurring in nature. To reduce the energy consumption, frictional resistance in the turbulence must be considered in fluid transportation. It has been known since the 1940s that a small amount of long-chain polymer additives can dramatically reduce such drag. The mechanism of drag reduction has attracted extensive attention. Two problems of particular interest are the upper limit of drag reduction (termed maximum drag reduction) and the polymer effects on the laminar-turbulent transition. In this thesis, full transient trajectories from marginal turbulent states towards sustained turbulence in both Newtonian and polymeric flows are monitored by direct numerical…
Advisors/Committee Members: Xi, Li, Chemical Engineering.
Subjects/Keywords: drag reduction; MDR; laminar-turbulent transition; edge state
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Bai, X. (2017). EFFECTS OF DRAG-REDUCING POLYMERS ON TURBULENCE GROWTH AND BURSTING IN NEAR MINIMAL CHANNELS AND EXTENDED DOMAINS. (Masters Thesis). McMaster University. Retrieved from http://hdl.handle.net/11375/21348
Chicago Manual of Style (16th Edition):
Bai, Xue. “EFFECTS OF DRAG-REDUCING POLYMERS ON TURBULENCE GROWTH AND BURSTING IN NEAR MINIMAL CHANNELS AND EXTENDED DOMAINS.” 2017. Masters Thesis, McMaster University. Accessed March 07, 2021.
http://hdl.handle.net/11375/21348.
MLA Handbook (7th Edition):
Bai, Xue. “EFFECTS OF DRAG-REDUCING POLYMERS ON TURBULENCE GROWTH AND BURSTING IN NEAR MINIMAL CHANNELS AND EXTENDED DOMAINS.” 2017. Web. 07 Mar 2021.
Vancouver:
Bai X. EFFECTS OF DRAG-REDUCING POLYMERS ON TURBULENCE GROWTH AND BURSTING IN NEAR MINIMAL CHANNELS AND EXTENDED DOMAINS. [Internet] [Masters thesis]. McMaster University; 2017. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/11375/21348.
Council of Science Editors:
Bai X. EFFECTS OF DRAG-REDUCING POLYMERS ON TURBULENCE GROWTH AND BURSTING IN NEAR MINIMAL CHANNELS AND EXTENDED DOMAINS. [Masters Thesis]. McMaster University; 2017. Available from: http://hdl.handle.net/11375/21348
Penn State University
28.
Maciejewski, Daniel.
Computation of Two-Phase Drag Reduction by Gas Injection.
Degree: 2012, Penn State University
URL: https://submit-etda.libraries.psu.edu/catalog/14753
► The skin friction drag on ships and other solid bodies moving through water can be reduced by introducing air through the solid surface into the…
(more)
▼ The skin friction
drag on ships and other solid bodies moving through water can be reduced by introducing air through the solid surface into the attached turbulent boundary layer.
This phenomenon is known as microbubble
drag reduction (MBDR), or simply bubble
drag reduction (BDR).
Air is typically introduced through micropores in sintered plates or through thin slots.
Continuing experimental efforts since the 1970s have revealed several physical mechanisms acting in the two-phase mixture to cause a localized
reduction in skin friction.
Motivated to reduce total vehicle
drag, researchers in this field have focused on finding the functional dependence of the
drag reduction.
A homogeneous, two-phase, compressible computational flow solver is used to simulate these flows.
The homogenized fluid's mixture properties are determined from local volume fractions of air and water.
Mixing of phases after injection is modeled through use of a turbulent dispersion term.
Experiments conducted by Madavan, Deutsch and Merkle (1984) in the twelve-inch water tunnel at ARL/PSU are used for validation.
Good agreement between experiment and model is found for the total
drag reduction with air injection.
The return to no-injection skin friction values downstream of the injection region is also predicted by the model.
Agreement with experiment is found for both single phase simulations and multiphase simulations with gas injection.
Validation was achieved by comparison of velocity profiles and wall-shear profiles between simulation and experiment.
Advisors/Committee Members: Eric G Paterson, Thesis Advisor/Co-Advisor, Scott Miller, Thesis Advisor/Co-Advisor.
Subjects/Keywords: microbubble drag reduction; turbulent boundary layer; CFD; multiphase; two-phase; turbulence
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Maciejewski, D. (2012). Computation of Two-Phase Drag Reduction by Gas Injection. (Thesis). Penn State University. Retrieved from https://submit-etda.libraries.psu.edu/catalog/14753
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Chicago Manual of Style (16th Edition):
Maciejewski, Daniel. “Computation of Two-Phase Drag Reduction by Gas Injection.” 2012. Thesis, Penn State University. Accessed March 07, 2021.
https://submit-etda.libraries.psu.edu/catalog/14753.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
MLA Handbook (7th Edition):
Maciejewski, Daniel. “Computation of Two-Phase Drag Reduction by Gas Injection.” 2012. Web. 07 Mar 2021.
Vancouver:
Maciejewski D. Computation of Two-Phase Drag Reduction by Gas Injection. [Internet] [Thesis]. Penn State University; 2012. [cited 2021 Mar 07].
Available from: https://submit-etda.libraries.psu.edu/catalog/14753.
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Council of Science Editors:
Maciejewski D. Computation of Two-Phase Drag Reduction by Gas Injection. [Thesis]. Penn State University; 2012. Available from: https://submit-etda.libraries.psu.edu/catalog/14753
Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation
Rice University
29.
Bolanos Ellis, Valerie.
Characterization of Friction Reducer Properties in Oil-Field Operations.
Degree: MS, Engineering, 2015, Rice University
URL: http://hdl.handle.net/1911/87709
► Friction reducers are essential additives used to economically achieve the high pumping rates required for slickwater fracturing. Decreased friction reducer performance in high-TDS brines has…
(more)
▼ Friction reducers are essential additives used to economically achieve the high pumping rates required for slickwater fracturing. Decreased friction reducer performance in high-TDS brines has been a major challenge for reusing produced water in hydraulic fracturing. Little work has been done to identify the specific parameters that affect polymeric friction
reduction. This research uses friction flow loop experiments to characterize the performance of partially hydrolyzed polyacrylamide friction reducers in conditions relevant to the oil field. Polymer concentration and degree of hydrolysis effects on friction
reduction are evaluated in the ranges of 0.25-2 gpt and 0-30%, respectively. The decrease in friction reducer performance is measured in brines up to 120,000 mg/L TDS with varying multivalent cation concentrations. The friction reducer interactions with Na+, Ca2+, Mg2+, Fe3+, and Al 3+ ions are individually assessed. The results are compared to experiments with a commercial friction reducer, and used to propose an empirical model to predict friction reducer performance based on water composition.
Advisors/Committee Members: Tomson, Mason B. (advisor), Alvarez, Pedro (committee member), Bedient, Philip (committee member), Tomson , Ross (committee member).
Subjects/Keywords: Friction Reducer; Drag Reducers; Slickwater Fracturing; Friction Reduction Degradation; Produced Water
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Bolanos Ellis, V. (2015). Characterization of Friction Reducer Properties in Oil-Field Operations. (Masters Thesis). Rice University. Retrieved from http://hdl.handle.net/1911/87709
Chicago Manual of Style (16th Edition):
Bolanos Ellis, Valerie. “Characterization of Friction Reducer Properties in Oil-Field Operations.” 2015. Masters Thesis, Rice University. Accessed March 07, 2021.
http://hdl.handle.net/1911/87709.
MLA Handbook (7th Edition):
Bolanos Ellis, Valerie. “Characterization of Friction Reducer Properties in Oil-Field Operations.” 2015. Web. 07 Mar 2021.
Vancouver:
Bolanos Ellis V. Characterization of Friction Reducer Properties in Oil-Field Operations. [Internet] [Masters thesis]. Rice University; 2015. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/1911/87709.
Council of Science Editors:
Bolanos Ellis V. Characterization of Friction Reducer Properties in Oil-Field Operations. [Masters Thesis]. Rice University; 2015. Available from: http://hdl.handle.net/1911/87709
Rice University
30.
Bolanos Ellis, Valerie.
Characterization of Friction Reducer Properties in Oil-Field Operations.
Degree: MS, Engineering, 2015, Rice University
URL: http://hdl.handle.net/1911/87710
► Friction reducers are essential additives used to economically achieve the high pumping rates required for slickwater fracturing. Decreased friction reducer performance in high-TDS brines has…
(more)
▼ Friction reducers are essential additives used to economically achieve the high pumping rates required for slickwater fracturing. Decreased friction reducer performance in high-TDS brines has been a major challenge for reusing produced water in hydraulic fracturing. Little work has been done to identify the specific parameters that affect polymeric friction
reduction. This research uses friction flow loop experiments to characterize the performance of partially hydrolyzed polyacrylamide friction reducers in conditions relevant to the oil field. Polymer concentration and degree of hydrolysis effects on friction
reduction are evaluated in the ranges of 0.25-2 gpt and 0-30%, respectively. The decrease in friction reducer performance is measured in brines up to 120,000 mg/L TDS with varying multivalent cation concentrations. The friction reducer interactions with Na+, Ca2+, Mg2+, Fe3+, and Al 3+ ions are individually assessed. The results are compared to experiments with a commercial friction reducer, and used to propose an empirical model to predict friction reducer performance based on water composition.
Advisors/Committee Members: Tomson, Mason B. (advisor), Alvarez, Pedro (committee member), Bedient, Philip (committee member), Tomson , Ross (committee member).
Subjects/Keywords: Friction Reducer; Drag Reducers; Slickwater Fracturing; Friction Reduction Degradation; Produced Water
Record Details
Similar Records
Cite
Share »
Record Details
Similar Records
Cite
« Share
❌
APA ·
Chicago ·
MLA ·
Vancouver ·
CSE |
Export
to Zotero / EndNote / Reference
Manager
APA (6th Edition):
Bolanos Ellis, V. (2015). Characterization of Friction Reducer Properties in Oil-Field Operations. (Masters Thesis). Rice University. Retrieved from http://hdl.handle.net/1911/87710
Chicago Manual of Style (16th Edition):
Bolanos Ellis, Valerie. “Characterization of Friction Reducer Properties in Oil-Field Operations.” 2015. Masters Thesis, Rice University. Accessed March 07, 2021.
http://hdl.handle.net/1911/87710.
MLA Handbook (7th Edition):
Bolanos Ellis, Valerie. “Characterization of Friction Reducer Properties in Oil-Field Operations.” 2015. Web. 07 Mar 2021.
Vancouver:
Bolanos Ellis V. Characterization of Friction Reducer Properties in Oil-Field Operations. [Internet] [Masters thesis]. Rice University; 2015. [cited 2021 Mar 07].
Available from: http://hdl.handle.net/1911/87710.
Council of Science Editors:
Bolanos Ellis V. Characterization of Friction Reducer Properties in Oil-Field Operations. [Masters Thesis]. Rice University; 2015. Available from: http://hdl.handle.net/1911/87710
◁ [1] [2] [3] [4] [5] [6] ▶
. 
Open Access Theses and Dissertations
