The Aerodynamics of Low Sweep Delta Wings

The aerodynamics of wings with moderately swept wings continues to be a challenging and important problem due to the current and future use in military aircraft. And yet, there is very little work devoted to the understanding of the aerodynamics of such wings. The problem is that such wings may be able to sustain attached flow next to broken-down delta-wing vortices, or stall like two-dimensional wings, while shedding vortices with generators parallel to their leading edge. To address this situation we studied the flow field over diamond-shaped planforms and sharp-edged finite wings. Possible mechanisms for flow control were identified and tested. We explored the aerodynamics of swept leading edges with no control. We presented velocity and vorticity distributions along planes normal and parallel to the free stream for wings with diamond shaped planform and sharp leading edges. We also presented pressure distributions over the suction side of the wing. Results indicated that in the inboard part of the wing, an attached vortex can be sustained, reminiscent of delta-wing type of a tip vortex, but further in the outboard region 2-D stall dominated even at 13° AOA and total stall at 21° AOA. To explore the unsteady flow field and the effectiveness of leading-edge control of the flow over a diamond-planform wing at 13° AOA, we employed Particle Image Velocimetry (PIV) at a Reynolds number of 43,000 in a water tunnel. Our results indicated that two-D-like vortices were periodically generated and shed. At the same time, an underline feature of the flow, a leading edge vortex was periodically activated, penetrating the separated flow, eventually emerging downstream of the trailing edge of the wing. To study the motion and its control at higher Reynolds numbers, namely 1.3 x 106 we conducted experiments in a wind tunnel. Three control mechanisms were employed, an oscillating mini-flap, a pulsed jet and spanwise continuous blowing. A finite wing with parallel leading and trailing edges and a rectangular tip was swept by 0°, 20°, and 40° and the pulsed jet employed as is control mechanism. A wing with a diamond-shaped-planform, with a leading edge sweep of 42°, was tested with the mini-flap. Surface pressure distributions were obtained and the control flow results were contrasted with the no-control cases. Our results indicated flow control was very effective at 20° sweep, but less so at 40° or 42°. It was found that steady spanwise blowing is much more effective at the higher sweep angle.