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研究生: 羅麥可
Michael - Estela Loretero
論文名稱: 聲波激勵對旋轉燃燒尾流的效應
Effects of Acoustic Excitation on a Reacting and Swirling Wake
指導教授: 黃榮芳
Rong-Fung Huang
口試委員: 趙振綱
Ching-Kong Chao
楊鏡堂
Jing-Tang Yang
牛仰堯
Yang-Yao Niu
沈澄宇
Cherng-Yeu Shen
孫珍理
Chen-Li Sun
學位類別: 博士
Doctor
系所名稱: 工程學院 - 機械工程系
Department of Mechanical Engineering
論文出版年: 2011
畢業學年度: 99
語文別: 英文
論文頁數: 277
中文關鍵詞: Reacting swirling wakeAcoustic excitationNonpremixed flame
外文關鍵詞: Reacting swirling wake, Acoustic excitation, Nonpremixed flame
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  • The present work aims to investigate experimentally the behavior of flame and
    flow at swirling wake when the fuel supply is acoustically driven. Excitation frequency,excitation amplitude, central jet flow and annular jet flow are successively varied. Fourdistinctive flame behaviors are generated and classified as wrinkled base flame,converged base flame, diverged base flame, and blue lifted flame. These effects are particularly strong when the excitation frequency is tuned close to 180 Hz and its harmonic frequencies due to fuel tube resonance. The flame lengths at various excitation amplitude, central jet flow and annular jet flow are measured using conventional flame photography technique. The central jet flow approach optimal condition at Rec = 2386 based on the flame reduction capacity of the acoustic generator. Laser-light sheet assisted Mie scattering method is employed to visualize the flow in the flame. The beads like vortex in the central jet induced a wrinkled base flame and when the excitation increases the beads like structure expand resulting to a converged base flame. The upward rolling vortex causes the diverged base flame while the periodically issuing fuel jet puts the flame into its blue lifted flame mode. Jet exit velocity fluctuations are measured by two components LDV to calculate the flow and turbulence properties. Optimum mixing condition is found at Rea = 528 and excitation level between 8 to 12 volts based on the Lagrangian integral length scale. The flow field characteristic at optimal condition is diagnosed by high speed PIV system to quantify the flow and turbulence properties in every phase of the acoustic cycle. Flame temperature is measured by Type-R thermocouple which describes a large heat release of the flame at optimal conditions. At such condition, faster rate of reaction is verified by concentration measurements of the products of combustion carried out using Rosemount gas analyzer.


    The present work aims to investigate experimentally the behavior of flame and
    flow at swirling wake when the fuel supply is acoustically driven. Excitation frequency,excitation amplitude, central jet flow and annular jet flow are successively varied. Fourdistinctive flame behaviors are generated and classified as wrinkled base flame,converged base flame, diverged base flame, and blue lifted flame. These effects are particularly strong when the excitation frequency is tuned close to 180 Hz and its harmonic frequencies due to fuel tube resonance. The flame lengths at various excitation amplitude, central jet flow and annular jet flow are measured using conventional flame photography technique. The central jet flow approach optimal condition at Rec = 2386 based on the flame reduction capacity of the acoustic generator. Laser-light sheet assisted Mie scattering method is employed to visualize the flow in the flame. The beads like vortex in the central jet induced a wrinkled base flame and when the excitation increases the beads like structure expand resulting to a converged base flame. The upward rolling vortex causes the diverged base flame while the periodically issuing fuel jet puts the flame into its blue lifted flame mode. Jet exit velocity fluctuations are measured by two components LDV to calculate the flow and turbulence properties. Optimum mixing condition is found at Rea = 528 and excitation level between 8 to 12 volts based on the Lagrangian integral length scale. The flow field characteristic at optimal condition is diagnosed by high speed PIV system to quantify the flow and turbulence properties in every phase of the acoustic cycle. Flame temperature is measured by Type-R thermocouple which describes a large heat release of the flame at optimal conditions. At such condition, faster rate of reaction is verified by concentration measurements of the products of combustion carried out using Rosemount gas analyzer.

    CHAPTER 1 INTRODUCTION........................................................1 1.1 Motivation................................................................1 1.2 Literature survey.........................................................1 1.3 Scope of present work ....................................................4 CHAPTER 2 EXPERIMENTAL METHODS................................................6 2.1 Physical description of swirl generator...................................6 2.2 Acoustic excitation of central fuel jet...................................7 2.3 Description of phase angle................................................8 2.4 Flame and flow visualization..............................................8 2.5 Jet exit velocity measurements by LDV....................................10 2.6 Reacting flow field velocity measurements by PIV ........................11 2.7 Temperature measurements ................................................13 2.8 Product concentrations measurements......................................13 CHAPTER 3 FLAME BEHAVIORS....................................................16 3.1 Unexcited flame behavior.................................................16 3.2 Excited flame behavior ..................................................18 3.3 Characteristic regimes of flame behaviors ...............................21 3.4 Flammability and stability limits .......................................24 3.5 Flame length ............................................................26 3.6 Optimized fuel flow rate.................................................31 3.7 Superimposed flame and flow images.......................................33 3.8 Description of motion pictures and elucidation of mixing mechanisms .....37 3.9 Flow behaviors at high swirl.............................................41 CHAPTER 4 FLOW CHARACTERISTICS AT CENTRAL JET EXIT...........................45 4.1 Jet exit velocity profile and sampling conditions .......................45 4.2 Oscillation of central jet, phase angle, and time series data ...........46 4.3 Strouhal number and effect of annular swirl strength ....................48 4.4 Probability distributions................................................52 4.5 Absolute turbulence intensity ...........................................53 4.6 Autocorrelation and Lagrangian integral turbulence time scale............54 4.7 The best operating conditions based on Lagrangian integral turbulence scales.......................................................................55 CHAPTER 5 TIME AVERAGED FLOW FIELD CHARACTERISTTICS..........................57 5.1 Particle seeding and flow conditions for PIV measurements ...............57 5.2 Time averaged velocity vectors and streamlines ..........................58 5.3 Time series data, power spectrum density function, and autocorrelation...60 5.4 Lagrangian integral turbulence time and length scales....................60 5.5 Average velocity distributions...........................................62 5.6 Absolute turbulence intensity distributions .............................63 5.7 Vorticity................................................................64 5.8 Stresses induced by total fluctuations...................................66 CHAPTER 6 PHASE-RESOLVED FLOW FIELD CHARACTERISTICS..........................69 6.1 Cycle variation at some critical points..................................69 6.2 Phase-resolved ensemble average velocity vectors and streamlines ........69 6.3 Contours of phase-resolved cycle variation intensities of velocity ......72 6.4 Contours of phase-resolved absolute turbulence intensity caused by turbulence fluctuations .....................................................75 6.5 Contours of phase-resolved vorticity.....................................77 6.6 Stresses induced by turbulence fluctuations .............................79 CHAPTER 7 TEMPERATURE FEILD..................................................81 7.1 Thermal structure for low swirl strength ................................81 7.2 Thermal structure for medium swirl strength .............................82 7.3 Thermal structure for high swirl strength ...............................83 CHAPTER 8 CONCENTRATION FEILD................................................85 8.1 Product species concentration for low swirl strength ....................85 8.2 Product species concentration for medium swirl strength..................86 8.3 Product species concentration for high swirl strength....................87 CHAPTER 9 DISCUSSION.........................................................89 9.1 Flame length and optimized central jet velocity..........................89 9.2 Oscillation of axial velocity along far field sound wave propagation ....89 9.3 Effects of mixing mechanism at the flame base on flame performance.......90 9.4 Contour of turbulence properties in relation with local flame behavior...91 9.5 Length scale, vorticity, and diffusivity ................................92 CHAPTER 10 CONCLUSIONS AND RECOMMENDATIONS...................................93 10.1 Conclusions.............................................................93 10.1 Recommendations.........................................................96 REFERENCES ..................................................................97

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