Control of vortex breakdown over a delta wing using forebody slot blowing

Abstract

In this paper we study the effectiveness of forebody slot blowing to control vortex breakdown over a generic delta wing-body configuration. The motivation is to exploit the benefits of both slot blowing and canards to control vortex breakdown over a delta wing. Parameters investigated include slot length, slot width, single and double-sided blowing, and the Reynolds number. Time-averaged flow images show that Reynolds number has little effect on vortex breakdown location, at least for the range of conditions studied here, and a single-sided blowing has favorable effects on the blowing side and unfavorable effects on the nonblowing side. It is postulated that when fluid is discharged from the slot at the forebody in the spanwise direction, it produces a vortex sheet that interacts with the freestream and is rolled up to form a trailing vortex further downstream. The rolled-up vortex sheet produces a downwash effect on the blowing side and a sideslip effect on the opposite side. The downwash modifies the flowfield around the leading edge of the wing, causing a delay in vortex breakdown. To compensate for the unfavorable effects of blowing on the opposite side, a much higher blowing momentum (more than two times the single-sided slot case) is needed to delay vortex breakdown on both sides of the wing when double-sided blowing is employed. Our results also show that for a given Reynolds number and angle of attack, increasing the blowing momentum leads to a substantial delay in the vortex breakdown position. In addition, for the same blowing momentum coefficient, varying the slot width has little effect on the breakdown location, whereas increasing the slot length has favorable effect, particularly at lower angles of attack.