Performance of a vertical axis wind turbine in grid generated turbulence

Abstract

The effect of external free-stream turbulence on the aerodynamic performance of a vertical axis wind turbine was studied via wind tunnel testing under controlled levels of wind turbulence. Three levels of turbulence intensity of 5%, 7.5%, and 10% were generated upstream of the vertical axis wind turbine using a grid turbulence generator. Turbulent flows generated downstream of the grid had uniform mean flow profiles, free of any wind shear effects. Turbulence characteristics were reported in terms of turbulence velocity fluctuations, probability density function, and power spectral density. It is demonstrated that the turbulence generated downstream of the current grid is quasi-isotropic. Results show that the turbine power output was substantially increased in the presence of the grid turbulence, even though the increase in turbine power coefficient due to the effect of grid turbulence was small at the same tip speed ratios. Among grid generated turbulent flows, the increase in power output with increasing turbulence intensity was marginal. Moreover, the self-starting behavior of the vertical axis wind turbine is improved under the influence of external free-stream turbulence.