subject:(internal excitation)

University of Southern California

1. Yang, Shanling. Boundary layer and separation control on wings at low Reynolds numbers.

Degree: PhD, Aerospace Engineering, 2013, University of Southern California

URL: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157

► In the transitional chord-based Reynolds number regime for aeronautics, 10⁴ ≤ Re ≤ 10⁵, fluid flow over a surface is prone to separation followed by… (more)

▼ In the transitional chord-based Reynolds number regime for aeronautics, 10⁴ ≤ Re ≤ 10⁵, fluid flow over a surface is prone to separation followed by possible reattachment and transition to turbulence. The amplification of disturbances in the boundary layer promotes transition to turbulence, so boundary layer and separation control methods are especially favorable in this transitional Re regime. The use of sound to control flow separation at transitional and moderate Re for various smooth airfoils has been experimentally studied in the literature. Optimum excitation frequencies are reported to match the frequency or sub harmonics of the naturally occurring instabilities in the shear layer, and correlations between optimum frequencies for external acoustic forcing and tunnel anti-resonances have been observed. However, reported optimum frequency values based on the Strouhal number scaling St/Re^(1/2) are not in complete agreement among the different reported studies. Little attention has been given to distinguish the effects of standing waves from traveling sound waves. Mathematical and experimental studies of sound and boundary layer instability interactions have also yielded mixed results, suggesting that there still lacks a full understanding about the mechanism by which acoustic waves affect boundary layer flows. ❧ Results on boundary layer and separation control through acoustic excitation at low Re numbers are reported. The Eppler 387 profile is specifically chosen because of its pre-stall hysteresis and bi-stable state behavior in the transitional Re regime, which is a result of flow separation and reattachment. External acoustic forcing on the wing yields large improvements (more than 70%) in lift-to-drag ratio and flow reattachment at forcing frequencies that correlate with the measured anti-resonances in the wind tunnel. The optimum St/Re^(1/2) range for Re = 60,000 matches the proposed optimum range in the literature, but there is less agreement for Re = 40,000, which suggests that correct St scaling has not been determined. The correlation of aerodynamic improvements to wind tunnel resonances implies that external acoustic forcing is facility-dependent, which inhibits practical application. Therefore, internal acoustic excitation for the same wing profile is also pursued. ❧ Internal acoustic forcing is designed to be accomplished by embedding small speakers inside a custom-designed wing that contains many internal cavities and small holes in the suction surface. However, initial testing of this semi-porous wing model shows that the presence of the small holes in the suction surface completely transforms the aerodynamic performance by changing the mean chordwise separation location and causing an originally separated, low-lift state flow to reattach into a high-lift state. The aerodynamic improvements are not caused by the geometry of the small holes themselves, but rather by Helmholtz resonance that occurs in the cavities, which generate tones that closely match the intrinsic flow instabilities.… Advisors/Committee Members: Spedding, Geoffrey R. (Committee Chair), Redekopp, Larry G. (Committee Member), Eliasson, Veronica (Committee Member), Bickers, Gene (Committee Member), Radovich, Charles (Committee Member).

Subjects/Keywords: low Reynolds numbers; separation control; acoustic excitation; active separation control; passive separation control; boundary layers; fluid dynamics; aerodynamics; Helmholtz resonance; local acoustic forcing; external acoustic excitation; internal excitation; flow control

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APA (6^th Edition):

Yang, S. (2013). Boundary layer and separation control on wings at low Reynolds numbers. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157

Chicago Manual of Style (16^th Edition):

Yang, Shanling. “Boundary layer and separation control on wings at low Reynolds numbers.” 2013. Doctoral Dissertation, University of Southern California. Accessed January 18, 2021. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157.

MLA Handbook (7^th Edition):

Yang, Shanling. “Boundary layer and separation control on wings at low Reynolds numbers.” 2013. Web. 18 Jan 2021.

Vancouver:

Yang S. Boundary layer and separation control on wings at low Reynolds numbers. [Internet] [Doctoral dissertation]. University of Southern California; 2013. [cited 2021 Jan 18]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157.

Council of Science Editors:

Yang S. Boundary layer and separation control on wings at low Reynolds numbers. [Doctoral Dissertation]. University of Southern California; 2013. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157

Brno University of Technology

2. Kramář, Ondřej. Návrh lineárního oscilačního pohonu s vnitřním buzením: Design of linear internal excitation drive with oscillative motion.

Degree: 2019, Brno University of Technology

URL: http://hdl.handle.net/11012/11706

► This thesis deals with design of linear internal excitation drive with oscillative motion. Here is shown the survey area of linear drives, as well as… (more)

Subjects/Keywords: lineární pohony; návrh lineárního oscilačního pohonu s vnitřním buzením; simulační modelování; linear drives; design of linear internal excitation drive with oscillative motion; simulation modeling

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APA (6^th Edition):

Kramář, O. (2019). Návrh lineárního oscilačního pohonu s vnitřním buzením: Design of linear internal excitation drive with oscillative motion. (Thesis). Brno University of Technology. Retrieved from http://hdl.handle.net/11012/11706

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Kramář, Ondřej. “Návrh lineárního oscilačního pohonu s vnitřním buzením: Design of linear internal excitation drive with oscillative motion.” 2019. Thesis, Brno University of Technology. Accessed January 18, 2021. http://hdl.handle.net/11012/11706.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Kramář, Ondřej. “Návrh lineárního oscilačního pohonu s vnitřním buzením: Design of linear internal excitation drive with oscillative motion.” 2019. Web. 18 Jan 2021.

Vancouver:

Kramář O. Návrh lineárního oscilačního pohonu s vnitřním buzením: Design of linear internal excitation drive with oscillative motion. [Internet] [Thesis]. Brno University of Technology; 2019. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/11012/11706.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Kramář O. Návrh lineárního oscilačního pohonu s vnitřním buzením: Design of linear internal excitation drive with oscillative motion. [Thesis]. Brno University of Technology; 2019. Available from: http://hdl.handle.net/11012/11706

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

University of Manchester

3. Davies, Matthew John. Optical Studies of InGaN/GaN Quantum Well Structures.

Degree: 2014, University of Manchester

URL: http://www.manchester.ac.uk/escholar/uk-ac-man-scw:221391

► In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on… (more)

▼ In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on the optical properties of InGaN/GaN single and multiple QW structures, measured at high excitation power densities. I show a correlation exists between the reduction in PL efficiency at high excitation power densities, the phenomenon so-called ``efficiency-droop'', and a broadening of the PL spectra. I also show a distinct change in recombination dynamics, measured by time-resolved photoluminescence (PL), which occurs at the excitation power densities for which efficiency droop is measured. The broadening of the PL spectra at high excitation power densities is shown to occur due to a rapidly redshifting, short-lived high energy emission band. The high energy emission band is proposed to be due to the recombination of weakly localised/delocalised carriers occurring as a consequence of the progressive saturation of the local potential fluctuations responsible for carrier localisation, at high excitation power densities. I report on the effects of varying threading dislocation (TD) density on the optical properties of InGaN/GaN multiple QW structures. No systematic relationship exists between the room temperature internal quantum efficiency (IQE) and the TD density, in a series of nominally identical InGaN/GaN multiple QWs deposited on GaN templates of varying TD density. I also show the excitation power density dependence of the PL efficiency, at room temperatures, is unaffected for variation in the TD density between 2 x107 and 5 x109 cm-2. The independence of the optical properties to TD density is proposed to be a consequence of the strong carrier localisation, and hence short carrier diffusion lengths. I report on the effects of including an InGaN underlayer on the optical and microstructural properties of InGaN/GaN multiple QW structures. I show an increase in the room temperature IQE occurs for the structure containing the InGaN underlayer, compared to the reference. I show using PL excitation spectroscopy that an additional carrier transfer and recombination process occurs on the high energy side of the PL spectrum associated with the InGaN underlayer. Using PL decay time measurements I show the additional recombination process for carriers excited in the underlayer occurs on a faster timescale than the recombination at the peak of the PL spectrum. The additional contribution to the spectrum from the faster recombination process is proposed as responsible for the increase in room temperature IQE. Advisors/Committee Members: Dawson, Philip.

Subjects/Keywords: InGaN; GaN; Quantum Wells; Semiconductors; Time resolved photoluminescence; Photoluminescence; Recombination dynamics; Efficiency droop; Threading dislocations; Underlayer; Prelayer; Photoluminescence excitation; Carrier localisation; Internal quantum efficiency; Gallium nitride; Indium gallium nitride; Crystal defects; Piezoelectric field screening

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Davies, M. J. (2014). Optical Studies of InGaN/GaN Quantum Well Structures. (Doctoral Dissertation). University of Manchester. Retrieved from http://www.manchester.ac.uk/escholar/uk-ac-man-scw:221391

Chicago Manual of Style (16^th Edition):

Davies, Matthew John. “Optical Studies of InGaN/GaN Quantum Well Structures.” 2014. Doctoral Dissertation, University of Manchester. Accessed January 18, 2021. http://www.manchester.ac.uk/escholar/uk-ac-man-scw:221391.

MLA Handbook (7^th Edition):

Davies, Matthew John. “Optical Studies of InGaN/GaN Quantum Well Structures.” 2014. Web. 18 Jan 2021.

Vancouver:

Davies MJ. Optical Studies of InGaN/GaN Quantum Well Structures. [Internet] [Doctoral dissertation]. University of Manchester; 2014. [cited 2021 Jan 18]. Available from: http://www.manchester.ac.uk/escholar/uk-ac-man-scw:221391.

Council of Science Editors:

Davies MJ. Optical Studies of InGaN/GaN Quantum Well Structures. [Doctoral Dissertation]. University of Manchester; 2014. Available from: http://www.manchester.ac.uk/escholar/uk-ac-man-scw:221391

University of Manchester

4. Davies, Matthew John. Optical studies of InGaN/GaN quantum well structures.

Degree: PhD, 2014, University of Manchester

URL: https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603270

► In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on… (more)

▼ In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on the optical properties of InGaN/GaN single and multiple QW structures, measured at high excitation power densities. I show a correlation exists between the reduction in PL efficiency at high excitation power densities, the phenomenon so-called ``efficiency-droop'', and a broadening of the PL spectra. I also show a distinct change in recombination dynamics, measured by time-resolved photoluminescence (PL), which occurs at the excitation power densities for which efficiency droop is measured. The broadening of the PL spectra at high excitation power densities is shown to occur due to a rapidly redshifting, short-lived high energy emission band. The high energy emission band is proposed to be due to the recombination of weakly localised/delocalised carriers occurring as a consequence of the progressive saturation of the local potential fluctuations responsible for carrier localisation, at high excitation power densities. I report on the effects of varying threading dislocation (TD) density on the optical properties of InGaN/GaN multiple QW structures. No systematic relationship exists between the room temperature internal quantum efficiency (IQE) and the TD density, in a series of nominally identical InGaN/GaN multiple QWs deposited on GaN templates of varying TD density. I also show the excitation power density dependence of the PL efficiency, at room temperatures, is unaffected for variation in the TD density between 2 x107 and 5 x109 cm-2. The independence of the optical properties to TD density is proposed to be a consequence of the strong carrier localisation, and hence short carrier diffusion lengths. I report on the effects of including an InGaN underlayer on the optical and microstructural properties of InGaN/GaN multiple QW structures. I show an increase in the room temperature IQE occurs for the structure containing the InGaN underlayer, compared to the reference. I show using PL excitation spectroscopy that an additional carrier transfer and recombination process occurs on the high energy side of the PL spectrum associated with the InGaN underlayer. Using PL decay time measurements I show the additional recombination process for carriers excited in the underlayer occurs on a faster timescale than the recombination at the peak of the PL spectrum. The additional contribution to the spectrum from the faster recombination process is proposed as responsible for the increase in room temperature IQE.

Subjects/Keywords: 537.6; InGaN; GaN; Quantum Wells; Semiconductors; Time resolved photoluminescence; Photoluminescence; Recombination dynamics; Efficiency droop; Threading dislocations; Underlayer; Prelayer; Photoluminescence excitation; Carrier localisation; Internal quantum efficiency; Gallium nitride; Indium gallium nitride; Crystal defects; Piezoelectric field screening

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Davies, M. J. (2014). Optical studies of InGaN/GaN quantum well structures. (Doctoral Dissertation). University of Manchester. Retrieved from https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603270

Chicago Manual of Style (16^th Edition):

Davies, Matthew John. “Optical studies of InGaN/GaN quantum well structures.” 2014. Doctoral Dissertation, University of Manchester. Accessed January 18, 2021. https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603270.

MLA Handbook (7^th Edition):

Davies, Matthew John. “Optical studies of InGaN/GaN quantum well structures.” 2014. Web. 18 Jan 2021.

Vancouver:

Davies MJ. Optical studies of InGaN/GaN quantum well structures. [Internet] [Doctoral dissertation]. University of Manchester; 2014. [cited 2021 Jan 18]. Available from: https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603270.

Council of Science Editors:

Davies MJ. Optical studies of InGaN/GaN quantum well structures. [Doctoral Dissertation]. University of Manchester; 2014. Available from: https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html ; http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603270

University of Technology, Sydney

5. Zhao, Mingming. A study of the dynamic response of wind turbine gearboxes.

Degree: 2016, University of Technology, Sydney

URL: http://hdl.handle.net/10453/89999

► Gearbox is an important component for large modern wind turbines incorporated either by a squirrel cage induction generator or a doubly fed induction generator. Wind… (more)

▼ Gearbox is an important component for large modern wind turbines incorporated either by a squirrel cage induction generator or a doubly fed induction generator. Wind turbine gearboxes have distinct features from standard gearboxes. They are used to increase the rotor speed to a speed suitable for the electricity generation and operate under varying load conditions, while standard gearboxes are designed to step down from high speed to low speed and operate under full load conditions. The modern wind energy industry has been experiencing high gearbox failure rates since its inception. However, the fundamental mechanisms of gearbox failures have not been fully understood yet. Thus, this thesis studies the dynamic response of wind turbine gearbox components in order to provide useful information to the wind energy industry to reduce the possibility of the gearbox failures at an early stage. The torsional vibrations of wind turbine gearbox are firstly investigated in this thesis. The nonlinear dynamic model developed considers the factors such as time-varying mesh stiffness, damping, static transmission error and gear backlash. Both the external excitation due to wind gust and the internal excitation due to static transmission error are included. With the help of time history, FFT spectrum, phase portrait, Poincare map and the effects of the static transmission error, mean-to-alternating force ratio and time-varying mesh stiffness on the dynamic behaviour of wind turbine gearbox components are investigated by using the numerical integration method. It is found that the external excitation has the most influence on the torsional vibrations of the wind turbine gearbox components. The gear mesh stiffness has more influence than the static transmission error, and the static transmission error has the least influence. Secondly, the dynamic response of a proposed four-degree-of-freedom (4DOF) wind turbine gearbox dynamic model is studied. The effects of different excitation conditions are discussed. The results show that the external excitation fluctuation has large influence on the dynamic responses of both the gears and bearings, and explain under which conditions the fretting corrosion, as one of the wind turbine gearbox failure modes, may occur. Thirdly, the effects of bending moments on the dynamic responses of a wind turbine planetary gearbox are analysed. The proposed six-degree-of-freedom (6DOF) dynamic model takes into account the key factors such as the time-varying mesh stiffness, bearing stiffness, damping, static transmission error, gear backlash and bearing clearances. It is found that the bending moments can affect the gear meshes. What is more, the driving torque may have the effect on the bending moments. Furthermore, the bearing clearance has negligible effect in the planetary gear stage.

Subjects/Keywords: Wind turbine gearboxes.; Squirrel cage induction generator.; Doubly fed induction generator.; High gearbox failure rates.; Torsional vibrations.; External and internal excitation.; Four-degree-of-freedom (4DOF) dynamic model.; Six-degree-of-freedom (6DOF) dynamic model.; Numerical integration method.

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Zhao, M. (2016). A study of the dynamic response of wind turbine gearboxes. (Thesis). University of Technology, Sydney. Retrieved from http://hdl.handle.net/10453/89999

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16^th Edition):

Zhao, Mingming. “A study of the dynamic response of wind turbine gearboxes.” 2016. Thesis, University of Technology, Sydney. Accessed January 18, 2021. http://hdl.handle.net/10453/89999.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7^th Edition):

Zhao, Mingming. “A study of the dynamic response of wind turbine gearboxes.” 2016. Web. 18 Jan 2021.

Vancouver:

Zhao M. A study of the dynamic response of wind turbine gearboxes. [Internet] [Thesis]. University of Technology, Sydney; 2016. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10453/89999.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Zhao M. A study of the dynamic response of wind turbine gearboxes. [Thesis]. University of Technology, Sydney; 2016. Available from: http://hdl.handle.net/10453/89999

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

6. Ogden, Melinda Anne. Two-photon total internal reflection microscopy for imaging live cells with high background fluorescence.

Degree: MS, Chemistry and Biochemistry, 2009, Georgia Tech

URL: http://hdl.handle.net/1853/34786

► Fluorescence microscopy allows for spatial and temporal resolution of systems which are inherently fluorescent or which can be selectively labeled with fluorescent molecules. Temporal resolution… (more)

▼ Fluorescence microscopy allows for spatial and temporal resolution of systems which are inherently fluorescent or which can be selectively labeled with fluorescent molecules. Temporal resolution is crucial for imaging real time processes in living samples. A common problem in fluorescence microscopy of biological samples is autofluorescence, fluorescence inherent to the system, which interferes with detection of fluorescence of interest by decreasing the signal to noise ratio. Two current methods for improved imaging against autofluorescence are two-photon excitation and total internal reflection microscopy. Two-photon excitation occurs when two longer wavelength photons are absorbed quasi-simultaneously by a single fluorophore. For this to take place there must be a photon density on the order of 1030 photons/(cm2)(s), which is achieved through use of a femtosecond pulsed laser and a high magnification microscope objective. Two-photon excitation then only occurs at the focal spot, significantly reducing the focal volume and therefore background autofluorescence. The second method, total internal reflection, is based on evanescent wave excitation, which decreases exponentially in intensity away from the imaging surface. This allows for excitation of a thin (~200 nm) slice of a sample. Since only a narrow region of interest is excited, an optical slice can be imaged, decreasing excitation of out-of-focus autofluorescence, and increasing the signal to noise ratio. By coupling total internal reflection with two-photon excitation, an entire cell can be imaged while still maintaining the use of lower energy photons to irradiate the sample and achieve two-photon excitation along the length traveled by the evanescent wave. This system allows for more sensitive detection of fluorescence of interest from biological systems as a result of a significant decrease in excitation volume and therefore a decrease in autofluorescence signal. In the two-photon total internal reflection microscopy setup detailed in this work, an excitation area of 20 μm by 30 μm is achieved, and used to image FITC-stained actin filaments in BS-C-1 cells Advisors/Committee Members: Payne, Christine (Committee Chair), Hernandez, Rigoberto (Committee Member), Perry, Joseph (Committee Member).

Subjects/Keywords: Fluorescence microscopy; Two-photon excitation; Total internal reflection; Imaging systems in biology; Microscopy; Multiphoton processes

…Evanescent wave excitation CCD camera Figure 1.4. Schematic of total internal reflection… …excitation volume in the lateral dimensions, total internal reflection is employed. Total internal… …the z direction. The combination of two-photon excitation with total internal reflection… …excitation area of 20 μm by 30 µm. 17 Figure 3.2 Two-photon total internal reflection microscopy… …angle, and therefore excitation by two-photon total internal reflection. Twophoton excitation…

10 more images…

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Ogden, M. A. (2009). Two-photon total internal reflection microscopy for imaging live cells with high background fluorescence. (Masters Thesis). Georgia Tech. Retrieved from http://hdl.handle.net/1853/34786

Chicago Manual of Style (16^th Edition):

Ogden, Melinda Anne. “Two-photon total internal reflection microscopy for imaging live cells with high background fluorescence.” 2009. Masters Thesis, Georgia Tech. Accessed January 18, 2021. http://hdl.handle.net/1853/34786.

MLA Handbook (7^th Edition):

Ogden, Melinda Anne. “Two-photon total internal reflection microscopy for imaging live cells with high background fluorescence.” 2009. Web. 18 Jan 2021.

Vancouver:

Ogden MA. Two-photon total internal reflection microscopy for imaging live cells with high background fluorescence. [Internet] [Masters thesis]. Georgia Tech; 2009. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/1853/34786.

Council of Science Editors:

Ogden MA. Two-photon total internal reflection microscopy for imaging live cells with high background fluorescence. [Masters Thesis]. Georgia Tech; 2009. Available from: http://hdl.handle.net/1853/34786

ETH Zürich

7. Fritsche, Daniel. Origin and control of thermoacoustic instabilities in lean premixed gas turbine combustion.

Degree: 2005, ETH Zürich

URL: http://hdl.handle.net/20.500.11850/47744

► Modern gas turbines use lean premixedcombustion to achieve the best compromise between pollutant emissions and efficiency. This type of combustion increases the flame receptivityto external… (more)

▼ Modern gas turbines use lean premixedcombustion to achieve the best compromise between pollutant emissions and efficiency. This type of combustion increases the flame receptivityto external perturbations thereby promoting the onset of large amplitude pressure oscillations called thermoacoustic instabilities. This phenomenon results from the resonant coupling of fluid dynamic, unsteady hcat release and acoustic properties of the combustion chambcr. In order to improve the understanding of stability properties in such complex Systems encountered in many industrial applications, the flame strueture ofan atmospheric swirl stabilized burner of 30 - 75kW was investigated as a functionoftotal massflow rate, mixture temperature, air/fuel equivalence ratio and combustion chamber length. This parametric investigation revealed the existence of several flame types aecording to air/fuel equivalence ratios, mixture temperatures and combustion chamber length. Transitions between flame states were sometimes smooth and continuous and, in some particular conditions, took place abruptly. The smooth transition coincided with isolines of the calculated Damköhler number while the sudden transition was associated with adiabatic flame temperatures. The flame types greatly influenced the pressure drops across the flame and the stability properties of the system. Unstable flames coincided with the large pressure drops measured across the flame. Moreover, acoustic measurements identified several unstable thermoacoustic modes with frequencies ranging from 200 Hz for the dominant mode, up to several kHz for the high frequency ones. The relative amplitude of the latest increased for very lean and rieh flames. Finally, acoustic measurements in the non-reacting flow for similar conditions revealed the existence of two hydrodynamic modes, which characteristic frequencies scaled with the average velocity at the burner outlet. Phase-averaged OH chemiluminescence pictures were obtained to visualize the characteristics of the flame along with thermoacoustic instabilities.The infiuence of the air/fuel equivalence ratio, the mixture temperature as well as the air mass flow rate on the flame shape, including the intensity of the reaction zone, the flame front, the position of the flame front and its movement within a period of oscillation were systematically investigated and assigned to the individual flame types. Additionally, a setup for the Planar Laser Induced Fluorescence(PLIF) diagnostic was built up enabling the correction of single-shot pictures for laser shot-to-shot intensity variations, laser sheet inhomogeneity and laser light absorption due to the investigated OH radical and the optical arrangement of the test facility. Furthermore, mediane far-infrared absorption and an acetone-PLIF technique were used in the upstream and downstream section of the combustor to determine the role of air/fuel equivalence ratio fluctuations and possible variations of the power density as a driving mechanism of thermoacoustic instabilities. The oscillations of… Advisors/Committee Members: Boulouchos, Konstantinos.

Subjects/Keywords: VERBRENNUNGSDYNAMIK (BRENNSTOFFTECHNOLOGIE); VERBRENNUNGSDRUCK + FLAMMENGESCHWINDIGKEIT + FLAMMENAUSBREITUNG (WÄRMELEHRE); GAS COMBUSTION (FUEL TECHNOLOGY); FUEL SUPPLY + CARBURETION (INTERNAL COMBUSTION ENGINES); BRENNKAMMERN (GASTURBINEN); THERMAL EXCITATION OF VIBRATIONS (ACOUSTICS); COMBUSTION CHAMBERS (GAS TURBINES); THERMISCHE SCHWINGUNGSERREGUNG (AKUSTIK); BRENNSTOFFZUFUHR + GEMISCHBILDUNG (VERBRENNUNGSMOTOREN); GASVERBRENNUNG (BRENNSTOFFTECHNOLOGIE); GASTURBINEN (VERBRENNUNGSKRAFTMASCHINEN); COMBUSTION DYNAMICS (FUEL TECHNOLOGY); COMBUSTION PRESSURE + FLAME SPEED + FLAME PROPAGATION (THERMOPHYSICS); GAS TURBINES, COMBUSTION TURBINES (INTERNAL COMBUSTION ENGINES); info:eu-repo/classification/ddc/620; info:eu-repo/classification/ddc/530; Engineering & allied operations; Physics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Fritsche, D. (2005). Origin and control of thermoacoustic instabilities in lean premixed gas turbine combustion. (Doctoral Dissertation). ETH Zürich. Retrieved from http://hdl.handle.net/20.500.11850/47744

Chicago Manual of Style (16^th Edition):

Fritsche, Daniel. “Origin and control of thermoacoustic instabilities in lean premixed gas turbine combustion.” 2005. Doctoral Dissertation, ETH Zürich. Accessed January 18, 2021. http://hdl.handle.net/20.500.11850/47744.

MLA Handbook (7^th Edition):

Fritsche, Daniel. “Origin and control of thermoacoustic instabilities in lean premixed gas turbine combustion.” 2005. Web. 18 Jan 2021.

Vancouver:

Fritsche D. Origin and control of thermoacoustic instabilities in lean premixed gas turbine combustion. [Internet] [Doctoral dissertation]. ETH Zürich; 2005. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/20.500.11850/47744.

Council of Science Editors:

Fritsche D. Origin and control of thermoacoustic instabilities in lean premixed gas turbine combustion. [Doctoral Dissertation]. ETH Zürich; 2005. Available from: http://hdl.handle.net/20.500.11850/47744

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