Thin/cambered/reflexed airfoil development for micro-air vehicles at Reynolds numbers of 60000 to

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Reid, Michael, "Thin/cambered/reflexed airfoil development for micro-air vehicles at Reynolds numbers of
60,000 to 150,000" (2006). Thesis. Rochester Institute of Technology. Accessed from
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THIN/CAMBERED/REFLEXED AIRFOIL DEVELOPMENT
FOR MICRO-AIR VEHICLES AT REYNOLDS NUMBERS OF
60,000 TO 150,000

By
MICHAEL R. REID

A Thesis Submitted in Partial Fulfillment of the Requirement
for Master of Science in Mechanical Engineering

Approved by:
Department of Mechanical Engineering Committee
Dr. Jeffery Kozak – Thesis Advisor _________________________________
Dr. Agamemnon Crassidis _________________________________
Dr. Kevin Kochersberger _________________________________
Dr. Edward Hensel – Dept. Representative _________________________________

Rochester Institute of Technology
Rochester, New York 14623
September 2006
PERMISSION TO REPRODUCE THE THESIS

Title of Thesis

THIN/CAMBERED/REFLEXED AIRFOIL DEVELOPMENT
FOR MICRO-AIR VEHICLES AT REYNOLDS NUMBERS OF
60,000 TO 150,000

I, MICHAEL R. REID, herby grant permission to the Wallace Memorial Library of
Rochester Institute of Technology to reproduce my thesis in the whole or part. Any
reproduction will not be for commercial use or profit.

September 2006
ABSTRACT

Previous micro-air vehicle research has addressed thin/cambered/reflexed airfoils on an
application specific basis, relying heavily on the shape characteristics of previously designed
airfoils. The motivation of the current research is to determine the relationship that exists
between thin/cambered/reflexed airfoil performance and the defining airfoil shape parameters
to improve future airfoil designs. An emphasis is placed on the effect each airfoil shape
parameter has on the overall airfoil performance and the effect of the interdependence of
each shape parameter. Maximum coefficient of lift, stall angle of attack, maximum
coefficient of lift/coefficient of drag and the angle of attack at which it occurs are found for a
variety of thin/cambered/reflexed airfoils and a number of correlations between changes in
shape parameters and airfoil performance are established. Changes in C and xC cause a 40%
variation of C and 40% variation of (cid:1) . Changes in R and xR cause a 15% variation of
l,max stall
C with no significant variation in (cid:1) . Changes in C and xC cause a 30% variation of
l,max stall
C/C and 50% variation of (cid:1) . Changes in R and xR cause a 20% variation of
l d,max Cl/Cd,max
C/C . Airfoil performance is determined using XFOIL, a two dimensional analysis code
l d,max
designed specifically to address airfoil boundary layer behavior at low Reynolds numbers. A
comparison of XFOIL results and known wind tunnel data is presented as validation of the
analysis code in addition to previously published validation studies. Wind tunnel testing
performed in Rochester Institute of Technology’s closed circuit low speed wind tunnel is
presented for a small subset of the airfoils analyzed as a comparison of the experimental and
analytic boundary layer behavior. The results showed good correlation between XFOIL
predictions and wind tunnel results for Bezier airfoils with camber less than 7%.
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ACKNOWLEDGEMENTS

I would like to thank my advisor Dr. Jeffery Kozak, whose laissez faire approach combined
with timely interjections of personal wisdom proved invaluable. I would also like to thank
the mechanical engineering faculty, who are undoubtedly responsible for what I have been
able to achieve.

I would like to thank my Mother, Father, and Sister who have provided nothing but love and
encouragement; they helped me maintain a positive attitude, and my sanity, throughout the
entire process.
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TABLE OF CONTENS

ABSTRACT.......................................................................................................................................................III
ACKNOWLEDGEMENTS..............................................................................................................................IV
TABLE OF CONTENS.......................................................................................................................................V
LIST OF FIGURES........................................................................................................................................VIII
NOMENCLATURE............................................................................................................................................X
1 INTRODUCTION.......................................................................................................................................1
1.1 BACKGROUND AND MOTIVATION........................................................................................................1
1.2 PREVIOUS RESEARCH...........................................................................................................................3
1.2.1 Laminar Separation Bubble Mechanics.........................................................................................3
1.2.1.1 Formation, Classification, and Effects.................................................................................................4
1.2.1.2 Determining Location..........................................................................................................................7
1.2.2 Airfoils at Low Reynolds Numbers.................................................................................................9
1.2.2.1 NACA 4-Digit Airfoils........................................................................................................................9
1.2.2.2 Characteristics of Low Reynolds Number Airfoils............................................................................10
1.2.3 Methods for Improved Low Reynolds Number Performance........................................................12
1.2.4 XFOIL...........................................................................................................................................14
1.2.4.1 Boundary Conditions.........................................................................................................................15
1.2.4.2 Transition Prediction..........................................................................................................................15
1.2.4.3 Validation...........................................................................................................................................16
1.3 THESIS OBJECTIVES...........................................................................................................................17
2 AIRFOIL DEVELOPMENT...................................................................................................................19
2.1 DESIRED AIRFOIL PERFORMANCE......................................................................................................19
2.2 PREVIOUS THIN AIRFOIL DESIGNS.....................................................................................................21
2.3 ISOLATION OF AIRFOIL SHAPE PARAMETERS.....................................................................................22
2.3.1 nth Order Polynomial Method.......................................................................................................23
2.3.2 Bezier Curve Description.............................................................................................................25
2.3.3 Bezier Curve Method....................................................................................................................27
2.4 AIRFOIL GENERATION........................................................................................................................29
2.4.1 Thickness, Leading Edge, and Trailing Edge...............................................................................29
2.4.2 Mean Camber Line Modifications................................................................................................31
2.4.3 MATLAB Functions......................................................................................................................31
3 TOOLS FOR ANALYSIS........................................................................................................................33
3.1 XFOIL...............................................................................................................................................33
3.1.1 History..........................................................................................................................................33
3.1.2 Variables.......................................................................................................................................34
3.1.2.1 Geometric Variables..........................................................................................................................34
3.1.2.2 Method Variables...............................................................................................................................37
3.1.2.3 Solution Variables..............................................................................................................................38
3.1.3 Sources of Error...........................................................................................................................39
3.1.4 Limitations....................................................................................................................................40
3.1.5 Validation.....................................................................................................................................41
3.1.5.1 Previous Validation............................................................................................................................42
3.1.5.2 Present Validation..............................................................................................................................42
3.2 EXPECT..............................................................................................................................................51
3.2.1 Background...................................................................................................................................51
3.2.2 Script.............................................................................................................................................51
3.2.3 Validation.....................................................................................................................................53
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3.3 DATA PROCESSING.............................................................................................................................53
3.3.1 Data File Format..........................................................................................................................54
3.3.2 Verification...................................................................................................................................54
4 AIRFOIL ANALYSIS..............................................................................................................................56
4.1 DATA ASSESSMENT............................................................................................................................56
4.1.1 Unconverged Angle of Attack.......................................................................................................56
4.1.2 C and (cid:1) ...............................................................................................................................58
l,max stall
4.1.3 C/C and (cid:1) ....................................................................................................................60
l d,max Cl/Cd,max
4.1.4 Lift Polar......................................................................................................................................60
4.2 RESULTS: CL,MAX AND (cid:2)STALL.................................................................................................................65
4.2.1 Max Camber and Position of Max Camber..................................................................................65
4.2.2 Max Reflex and Position of Max Reflex........................................................................................74
4.2.3 Thickness......................................................................................................................................77
4.3 RESULTS: CL/CD,MAX AND (cid:2)CL/CD,MAX.....................................................................................................78
4.3.1 Max Camber and Position of Max Camber..................................................................................79
4.3.2 Max Reflex and Position of Max Reflex........................................................................................85
4.3.3 Thickness......................................................................................................................................88
4.4 DESIGN METHODOLOGY....................................................................................................................89
4.4.1 Design for C ............................................................................................................................90
l,max
4.4.2 Design for C/C .......................................................................................................................92
l d,max
4.4.3 Limitations....................................................................................................................................93
4.5 CONCLUSIONS....................................................................................................................................94
5 AIRFOIL TESTING.................................................................................................................................96
5.1 EXPERIMENTAL AIRFOILS..................................................................................................................96
5.1.1 Airfoil Construction......................................................................................................................97
5.1.2 Airfoil Measurements.................................................................................................................100
5.2 EXPERIMENTAL SET-UP....................................................................................................................100
5.2.1 Wind Tunnel................................................................................................................................101
5.2.2 Measurement Devices and Error................................................................................................102
5.2.2.1 Velocity and Pressure.......................................................................................................................102
5.2.2.2 Temperature.....................................................................................................................................103
5.2.2.3 Angle of Attack................................................................................................................................104
5.2.2.4 Surface Oil Feature Location...........................................................................................................104
5.2.3 Experimental Sources of Error...................................................................................................105
5.3 EXPERIMENT OUTLINE.....................................................................................................................107
5.3.1 Experimental Procedure.............................................................................................................107
5.3.2 Surface Oil Flow Description.....................................................................................................108
5.4 VALIDATION....................................................................................................................................110
5.4.1 Known Data................................................................................................................................111
5.4.2 Validation Results and Discussion.............................................................................................111
5.5 SURFACE OIL FLOW: RESULTS AND DISCUSSION.............................................................................113
5.5.1 BEZ032037516...........................................................................................................................113
5.5.2 BEZ083018513...........................................................................................................................115
5.5.3 Conclusions................................................................................................................................117
6 CONCLUSIONS.....................................................................................................................................119
6.1 GENERAL CONCLUSIONS..................................................................................................................119
6.2 CONCLUSIONS: ANALYSIS................................................................................................................120
6.3 CONCLUSIONS: TESTING..................................................................................................................121
6.4 RECOMMENDATIONS FOR FUTURE WORK........................................................................................123
REFERENCES.................................................................................................................................................125
APPENDIX A...................................................................................................................................................129
APPENDIX B....................................................................................................................................................136
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APPENDIX C...................................................................................................................................................137
C1. EXPECT SCRIPT FOR XFOIL AUTOMATION............................................................................................137
Expfoil_V4.tcl...........................................................................................................................................137
C2. MATLAB CODE: BEZIER AIRFOIL GENERATION.....................................................................................144
Load_Airfoil_Variables.m.........................................................................................................................144
Bezier_Airfoil_Generator.m.....................................................................................................................145
Bezier.m....................................................................................................................................................147
Add_Thickness.m......................................................................................................................................152
C3. DATA ANALYSIS......................................................................................................................................155
Load_variables.m......................................................................................................................................155
SavePolarData_X_v3.m............................................................................................................................156
APPENDIX D...................................................................................................................................................165
D1. SURFACE OIL FLOW VISUALIZATION RESULTS........................................................................................165
BEZ032037516.........................................................................................................................................165
BEZ053018513.........................................................................................................................................167
BEZ062518513.........................................................................................................................................168
BEZ072018013.........................................................................................................................................169
BEZ083018513.........................................................................................................................................170
D2. SURFACE OIL FLOW VISUALIZATION PHOTOGRAPHS...............................................................................171

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LIST OF FIGURES

Figure 1.1: Laminar Separation Bubble (courtesy of Gad-El-Hak).........................................4
Figure 1.2: Laminar Separation Bubble Pressure Distribution (courtesy of Gad-El-Hak)......7
Figure 1.3: Surface Oil Flow – Example (courtesy of Lyon)..................................................9
Figure 1.4: Effect of Surface Roughness (courtesy of Gad-El Hak).....................................13
Figure 1.5: Drag Comparison of Tripped and Un-tripped Airfoils (courtesy of Lyon).........14
Figure 2.1: Modified S5010-top MCL (courtesy of Shkarayev)...........................................21
Figure 2.2: Example of an nth Order Polynomial MCL.........................................................22
Figure 2.3: Description of Airfoil Shape Parameters.............................................................23
Figure 2.4: Comparison of nth Order MCLs..........................................................................24
Figure 2.5: Bezier Curve with Defining Polygon and Control Points...................................26
Figure 2.6: Bezier MCL with Defining Polygon and Control Points....................................28
Figure 2.7: Comparison of Bezier MCLs..............................................................................28
Figure 2.8: Bezier Airfoil Leading Edge Shape Detail..........................................................30
Figure 2.9: Bezier Airfoil Trailing Edge Shap Detail............................................................31
Figure 3.1: Panel Convergence Test......................................................................................36
Figure 3.2: XFOIL Panel Distribution...................................................................................37
Figure 3.3 Average Least Squares Regression: Lift / Drag...................................................44
Figure 3.4: Average Least Squares Regression: Re Number.................................................45
Figure 3.5: Ncrit Comparison: Lift, E387, Re = 60K............................................................46
Figure 3.6: Ncrit Comparison: Lift, E387, Re = 200K..........................................................46
Figure 3.7: Ncrit Comparison: Lift, CD7080, Re = 60K.......................................................47
Figure 3.8: Ncrit Comparison: Lift, SD7080, Re = 200K.....................................................47
Figure 3.9: Ncrit Comparison: Lift, NACA0009, Re = 60K.................................................48
Figure 3.10: Ncrit Comparison: Lift, NACA0009, Re = 100K.............................................48
Figure 3.11: Ncrit Comparison: Lift, NACA0009, Re = 200K.............................................49
Figure 3.12: Ncrit Comparison: Drag, E387, Re = 60K........................................................49
Figure 3.13: Ncrit Comparison: Drag, E387, Re = 60K........................................................50
Figure 3.14: Ncrit Comparison: Drag, E387, Re = 200K......................................................50
Figure 3.15: EXPECT Script Validation...............................................................................53
Figure 4.1: Data Evaluation Flow Chart................................................................................58
Figure 4.2: Example C Plot...................................................................................................59
l
Figure 4.3: Example C/C Plot..............................................................................................60
l d
Figure 4.4: Typical Jump C...................................................................................................61
l
Figure 4.5: Jump in C for Increasing and Decreasing Angle of Attack................................62
l
Figure 4.6: Transition Plot for Large Jump in C ...................................................................63
l
Figure 4.7: Example of Large Jump in C ..............................................................................64
l
Figure 4.8: Transition Plot for Small jump in C ...................................................................64
l
Figure 4.9: Example of Small Jump in C ..............................................................................65
l
Figure 4.10: C/xC Evaluation: C (R=1, xR=80, T=0.10, Re=60K).................................66
l,max
Figure 4.11: C/xC Evaluation: C (R=1, xR=80, T=0.10, Re=100K)...............................66
l,max
Figure 4.12: C/xC Evaluation: C (R=1, xR=80, T=0.10, Re=150K)...............................67
l,max
Figure 4.13: C/Re Evaluation: C (xC=25, R=1, xR=85, T=0.10)...................................68
l,max
Figure 4.14: C/Re Evaluation: C (xC=20, R=1, xR=85, T=0.10)...................................68
l,max
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Figure 4.15: C Transition (xC=25, R=1, xR=85, T=0.10,Re=100).......................................70
Figure 4.16: C Transition (xC=25, R=1, xR=85, T=0.10,Re=150).......................................70
Figure 4.17: C/xC Evaluation: (cid:1) (R=1, xR=80, T=0.10, Re=60K)...................................71
stall
Figure 4.18: C/xC Evaluation: (cid:1) (R=1, xR=80, T=0.10, Re=100K).................................71
stall
Figure 4.19: C/xC Evaluation: (cid:1) (R=1, xR=80, T=0.10, Re=150K).................................72
stall
Figure 4.20: C/Re Evaluation: (cid:1) (xC=25, R=1, xR=85, T=0.10)......................................73
stall
Figure 4.21: C/Re Evaluation: (cid:1) (xC=20, R=1, xR=85, T=0.10)......................................73
stall
Figure 4.22: R/xR Evaluation: C (C=5, xC=25, T=0.10, Re=60K).................................74
l,max
Figure 4.23: R/xR Evaluation: C (C=5, xC=25, T=0.10, Re=100K)...............................74
l,max
Figure 4.24: R/xR Evaluation: C (C=5, xC=25, T=0.10, Re=150K)...............................75
l,max
Figure 4.25: Cp/R Evaluation (Re=60K, (cid:1)=8°)......................................................................76
Figure 4.26: Cp/xR Evaluation (Re=60K, (cid:1)=8°)....................................................................77
Figure 4.27: R/xR Evaluation: (cid:1) (C=4, xC=25,T=0.10, Re=150K)...................................77
stall
Figure 4.28: Cp/T Evaluation (Re=60K, (cid:1)=10°)....................................................................78
Figure 4.29: Quadrant Description........................................................................................79
Figure 4.30: C/xC Evaluation: C/C (R=2, xR=75, T=0.10, Re=100K)..........................80
l d,max
Figure 4.31: C/xC Evaluation: C/C (R=1, xR=80, T=0.10, Re=100K)..........................80
l d,max
Figure 4.32: C/xC Evaluation: C/C (R=3, xR=80, T=0.10, Re=60K)............................81
l d,max
Figure 4.33: C/xC Evaluation: C/C (R=2, xR=85, T=0.10, Re=100K)..........................81
l d,max
Figure 4.34: Transition Plot/Drag Polar – BEZ072027510...................................................82
Figure 4.35: Transition Plot/Drag Polar – BEZ072028510...................................................83
Figure 4.36: C/xC Evaluation: (cid:1) (R=2, xR=75, T=0.10, Re=100K)..........................84
Cl/Cd,max
Figure 4.37: C/xC Evaluation: (cid:1) (R=1, xR=80, T=0.10, Re=60K)............................84
Cl/Cd,max
Figure 4.38: C/xC Evaluation: (cid:1) (R=2, xR=85, T=0.10, Re=100K)..........................85
Cl/Cd,max
Figure 4.39: R/xR Evaluation: C/C (C=4, xC=20, T=0.10, Re=60K)............................86
l d,max
Figure 4.40: R/xR Evaluation: C/C (C=6, xC=30, T=0.10, Re=150K)..........................86
l d,max
Figure 4.41: R/xR Evaluation: C/C Polar (C=6, xC=30, T=0.10, Re=150K).....................87
l d
Figure 4.42: Separation/Transition/Reattachment: BEZ062537510, Re=60K......................89
Figure 4.43: Separation/Transition/Reattachment: BEZ062537515, Re=60K......................89
Figure 4.44: C Polar: BEZ082518510, Re=60K...................................................................91
l
Figure 4.45: C/C Polar: BEZ082518510, Re=60K..............................................................91
l d
Figure 4.46: BEZ082518510.................................................................................................92
Figure 4.47: BEZ062538510.................................................................................................93
Figure 4.48: C/C Polar: BEZ062538510, Re=60K..............................................................93
l d
Figure 5.1: Wind Tunnel Results: E387, With and Without Screens..................................106
Figure 5.2: BEZ053018513, Re = 100K, (cid:1) = 0°...................................................................109
Figure 5.3: BEZ053018513, Re = 100K, (cid:1) = 6°...................................................................110
Figure 5.4: Wind Tunnel Results: E387 Validation.............................................................112
Figure 5.5: Wind Tunnel Results: BEZ032037516, Re=100K............................................114
Figure 5.6: Wind Tunnel Results: BEZ032037516, Re=150K............................................115
Figure 5.7: Wind Tunnel Results: BEZ083018513, Re=100K............................................116
Figure 5.8: Wind Tunnel Results: BEZ083018513, Re=150K............................................116
Figure 5.9: H Evaluation, BEZ032037510, BEZ083018510, (cid:1)=6°.....................................117

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