INVESTIGATION OF THE UNSTEADY-FLOW VELOCITY-FIELD ABOVE AN AIRFOIL PITCHING UNDER DEEP DYNAMIC STALL CONDITIONS

The unsteady flow field above a NACA 0012 airfoil pitching under deep dynamic stall conditions has been investigated in a low-speed wind tun nel by means of particle image velocimetry. The measurements of the in stantaneous flow velocity field show the characteristic features of th e dynamic stall process: formation and development of an organized vor tex structure for increasing incidences and the subsequent separation. Vorticity and divergence estimated from the measured data give a good insight into the complex flow behaviour during the downstroke motion. Furthermore, small-scale structures could be observed in the separate d flow field and even within the dynamic stall vortex.