Unsteady Aerodynamics of Rotorcraft at Low Advance Ratios in Ground Effect Balakrishnan Ganesh

236 Pages·2006·16.29 MB·English

Unsteady Aerodynamics of Rotorcraft at Low Advance
Ratios in Ground Effect
A Thesis
Presented to
The Academic Faculty
by
Balakrishnan Ganesh
In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy in the
School of Aerospace Engineering
Georgia Institute of Technology
May 2006
Unsteady Aerodynamics of Rotorcraft at Low Advance
Ratios in Ground Effect
Approved by:
Dr. Narayanan Komerath, Advisor Dr. Mark F. Costello
School of Aerospace Eng School of Aerospace Eng
Georgia Inst of Technology Georgia Inst of Technology
Dr. LN Sankar Dr. A.T. Conlisk
School of Aerospace Eng School of Mechanical Eng
Georgia Inst of Technology The Ohio State University
Dr. JVR Prasad
School of Aerospace Eng
Georgia Inst of Technology
Date Approved: Mar 24, 2006
Dedicated to my brother.
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ACKNOWLEDGEMENTS
I wish to thank Prof. Narayanan Komerath for his guidance and support. I also express my
appreciation to Prof. LN Sankar for his help and advice. I also acknowledge the members
of my committee, Prof. JVR Prasad, Prof. M. Costello and Prof. A.T. Conlisk, for their
assistance with the thesis.
IgratefullyacknowledgemyfellowstudentsattheWindTunnel,whohelpedmewithout
complaint. I also thank the Aerospace Shop Staff members for their help with machining
jobs.
I thank Mr. Alan Egolf of Sikorsky Aircraft for sharing his experiences with ground
effect operations. His practical insights are greatly appreciated.
This work was sponsored by the U.S Army Research Office under the Center of Ro-
torcraft Excellence Program. Their support is most appreciated. The reviewers from the
Army Research Office provided valuable inputs that guided the progress of this study. I
thank them for their guidance.
Finally, I thank my parents for their help and guidance.
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TABLE OF CONTENTS
DEDICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
I INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Summary of Flight Characteristics and Handling Qualities in Ground effect 6
1.2 Previous Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
II RESEARCH PLAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.2 Planned Approach. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Experimental Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
III FLOW VISUALIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2 In Ground Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.1 Recirculation Regime . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.2 Ground Vortex Regime . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 Out of Ground Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.3.1 Jitter of Tip Vortices . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3.2 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
IV HOTWIRE MEASUREMENTS . . . . . . . . . . . . . . . . . . . . . . . . 37
4.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3.1 Inflow Velocities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.3.2 Velocities near the Ground Vortex . . . . . . . . . . . . . . . . . . . 40
v
4.3.3 Frequency Analysis of the Wake Structure . . . . . . . . . . . . . . 47
4.4 Analysis of Recirculation Frequency Fluctuation at the Upwind Tip of the
Rotor Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
V FUSELAGE FORCE MEASUREMENTS . . . . . . . . . . . . . . . . . . 58
5.1 Objectives and Selection of Fuselage Shape . . . . . . . . . . . . . . . . . . 58
5.2 Experimental Set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.3.1 Frequency Components of Fuselage Load Measurements . . . . . . 63
5.3.2 Circular Cross-section Fuselage Forces . . . . . . . . . . . . . . . . 63
5.3.3 Comparison of Circular Cross-section and Flattened Fuselage Loads 71
5.4 Discussion on Measurement Error . . . . . . . . . . . . . . . . . . . . . . . 76
5.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
VI SURFACE FLOW VISUALIZATION OF GROUND VORTEX . . . . 77
6.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.2 Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.3.1 Advance Ratio 0.03 . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.3.2 Advance Ratio 0.04 . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.3.3 Advance Ratio 0.05 . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.3.4 Advance Ratio 0.06 . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.3.5 Advance Ratio 0.07 . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.3.6 Advance Ratio 0.08 . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.3.7 Advance Ratio 0.09 . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.3.8 Advance Ratio 0.10 . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
6.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
VIIMEASUREMENT OF ROTOR POWER . . . . . . . . . . . . . . . . . . 91
7.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.2 Experimental Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
7.3.1 Measurement Validation . . . . . . . . . . . . . . . . . . . . . . . . 92
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7.3.2 C Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
P
7.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
VIII PIV OF THE GROUND VORTEX . . . . . . . . . . . . . . . . . . . . . 96
8.1 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.2 Introduction to PIV . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.3 Experimental Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
8.4 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
8.4.1 Advance Ratio 0.05 . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.4.2 Advance Ratio 0.06 . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.4.3 Advance Ratio 0.07 . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
8.4.4 Advance Ratio 0.08 . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
8.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104
8.6 Error Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
8.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
IX CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . . . . . 108
9.1 Summary of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
9.1.1 General Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
9.1.2 Results: Unsteady Phenomena . . . . . . . . . . . . . . . . . . . . . 109
9.1.3 Results: Quasi-steady Phenomena . . . . . . . . . . . . . . . . . . . 110
9.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
9.3 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
VITA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
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LIST OF TABLES
1 Rotor Specifications and Test Conditions . . . . . . . . . . . . . . . . . . . 20
2 Tip Vortex Jitter OGE vs IGE . . . . . . . . . . . . . . . . . . . . . . . . . 35
3 Frequency of Recirculation Fluctuation . . . . . . . . . . . . . . . . . . . . . 57
viii
LIST OF FIGURES
1 Accident Statistics from 1963 to 1997 . . . . . . . . . . . . . . . . . . . . . 2
2 Loss of Control Accidents by Phase of Operation . . . . . . . . . . . . . . . 3
3 Loss of Control Accidents by Cause . . . . . . . . . . . . . . . . . . . . . . . 4
4 Loss of Control Accidents by Axis Lost . . . . . . . . . . . . . . . . . . . . . 5
5 Schematic of Flow Regimes in Ground Effect. (Courtesy: NASA Civil Heli-
copter Safety Website) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6 Power Requirements in Ground Effect. (Courtesy: NASA Civil Helicopter
Safety Website) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7 Lateral Stick Requirements in Ground Effect. (Courtesy: NASA Civil Heli-
copter Safety Website) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8 Thrust Ratio in Ground Effect . . . . . . . . . . . . . . . . . . . . . . . . . 11
9 Two Regimes of Flight in Ground Effect at Low Advance Ratios . . . . . . 14
10 Planned Approach to Research . . . . . . . . . . . . . . . . . . . . . . . . . 19
11 Rotor Setup in the Harper Wind Tunnel . . . . . . . . . . . . . . . . . . . . 21
12 Co-ordinate System of the Rotor Setup. . . . . . . . . . . . . . . . . . . . . 22
13 The Ground plane in the Tunnel . . . . . . . . . . . . . . . . . . . . . . . . 23
14 Co-ordinate System of the Rotor Setup. . . . . . . . . . . . . . . . . . . . . 24
15 Recirculation of vortices at µ = 0.03 . . . . . . . . . . . . . . . . . . . . . . 26
16 Flowfield at µ = 0.04 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
17 Trajectory of tip vortices at µ = 0.03 . . . . . . . . . . . . . . . . . . . . . . 28
18 Ground Vortex at µ = 0.06 . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
19 Ground Vortex at µ = 0.07 . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
20 Position of Ground Vortex . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
21 Difference in tip vortex trajectory- OGE vs IGE . . . . . . . . . . . . . . . 34
22 Steady tip vortex trajectory OGE µ = 0.04 . . . . . . . . . . . . . . . . . . 36
23 Hotwire Measurement Setup in the Harper Wind Tunnel . . . . . . . . . . . 38
24 Hotwire Measurement Locations close to the ground . . . . . . . . . . . . . 39
25 Comparison of Inflow Velocities: IGE vs OGE . . . . . . . . . . . . . . . . . 42
26 Measurement Position and Inflow spectra . . . . . . . . . . . . . . . . . . . 43
27 Hotwire Measurements µ = 0.05 . . . . . . . . . . . . . . . . . . . . . . . . 44
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28 Hotwire Measurements µ = 0.06 . . . . . . . . . . . . . . . . . . . . . . . . 45
29 Hotwire Measurements µ = 0.07 . . . . . . . . . . . . . . . . . . . . . . . . 46
30 Hotwire Measurement Peak Frequencies (Hz) µ = 0.03 . . . . . . . . . . . . 49
31 Hotwire Measurement Peak Frequencies (Hz) µ = 0.04 . . . . . . . . . . . . 50
32 Hotwire Measurement Peak Frequencies (Hz) µ = 0.05 . . . . . . . . . . . . 51
33 Hotwire Measurement Peak Frequencies (Hz) µ = 0.06 . . . . . . . . . . . . 52
34 Hotwire Measurement Peak Frequencies (Hz) µ = 0.07 . . . . . . . . . . . . 53
35 C Measurements and Polynomial Interpolation . . . . . . . . . . . . . . . 56
T
36 Test Fuselage Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
37 Fuselage Load Measurement Experimental Setup . . . . . . . . . . . . . . . 61
38 Fuselage Load Measurement Experimental Setup . . . . . . . . . . . . . . . 62
39 Circular Cross-section Fuselage Downforce. Non-dimensionalized by density,
tip speed and circular cross-section fuselage planform area. . . . . . . . . . 67
40 Circular Cross-section Fuselage Side force. Non-dimensionalized by density,
tip speed and circular cross-section fuselage planform area. . . . . . . . . . 68
41 Side Force Center of Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . 69
42 Circular Cross-section Fuselage Drag force. Non-dimensionalized by density,
tip speed and circular cross-section fuselage planform area. . . . . . . . . . 70
43 ComparisonofNon-DimensionalLiftForceofCircularcross-sectionandFlat-
tened Fuselage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
44 Comparison of Non-Dimensional Drag Force of Circular cross-section and
Flattened Fuselage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
45 Comparison of Non-Dimensional Side Force of Circular cross-section and
Flattened Fuselage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
46 Tuft Surface Visualization Experiment . . . . . . . . . . . . . . . . . . . . . 78
47 Schematic of Tuft Surface Visualization Experimental Set-up . . . . . . . . 79
48 Tuft Surface Visualization at advance ratio 0.03 . . . . . . . . . . . . . . . . 82
49 Tuft Surface Visualization at advance ratio 0.04 . . . . . . . . . . . . . . . . 83
50 Tuft Surface Visualization at advance ratio 0.05 . . . . . . . . . . . . . . . . 84
51 Tuft Surface Visualization at advance ratio 0.06 . . . . . . . . . . . . . . . . 85
52 Tuft Surface Visualization at advance ratio 0.07 . . . . . . . . . . . . . . . . 86
53 Tuft Surface Visualization at advance ratio 0.08 . . . . . . . . . . . . . . . . 87
54 Tuft Surface Visualization at advance ratio 0.09 . . . . . . . . . . . . . . . . 88
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