Predicting the Onset of Dynamic Stall on Large Wind Turbines

Abstract. This study addresses the challenge of predicting dynamic stall on wind turbine airfoils, focusing on the development of a reduced-order model applicable to thick airfoils (t/c > 0.21). Utilizing a Delayed Detached-Eddy simulation of a pitching FFA-W3-211 airfoil at Re = 15 M, our analysis identifies the transition from the primary instability phase to the vortex formation stage as a critical aspect of dynamic stall. By examining the dynamic time scales, we observed a ten-fold increase in the growth rate of the shear layer height during the transition of these stages. The stall delays attributed to these stages are substantially dependent on the airfoil's camber distribution and the location of the maximum thickness. We discovered that the Leading-Edge Suction-Parameter (LESP) proposed by Ramesh et al. (2014) for thin airfoils is also helpful in predicting the onset of the vortex formation stage for thick airfoils. Based on this finding, we propose a Mid-Chord Suction-Parameter (MCSP), that is more effective for wind turbine airfoils. The MCSP exhibits a breakdown in magnitude at the onset of the vortex formation stage and deep stall.