Low Reynolds number aerodynamics is important to a number of natural and man-made flyers. Birds, bats, and insects have been of interest to biologists for years, and active study in the aerospace engineering community, motivated by interest in micro air vehicles (MAVs), has been increasing rapidly. The primary focus of this book is the aerodynamics associated with fixed and flapping wings. The book consider both biological flyers and MAVs, including a summary of the scaling laws-which relate the aerodynamics and flight characteristics to a flyer's sizing on the basis of simple geometric and dynamics analyses, structural flexibility, laminar-turbulent transition, airfoil shapes, and unsteady flapping wing aerodynamics. The interplay between flapping kinematics and key dimensionless parameters such as the Reynolds number, Strouhal number, and reduced frequency is highlighted. The various unsteady lift enhancement mechanisms are also addressed, including leading-edge vortex, rapid pitch-up and rotational circulation, wake capture, and clap-and-fling.
Author(s): Wei Shyy, Yongsheng Lian, Jian Tang, Dragos Viieru, Hao Liu
Series: Cambridge Aerospace Series
Edition: illustrated edition
Publisher: Cambridge University Press
Year: 2007
Language: English
Commentary: 41337
Pages: 213
Tags: Механика;Механика жидкостей и газов;Аэродинамика;
Cover......Page 1
Half-title......Page 3
Series-title......Page 5
Title......Page 7
Copyright......Page 8
Contents......Page 9
Nomenclature......Page 13
List of Abbreviations......Page 17
References......Page 19
CHAPTER ONE Introduction......Page 21
1.1 Flapping Flight in Nature......Page 26
1.1.1 Unpowered Flight: Gliding and Soaring......Page 27
1.1.2 Powered Flight: Flapping......Page 28
1.1.3 Hovering......Page 29
1.1.4 Forward Flight......Page 30
1.2 Scaling......Page 34
1.2.1 Geometric Similarity......Page 36
1.2.3 Wing Area......Page 37
1.2.5 Aspect Ratio......Page 38
1.2.6 Wing-Beat Frequency......Page 39
1.3 Power Implication of a Flapping Wing......Page 40
1.3.1 Upper and Lower Limits......Page 41
1.3.2 Drag and Power......Page 43
1.4 Concluding Remarks......Page 46
CHAPTER TWO Fixed, Rigid-Wing Aerodynamics......Page 48
2.1 Laminar Separation and Transition to Turbulence......Page 49
2.1.1 Navier-Stokes Equation and the Transition Model......Page 55
2.1.2 The eN Method......Page 57
2.1.3 Case Study: SD 7003......Page 59
2.2 Factors Influencing Low Reynolds Number Aerodynamics......Page 64
2.2.1 Re = 103 – 104......Page 65
2.2.2 Re = 104–106......Page 67
2.2.3 Effect of Free-Stream Turbulence......Page 70
2.2.4 Effect of Unsteady Free-Stream......Page 74
2.3 Three-Dimensional Wing Aerodynamics......Page 77
2.3.1 Unsteady Phenomena at High Angles of Attack......Page 81
2.3.2 Aspect Ratio and Tip Vortices......Page 83
2.3.3 Wingtip Effect......Page 90
2.3.4 Unsteady Tip Vortices......Page 93
2.4 Concluding Remarks......Page 96
3.1 General Background of Flexible-Wing Flyers......Page 98
3.2.1 Linear Membrane Model......Page 105
3.2.2 Hyperelastic Membrane Model......Page 109
3.2.3 Combined Fluid–Structural Dynamics Computation......Page 111
3.3.1 Flexible Airfoils......Page 112
3.3.2 Membrane-Wing Aerodynamics......Page 114
3.4 Concluding Remarks......Page 120
CHAPTER FOUR Flapping-Wing Aerodynamics......Page 121
4.1.1 Flapping Motion......Page 122
4.1.2 Reynolds Number......Page 126
4.1.3 Strouhal Number and Reduced Frequency......Page 127
4.2 Nonstationary Airfoil Aerodynamics......Page 129
4.2.1 Dynamic Stall......Page 131
4.2.2 Thrust Generation of a Pitching/Plunging Airfoil......Page 134
4.3 Simplified Flapping-Wing Aerodynamics Model......Page 137
4.4 Lift-Enhancement Mechanisms in Flapping Wings......Page 142
4.4.1 Leading-Edge Vortex......Page 144
4.4.2 Rapid Pitch-Up......Page 151
4.4.3 Wake Capture......Page 154
4.4.4 Clap-and-Fling Mechanism......Page 156
4.4.5 Wing Structural Flexibility......Page 158
4.5.1 Hovering Kinematics......Page 164
4.5.2 Scaling Effect on Force Generation for Hovering Airfoils......Page 168
4.6 Aerodynamics of a Hovering Hawkmoth......Page 171
4.6.1 Downstroke......Page 172
4.6.2 Supination......Page 173
4.6.5 Evaluation of Aerodynamic Forces......Page 175
4.6.6 Aerodynamic and Inertial Powers of Flapping Wings......Page 176
4.7 Concluding Remarks......Page 177
Index......Page 195
