+publisher:"University of Texas – Austin" +contributor:("Raman, Venkat")

University of Texas – Austin

1. Kim, Sin Hyen. Effect of jet configuration on transverse jet mixing process.

Degree: MSin Engineering, Aerospace Engineering, 2011, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2011-05-3610

► Transverse jets in crossflow are widely used to enhance mixing between two flow streams. Such jets exhibit complex flow features, and are highly sen- sitive… (more)

Subjects/Keywords: Jet in crossflow; Transverse jet; Turbulent mixing

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APA (6^th Edition):

Kim, S. H. (2011). Effect of jet configuration on transverse jet mixing process. (Masters Thesis). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2011-05-3610

Chicago Manual of Style (16^th Edition):

Kim, Sin Hyen. “Effect of jet configuration on transverse jet mixing process.” 2011. Masters Thesis, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2011-05-3610.

MLA Handbook (7^th Edition):

Kim, Sin Hyen. “Effect of jet configuration on transverse jet mixing process.” 2011. Web. 22 Jan 2021.

Vancouver:

Kim SH. Effect of jet configuration on transverse jet mixing process. [Internet] [Masters thesis]. University of Texas – Austin; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2011-05-3610.

Council of Science Editors:

Kim SH. Effect of jet configuration on transverse jet mixing process. [Masters Thesis]. University of Texas – Austin; 2011. Available from: http://hdl.handle.net/2152/ETD-UT-2011-05-3610

University of Texas – Austin

2. Singh, Ravi Ishwar. Direct numerical simulation and reaction path analysis of titania formation in flame synthesis.

Degree: MSin Engineering, Mechanical Engineering, 2012, University of Texas – Austin

URL: http://hdl.handle.net/2152/23016

► Flame-based synthesis is an attractive industrial process for the large scale generation of nanoparticles. In this aerosol process, a gasifi ed precursor is injected into… (more)

▼ Flame-based synthesis is an attractive industrial process for the large scale generation of nanoparticles. In this aerosol process, a gasifi ed precursor is injected into a high-temperature turbulent flame, where oxidation followed by particle nucleation and other solid phase dynamics create nanoparticles. Precursor oxidation, which ultimately leads to nucleation, is strongly influenced by the turbulent flame dynamics. Here, direct numerical simulation (DNS) of a canonical homogeneous flow is used to understand the interaction between a methane/air flame and titanium tetrachloride oxidation to titania. Detailed chemical kinetics is used to describe the combustion and precursor oxidation processes. Results show that the initial precursor decomposition is heavily influenced by the gas phase temperature field. However, temperature insensitivity of subsequent reactions in the precursor oxidation pathway slow down conversion to the titania. Consequently, titania formation occurs at much longer time scales compared to that of hydrocarbon oxidation. Further, only a fraction of the precursor is converted to titania, and a signi cant amount of partially-oxidized precursor species are formed. Introducing the precursor in the oxidizer stream as opposed to the fuel stream has only a minimal impact on the oxidation dynamics. In order to understand modeling issues, the DNS results are compared with the laminar flamelet model. It is shown that the flamelet assumption qualitatively reproduces the oxidation structure. Further, reduced oxygen concentration in the near-flame location critically a ffects titania formation. The DNS results also show that titania forms on the lean and rich sides of the flame. A reaction path analysis (RPA) is conducted. The results illustrate the di ffering reaction pathways of the detailed chemical mechanism depending on the composition of the mixture. The RPA results corroborate with the DNS results that titania formation is maximized at two mixture fraction values, one on the lean side of the flame, and one on the rich side. Advisors/Committee Members: Ezekoye, Ofodike A. (advisor), Raman, Venkat (advisor).

Subjects/Keywords: Direct numerical simulation (DNS); Combustion; Turbulence; Titania; Nanoparticles; Detailed chemical kinetics

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APA (6^th Edition):

Singh, R. I. (2012). Direct numerical simulation and reaction path analysis of titania formation in flame synthesis. (Masters Thesis). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/23016

Chicago Manual of Style (16^th Edition):

Singh, Ravi Ishwar. “Direct numerical simulation and reaction path analysis of titania formation in flame synthesis.” 2012. Masters Thesis, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/23016.

MLA Handbook (7^th Edition):

Singh, Ravi Ishwar. “Direct numerical simulation and reaction path analysis of titania formation in flame synthesis.” 2012. Web. 22 Jan 2021.

Vancouver:

Singh RI. Direct numerical simulation and reaction path analysis of titania formation in flame synthesis. [Internet] [Masters thesis]. University of Texas – Austin; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/23016.

Council of Science Editors:

Singh RI. Direct numerical simulation and reaction path analysis of titania formation in flame synthesis. [Masters Thesis]. University of Texas – Austin; 2012. Available from: http://hdl.handle.net/2152/23016

University of Texas – Austin

3. Ebi, Dominik Fabian. Boundary layer flashback of swirl flames.

Degree: PhD, Aerospace Engineering, 2016, University of Texas – Austin

URL: http://hdl.handle.net/2152/38721

► Flame flashback in the boundary layer of swirling flows is investigated experimentally in a model swirl combustor. The model combustor features a mixing tube with… (more)

▼ Flame flashback in the boundary layer of swirling flows is investigated experimentally in a model swirl combustor. The model combustor features a mixing tube with an axial swirler and an attached center body. The findings provide novel insight into the mechanism facilitating boundary layer flashback of swirl flames. Turbulent, lean-premixed flames of methane and hydrogen are studied at atmospheric pressure and bulk flow velocities up to 5 m/s. Hydrogen contents range from 0% to 95% and equivalence ratios range from 0.4 to 1. The focus in the present work is on the upstream flame propagation inside the mixing tube. Stereoscopic particle image velocimetry (PIV) is applied at kilohertz-rate to provide the time-resolved, three-component velocity field. The flame front is detected simultaneously based on the acquired Mie scattering images. Simultaneous high-speed chemiluminescence imaging provides the overall flame shape and global propagation direction. In addition to the planar measurements, a technique capable of detecting the instantaneous, time-resolved, 3D flame front topography is developed and applied successfully. Oil droplets, which vaporize in the preheat zone of the flame, serve as the marker for the flame front. The droplets are illuminated with a laser and imaged from four different views followed by a tomographic reconstruction to obtain the volumetric particle field. The velocity field in the unburnt gas is measured using tomographic PIV. The resulting data include the simultaneous 3D flame front and volumetric velocity field at 5 kHz. Flashback is found to occur in the form of large-scale, convex-shaped flame tongues, which swirl in the bulk flow direction as they propagate in the negative axial direction along the center body wall. Gas dilatation associated with the heat release imposes a blockage effect on the approach flow, which causes a 3D deflection of streamlines. As a result, a region of negative axial velocity forms along the leading side of the flame tongues, which facilitates flashback. These regions of negative axial velocity, already observed in previous studies, are shown to be the result of a predominantly swirling fluid motion as opposed to boundary layer separation or flow recirculation. The effect of hydrogen addition on flashback is investigated. Flashback occurs at significantly leaner conditions for hydrogen-rich flames, but the mechanism driving flashback is found to be independent of the hydrogen content for the conditions investigated in the present work. Quantitative differences in the flame-flow interaction between methane and hydrogen-rich flashbacks are discussed in detail. Advisors/Committee Members: Clemens, Noel T. (advisor), Ezekoye, Ofodike A (committee member), Raja, Laxminarayan (committee member), Raman, Venkat (committee member), Varghese, Philip L (committee member).

Subjects/Keywords: Turbulent flames; Flashback; High-speed PIV; Tomographic PIV

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APA (6^th Edition):

Ebi, D. F. (2016). Boundary layer flashback of swirl flames. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/38721

Chicago Manual of Style (16^th Edition):

Ebi, Dominik Fabian. “Boundary layer flashback of swirl flames.” 2016. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/38721.

MLA Handbook (7^th Edition):

Ebi, Dominik Fabian. “Boundary layer flashback of swirl flames.” 2016. Web. 22 Jan 2021.

Vancouver:

Ebi DF. Boundary layer flashback of swirl flames. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2016. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/38721.

Council of Science Editors:

Ebi DF. Boundary layer flashback of swirl flames. [Doctoral Dissertation]. University of Texas – Austin; 2016. Available from: http://hdl.handle.net/2152/38721

University of Texas – Austin

4. Koo, Heeseok. Large-eddy simulations of scramjet engines.

Degree: PhD, Aerospace Engineering, 2011, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2011-05-3203

► The main objective of this dissertation is to develop large-eddy simulation (LES) based computational tools for supersonic inlet and combustor design. In the recent past,… (more)

▼ The main objective of this dissertation is to develop large-eddy simulation (LES) based computational tools for supersonic inlet and combustor design. In the recent past, LES methodology has emerged as a viable tool for modeling turbulent combustion. LES computes the large scale mixing process accurately, thereby providing a better starting point for small-scale models that describe the combustion process. In fact, combustion models developed in the context of Reynolds-averaged Navier Stokes (RANS) equations exhibit better predictive capability when used in the LES framework. The development of a predictive computational tool based on LES will provide a significant boost to the design of scramjet engines. Although LES has been used widely in the simulation of subsonic turbulent flows, its application to high-speed flows has been hampered by a variety of modeling and numerical issues. In this work, we develop a comprehensive LES methodology for supersonic flows, focusing on the simulation of scramjet engine components. This work is divided into three sections. First, a robust compressible flow solver for a generalized high-speed flow configuration is developed. By using carefully designed numerical schemes, dissipative errors associated with discretization methods for high-speed flows are minimized. Multiblock and immersed boundary method are used to handle scramjet-specific geometries. Second, a new combustion model for compressible reactive flows is developed. Subsonic combustion models are not directly applicable in high-speed flows due to the coupling between the energy and velocity fields. Here, a probability density function (PDF) approach is developed for high-speed combustion. This method requires solution to a high dimensional PDF transport equation, which is achieved through a novel direct quadrature method of moments (DQMOM). The combustion model is validated using experiments on supersonic reacting flows. Finally, the LES methodology is used to study the inlet-isolator component of a dual-mode scramjet. The isolator is a critical component that maintains the compression shock structures required for stable combustor operation in ramjet mode. We simulate unsteady dynamics inside an experimental isolator, including the propagation of an unstart event that leads to loss of compression. Using a suite of simulations, the sensitivity of the results to LES models and numerical implementation is studied. Advisors/Committee Members: Raman, Venkat (advisor), Varghese, Philip L. (committee member), Clemens, Noel T. (committee member), Moser, Robert D. (committee member), Ezekoye, Ofodike A. (committee member).

Subjects/Keywords: Large-eddy simulations; Combustion model; DQMOM; Direct quadrature method of moments; Compressible flow; Shock capturing method; Hyperviscosity; Scramjet; Inlet-isolator; Unstart

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APA (6^th Edition):

Koo, H. (2011). Large-eddy simulations of scramjet engines. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2011-05-3203

Chicago Manual of Style (16^th Edition):

Koo, Heeseok. “Large-eddy simulations of scramjet engines.” 2011. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2011-05-3203.

MLA Handbook (7^th Edition):

Koo, Heeseok. “Large-eddy simulations of scramjet engines.” 2011. Web. 22 Jan 2021.

Vancouver:

Koo H. Large-eddy simulations of scramjet engines. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2011-05-3203.

Council of Science Editors:

Koo H. Large-eddy simulations of scramjet engines. [Doctoral Dissertation]. University of Texas – Austin; 2011. Available from: http://hdl.handle.net/2152/ETD-UT-2011-05-3203

University of Texas – Austin

5. Marr, Kevin Chek-Shing. Investigation of acoustically forced non-premixed jet flames in crossflow.

Degree: PhD, Aerospace Engineering, 2011, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2011-05-3133

► The work presented here discusses the effects of strong acoustic forcing on jet flames in crossflow (JFICF) and the physical mechanisms behind theses effects. For… (more)

▼ The work presented here discusses the effects of strong acoustic forcing on jet flames in crossflow (JFICF) and the physical mechanisms behind theses effects. For forced non-premixed JFICF, the jet fuel flow is modulated using an acoustic speaker system, which results in a drastic decrease in flame length and soot luminosity. Forced JFICF are characterized by periodic ejections of high-momentum, deeply penetrating vortical structures, which draws air into the jet nozzle and enhances mixing in the nearfield region of the jet. Mixture fraction images of the non-reacting forced jet in crossflow are obtained from acetone planar laser-induced fluorescence and show that the ejected jet fluid is effectively partially premixed. Flame luminosity images and exhaust gas measurements show that forced non-premixed JFICF exhibit similar characteristics to unforced partially-premixed JFICF. Both strong forcing and air dilution result in net reductions in NOx, but increases in CO and unburned hydrocarbons. NOx scaling analysis is presented for both forced non-premixed and unforced partially-premixed flames. Using flame volume arguments, EINOx scales with amplitude ratio for forced non- premixed flames, but does not scale with air dilution for unforced partially-premixed flames. The difference in scaling behavior is attributed to differences in flame structure. The effect of forcing on the flowfield dynamics of non-premixed JFICF is investigated using high-speed stereoscopic particle image velocimetry and luminosity imaging. The frequency spectra of the windward and lee-side flame base motions obtained from luminosity movies of the forced JFICF show a peak at the forcing frequency in the lee-side spectrum, but not on the windward-side spectrum. The lee-side flame base responds to the forcing frequency because the lee-side flame base stabilizes closer to the jet exit. The windward-side flame base does not respond to the forcing frequency because the integrated effect of the incident crossflow and vortical ejections leads to extinction of the flame base. From the PIV measurements, flowfield statistics are conditioned at the flame base. The local gas velocity at the flame base did not collapse for forced and unforced JFICF and was found to exceed 3SL. The flame propagation velocity was determined from the motion of the flame base, which is inferred from regions of evaporated seed particles in the time-resolved PIV images. The flame propagation velocity collapses for forced and unforced JFICF, which implies that the flame base is an edge flame; however, the most probable propagation velocity, approximately 2-3SL, is larger than propagation velocity predicted by edge flame theories. A possible explanation is that the flame propagation is enhanced by turbulent intensities and flame curvature. Advisors/Committee Members: Clemens, Noel T. (advisor), Ezekoye, Ofodike A. (advisor), Hall, Matthew J. (committee member), Raman, Venkat (committee member), Varghese, Philip L. (committee member).

Subjects/Keywords: Pulsed combustion; Acoustics; Jet flames; Emissions; Flame stability

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APA (6^th Edition):

Marr, K. C. (2011). Investigation of acoustically forced non-premixed jet flames in crossflow. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2011-05-3133

Chicago Manual of Style (16^th Edition):

Marr, Kevin Chek-Shing. “Investigation of acoustically forced non-premixed jet flames in crossflow.” 2011. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2011-05-3133.

MLA Handbook (7^th Edition):

Marr, Kevin Chek-Shing. “Investigation of acoustically forced non-premixed jet flames in crossflow.” 2011. Web. 22 Jan 2021.

Vancouver:

Marr KC. Investigation of acoustically forced non-premixed jet flames in crossflow. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2011-05-3133.

Council of Science Editors:

Marr KC. Investigation of acoustically forced non-premixed jet flames in crossflow. [Doctoral Dissertation]. University of Texas – Austin; 2011. Available from: http://hdl.handle.net/2152/ETD-UT-2011-05-3133

University of Texas – Austin

6. Lietz, Christopher Fernandez. Large-Eddy simulation of gas turbine combustors using Flamelet Manifold methods.

Degree: PhD, Aerospace engineering, 2015, University of Texas – Austin

URL: http://hdl.handle.net/2152/32911

► The main objective of this work was to develop a large-eddy simulation (LES) based computational tool for application to both premixed and non- premixed combustion… (more)

▼ The main objective of this work was to develop a large-eddy simulation (LES) based computational tool for application to both premixed and non- premixed combustion of low-Mach number flows in gas turbines. In the recent past, LES methodology has emerged as a viable tool for modeling turbulent combustion. LES is particularly well-suited for the compu- tation of large scale mixing, which provides a firm starting point for the small scale models which describe the reaction processes. Even models developed in the context of Reynolds averaged Navier-Stokes (RANS) exhibit superior results in the LES framework. Although LES is a widespread topic of research, in industrial applications it is often seen as a less attractive option than RANS, which is computationally inexpensive and often returns sufficiently accurate results. However, there are many commonly encountered problems for which RANS is unsuitable. This work is geared towards such instances, with a solver developed for use in unsteady reacting flows on unstructured grids. The work is divided into two sections. First, a robust CFD solver for a generalized incompressible, reacting flow configuration is developed. The computational algorithm, which com- bines elements of the low-Mach number approximation and pressure projection methods with other techniques, is described. Coupled to the flow solver is a combustion model based on the flamelet progress variable approach (FPVA), adapted to current applications. Modifications which promote stability and accuracy in the context of unstructured meshes are also implemented. Second, the LES methodology is used to study three specific problems. The first is a channel geometry with a lean premixed hydrogen mixture, in which the unsteady flashback phenomenon is induced. DNS run in tandem is used for establishing the validity of the LES. The second problem is a swirling gas turbine combustor, which extends the channel flashback study to a more practical application with stratified premixed methane and hydrogen/methane mixtures. Experimental results are used for comparison. Finally, the third problem tests the solver’s abilities further, using a more complex fuel JP-8, Lagrangian fuel droplets, and a complicated geometry. In this last configu- ration, experimental results validate early simulations while later simulations examine the physics of reacting sprays under high centripetal loading. Advisors/Committee Members: Clemens, Noel T. (advisor), Raman, Venkat (advisor), Ezekoye, Ofodike A (committee member), Goldstein, David B (committee member), Varghese, Philip L (committee member).

Subjects/Keywords: Computational fluid dynamics (CFD); Large-Eddy simulation (LES); Combustion; Flamelet progress variable approach (FPVA)

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APA (6^th Edition):

Lietz, C. F. (2015). Large-Eddy simulation of gas turbine combustors using Flamelet Manifold methods. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/32911

Chicago Manual of Style (16^th Edition):

Lietz, Christopher Fernandez. “Large-Eddy simulation of gas turbine combustors using Flamelet Manifold methods.” 2015. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/32911.

MLA Handbook (7^th Edition):

Lietz, Christopher Fernandez. “Large-Eddy simulation of gas turbine combustors using Flamelet Manifold methods.” 2015. Web. 22 Jan 2021.

Vancouver:

Lietz CF. Large-Eddy simulation of gas turbine combustors using Flamelet Manifold methods. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2015. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/32911.

Council of Science Editors:

Lietz CF. Large-Eddy simulation of gas turbine combustors using Flamelet Manifold methods. [Doctoral Dissertation]. University of Texas – Austin; 2015. Available from: http://hdl.handle.net/2152/32911

7. Heye, Colin Russell. Adaptive and convergent methods for large eddy simulation of turbulent combustion.

Degree: PhD, Aerospace Engineering, 2014, University of Texas – Austin

URL: http://hdl.handle.net/2152/29141

► In the recent past, LES methodology has emerged as a viable tool for modeling turbulent combustion. LES computes the large scale mixing process accurately, thereby… (more)

▼ In the recent past, LES methodology has emerged as a viable tool for modeling turbulent combustion. LES computes the large scale mixing process accurately, thereby providing a better starting point for small-scale models that describe the combustion process. Significant effort has been made over past decades to improve accuracy and applicability of the LES approach to a wide range of flows, though the current conventions often lack consistency to the problems at hand. To this end, the two main objectives of this dissertation are to develop a dynamic transport equation-based combustion model for large- eddy simulation (LES) of turbulent spray combustion and to investigate grid- independent LES modeling for scalar mixing. Long-standing combustion modeling approaches have shown to be suc- cessful for a wide range of gas-phase flames, however, the assumptions required to derive these formulations are invalidated in the presence of liquid fuels and non-negligible evaporation rates. In the first part of this work, a novel ap- proach is developed to account for these evaporation effects and the resulting multi-regime combustion process. First, the mathematical formulation is de- rived and the numerical implementation in a low-Mach number computational solver is verified against one-dimensional and lab scale, both non-reacting and reacting spray-laden flows. In order to clarify the modeling requirements in LES for spray combustion applications, results from a suite of fully-resolved direct numerical simulations (DNS) of a spray laden planar jet flame are fil- tered at a range of length scales. LES results are then validated against two sets of experimental jet flames, one having a pilot and allowing for reduced chemistry modeling and the second requiring the use of detail chemistry with in situ tabulation to reduce the computational cost of the direct integration of a chemical mechanism. The conventional LES governing equations are derived from a low-pass filtering of the Navier-Stokes equations. In practice, the filter used to derive the LES governing equations is not formally defined and instead, it is assumed that the discretization of LES equations will implicitly act as a low-pass filter. The second part of this study investigates an alternative derivation of the LES governing equations that requires the formal definition of the filtering operator, known as explicitly filtered LES. It has been shown that decoupling the filter- ing operation from the underlying grid allows for the isolation of subfilter-scale modeling errors from numerical discretization errors. Specific to combustion modeling are the aggregate errors associated with modeling sub-filter distribu- tions of scalars that are transported by numerical impacted turbulent fields. Quantities of interest to commonly-used combustion models, including sub- filter scalar variance and filtered scalar dissipation rate, are investigated for both homogeneous and shear-driven turbulent mixing. Advisors/Committee Members: Raman, Venkat (advisor).

Subjects/Keywords: Computational fluid dynamics; Large eddy simulation; Spray combustion; Transported pdf; Explicit filtering; Scalar mixing

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APA (6^th Edition):

Heye, C. R. (2014). Adaptive and convergent methods for large eddy simulation of turbulent combustion. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/29141

Chicago Manual of Style (16^th Edition):

Heye, Colin Russell. “Adaptive and convergent methods for large eddy simulation of turbulent combustion.” 2014. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/29141.

MLA Handbook (7^th Edition):

Heye, Colin Russell. “Adaptive and convergent methods for large eddy simulation of turbulent combustion.” 2014. Web. 22 Jan 2021.

Vancouver:

Heye CR. Adaptive and convergent methods for large eddy simulation of turbulent combustion. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2014. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/29141.

Council of Science Editors:

Heye CR. Adaptive and convergent methods for large eddy simulation of turbulent combustion. [Doctoral Dissertation]. University of Texas – Austin; 2014. Available from: http://hdl.handle.net/2152/29141

8. Braman, Kalen Elvin. Parametric uncertainty and sensitivity methods for reacting flows.

Degree: PhD, Aerospace Engineering, 2014, University of Texas – Austin

URL: http://hdl.handle.net/2152/25067

► A Bayesian framework for quantification of uncertainties has been used to quantify the uncertainty introduced by chemistry models. This framework adopts a probabilistic view to… (more)

▼ A Bayesian framework for quantification of uncertainties has been used to quantify the uncertainty introduced by chemistry models. This framework adopts a probabilistic view to describe the state of knowledge of the chemistry model parameters and simulation results. Given experimental data, this method updates the model parameters' values and uncertainties and propagates that parametric uncertainty into simulations. This study focuses on syngas, a combination in various ratios of H2 and CO, which is the product of coal gasification. Coal gasification promises to reduce emissions by replacing the burning of coal with the less polluting burning of syngas. Despite the simplicity of syngas chemistry models, they nonetheless fail to accurately predict burning rates at high pressure. Three syngas models have been calibrated using laminar flame speed measurements. After calibration the resulting uncertainty in the parameters is propagated forward into the simulation of laminar flame speeds. The model evidence is then used to compare candidate models. Sensitivity studies, in addition to Bayesian methods, can be used to assess chemistry models. Sensitivity studies provide a measure of how responsive target quantities of interest (QoIs) are to changes in the parameters. The adjoint equations have been derived for laminar, incompressible, variable density reacting flow and applied to hydrogen flame simulations. From the adjoint solution, the sensitivity of the QoI to the chemistry model parameters has been calculated. The results indicate the most sensitive parameters for flame tip temperature and NOx emission. Such information can be used in the development of new experiments by pointing out which are the critical chemistry model parameters. Finally, a broader goal for chemistry model development is set through the adjoint methodology. A new quantity, termed field sensitivity, is introduced to guide chemistry model development. Field sensitivity describes how information of perturbations in flowfields propagates to specified QoIs. The field sensitivity, mathematically shown as equivalent to finding the adjoint of the primal governing equations, is obtained for laminar hydrogen flame simulations using three different chemistry models. Results show that even when the primal solution is sufficiently close for the three mechanisms, the field sensitivity can vary. Advisors/Committee Members: Raman, Venkat (advisor).

Subjects/Keywords: Combustion chemistry; Chemical kinetics; Sensitivity; Uncertainty quantification; Laminar flames

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APA (6^th Edition):

Braman, K. E. (2014). Parametric uncertainty and sensitivity methods for reacting flows. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/25067

Chicago Manual of Style (16^th Edition):

Braman, Kalen Elvin. “Parametric uncertainty and sensitivity methods for reacting flows.” 2014. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/25067.

MLA Handbook (7^th Edition):

Braman, Kalen Elvin. “Parametric uncertainty and sensitivity methods for reacting flows.” 2014. Web. 22 Jan 2021.

Vancouver:

Braman KE. Parametric uncertainty and sensitivity methods for reacting flows. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2014. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/25067.

Council of Science Editors:

Braman KE. Parametric uncertainty and sensitivity methods for reacting flows. [Doctoral Dissertation]. University of Texas – Austin; 2014. Available from: http://hdl.handle.net/2152/25067

9. Voelkel, Stephen Joseph. Thermal nonequilibrium models for high-temperature reactive processes.

Degree: PhD, Computational Science, Engineering, and Mathematics, 2016, University of Texas – Austin

URL: http://hdl.handle.net/2152/47234

► This dissertation examines how thermal nonequilibrium affects mixing and combustion in high-enthalpy, high-speed systems such as reentry vehicles, scramjets, and detonation-driven engines. Specifically, the focus… (more)

▼ This dissertation examines how thermal nonequilibrium affects mixing and combustion in high-enthalpy, high-speed systems such as reentry vehicles, scramjets, and detonation-driven engines. Specifically, the focus is in the development of physical models that accurately describe thermal nonequilibrium in a continuum-scale ow and its relative effect on mixing and reaction processes. To this end, the quasi-classical trajectory method is utilized, in which bimolecular collisions (or trajectories) are individually simulated. The aggregate of the outcomes from many trajectories is then used to calculate the macroscopic reaction and scattering rates of the system. A QCT program is presented for massively parallel simulations, which includes an algorithm for calculating and tabulating the potential energy surface throughout the QCT simulation. Using the QCT program, chain-reactions in hydrogen combustions are simulated, and the subsequent rates are used directly in CFD simulations as well as to develop vibrational nonequilibrium reaction rate models. Also, nitrogen dissociation is simulated to calculate the dissociation rate as a function of independent translational, rotational, and vibrational temperatures, thus extending the conventional two-temperature model. This simulation is made tractable via a new method for selectively sampling trajectories. Finally, the QCT program is utilized to calculate N₂-O₂ inelastic cross-sections. This work was motivated by CFD simulations of experimental observations which indicated that the conventional N₂-O₂ vibrational exchange rates were invalid at moderate temperatures. The QCT-calculated rates support these observations. In addition to QCT-based simulations, 1D and 2D simulations of detonation waves with vibrational nonequilibrium (modeled using the aforementioned data) are analyzed. It is observed that nonequilibrium only marginally affects the induction zone of the detonation wave. However, in the 2D simulations, it is observed that vibrational nonequilibrium plays a critical role in determining detonation cell sizes. In summary, vibrational nonequilibrium is analyzed using QCT for a variety of systems, and the resulting data is utilized to develop CFD-scale models. We have high confidence in the resulting models because they are derived from first principles and microscopic observations as opposed to simplified models or empirical fits. Advisors/Committee Members: Varghese, Philip L. (advisor), Raman, Venkat (advisor), Arbogast, Todd J (committee member), Dawson, Clint N (committee member), Moser, Robert D (committee member), Stanton, John F (committee member).

Subjects/Keywords: Thermal nonequilibrium; Scramjet; Reentry vehicle; Quasi-classical trajectory; QCT; Hydrogen combustion; Nitrogen dissociation; Nitrogen-oxygen scattering

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APA (6^th Edition):

Voelkel, S. J. (2016). Thermal nonequilibrium models for high-temperature reactive processes. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/47234

Chicago Manual of Style (16^th Edition):

Voelkel, Stephen Joseph. “Thermal nonequilibrium models for high-temperature reactive processes.” 2016. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/47234.

MLA Handbook (7^th Edition):

Voelkel, Stephen Joseph. “Thermal nonequilibrium models for high-temperature reactive processes.” 2016. Web. 22 Jan 2021.

Vancouver:

Voelkel SJ. Thermal nonequilibrium models for high-temperature reactive processes. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2016. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/47234.

Council of Science Editors:

Voelkel SJ. Thermal nonequilibrium models for high-temperature reactive processes. [Doctoral Dissertation]. University of Texas – Austin; 2016. Available from: http://hdl.handle.net/2152/47234

10. Martinez, Jaime, master of science in engineering. Large eddy simulation analysis of non-reacting sprays inside a high-g combustor.

Degree: MSin Engineering, Aerospace Engineering, 2012, University of Texas – Austin

URL: http://hdl.handle.net/2152/19683

► Inter-turbine burners are useful devices for increasing engine power. To reduce the size of these combustion devices, ultra-compact combustor (UCC) concepts are necessary. One such… (more)

Subjects/Keywords: Turbulence modeling; Kolmogorov scales; Spray simulation; Droplet simulation; LES; RANS; Lagrangian droplets; Navier Stokes Equations; OpenFOAM

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APA (6^th Edition):

Martinez, Jaime, m. o. s. i. e. (2012). Large eddy simulation analysis of non-reacting sprays inside a high-g combustor. (Masters Thesis). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/19683

Chicago Manual of Style (16^th Edition):

Martinez, Jaime, master of science in engineering. “Large eddy simulation analysis of non-reacting sprays inside a high-g combustor.” 2012. Masters Thesis, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/19683.

MLA Handbook (7^th Edition):

Martinez, Jaime, master of science in engineering. “Large eddy simulation analysis of non-reacting sprays inside a high-g combustor.” 2012. Web. 22 Jan 2021.

Vancouver:

Martinez, Jaime mosie. Large eddy simulation analysis of non-reacting sprays inside a high-g combustor. [Internet] [Masters thesis]. University of Texas – Austin; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/19683.

Council of Science Editors:

Martinez, Jaime mosie. Large eddy simulation analysis of non-reacting sprays inside a high-g combustor. [Masters Thesis]. University of Texas – Austin; 2012. Available from: http://hdl.handle.net/2152/19683

11. Dyson, Thomas Earl. Experimental and computational investigation of film cooling on a large scale C3X turbine vane including conjugate effects.

Degree: PhD, Mechanical Engineering, 2012, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2012-12-6743

► This study focused on the improvement of film cooling for gas turbine vanes using both computational and experimental techniques. The experimental component used a matched… (more)

▼ This study focused on the improvement of film cooling for gas turbine vanes using both computational and experimental techniques. The experimental component used a matched Biot number model to measure scaled surface temperature (overall effectiveness) distributions representative of engine conditions for two new configurations. One configuration consisted of a single row of holes on the pressure surface while the other used numerous film cooling holes over the entire vane including a showerhead. Both configurations used internal impingement cooling representative of a 1st vane. Adiabatic effectiveness was also measured. No previous studies had shown the effect of injection on the mean and fluctuating velocity profiles for the suction surface, so measurements were made at two locations immediately upstream of film cooling holes from the fully cooled cooling configuration. Different blowing conditions were evaluated. Computational tools are increasingly important in the design of advanced gas turbine engines and validation of these tools is required prior to integration into the design process. Two film cooling configurations were simulated and compared to past experimental work. Data from matched Biot number experiments was used to validate the overall effectiveness from conjugate simulations in addition to adiabatic effectiveness. A simulation of a single row of cooling holes on the suction side also gave additional insight into the interaction of film cooling jets with the thermal boundary layer. A showerhead configuration was also simulated. The final portion of this study sought to evaluate the performance of six RANS models (standard, realizable, and renormalization group k-ε; standard k-ω; k-ω SST; and Transition SST) with respect to the prediction of thermal boundary layers. The turbulent Prandtl number was varied to test a simple method for improvement of the thermal boundary layer predictions. Advisors/Committee Members: Bogard, David G. (advisor), Bradshaw, Sean (committee member), Murthy, Jayathi (committee member), Raman, Venkat (committee member), Shi, Li (committee member).

Subjects/Keywords: Film cooling; Conjugate; RANS CFD; Boundary layers

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APA (6^th Edition):

Dyson, T. E. (2012). Experimental and computational investigation of film cooling on a large scale C3X turbine vane including conjugate effects. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2012-12-6743

Chicago Manual of Style (16^th Edition):

Dyson, Thomas Earl. “Experimental and computational investigation of film cooling on a large scale C3X turbine vane including conjugate effects.” 2012. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2012-12-6743.

MLA Handbook (7^th Edition):

Dyson, Thomas Earl. “Experimental and computational investigation of film cooling on a large scale C3X turbine vane including conjugate effects.” 2012. Web. 22 Jan 2021.

Vancouver:

Dyson TE. Experimental and computational investigation of film cooling on a large scale C3X turbine vane including conjugate effects. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2012-12-6743.

Council of Science Editors:

Dyson TE. Experimental and computational investigation of film cooling on a large scale C3X turbine vane including conjugate effects. [Doctoral Dissertation]. University of Texas – Austin; 2012. Available from: http://hdl.handle.net/2152/ETD-UT-2012-12-6743

12. Donde, Pratik Prakash. LES/PDF approach for turbulent reacting flows.

Degree: PhD, Aerospace Engineering, 2012, University of Texas – Austin

URL: http://hdl.handle.net/2152/19481

► The probability density function (PDF) approach is a powerful technique for large eddy simulation (LES) based modeling of turbulent reacting flows. In this approach, the… (more)

▼ The probability density function (PDF) approach is a powerful technique for large eddy simulation (LES) based modeling of turbulent reacting flows. In this approach, the joint-PDF of all reacting scalars is estimated by solving a PDF transport equation, thus providing detailed information about small-scale correlations between these quantities. The objective of this work is to further develop the LES/PDF approach for studying flame stabilization in supersonic combustors, and for soot modeling in turbulent flames. Supersonic combustors are characterized by strong shock-turbulence interactions which preclude the application of conventional Lagrangian stochastic methods for solving the PDF transport equation. A viable alternative is provided by quadrature based methods which are deterministic and Eulerian. In this work, it is first demonstrated that the numerical errors associated with LES require special care in the development of PDF solution algorithms. The direct quadrature method of moments (DQMOM) is one quadrature-based approach developed for supersonic combustion modeling. This approach is shown to generate inconsistent evolution of the scalar moments. Further, gradient-based source terms that appear in the DQMOM transport equations are severely underpredicted in LES leading to artificial mixing of fuel and oxidizer. To overcome these numerical issues, a new approach called semi-discrete quadrature method of moments (SeQMOM) is formulated. The performance of the new technique is compared with the DQMOM approach in canonical flow configurations as well as a three-dimensional supersonic cavity stabilized flame configuration. The SeQMOM approach is shown to predict subfilter statistics accurately compared to the DQMOM approach. For soot modeling in turbulent flows, an LES/PDF approach is integrated with detailed models for soot formation and growth. The PDF approach directly evolves the joint statistics of the gas-phase scalars and a set of moments of the soot number density function. This LES/PDF approach is then used to simulate a turbulent natural gas flame. A Lagrangian method formulated in cylindrical coordinates solves the high dimensional PDF transport equation and is coupled to an Eulerian LES solver. The LES/PDF simulations show that soot formation is highly intermittent and is always restricted to the fuel-rich region of the flow. The PDF of soot moments has a wide spread leading to a large subfilter variance. Further, the conditional statistics of soot moments conditioned on mixture fraction and reaction progress variable show strong correlation between the gas phase composition and soot moments. Advisors/Committee Members: Raman, Venkat (advisor), Clemens, Noel (committee member), Ezekoye, Ofodike (committee member), Goldstein, David (committee member), Moser, Robert (committee member).

Subjects/Keywords: Probability density function approach; Large eddy simulation; Supersonic combustion modeling; Soot modeling; Turbulent reacting flows; Direct quadrature method of moments; Semi-discrete quadrature method of moments; Quadrature based methods; Lagrangian Monte Carlo methods; Supersonic combustors; Flame stabilization; Polycyclic aromatic hydrocarbons; Soot-turbulence-chemistry interactions; Shock-turbulence-chemistry interactions

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APA (6^th Edition):

Donde, P. P. (2012). LES/PDF approach for turbulent reacting flows. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/19481

Chicago Manual of Style (16^th Edition):

Donde, Pratik Prakash. “LES/PDF approach for turbulent reacting flows.” 2012. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/19481.

MLA Handbook (7^th Edition):

Donde, Pratik Prakash. “LES/PDF approach for turbulent reacting flows.” 2012. Web. 22 Jan 2021.

Vancouver:

Donde PP. LES/PDF approach for turbulent reacting flows. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/19481.

Council of Science Editors:

Donde PP. LES/PDF approach for turbulent reacting flows. [Doctoral Dissertation]. University of Texas – Austin; 2012. Available from: http://hdl.handle.net/2152/19481

13. Chang, Shu-Hao. Numerical simulation of steady and unsteady cavitating flows inside water-jets.

Degree: PhD, Civil Engineering, 2012, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2012-08-6310

► A numerical panel method based on the potential flow theory has been refined and applied to the simulations of steady and unsteady cavitating flows inside… (more)

▼ A numerical panel method based on the potential flow theory has been refined and applied to the simulations of steady and unsteady cavitating flows inside water-jet pumps. The potential flow inside the water-jet is solved simultaneously in order to take the interaction of all geometries (blades, hub and casing) into account. The integral equation and boundary conditions for the water-jet problem are formulated and solved by distributing constant dipoles and sources on blades, hub and shroud surfaces, and constant dipoles in the trailing wake sheets behind the rotor (or stator) blades. The interaction between the rotor and stator is carried out based on an iterative procedure by considering the circumferentially averaged velocities induced on each one by the other. The present numerical scheme is coupled with a 2-D axisymmetric version of the Reynolds Averaged Navier-Stokes (RANS) solver to evaluate the pressure rise on the shroud and simulate viscous flow fields inside the pump. A tip gap model based on a 2-D orifice equation derived from Bernoulli’s obstruction theory is implemented in the present method to analyze the clearance effect between the blade tip and the shroud inner wall in a global sense. The reduction of the flow from losses in the orifice can be defined in terms of an empirically determined discharge coefficient (CQ) representing the relationship between the flow rate and the pressure difference across the gap because of the viscous effect in the tip gap region. The simulations of the rotor/stator interaction, the prediction of partial and super cavitation on the rotor blade and their effects on the hydrodynamic performance including the thrust/torque breakdown of a water-jet pump are presented. The predicted results, including the power coefficient (P*), head coefficient (H*), pump efficiency (η), thrust and torque coefficients (KT and KQ), as well as the cavity patterns are compared and validated against the experimental data from a series of on the ONR AxWJ-2 pump at NSWCCD. Advisors/Committee Members: Kinnas, Spyros A. (advisor), Liljestrand, Howard (committee member), Hodges, Ben (committee member), Moser, Robert (committee member), Raman, Venkat (committee member).

Subjects/Keywords: Water-jets; Panel method; RANS; Super-cavitation; Thrust/torque breakdown

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APA (6^th Edition):

Chang, S. (2012). Numerical simulation of steady and unsteady cavitating flows inside water-jets. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2012-08-6310

Chicago Manual of Style (16^th Edition):

Chang, Shu-Hao. “Numerical simulation of steady and unsteady cavitating flows inside water-jets.” 2012. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2012-08-6310.

MLA Handbook (7^th Edition):

Chang, Shu-Hao. “Numerical simulation of steady and unsteady cavitating flows inside water-jets.” 2012. Web. 22 Jan 2021.

Vancouver:

Chang S. Numerical simulation of steady and unsteady cavitating flows inside water-jets. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2012-08-6310.

Council of Science Editors:

Chang S. Numerical simulation of steady and unsteady cavitating flows inside water-jets. [Doctoral Dissertation]. University of Texas – Austin; 2012. Available from: http://hdl.handle.net/2152/ETD-UT-2012-08-6310

14. Chang, Henry, 1976-. Modeling turbulence using optimal large eddy simulation.

Degree: PhD, Computational and Applied Mathematics, 2012, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2012-05-4988

► Most flows in nature and engineering are turbulent, and many are wall-bounded. Further, in turbulent flows, the turbulence generally has a large impact on the… (more)

▼ Most flows in nature and engineering are turbulent, and many are wall-bounded. Further, in turbulent flows, the turbulence generally has a large impact on the behavior of the flow. It is therefore important to be able to predict the effects of turbulence in such flows. The Navier-Stokes equations are known to be an excellent model of the turbulence phenomenon. In simple geometries and low Reynolds numbers, very accurate numerical solutions of the Navier-Stokes equations (direct numerical simulation, or DNS) have been used to study the details of turbulent flows. However, DNS of high Reynolds number turbulent flows in complex geometries is impractical because of the escalation of computational cost with Reynolds number, due to the increasing range of spatial and temporal scales. In Large Eddy Simulation (LES), only the large-scale turbulence is simulated, while the effects of the small scales are modeled (subgrid models). LES therefore reduces computational expense, allowing flows of higher Reynolds number and more complexity to be simulated. However, this is at the cost of the subgrid modeling problem. The goal of the current research is then to develop new subgrid models consistent with the statistical properties of turbulence. The modeling approach pursued here is that of "Optimal LES". Optimal LES is a framework for constructing models with minimum error relative to an ideal LES model. The multi-point statistics used as input to the optimal LES procedure can be gathered from DNS of the same flow. However, for an optimal LES to be truly predictive, we must free ourselves from dependence on existing DNS data. We have done this by obtaining the required statistics from theoretical models which we have developed. We derived a theoretical model for the three-point third-order velocity correlation for homogeneous, isotropic turbulence in the inertial range. This model is shown be a good representation of DNS data, and it is used to construct optimal quadratic subgrid models for LES of forced isotropic turbulence with results which agree well with theory and DNS. The model can also be filtered to determine the filtered two-point third-order correlation, which describes energy transfer among filtered (large) scales in LES. LES of wall-bounded flows with unresolved wall layers commonly exhibit good prediction of mean velocities and significant over-prediction of streamwise component energies in the near-wall region. We developed improved models for the nonlinear term in the filtered Navier-Stokes equation which result in better predicted streamwise component energies. These models involve (1) Reynolds decomposition of the nonlinear term and (2) evaluation of the pressure term, which removes the divergent part of the nonlinear models. These considerations significantly improved the performance of our optimal models, and we expect them to apply to other subgrid models as well. Advisors/Committee Members: Moser, Robert deLancey (advisor), Engquist, Bjorn (committee member), Ghattas, Omar (committee member), Hughes, Thomas J. (committee member), Raman, Venkat (committee member).

Subjects/Keywords: Turbulence simulation; Large eddy simulation; Optimal large eddy simulation; Turbulence modeling; Subgrid models; Wall-bounded turbulence; Channel flow; Three-point third-order velocity correlation; Triple velocity correlation

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APA (6^th Edition):

Chang, Henry, 1. (2012). Modeling turbulence using optimal large eddy simulation. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2012-05-4988

Chicago Manual of Style (16^th Edition):

Chang, Henry, 1976-. “Modeling turbulence using optimal large eddy simulation.” 2012. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2012-05-4988.

MLA Handbook (7^th Edition):

Chang, Henry, 1976-. “Modeling turbulence using optimal large eddy simulation.” 2012. Web. 22 Jan 2021.

Vancouver:

Chang, Henry 1. Modeling turbulence using optimal large eddy simulation. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2012-05-4988.

Council of Science Editors:

Chang, Henry 1. Modeling turbulence using optimal large eddy simulation. [Doctoral Dissertation]. University of Texas – Austin; 2012. Available from: http://hdl.handle.net/2152/ETD-UT-2012-05-4988

15. Sung, Yonduck. Large eddy simulation of TiO₂ nanoparticle evolution in turbulent flames.

Degree: PhD, Mechanical Engineering, 2011, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2011-12-4465

► Flame based synthesis is a major manufacturing process of commercially valuable nanoparticles for large-scale production. However, this important industrial process has been advanced mostly by… (more)

▼ Flame based synthesis is a major manufacturing process of commercially valuable nanoparticles for large-scale production. However, this important industrial process has been advanced mostly by trial-and-error based evolutionary studies owing to the fact that it involves tightly coupled multiphysics flow phenomena. For large scale synthesis of nanoparticles, different physical and chemical processes exist, including turbulence, fuel combustion, precursor oxidation, and nanoparticle dynamics exist. A reliable and predictive computational model based on fundamental physics and chemistry can provide tremendous insight. Development of such comprehensive computational models faces challenges as they must provide accurate descriptions not only of the individual physical processes but also of the strongly coupled, nonlinear interactions among them. In this work, a multiscale computational model for flame synthesis of TiO2 nanoparticles in a turbulent flame reactor is presented. The model is based on the large-eddy simulation (LES) methodology and incorporates detailed gas phase combustion and precursor oxidation chemistry as well as a comprehensive nanoparticle evolution model. A flamelet-based model is used to model turbulence-chemistry interactions. In particular, the transformation of TiCl4 to the solid primary nucleating TiO2 nanoparticles is represented us- ing an unsteady kinetic model considering 30 species and 70 reactions in order to accurately describe the critical nanoparticle nucleation process. The evolution of the TiO2 number density function is tracked using the quadrature method of moments (QMOM) for univariate particle number density function and conditional quadrature method of moments (CQMOM) for bivariate density distribution function. For validation purposes, the detailed computational model is compared against experimental data obtained from a canonical flame- based titania synthesis configuration, and reasonable agreement is obtained. Advisors/Committee Members: Moser, Robert deLancey (advisor), Raman, Venkat (advisor), Ezekoye, Ofodike A. (committee member), Matthews, Ronald D. (committee member), Clemens, Noel T. (committee member).

Subjects/Keywords: Large eddy simulation; TiO2 nanoparticle; Detailed TiCl4 oxidation chemistry; Quadrature method of moments; Moment correction

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APA (6^th Edition):

Sung, Y. (2011). Large eddy simulation of TiO₂ nanoparticle evolution in turbulent flames. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2011-12-4465

Chicago Manual of Style (16^th Edition):

Sung, Yonduck. “Large eddy simulation of TiO₂ nanoparticle evolution in turbulent flames.” 2011. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2011-12-4465.

MLA Handbook (7^th Edition):

Sung, Yonduck. “Large eddy simulation of TiO₂ nanoparticle evolution in turbulent flames.” 2011. Web. 22 Jan 2021.

Vancouver:

Sung Y. Large eddy simulation of TiO₂ nanoparticle evolution in turbulent flames. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2011-12-4465.

Council of Science Editors:

Sung Y. Large eddy simulation of TiO₂ nanoparticle evolution in turbulent flames. [Doctoral Dissertation]. University of Texas – Austin; 2011. Available from: http://hdl.handle.net/2152/ETD-UT-2011-12-4465

16. Kaul, Colleen Marie, 1983-. Subfilter scalar variance modeling for large eddy simulation.

Degree: PhD, Aerospace Engineering, 2011, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2011-08-3805

► Accurate models for the mixing of fuel and oxidizer at small, unresolved flow length scales are critical to the predictive skill of large eddy simulation… (more)

▼ Accurate models for the mixing of fuel and oxidizer at small, unresolved flow length scales are critical to the predictive skill of large eddy simulation (LES) of turbulent combustion. Subfilter scalar variance and subfilter scalar dissipation rate are important parameters in combustion modeling approaches based on a conserved scalar, but are prone to numerical and modeling errors due to the nature of practical LES computations. This work examines the errors incurred in these models using a novel method that couples LES scalar modeling with direct numerical simulation (DNS) of homogeneous isotropic turbulence and offers modeling and numerical techniques to address these errors. In the coupled DNS-LES method, DNS velocity fields are evolved simultaneously with LES scalar fields. The filtered DNS velocities are supplied to the LES scalar equations, instead of solving the LES momentum equations. This removes the effect of errors in the filtered scalar evolution from the scalar modeling analysis. Results obtained using the coupled DNS-LES approach, which permits detailed study of physics-related and numerical errors in scalar modeling, show that widely used algebraic dynamic models for subfilter scalar variance lack accuracy due to faulty equilibrium modeling assumptions and sensitivity to numerical error. Transport equation models for variance show superior performance, provided that the scalar dissipation rate model coefficient is set appropriately. For this purpose, a new dynamic approach for nonequilibrium modeling of subfilter scalar dissipation rate is developed and validated through a priori tests in an inhomogeneous jet flow and using the coupled DNS-LES method for assessment of numerical error effects. Explicit filtering is assessed as means to control numerical error in LES scalar modeling and the scalar equations are reformulated to account for the explicit filtering technique. Numerical convergence of the mean subfilter scalar variance prediction with increasing grid resolution is demonstrated. Advisors/Committee Members: Raman, Venkat (advisor), Clemens, Noel T. (committee member), Moser, Robert D. (committee member), Ezekoye, Ofodike A. (committee member), Varghese, Philip L. (committee member).

Subjects/Keywords: Large eddy simulation; Turbulent reactive flows; Combustion modeling

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APA (6^th Edition):

Kaul, Colleen Marie, 1. (2011). Subfilter scalar variance modeling for large eddy simulation. (Doctoral Dissertation). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2011-08-3805

Chicago Manual of Style (16^th Edition):

Kaul, Colleen Marie, 1983-. “Subfilter scalar variance modeling for large eddy simulation.” 2011. Doctoral Dissertation, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2011-08-3805.

MLA Handbook (7^th Edition):

Kaul, Colleen Marie, 1983-. “Subfilter scalar variance modeling for large eddy simulation.” 2011. Web. 22 Jan 2021.

Vancouver:

Kaul, Colleen Marie 1. Subfilter scalar variance modeling for large eddy simulation. [Internet] [Doctoral dissertation]. University of Texas – Austin; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2011-08-3805.

Council of Science Editors:

Kaul, Colleen Marie 1. Subfilter scalar variance modeling for large eddy simulation. [Doctoral Dissertation]. University of Texas – Austin; 2011. Available from: http://hdl.handle.net/2152/ETD-UT-2011-08-3805

University of Texas – Austin

17. Kaul, Colleen Marie, 1983-. Numerical errors in subfilter scalar variance models for large eddy simulation of turbulent combustion.

Degree: MSin Engineering, Aerospace Engineering, 2009, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2009-05-47

► Subfilter scalar variance is a key quantity for scalar mixing at the small scales of a turbulent flow and thus plays a crucial role in… (more)

▼ Subfilter scalar variance is a key quantity for scalar mixing at the small scales of a turbulent flow and thus plays a crucial role in large eddy simulation (LES) of combustion. While prior studies have mainly focused on the physical aspects of modeling subfilter variance, the current work discusses variance models in conjunction with numerical errors due to their implementation using finite difference methods. Because of the prevalence of grid-based filtering in practical LES, the smallest filtered scales are generally under-resolved. These scales, however, are often important in determining the values of subfilter models. A priori tests on data from direct numerical simulation (DNS) of homogenous isotropic turbulence are performed to evaluate the numerical implications of specific model forms in the context of practical LES evaluated with finite differences. As with other subfilter quantities, such as kinetic energy, subfilter variance can be modeled according to one of two general methodologies. In the first of these, an algebraic equation relating the variance to gradients of the filtered scalar field is coupled with a dynamic procedure for coefficient estimation. Although finite difference methods substantially underpredict the gradient of the filtered scalar field, the dynamic method is shown to mitigate this error through overestimation of the model coefficient. The second group of models utilizes a transport equation for the subfilter variance itself or for the second moment of the scalar. Here, it is shown that the model formulation based on the variance transport equation is consistently biased toward underprediction of the subfilter variance. The numerical issues stem from making discrete approximations to the chain rule manipulations used to derive convective and diffusive terms in the variance transport equation associated with the square of the filtered scalar. This set of approximations can be avoided by solving the equation for the second moment of the scalar, suggesting that model's numerical superiority. Advisors/Committee Members: Raman, Venkat (advisor), Clemens, Noel T. (committee member).

Subjects/Keywords: Large eddy simulation; turbulent combustion; numerical error analysis

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APA (6^th Edition):

Kaul, Colleen Marie, 1. (2009). Numerical errors in subfilter scalar variance models for large eddy simulation of turbulent combustion. (Masters Thesis). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2009-05-47

Chicago Manual of Style (16^th Edition):

Kaul, Colleen Marie, 1983-. “Numerical errors in subfilter scalar variance models for large eddy simulation of turbulent combustion.” 2009. Masters Thesis, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2009-05-47.

MLA Handbook (7^th Edition):

Kaul, Colleen Marie, 1983-. “Numerical errors in subfilter scalar variance models for large eddy simulation of turbulent combustion.” 2009. Web. 22 Jan 2021.

Vancouver:

Kaul, Colleen Marie 1. Numerical errors in subfilter scalar variance models for large eddy simulation of turbulent combustion. [Internet] [Masters thesis]. University of Texas – Austin; 2009. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2009-05-47.

Council of Science Editors:

Kaul, Colleen Marie 1. Numerical errors in subfilter scalar variance models for large eddy simulation of turbulent combustion. [Masters Thesis]. University of Texas – Austin; 2009. Available from: http://hdl.handle.net/2152/ETD-UT-2009-05-47

University of Texas – Austin

18. Wu, Nathan Gabriel. Sensitivity calculations on a soot model using a partially stirred reactor.

Degree: MSin Engineering, Aerospace Engineering, 2010, University of Texas – Austin

URL: http://hdl.handle.net/2152/ETD-UT-2010-05-1472

► Sensitivity analysis was performed on a soot model using a partially stirred reactor (PaSR) in order to determine the effects of mixing model parameters on… (more)

Subjects/Keywords: Partially stirred reactor; Sensitivity analysis; Soot modeling

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APA (6^th Edition):

Wu, N. G. (2010). Sensitivity calculations on a soot model using a partially stirred reactor. (Masters Thesis). University of Texas – Austin. Retrieved from http://hdl.handle.net/2152/ETD-UT-2010-05-1472

Chicago Manual of Style (16^th Edition):

Wu, Nathan Gabriel. “Sensitivity calculations on a soot model using a partially stirred reactor.” 2010. Masters Thesis, University of Texas – Austin. Accessed January 22, 2021. http://hdl.handle.net/2152/ETD-UT-2010-05-1472.

MLA Handbook (7^th Edition):

Wu, Nathan Gabriel. “Sensitivity calculations on a soot model using a partially stirred reactor.” 2010. Web. 22 Jan 2021.

Vancouver:

Wu NG. Sensitivity calculations on a soot model using a partially stirred reactor. [Internet] [Masters thesis]. University of Texas – Austin; 2010. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/2152/ETD-UT-2010-05-1472.

Council of Science Editors:

Wu NG. Sensitivity calculations on a soot model using a partially stirred reactor. [Masters Thesis]. University of Texas – Austin; 2010. Available from: http://hdl.handle.net/2152/ETD-UT-2010-05-1472

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