Laser Velocimetry Measurements of Oscillating Airfoil Dynamic Stall Flow Field

Abstract

Ensemble averaged two components velocity measurements over an airfoil experiencing oscillatory dynamic stall under compressibility conditions were obtained. The measurements show the formation of a separation bubble over the airfoil that persists till angles of attack close to when the dynamic stall vortex forms and convects. The fluid attains mean velocities as large as 1.6 times the free stream velocity (U(infinity)) with instantaneous values of 1.80 U(infinity). The airfoil motion induces these large velocities in regions that are far removed from its surface. Also, depending upon the behavior of the separation bubble, the wall jet profiles near the leading edge region could become wake like over the airfoil in a cycle at different phase angles. Vorticity contours indicate that the levels around the leading edge continuously increase till the vortex begins to convect. Some of the measurements difficulties, especially, particle behavior are discussed as well.