Page 7 - Wind Energy Handbook

CONTENTS vii

3.10.2 Glauert’s momentum theory for the yawed rotor 99
3.10.3 Vortex cylinder model of the yawed actuator disc 103
3.10.4 Flow expansion 107
3.10.5 Related theories 112
3.10.6 Wake rotation for a turbine rotor in steady yaw 113
3.10.7 The blade element theory for a turbine rotor in steady yaw 115
3.10.8 The blade element–momentum theory for a rotor in steady yaw 116
3.10.9 Calculated values of induced velocity 120
3.10.10 Blade forces for a rotor in steady yaw 121
3.10.11 Yawing and tilting moments in steady yaw 122
3.11 The Method of Acceleration Potential 125
3.11.1 Introduction 125
3.11.2 The general pressure distribution theory 126
3.11.3 The axi-symmetric pressure distributions 129
3.11.4 The anti-symmetric pressure distributions 133
3.11.5 The Pitt and Peters model 136
3.11.6 The general acceleration potential method 137
3.11.7 Comparison of methods 137
3.12 Stall Delay 138
3.13 Unsteady Flow – Dynamic Inflow 141
3.13.1 Introduction 141
3.13.2 Adaptation of the acceleration potential method to unsteady flow 142
3.13.3 Unsteady yawing and tilting moments 146
3.13.4 Quasi-steady aerofoil aerodynamics 148
3.13.5 Aerodynamic forces caused by aerofoil acceleration 149
3.13.6 The effect of the wake on aerofoil aerodynamics in unsteady flow 150
References 154
Bibliography 155
Appendix: Lift and Drag of Aerofoils 156
A3.1 Definition of Drag 156
A3.2 Drag Coefficient 159
A3.3 The Boundary Layer 160
A3.4 Boundary-layer Separation 160
A3.5 Laminar and Turbulent Boundary Layers 161
A3.6 Definition of Lift and its Relationship to Circulation 163
A3.7 The Stalled Aerofoil 166
A3.8 The Lift Coefficient 167
A3.9 Aerofoil Drag Characteristics 168
A3.10 Variation of Aerofoil Characteristics with Reynolds Number 169
A3.11 Cambered Aerofoils 170

4 Wind-turbine Performance 173
4.1 The Performance Curves 173
4.1.1 The C P º performance curve 173
4.1.2 The effect of solidity on performance 174
4.1.3 The C Q º curve 176
4.1.4 The C T º curve 176