Numerical simulation and experimental study of blade pitch effect on Darrieus straight-bladed wind turbine with high solidity

Abstract

Increasing the solidity in vertical axis wind turbines (VAWT) leads to the decreased coefficient of performance (COP) despite the improved start-up performance. To overcome this problem, the pitch regulation system is proposed in this paper for increasing the solidity. In most of the previous investigations, the effect of pitch angle was tested on low-solidity VAWT at uniform flow conditions and low turbulence intensity in wind tunnel test sections, which are different from the real conditions. In this investigation, the influence of pitch angle on the aerodynamic performance of a small Darrieus-type straight-bladed high-solidity VAWT equipped with a pitch regulation system is investigated numerically and experimentally under realistic condition. The proposed numerical procedure is validated through experimental test results. The COP is measured and calculated at different tip speed ratios and two pitch angles of 0 and 5°. The results reveal 25% enhancement in maximum COP with the increase of pitch angle up to 5°. Moreover, according to the numerical results, higher accuracy can be obtained at lower tip speed ratios for both pitch angles. Then, the numerical method is employed to calculate the power (performance) and torque coefficients as a function of Azimuth position as well as the flow field in rotor affected zone and lateral distance. It is found that increasing the pitch angle at a constant tip speed ratio is followed by accelerated vorticity generation, occurrence of maximum COP at lower tip speed ratio and smoother velocity profile in lateral distances of the rotor.