Effect of Inclined Cavities on Vortex Evolution in a Vertical-Axis Wind Turbine

Abstract

This study investigates the influence of inclined surface cavities on vortex evolution and aerodynamic performance in a three-bladed H-Darrieus vertical-axis wind turbine. A baseline NACA0012 rotor and four cavity-modified configurations were evaluated using two-dimensional transient computational fluid dynamics with a Moving Mesh formulation and the shear stress transport turbulence model. Thirty-five simulations were performed over tip speed ratios from 0.5 to 3.5. The analysis combined mean and instantaneous aerodynamic coefficients with phase-resolved vorticity fields to assess vortex formation, convection, persistence, dissipation, and blade-wake interaction. The results show that cavity effectiveness depends strongly on operating condition and chordwise placement. Configurations with cavities distributed over the downstream two-thirds of the blade extrados improved performance in the positive-torque regime, whereas cavities restricted to the final third generally underperformed the baseline. The best configuration, using smaller and more densely spaced cavities, increased the power coefficient by approximately 20.1% at a tip speed ratio of 2.5. The corresponding flow fields showed smaller, less persistent vortical structures and weaker interaction with the following blade.