Study on flow around straight-bladed vertical axis wind turbine under low tip speed ratio

Abstract

The flow field around a vertical axis wind turbine (VAWT) is very complicated because the blades pass in non-uniform flow field by the blade wake during rotation. There is some difficulty in measuring the aerodynamics acting on VAWT at a low tip speed ratio during rotation, because the relative wind speed and the angle of attack for the blade are periodically changing. So few experimental data are available for the low tip speed ratio compared with the high tip speed ratio. This paper presents a method for wind velocity distribution around VAWT at low tip speed ratios. According to this research, the flow field around a straight-bladed VAWT which has three blades is analyzed. The wind velocity in flow field is measured by using the Laser Doppler Velocimeter (LDV) in wind tunnel, and the wind velocity distribution is obtained under different azimuth angles. Flow field characteristics are also investigated for several values of tip speed ratio. Firstly, a wide low wind velocity field appears from the wind turbine internal region to downstream region. Secondly, from upstream to downstream region, the velocity deficit has become greater in the mainstream direction, at the same time, the reverse flow is only generated in the back of the cover of the rotation axis at optimum tip speed ratio. Finally, large turbulence intensity is generated at the inside of wind turbine.

Keywords

• vertical axis wind turbine (vawt)
• flow field
• low tip speed ratio
• laser doppler velocimeter (ldv)
• velocity deficit
• turbulence intensity