Pressure-plotting measurements on an 8 per cent thick aerofoil with trailing-edge flap blowing

Abstract

Wind-tunnel experiments were carried out on all 8 per cent thick aerofoil between end plates, with Mowing from a slot in the knee of a 25 per cent chord trailing-edge flap, to improve the lifting efficiency of the flap. Both the blowing-slot width and position were varied. The sectional lift and pitching moment were derived by chordwise integration of the surface static pressures measured at the mid-span station. Tuft observations as well as surface-pressure measurements were made to determine the extent of the turbulent separation region on the trailing-edge flap and of the laminar separation bubble on the aerofoil nose. The blowing momentum required to prevent flow separation on the flap, at a given flap angle and zero wing incidence, proved much less than might have been expected from earlier two-dimensional experiments on thicker wings with blowing over the flap from the shroud. This reduction is probably associated with the low effective aspect ratio of the present quasi two-dimensional model as well as with improvements in blowing techniques. The separation bubble on the aerofoil nose began to expand markedly (with the flap deflected) when the incidence reached only a few degrees, and simultaneously the blowing momentum needed to prevent flow separation on the flap tended to increase.