Influence of Solidity and Wind Shear on the Performance of VAWT using a Free Vortex Model

Abstract

Performance analysis of a VAWT and HAWT is highly complex due to fluid structure interactions and blade vortex interactions.However, there are simplified methods such as momentum theory to most expensive CFD modelsavailable forperformance prediction. CACTUS is neither as simple as the momentum theory nor as complex as the CFD models, it is an open source code that uses the free vortex method to predict the performance of a wind turbine.In this paper, the effect of solidity and wind shear on the performance of an H-type Darrius VAWT is studied using CACTUS. Variation of solidity was achieved by changing the chord length (c/R0.04-0.07) and number of blades (N2,3). It has been observed that at lower tip speed ratio (TSR < 3) the turbine with longer c/R was found to be more efficient due to large wind interception by the blades; and at higher TSR ( > 3)  shorter c/R was more efficient due to relatively low wake blade interaction. Effect of wind shear due to the tower height from the ground using the power law equation with values of power law coefficient ranging from 0.1 to 0.3has also been studied.Itis observedthat the power coefficients of the VAWT under a turbulent boundary layer are in congruence with the experimental results.