Experimental investigation of the three-dimensional unsteady flow over a pitching backward swept wing

Unsteady flow over a pitching swept airfoil has been studied for a range of sweep angles and dimensionless pitch rates. Measurements were taken at different angles of attack during pitch-up motion of the airfoil. The unsteady pressure was measured at different spanwise locations and at different angles of attack. The surface vorticity was then calculated from the measured pressure distributions. The unsteady pressure and vorticity flux information was analyzed to study the effects of cross flow on the unsteady flow development. Vortex propagation patterns over the suction surface and changes of these patterns with sweep angle were identified. Results show that for 0;The surface pressure distributions were also investigated for the same parameter ranges with the application of leading-edge suction to study the feasibility of controlling the dynamic-stall vortex. The volume flow rate of fluid removed from the near-leading-edge region was used to quantify the suction control level. To find the optimum suction for complete suppression of the dynamic-stall vortex at each pitch rate, the suction flow rates were measured along with the pressure distributions at different spanwise locations. The results show that the suction requirement for complete suppression of the vortex is dictated by the region where vortex detachment occurs first. The spanwise location of this region is a function of the sweep angle.