Particle image velocimetry (PIV) measurements of tip vortex wake structure of wind turbine

Large-view flow field measurements using the particle image velocimetry (PIV) technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented Φ3.2 m wind tunnel.The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine.The results show that the tip vortex first moves inward for a very short period and then moves outward with the wake expansion,while its vorticity decreases with time after being trailed from the trailing edge of the blade tip,and then increases continuously with the rapid rolling-up to form a strong tip vortex.The measurements also indicate that the downstream movement of the tip vortex is nearly linear in the very near wake under the test condition.