A study on rotational effects and different stall delay models using a prescribed wake vortex scheme and NREL phase VI experiment data



Understanding of the stall delay phenomenon on wind turbines remains, to this day, incomplete. A correct modelling of this phenomenon, which results from three-dimensional rotational effects, is essential in order to make reliable wind turbine simulations on the basis of two-dimensional airfoil data, such as with the widely used blade element momentum method. The present study addresses this issue by testing six existing models intended to correct for stall delay effects, namely those developed by Snel et al., Chaviaropoulos and Hansen, Raj, Bak et al., Corrigan and Schillings and Lindenburg. For this purpose, the models are implemented into a lifting-line-prescribed wake vortex scheme. Forces along the blades as well as power and root flap bending moment in a head-on flow configuration are predicted based on these models, and are compared to wind tunnel data from NREL's phase VI experiment. While load over-prediction in the presence of stall is in general observed from the use of the different models, significant differences between the models are still seen. Local over-prediction is generally seen in the tip region, while discrepancies are obtained, even at low wind speed, for the root flap bending moment. The results obtained are discussed in terms of deficiencies and strengths of the current correction schemes, and from there a basis is provided for the development of improved correction models. Copyright © 2008 John Wiley & Sons, Ltd.