Influence of finite span and sweep on active flow control efficacy

Active flow control efficacy was investigated by means of leading-edge and flap-shoulder zero mass-flux blowing slots on a semispan wing model that was tested in unswept (standard) and swept configurations. On the standard configuration, the stall commenced inboard; with sweep, the wing stalled initially near the tip. On both configurations, the leading-edge perturbations increased the C-L,C-max and the poststall lift, both with and without deflected flaps. Without sweep, the effect of control was approximately uniform across the wing span, but remained effective to high angles of attack near the tip; when sweep was introduced, a significant effect was noted inboard, but this effect degraded along the span and produced virtually no meaningful lift enhancement near the tip, irrespective of the tip configuration. In the former case, control strengthened the wing tip vortex; in the latter case, a simple semi-empirical model, based on the trajectory or streamline of the evolving perturbation, served to explain the observations. In the absence of sweep, control on finite-span flaps did not differ significantly from their nominally two-dimensional counterpart. Control from the flap produced the expected lift enhancement and C-L,C-max improvements in the absence of sweep, but these improvements degraded with the introduction of sweep.