Influence of fluctuating wind conditions on vertical axis wind turbine using a three dimensional CFD model

In practical situations, it is important to analyze the performance of VAWT considering the fluctuations of free stream wind. In the present paper, 3D unsteady numerical analysis is employed to investigate the effect of fluctuating wind conditions on the performance of a 1.1 kW commercially viable VAWT. VAWT is 3 straight bladed, Darrieus type having NACA 0015 airfoil profile. Turbulence is modeled using Transition SST K-ω model. Free stream velocity U∞ is varied in sinusoidal manner with respect to flow time for Umean=10 m/s. In this study, the effect of variation of fluctuation amplitude Uamp, fluctuation frequency fc and tip speed ratio λon the performance of VAWT is investigated. The vortex structures are studied for Uamp =10% and 50%. From the results, it is observed that the uniform and fluctuating wind CP curves do not trace each other. Cycle averaged CP increases with Uamp. A maximum CP of 0.33 is obtained corresponding to Uamp =50%. Cycle averaged CP increases to a maximum value and then decreases with λmean. Maximum CP of 0.31 is obtained corresponding to λmean=2. Cycle averaged CP increases to a maximum value and then marginally decreases with fc. Maximum CP of 0.31 is obtained corresponding to fc =1 Hz. Hence the overall performance under fluctuating wind conditions improved when VAWT is operated at higher Uamp, λmean≥2 and fc close to 1 Hz.