1 numerical simulation of plasma assisted turbulent combustion by anand srinivas ankala a thesis ...

69 Pages·2011·2.25 MB·English

NUMERICAL SIMULATION OF PLASMA ASSISTED TURBULENT COMBUSTION

BY
ANAND SRINIVAS ANKALA

A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE
DEGREE OF MASTER OF SCIENCE
UNIVERSITY OF FLORIDA
2011
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©2011 Anand Srinivas Ankala

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This document is dedicated to my parents who have supported me in all my endeavors.

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ACKNOWLEDGMENTS
First of all, I would like to thank Dr. Subrata Roy, the chairman of my graduate
committee, for providing me with an opportunity to work under his guidance as a part of
his research group. Dr. Roy shared with me his extensive knowledge and always
motivated me to perform better. I would also be grateful to Dr. William Lear and Dr.
Corin Segal, for accepting to be members in my committee. I would like to thank Dr.
Chin Chen Wang for his every help in successful completion of my thesis.
In addition, I would like to thank Navya, Jignesh, Tomas, Mark, Ankush, Ariel,
Moses, members of CPDLT lab and my friends, Uday, Abhijyoth and Bhageerath for
their academic help.
Above all I would like to express my gratitude to my parents for their unwavering
support and blessings.
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TABLE OF CONTENTS

page
ACKNOWLEDGMENTS .................................................................................................. 4
LIST OF TABLES ............................................................................................................ 7
LIST OF FIGURES .......................................................................................................... 8
LIST OF KEY SYMBOLS .............................................................................................. 10
ABSTRACT ................................................................................................................... 12
CHAPTER
1 INTRODUCTION .................................................................................................... 14
2 THEORY ................................................................................................................. 18
2.1 Combustion Concepts ....................................................................................... 18
2.1.1 Equivalence Ratio ................................................................................... 18
2.1.2 Lean Mixture ............................................................................................ 18
2.1.3 Classification ........................................................................................... 18
2.1.4 Damkohler Number ................................................................................. 18
2.2 Turbulent Combustion Theory .......................................................................... 19
2.2.1 Interaction between Flames and Turbulence ........................................... 19
2.2.2 Reynolds Average Navier Stokes (RANS) Simulation ............................. 21
2.2.2.1 Boussinesq hypothesis ................................................................ 21
2.2.2.2 Reynolds stress model ................................................................. 21
2.2.3 Large Eddy Simulation (LES) .................................................................. 21
2.2.3.1 Filtered balance equations ........................................................... 22
2.2.3.2 Smagorinsky model ..................................................................... 23
2.2.4 Detached Eddy Simulation (DES) ........................................................... 24
2.2.5 Governing Equations in the Standard k- Model ..................................... 24
2.3 Plasma Assisted Combustion ........................................................................... 25
2.4 Plasma Theory .................................................................................................. 31
2.4.1 Electric Circuit ......................................................................................... 31
2.4.2 Force Approximation for Plasma Actuator ............................................... 31
2.4.2.1 Geometry description ................................................................... 32
2.4.2.2 Numerical details ......................................................................... 32
3 COMPUTATIONAL MODEL ................................................................................... 34
3.1 Description of Combustion Chamber Geometry ............................................... 34
3.2 Computational Model of Combustion Chamber ................................................ 35
3.3 Advantages of Carrying Out CFD Analysis ....................................................... 35
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3.3.1 Speed ...................................................................................................... 35
3.3.2 Detailed Information ................................................................................ 35
3.3.3 Reduction of Experimental Risks ............................................................. 36
3.4 Steps for CFD Analysis ..................................................................................... 36
3.5 Grid Generation ................................................................................................ 36
3.6 Meshing Procedure ........................................................................................... 36
3.6.1 Creation of Coordinates ........................................................................... 36
3.6.2 Construction of Edges ............................................................................. 36
3.6.3 Construction of Faces .............................................................................. 37
3.6.4 Creation of Volumes ................................................................................ 37
3.6.5 Meshing ................................................................................................... 37
3.7 Solving .............................................................................................................. 39
3.7.1 Solvers .................................................................................................... 40
3.7.2 Energy Equation ...................................................................................... 40
3.7.3 Viscous Model ......................................................................................... 41
3.7.4 Species Transport ................................................................................... 41
3.7.5 Materials .................................................................................................. 42
3.7.6 Boundary Conditions ............................................................................... 42
3.7.7 User Defined Function ............................................................................. 43
3.7.8 Residuals ................................................................................................. 44
3.7.9 Convergence ........................................................................................... 44
3.7.10 Discretization ......................................................................................... 44
3.7.11 Initialization ............................................................................................ 45
3.7.12 Iteration ................................................................................................. 45
3.8 Grid Refinement Study ...................................................................................... 46
3.9 Application of Plasma ....................................................................................... 46
4 RESULTS AND DISCUSSIONS ............................................................................. 47
4.1 Non Reacting Flow............................................................................................ 47
4.2 2-D Steady State RANS Results ....................................................................... 50
4.3 3D Steady State RANS Solution ....................................................................... 51
4.4 3D DES Results ................................................................................................ 55
4.5 3D DES Results with Plasma Activation ........................................................... 59
4.6 NO Emissions ................................................................................................. 62
X
4.7 Fuel Concentration............................................................................................ 63
5 CONCLUSIONS ..................................................................................................... 65
6 RECOMMENDATIONS FOR FUTURE STUDY ..................................................... 66
LIST OF REFERENCES ............................................................................................... 67
BIOGRAPHICAL SKETCH ............................................................................................ 69
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LIST OF TABLES
Table page

3-1 Dimensions and the flow conditions ................................................................... 34
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LIST OF FIGURES
Figure page

1-1 Generic (standard) linear dielectric barrier discharge plasma actuator ............... 15
2-1 Regimes for turbulent non premixed combustion ............................................... 19
2-2 Plasma igniter in operation ................................................................................. 26
2-3 Reverse vortex combustor with 10W spatial arc ................................................. 27
2-4 Coaxial dielectric barrier discharge reactor ........................................................ 28
2-5 Combustion without plasma and increasing powers of plasma .......................... 29
2-6 Variation of NO, NO NO concentrations with applied voltage ......................... 30
2 , x
2-7 Electric circuit diagram ....................................................................................... 31
2-8 Geometry description of plasma actuator ........................................................... 33
3-1 Schematic of the combustor ............................................................................... 34
3-2 2D mesh of the combustion chamber ................................................................. 38
3-3 Zoomed view of the mesh of 2D combustion chamber ....................................... 39
3-4 3D mesh of the combustion chamber. ................................................................ 39
3-5 Solver parameters .............................................................................................. 40
3-6 Viscous model parameters ................................................................................. 41
3-7 Fuel inlet specifications ...................................................................................... 42
3-8 Pressure outlet specifications ............................................................................. 43
3-9 Iterate panel data ................................................................................................ 45
3-10 Region of application of plasma in the combustor. ............................................. 46
4-1 Velocity (m/s) contour plot without plasma force ................................................ 48
4-2 Velocity (m/s) contour plot with plasma force using a potential of 20 kV ............ 48
4-3 Velocity (m/s) contour plot with plasma force using a potential of 25 kV ............ 49
4-4 Velocity (m/s) contour plot with plasma force using a potential of 35 kV ............ 49
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4-5 2D steady state temperature plots ...................................................................... 50
4-6 2D steady state axial velocity plots ..................................................................... 51
4-7 3D steady state temperature plots ...................................................................... 52
4-8 3D steady state y velocity plots .......................................................................... 52
4-9 3D steady state z velocity plots .......................................................................... 53
4-10 3D steady state methane concentration plots ..................................................... 53
4-11 3D steady state oxygen concentration plots ....................................................... 54
4-12 Radial profiles of mean temperature (K) at z/R = 0.89 ....................................... 56
4-13 Radial profiles of mean temperature (K) at z/R = 1.57........................................ 56
4-14 Radial profiles of mean temperature (K) at z/R = 4.52 ....................................... 57
4-15 Radial profiles of mean axial velocity (m/s) at z/R = 0.14 ................................... 57
4-16 Radial profiles of mean axial velocity (m/s) at z/R = 0.38 ................................... 58
4-17 Radial profiles of mean axial velocity (m/s) at z/R = 4.67 ................................... 58
4-18 Radial profiles of mean axial temperature at z/R = 0.89 ..................................... 59
4-19 Radial profiles of mean axial temperature at z/R = 4.52 ..................................... 60
4-20 Radial profiles of mean axial temperature at z/R = 5.20 ..................................... 60
4-21 Radial profiles of mean axial velocity at z/R = 0.38 ............................................ 61
4-22 Radial profiles of mean axial velocity at z/R = 4.67 ............................................ 61
4-23 Radial distribution of mean fuel concentration .................................................... 64
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LIST OF KEY SYMBOLS
C Model constant
s
F Electrodynamic force (N)
h Enthalpy (kJ/kg)
k Turbulent kinetic energy (J)
Turbulent length scale (m)
r Radius (m)
Re Reynolds number
S Shear stress (N/m2)
Sc Schmidt number
k
t Time (s)
u Velocity (m/s)
Y Mixture fraction
Grid Size (m)
Greek Letters
Function of dielectric material
Dissipation rate (m2/s2)
Kinematic viscosity (m2/s)
Timescale (s)
Density (kg/m3)
Turbulent viscosity (m2/s)
Absolute viscosity (kg/ms)
Turbulent Prandtl number for kinetic energy
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