Experimental studies on velocity field around wind turbine rotor

This paper describes the behavior of the flow field around rotor blades. A three-bladed upwind rotor was tested in a single return type wind tunnel. The rotor had a diameter of 2.4 m. The flow field around the rotor blades was measured using two-dimensional LDV. The three velocity components of flow field were measured in the x-y plane. The velocity vectors at optimum operation showed a smooth flow around the blade and the bound vortex around blade cross-section seemed persistent. On the other hand, the velocity vectors in stall condition demonstrated significant fluctuations in the near wake and separation on the blade suction side was observed. The circulation around a blade span-wise section was calculated at a certain control volume. From observations of the flow field and the calculated results of circulation, it seems that the flow is separated at the blade from the middle-span region to the tip region in stall condition. No separation was observed at the blade's root region.