摘要: The geometric features of aerofoils are discussed before considering the lift and drag. variation with Reynolds number aerofoil shape is highlighted because their crucial importance for small wind turbines. For same reason, behaviour at large angles attack reviewed compared simple but useful analytic approximations. Finally, relationship between blade element circulation ideal case where axisymmetric rotor geometry can be equated to a two-dimensional infinite cascade. Circulation prominently in Chap. 5 discussion optimum power extraction.