Forced unsteady vortex flows driven by pitching airfoils

Abstract : Experiments were conducted with a NACA 0015 airfoil pitching rapidly to high angles of attack to study the initiation, development, and evolution of dynamic stall vortex flows. The airfoil was pitched about its quarter-chord axis from zero to 60 degrees geometric angle of attack at rates from 115 deg/sec to 1380 deg/sec at flow speeds from 10 to 80 ft/sec (chord Reynolds numbers from 25,000 to 200,000). Smoke-wire flow visualization, dynamic surface velocity magnitude measurement experiments were performed and correlated to determine the nature of the elicited time dependent vortex flows. Lift, pressure drag, and moment coefficients were calculated to be far in excess of the maximum steady flow values and were shown to be functions of the non-dimensional pitch rate. (EDC)