Modelling the unsteady aerodynamics of wind turbines

This thesis develops models to simulate and evaluate the unsteady aerodynamics of wind turbines, so as to enable greater insight into blade airflow conditions and the resultant effects upon turbine loading and performance. Using a Blade Element Momentum based approach simulation models with extensions for both dynamic stall and dynamic inflow four typical turbine operating states have been simulated: steady state, starting, gust, and stopping states. The magnitude of the unsteady aerodynamic response for each of these states has been evaluated using a reduced frequency approach, which has enabled easy comparison of results. It was found that unsteady aerodynamics effects are significant during stopping with active braking, with lesser magnitudes of reduced frequency found during gust operating states. During starting minimal unsteady aerodynamic effects were determined, and the use of quasi-steady BEM methods for simulating starting calculations was also validated. Steady state operating conditions have also been successfully simulated with a high degree of accuracy using corrections for stall delay through the use of modified Viterna-Corrigan equations for lift and drag coefficients. This thesis has determined that unsteady aerodynamics affect wind turbine loading and performance depending upon the operating state of the turbine. All simulation codes used in this thesis have been written by the author.