Use of turbulence generators as stall-delaying devices in flight at low Reynolds numbers

Abstract

Abstract

Wings flying at low Reynolds numbers enter a stalled flow regime by laminar boundary layer separation at the leading edge. A way to improve the flying performance of these wings at the angle of attack close to stalling is by forcing the transition of the upper-side wing boundary layer from laminar flow to turbulent flow. To force such a transition several devices can be used, the simplest one being a wire parallel to the wing leading edge. The efficiency of such a turbulence generator has been checked by testing two wing models in a low turbulence wind tunnel. One of the wings is of elliptic planform and is equipped with a leading edge wire placed along 62 per cent of the wing span. The second model simulates the wing of the very primitive bird Archaeopteryx, and it is also equipped with a wire at the leading edge which simulates one of the long fingers emerging from the leading edge of the wings of this bird. In both cases, experimental results show that these leading-edge devices are effective in delaying wing stall.