Numerical prediction of switching gurney flap effects on straight bladed VAWT power performance

Abstract

Based on the lift mechanism of the Gurney flap (GF) applied on isolated airfoil trailing edge, an active GF was designed to vary its height with the rotation of VAWT blades. The active GF extrudes over the blade when the blade is in the upwind area and retreats into the blades in the downwind area. The VAWT performance was studied by two-dimensional CFD numerical simulation for varied tip speed ratios. Results show that the VAWT power coefficients with active GFs increased over all tip speed ratios. The relative increase of power coefficient was 5.14 % at the operation condition of maximum power coefficient. Proper orthogonal decomposition analysis reveals the small-scale coherent vortex structure in the wake of the VAWT, which exists in the high order modes. It spreads in the rotating domain of the impeller and generates major energy loss. Active GF limits the vortex strength of the 5th order structures during the blade rotation.