Active flow control on a nonslender delta wing

The effects of active flow control by oscillatory blowing at the leading edge of a nonslender delta wing with a 50-degree sweep angle have been investigated. Pressure measurements and particle image velocimetry measurements were conducted to investigate the formation of leading-edge vortices for oscillatory blowing, compared with completely stalled flow for the no-blowing case. Stall has been delayed substantially and significant increases in the upper surface suction force have been observed. For a given angle of attack, there is an optimal momentum coefficient, after which forcing at higher momentum coefficients has negligible effect. For the poststall region, as the angle of attack increases, the optimal momentum coefficient increases. Velocity measurements show that the flow reattachment is promoted with forcing, and a vortex flow pattern develops. The time-averaged location of the center of the vortical region moves outboard with excitation. The near-surface flow pattern obtained from the particle image velocimetry measurements shows the reattachment clearly in the forward part of the wing. There is no jetlike axial flow in the core of the vortex, which seems to have breakdown at or very near the apex. Phase-averaged measurements reveal the perturbation due to the pulsed blowing, its interaction with the shear layer and vortex, apparent displacement of the vortex core, and relaxation of the reattachment region. Experiments with excitation from finite span slots located in the forward half of the wing show that partial blowing may be more effective at low momentum coefficients and promote reattachment upstream of the slot.