Rotational and turbulence effects on a wind turbine blade. Investigation of the stall mechanisms

The aim of this study was to evaluate experimentally rotation and turbulence effects on a wind turbine blade aerodynamics, focusing particularly on stall mechanisms. The wind tunnel tests consisted in surface pressure measurements on a horizontal axis wind turbine airfoil subjected to freestream turbulence levels varying from 4.5% to 12%. A method to determine the position of the separation point on the rotating blade, based on the chordwise pressure gradient in the separated area, is proposed. The results showed an influence of the freestream turbulence level on the separation point position. Experimental results in the literature showed lift augmentation for a rotating blade. In our case, the study of the separation point position coupled with the pressure distributions on the airfoil shows that this lift augmentation seems related to a lower value of the pressure in the separated area rather than to a stall delay phenomenon.