Stall in Yawed Flow Conditions: a Correlation of Blade Element Momentum Predictions with Experiments

Yawed ∞ow conditions introduce unsteady loads in a wind turbine that afiect generated power quality and fatigue life. An unsteady phenomenon of special concern is dynamic stall, due to the signiflcant load ∞uctuations associated with it. Although the assumptions underlying BEM models are totally inadequate in yawed ∞ow conditions, these models, modifled with engineering models, are still widely used in industry. It is therefore relevant to assess the capabilities of BEM models in predicting the location of dynamic stall on the blade for a rotor in yawed ∞ow conditions. A rotor model is placed in an open jet wind tunnel and tested in yawed ∞ow conditions. The locations of dynamic stall on the blade of a rotor model as a function of the blade position are observed. Two experimental techniques are used; tufts glued to the blade and hot-fllm anemometry in the near wake. The results from the two techniques are compared and possible causes for difierences are identifled. Furthermore, the rotor model in yaw is modelled with a simple BEM model, utilizing a Gormont dynamic stall model. The regions of dynamic stall on the blades predicted by the BEM model are compared with the experimental results. The BEM model seems capable of a crude prediction of the dynamic stall locations found for the rotor model in yawed ∞ow conditions.