Aerodynamics of a pitching wind turbine blade at high reduced frequencies

Abstract

This paper reports the effect of high reduced frequency on the aerodynamics of wind turbine blade under a deep dynamic stall at Reynolds number 135,000, of which the cross section is NACA0012 aerofoil with a constant chord length. Large-eddy simulations (LES) at reduced frequencies 0.1 and 0.15 were validated against reference data in the literature. Our LES data suggest that the lift, drag and moment coefficients are evidently dependent on the pitching frequency. The lift coefficient at the reduced frequency 0.4 increases up to 22% during the upstroke, and 64\% during the downstroke compared to at the reduced frequency 0.2. The peak drag coefficient decreases up to 26% at the reduced frequency 0.4 compared to at the reduced frequency 0.2. The phase angle of dynamic stall shifts towards the downstroke regime as the reduced frequency increases. Pitching motion at the high reduced frequency (e.g. 0.4) significantly enhances the suppression of leading edge vortex during the upstroke, and delays the reattachment of the boundary layer until a very low angle of attack in the downstroke. This study can be beneficial for improvement in the parameterisation of the operational blade element method (BEM) of wind turbine blade design.

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ORCID for Zheng-Tong Xie: orcid.org/0000-0002-8119-7532

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