STATUS OF THESIS
Title of thesis
QUANTITATIVE SCHLIEREN MEASUREMENT OF 3 DIMENSIONAL TEMPERATURE, CONCENTRATION AND
VELOCITY FIELDS IN A GAS FLOW
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EMISHAW DANDENA IFFA
UNIVERSITI TEKNOLOGI PETRONAS
QUANTITATIVE SCHLIEREN MEASUREMENT OF 3 DIMENSIONAL TEMPERATURE, CONCENTRATION AND VELOCITY FIELDS IN A GAS
FLOW
by
EMISHAW DANDENA IFFA
The undersigned certify that they have read, and recommend to the Postgraduate Studies Programme for acceptance of this thesis for the fulfillment of the
requirements for the degree stated.
Signature: _____________________________________
Main Supervisor: _____________________________________
Signature: _____________________________________
Co-Supervisor: _____________________________________
Signature: _____________________________________
Head of Department: _____________________________________
Date: _____________________________________
Assoc. Prof. Dr. A. Rashid A. Aziz
Dr. Aamir Saeed Malik
Assoc. Prof. Dr. Ahmad Majdi Bin Abdul Rani
QUANTITATIVE SCHLIEREN MEASUREMENT OF 3 DIMENSIONAL TEMPERATURE, CONCENTRATION AND VELOCITY
FIELDS IN A GAS FLOW
by
EMISHAW DANDENA IFFA
A Thesis
Submitted to the Postgraduate Studies Programme as a Requirement for the Degree of
DOCTOR OF PHILOSOPHY
MECHANICAL ENGINEERING DEPARTMENT UNIVERSITI TEKNOLOGI PETRONAS
BANDAR SERI ISKANDAR, PERAK
May, 2011
DECLARATION OF THESIS
Title of thesis
QUANTITATIVE SCHLIEREN MEASUREMENT OF 3 DIMENSIONAL TEMPERATURE, CONCENTRATION AND
VELOCITY FIELDS IN A GAS FLOW
I, __________________________________________________________________
hereby declare that this thesis is based on my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously or concurrently submitted for any other degree at Universiti Teknologi PETRONAS or other institutions.
Witnessed by
_______________________________ _______________________________
Signature of Author Signature of Supervisor
Permanent address H.NO.1333 Kebele13/14 Kolfe Keranio sub-City Addis Ababa, Ethiopia
Name of Supervisor
Assoc. Prof. Dr. A. Rashid Aziz
Date:___________________________ Date:__________________________
EMISHAW DANDENA IFFA
ACKNOWLEDGEMENTS
I am eternally grateful for all the wonderful things God has given me and showed me during this study. He was my strength and hope during the difficult times.
I owe my deepest gratitude to my supervisor, AP. Dr. A. Rashid A. Aziz, whose encouragement, guidance and support from the initial to the final level of this research work. I am also very much thankful for his crucial comments and guidance in shaping and improving this dissertation.
I am heartily thankful to My Co- Supervisor, Dr. Aamir Saeed Malik, for making his support available throughout this research work.
I would like to thank Prof. Morgan R. Heikal of University of Brighton for his guidance at several stages of this project and during developing this dissertation.
It is my pleasure to thank members of Postgraduate Office and Department of Mechanical Engineering for their support by offering me Graduate Assistantship and providing laboratory facilities.
I am indebted to all of my colleagues in Center for Automotive Research (CAR) for their extended support while conducting experiments.
I extend my sincere thanks to Yohaness Tamirat, Ftwi Yohannes, Salahdin El- Sakin, Firmansyah, Benyam Seyoum, Mui’ Nuddin Bin Moharun, Noraz Al-Khari Bin Noran, Dr. Umesh Deshanavar, Kahirul Anwar Ahmed, Janni Alang Ahmed and Zailan Alang Ahmed for their support and kind assistance.
Finally, special thanks are due to my family for all of the extended hours I spent for developing this project and writing the thesis instead of being with them, and to my parents, brother and sister for their encouragement and support.
ABSTRACT
Background Oriented Schlieren (BOS) estimates the flow behaviour that exists between the camera and background from the shift in the background image features due to the change in the transfer channel function. The current optical flow techniques used to find the deflection vectors of the change in background images rely on two main assumptions: global constant value of intensity and continuity of local motion. The global intensity invariance assumption hardly works for BOS technique when imaging a self luminous flow. In this thesis, an optical flow equation which takes the change in intensity into account and an estimation motion model that considers both translational and rotational deflections were developed. The results showed that for a transparent gas jet all the tested optical flow algorithms worked well. However the proposed model gave better results for BOS images taken through natural gas flames and smoke from a fog generator. The developed deflection vector estimation algorithm and optical tomography served as a tool to extract the index of refraction of the gaseous fields. The Gladstone-Dale relationship was used to show the direct correlation between the index of refraction and density of the flow. Three different types of axi-symmetric flows were used as gas sample media. These were a CNG injected fuel jet, an open methane flame and a hot air jet. Based on the measured index of refraction the species mole fractions of CNG injected jet and methane flame were measured. In addition, the three dimensional temperature fields of the methane flame and the hot air were also measured and displayed. The other main contribution of this research was the use of Background Oriented Schlieren (BOS) technique for the measurement of the velocity field of a variable density round jet. The density field was further exploited to extract the axial and radial velocity vectors for six different jet-exit temperature values with the aid of the continuity and energy equations. Results of the measured temperature and velocity vector fields were compared with thermocouples and hot wire anemometry readings respectively and showed good agreements.
ABSTRAK
Latar Belakang Berorientasikan Schlieren (Background Oriented Schlieren, BOS) menganggarkan kelakuan aliran yang muncul di antara kamera dan latar belakang dari pegalihan dalam ciri-ciri gambar latar belakang akibat perubahan fungsi saluran pemindahan. Teknik-teknik arus optik yang digunakan sekarang untuk mencari pembiasan vektor dari perubahan imej latar belakang bergantung pada dua andaian utama: pemalar nilai keamatan menyeluruh dan gerakan berterusan setempat.
Dalam tesis ini, persamaan aliran optik yang mengambil kira perubahan keamatan dan anggaran gerakan model mempertimbangkan kedua-dua pelenturan penjelmaan dan putaran dibangunkan. Model yang dicadangkan memberikan hasil yang lebih baik untuk gambar-gambar BOS yang diambil melalui nyalaan gas asli dan asap dari generator kabut. Vektor pelenturan algoritma anggaran yang dibangunkan dan tomografi optik berperanan sebagai alat untuk mengekstrak indeks bias bidang gas. Hubungan Gladstone-Dale digunakan untuk menunjukkan hubungan langsung antara indeks biasan dan kepadatan aliran. Tiga jenis arus axi-simetri telah digunakan sebagai media sampel gas. Gas-gas tersebat adalah jet suntikan bahan bakar CNG, bukaan nyalaan metana dan jet udara panas. Berdasarkan kiraan indeks biasan, pecahan mol dari jet suntikan CNG dan nyalaan metana dihitung. Tambahan pula, medan suhu 3-dimensi dari nyalaan metana dan udara panas juga dihitung dan dipaparkan. Sumbangan utama yang lainnya dari kajian ini adalah penggunaan Latar Belakang Berorientasikan Schlieren (BOS) teknik untuk menghitung medan kelajuan jet pada pelbagai pembolehubah kepadatan. Medan kepadatan selanjutnya dimanfaatkan untuk mengekstrak vektor kelajuan paksi dan jejari untuk enam nilai suhu jet-keluar berbeza dengan bantuan daripada persamaan kesinambungan dan persamaan tenaga. Hasil keputusan dari perhitungan suhu dilandingkan dengan termokopel manakala vektor kelajuan dibandingkan dengan bacaan kawat panas anemometry dan masing-masing menunjukkan persamaan yang baik.
COPYRIGHT
In compliance with the terms of the Copyright Act 1987 and the IP Policy of the university, the copyright of this thesis has been reassigned by the author to the legal entity of the university,
Institute of Technology PETRONAS Sdn Bhd.
Due acknowledgement shall always be made of the use of any material contained in, or derived from, this thesis.
© Emishaw Dandena Iffa
, May 2011 Institute of Technology PETRONAS Sdn Bhd All rights reserved.TABLE OF CONTENTS
ACKNOWLEDGEMENTS ... v
ABSTRACT ... vi
COPYRIGHT ... x
LIST OF TABLES ... xv
LIST OF FIGURES ... xvii
LIST OF PLATES ... xxii
NOMENCLATURE ... xxiii
Chapter 1. INTRODUCTION……….……..……….1
1.1 Overview of the Schlieren Technique………..1
1.2 Problem Statement………...4
1.3 Research Objective………..5
1.4 Scope of the Research………..6
1.5 Research Methodology………7
1.6 Thesis Outline………..7
2. LITERATURE REVIEW………..….……11
2.1 Introduction………...…11
2.2 Geometric Flow Parameters Measurement…………...……...….………..11
2.3 Thermodynamic Flow Parameter Diagnostic Tools………….…………..13
2.3.1 Molecular Based Techniques………..……….13
2.3.1.1 Rayleigh Scattering………...………..15
2.3.1.2 Raman Scattering………...………….16
2.3.2.2 Particle Image Velocimetry (PIV)……….18
2.3.2.3 Laser Doppler Annemometry (LDA)……….19
2.3.2.4 Phase Doppler Interferometry (PDI)………..20
2.4 Quantitative Schlieren………20
2.4.1 Color Schlieren………...20
2.4.2 Laser Schlieren………23
2.4.3 Background Oriented Schlieren (BOS)………...23
2.5 Summary……….28
3. THEORY AND MATHEMATICAL MODELLING……….……29
3.1 Introduction ... .29
3.2 Theoretical Background... 29
3.3 Light Beam Deflection Vector Estimation ... 31
3.3.1 Estimating Motion ... Error! Bookmark not defined. 3.3.2 Incorporating Intensity Variance Error! Bookmark not defined. 3.3.3 Modifying Optical Flow Equation ... Error! Bookmark not defined. 3.3.4 Algorithm Design... Error! Bookmark not defined. 3.4 Computed Tomography ... Error! Bookmark not defined. 3.5 Thermodynamic Data Extraction ... Error! Bookmark not defined. 3.5.1 Temperature and Concentration Field of a Non-reacting Flow Error! Bookmark not defined. 3.5.2 Temperature and Concentration Field of a Reacting Flow .. Error! Bookmark not defined. 3.5.3 Velocity Field Measurement ... Error! Bookmark not defined. 3.5.4 Turbulence Statistics ... Error! Bookmark not defined. 3.6 Summary ... Error! Bookmark not defined. 4. EXPERIMENTAL METHODS……….……….59 4.1 Introduction ... Error! Bookmark not defined.
4.2 BOS Working Principles ... Error! Bookmark not defined.
4.3 BOS Optical Setup ... Error! Bookmark not defined.
4.3.1 Camera Setup ... Error! Bookmark not defined.
4.3.2 Background Selection ... Error! Bookmark not defined.
4.3.3 Overall BOS Setup ... Error! Bookmark not defined.
4.3.4 Experimental Error Analysis……….…...……..…………Error!
Bookmark not defined.
4.3.5 Experimental Verification of the Developed Model……..….…. 70
4.4 Fluid Flow/ Injection Set-up ... 71
4.4.1 CNG DI Set-up ... 72
4.4.2 Methane Flame Set-up ... 73
4.4.3 Hot Air Flow Set-up.………...73
4.5 The Thermocouple and Hot Wire Anemometer Measurements ... 73
4.6 Experimental Planning ... Error! Bookmark not defined. 4.7 Summary ... Error! Bookmark not defined. 5. RESULTS AND DISCUSSIONS………...79
5.1 Introduction ... Error! Bookmark not defined. 5.2 Deflection Vector Estimation ... Error! Bookmark not defined. 5.3 CNG Concentration Measurement ... Error! Bookmark not defined. 5.4 Methane Flame Temperature and Concentration Measurement ... Error! Bookmark not defined. 5.5 Hot Round Jet Velocity Vector and Temperature Fields Measurement ... 97
5.6 Comparing Results with Other Algorithms……….………...Error! Bookmark not defined. 5.7 Summary...114
6. CONCLUSIONS AND RECOMMENDATIONS………...115
6.1 Conclusions...115
6.2 Suggestions for Future Works...117
REFERENCES……….……..………..118
PUBLICATIONS……….……….………….…………...………...128
APPENDIX ……….……….…...……….129
LIST OF TABLES
Table 2.1: overview of optical diagnostic tools...14
Table 2.2: Researchers’ and their role towards today’s BOS...26-27 Table 4.1: Framing rate Vs image resolution ...62
Table 4.2: Shutter speed Vs framing rate ...64
Table 4.3: Change in intensity of a background image under different flow conditions...70
Table 4.4: Fuel injection parameters...72
Table 4.5: Optical measurements setup...72
Table 4.6: The relative distances between BOS apparatuses and the flow...75
Table 5.1: Percentage RMS error of optical flow algorithms...81
Table 5.2: Comparison of the various variants of the proposed method...81
Table 5.3: SSIM criteria for flame images...92
Table 5.4: Chemical Species with their respective mole fractions...94
Table 5.5: COV of different velocity parameters...105
LIST OF FIGURES
Figure 1.1: Leonardo Da Vinci’s water jet visualization sketch ...1
Figure 1.2: Hooke’s Schlieren setup ...2
Figure 1.3: Toepler’s Schlieren apparatus ...3
Figure 1.4: Conventional Schlieren setup...4
Figure 1.5: Flow diagram of the research methodology...9
Figure 2.1: Rayleigh scattering Setup ...15
Figure 2.2: Raman scattering setup ...16
Figure 2.3: PIV setup ...19
Figure 2. 4: LDA/ PDI setup...19
Figure 2.5: Rainbow Schlieren filter...22
Figure 3.1: BOS setup...30
Figure 3.2: Discrete wavelet transform image decomposition……….…...31
Figure 3.3: principle of light refraction...32
Figure 3.4: Wave fronts of a light beam...32
Figure 3.5: Approximate coefficients decomposition...40
Figure 3.6: The five levels of BOS image down-sampling...41
Figure 3.7: Comparison of the developed algorithm complexity...44
Figure 3.8 Algorithm of the optical flow estimation...45
Figure 3.9: Flow of filtered back projection reconstruction...46
Figure 3.10: Flow of direct Fourier transform algorithm...47
Figure. 3.11: The light rays deflection in plane t and s... 47
Figure 3.12: The velocity and the normal vector of an elemental area...54
Figure 3.13(a): Model for Axi-symmetric jet’s frontal view ...55 Figure 3.13(b): Cross sectional area of a jet along
Figure 4.3 direct visualization of a candle plume
with different shutter speed at 60fps...63
Figure 4.4: Different backgrounds of BOS (a) wavelet noise (b) lined background (c) random noise...64
Figure 4.5: Simplified BOS setup...66
Figure 4.6: Effects of distances between camera, background and flow media in BOS sensitivity...67
Figure 4.7: Percentage error propagation against uncertainty of the deflection vector...69
Figure 4.8: Validation algorithm……….…71
Figure 4.9: BOS experimental setup...73
Figure. 4.10: Experimental Procedure...77
Figure 5.1: Background displacement vectors due to the natural gas flame...80
Figure 5.2: The deflection vectors of different flows ...80
Figure 5.3: Effects of the proposed method parameters...82
Figure 5.4: Angular deflection vectors along radial axis at maximum tip penetration and 12 bar injection pressure...85
Figure 5.5: Change in index of refraction at different planes perpendicular to the jet axis at maximum tip penetration and 12 bar injection pressure...86
Figure 5.6: CNG concentrations at different planes perpendicular to the jet axis at maximum tip penetration and 12 bar injection pressure...88
Figure 5.7: Normalized density distribution near nozzle along the jet axis at maximum tip penetration. ...88
Figure 5.8: CNG concentrations in a plane parallel to the jet axis at 18bars injection pressure...89
Figure 5.9: CNG concentrations in a plane parallel to the jet axis at 14bars injection pressure...89
Figure 5.10: Direct Flame Visualization...90
Figure 5.11: (a) - The gas flow Schlieren image before ignition (b) the flame Schlieren image after ignition...91
Figure 5.12: The BOS image taken without and through gas flame media...92
Figure 5.13: Displacement vector field...93
Figure. 5.14. (a) - (c): Mole fraction of CO2 in 30ms interval...94
Figure 5.15-(a): Plane used to show temperature distribution.
(b)- (d) Temperature distribution...96
Figure 5.16: Mean temperature values at (a) Z=3D (b) Z=5D...96
Figure 5.17: Mean temperature and Standard deviation between BOS and thermocouple readings at 3D and 5D planes perpendicular to the flame axis………..…………..97
Figure 5.18: Centerline density distribution of different exit temperatures and their respective trend lines. ...98
Figure 5.19: Center line velocity decay at different jet exit temperatures...99
Figure 5.20: The axial velocity distribution of the jet at 473K...99
Figure 5.21: The axial velocity profile of a heated jet...100
Figure 5.22: The Tangential velocity profile of a heated jet...100
Figure 5.23: The vorticity vector of the injected air at 473K...101
Figure 5.24: Velocity variance o i i U v v (a) axial, (b) tangential velocity... 102
Figure 5.25: Power Spectral density of the axial velocity at T=473K...103
Figure 5.26: (a) axial and (b) tangential velocity measurements using BOS and hot wire anemometry at 323K exit temperature ...104
Figure 5.27: percentage coefficient of variation between BOS and Hot wire Anemometry readings of velocity decay at 302K and 323K...106
Figure 5.28: Temperature field measurement at 523K (a) at y=0and Z=3D (b) y=0 and Z=5D...107
Figure 5.29: COV between BOS and thermocouple readings at 523K jet exit temperature...108
Figure 5.30: Temperature field measurement at 473K (a) at y=0and Z=3D (b) y=0 and Z=5D...109
Figure 5.31: COV between BOS and thermocouple readings at 4730K jet exit temperature...110 Figure 5.32: Temperature field measurement at 4730K (a) at y=0and Z=3D
Figure 5.35: Standard deviation between thermocuple reading and BOS
measurement using several optical flow algorithms………...113 Figure 5.34: Percentage COVbetween hotwire annemometry and BOS measurement
using several optical flow algorithms………...113
NOMENCLATURE
Variable Description Units
a, b, c, d e, f
f i
l m me
N R
t
u ,s x, y, z A, B
C1 and C2
E(S) G
k kv
Gv
I ) , (k l N
N’
L2 L
Affine constants of rotation, dilation and shear Affine units of translation
The oscillatory strength
The level of the wavelet transform Molecular weight
The mass of an electron Index of refraction Position vector
Instantaneous time where image is recorded The shift and rescaling parameters of wavelet transform
Cartesian coordinates
Constants incorporated to account intensity variation
Standard deviations of images Fourier transform of deflection vector Gladstone-Dale constant
Power Spectral density Image intensity
2D Fourier transform of index of refraction Gradient of index of refraction
Domain of natural numbers Optical path length
(-) (-) (-) (-) (-) (kg)
(-) (m) (sec)
(-) (-) (-) (-)
(-) (nm-sec)
(m3/kg) (db)
(-) (-) (-) (-) (m)
R S To and T
Ui
Vi
Xi Zbm Zml
Zbl
Zf
The radon transform matrix Wave front arc length
Ambient and measured temperatures Mean velocity
Fluctuation component of velocity Species mole fraction
Distance between background and flow media Distance between flow media and lens
The distance between background and lens The focal length of the camera
(-) (m) (K) (m/sec) (m/sec)
(-) (m)
(m) (m) (m)
θ
x, y α
μ, ν
and i yb
yi
x andy
x, y
Gas density Angle of refraction
Light beam deflection angles Affine rotational coefficient
Translation terms along x and y axis Wavelet function
Frequency and resonance frequency
Imaginary deflection vector on the background The deflection recorded in the camera
Mean intensity images
Constantsadded to avoid zero denominators
(kg/m3) (rads)
(rads) (-) (m)
(-) (Hz) (m) (m) (-) (-) (-)
Abbreviations
BOS Background Oriented Schlieren CNG Compressed natural gas
COV Coefficient of variation HWA Hot wire annemometry OF Optical flow
OPL Optical path length
