The effect of pitch angle on the performance of a vertical-axis wind turbine

Wind energy is a highly promising resource to approach a sustainable built environment. Vertical axis wind turbines (VAWT) offer the advantage of omni-directional operation over horizontal axis wind turbines (HAWT). This makes them ideal for utilization in urban environments which are characterized by frequently varying wind direction. However, a comparatively small amount of research on VAWTs has resulted in low power coefficients (CP) compared to HAWT. The pitch angle (β) is a parameter which is commonly used in HAWTs to enhance their performance and is a potential optimization parameter for VAWT as well. However, a recent study based on inviscid modeling states that it will not have any significant effect on CP . Therefore, in order to elucidate this claim using a viscous calculation, performance optimization of VAWTs by varying β is investigated in the current paper. CP, moment and thrust coefficient (Cm and CT) and angle of attack are obtained from a CFD simulation of a straight-bladed H-type VAWT using 2D Detached Eddy Simulations (DES). The turbine is operating at a tip speed ratio (TSR) of 4 and β-values of 0˚, +3˚, and -3˚ are investigated. The results show that unlike the inviscid results, increasing β from 0˚ to +3˚ would increase C P by 4% while decreasing it to -3˚ will result in a 16% reduction in CP. Furthermore, a change in β shifts the instantaneous loads between the upwind and downwind halves of the turbine. These results can be helpful for designing more optimized VAWTs.