Abstract
In order to grasp the three-dimensional flow field around Vertical Axis Wind Turbines(VAWTs), measurements of three components of flow velocity had been conducted in the wake of a small VAWT(4-blade rotor, airfoil:NACA 0012, rotor diameter:0.6 m, blade length：0.47 m, chord length:0.075 m)by using an ultrasonic anemometer. Counterflow in the direction of the mainstream was observed even in the averaged wake-flow-field. For a more detail investigation on the
counterflow regions, the three-dimensional flow field was reconstructed in a computer from the velocity data obtained at each measuring point and was analyzed by velocity vector maps, vorticity distributions, and path lines. An obvious swirl pattern in two-dimensional path lines was observed near the counterflow region on the equatorial plane in the wake; however, the vorticity of the swirl pattern part was not so strong.
