Unsteady flow physics of airfoil dynamic stall

A series of wind-tunnel experiments were conducted on a dynamically pitching airfoil in order to understand the unsteady flow physics associated with dynamic stall. An NACA 0012 airfoil was dynamically pitched about the quarter-chord axis using with a linear ramp maneuver at Re = 500,000 and ω⁺= 0.05. A series of high-frequency unsteady surface pressure measurements were acquired, which actively displayed the movement of boundary-layer transition across the surface, along with the formation and convection of the dynamic stall vortex. A detailed time-frequency analysis of the surface pressure measurements also revealed the evolutionary behavior of the unsteady flow structures during the pitch maneuver, including the development of high-frequency turbulent flow oscillations prior to the formation of the dynamic stall vortex. Time-resolved particle image velocimetry data revealed the formation of coherent vortical structures after suction breakdown at the airfoil leading-edge region, which collectively interact to form the dynamic stall vortex.