Dual Location Separation Control on a Semispan Wing

Abstract

Separation is controlled on a semispan wing via nominally two-dimensional zero mass-flux perturbations that are introduced at 1) the leading edge, 2) the shoulder of deflected flaps (20-40 deg deflection), and 3) both locations simultaneously. Leading-edge perturbations mimic the effect of a leading-edge device and flap-shoulder perturbations simulate additional flap deflection while simultaneously reducing drag. When perturbations are introduced simultaneously, at reduced frequencies of O(1) at poststall angles of attack, their combined effect on the wing's lift exceeds each individual contribution. When the physical frequencies are the same, lift is strongly dependent on the difference in phase between the two perturbations and an optimum is reached when the suction portion of flap-shoulder control coincides with the minimum shear layer proximity to the flap surface. At the optimum phase difference, increases in lift are observed over the entire semispan, resulting in an overall increase in the wing maximum lift coefficient between 0.24 and 0.44 depending on the flap deflection configuration and angle. Flap-shoulder control effectiveness does not diminish at the extremities of the finite inboard flap; neither inboard in the vicinity of the junction vortex, nor outboard in the vicinity of the flap-edge vortex. With a large flap deflection across the entire span, flap-shoulder control perturbations produce a powerful tip vortex that may be exploited for lift enhancement on low aspect ratio wings. The sensitivity to perturbation phase difference, however, diminished significantly toward the wing tip.