Further Aerodynamic Topics for Wind Turbines

This chapter deals with rotor–wind misalignment and also with unsteady aerodynamics of the rotor resulting from this misalignment and from other effects that cause rapid changes in the flow conditions. The application of the momentum theory to an actuator disc representing a yawed rotor is somewhat problematical. Dynamic stall will occur on a wind turbine when the rotor is yawed and at a low tip speed ratio, when the rotor encounters a gust, and on emerging from tower shadow. The loads experienced by a blade during dynamic stall can be large and can cause significant fatigue damage. The chapter introduces computational fluid dynamics (CFD) as a predictive tool for wind turbine aerodynamics. Most problems in wind energy requiring CFD methods to be used involve inherently unsteady flow, and convergence issues only relate to sub‐step iteration needed within each time step to deal with the pressure.