Flow Visualization of Separated Flows around Oscillating Airfoil

Dynamic stall phenomena have been investigated numerically by solving incompressible Navier-Stokes equations by a third-order upwind scheme in order to reveal the flow structure and mechanism of dynamic stall. Separated flows around oscillating airfoil in pitch are calculated by using moving mesh system. The calculated separated region is small in pitchingup process and it becomes large in a pitching-down process. Quite different characteristics of flow patterns between in a pitching-up and pitching-down processes are obtained. Hysteresis curves of CL and CM are simulated. Also the separated flow fields around pitching airfoil are visualized experimentally. The results show the flow patterns and extent of separated region in pitching-up and pitching-down processes are quite different and significant characteristics of dynamic stall is obtained.