Geometry optimisation of vertical axis wind turbine with Gurney flap for performance enhancement at low, medium and high ranges of tip speed ratios

Optimisation of Gurney flap (GF) geometries mounted on a three-straight-bladed vertical axis wind turbine (VAWT) is evaluated with computational fluid dynamics (CFD) solution and Taguchi method, considering the blade rotating effect at three tip speed ratios (TSRs) of low, medium and high ranges. A hybrid RANS-LES model applying stress-blended eddy simulation with transition shear-stress transport turbulence model is adopted. Results analysis confirms that GF geometry optimisation needs to consider multiple rotational blades rather than a single stationary one, owing to different optimum GF geometries and their performances at a different range of TSRs. It is found that VAWT with GF can significantly improve the power coefficient at low range TSRs (up to 233.19%), but it decreases with the increase of TSRs ranges (up to 69.94% and 41.36% at medium and high ranges of TSRs, respectively).