Wind-tunnel tests on the prevention of boundary-layer separation by distributed suction at the rear of a thick aerofoil (NPL 153)

Abstract

Tests of a preliminary nature have been carried out on a 33 per cent thick symmetrical aerofoil (NPL 153) with suction through a porous surface from 0- 80 chord to the trailing edge, which was rounded and fitted with a Thwaites flap. The distributed suction was found to prevent separation and to reduce the wake drag to zero. The overall effective drag (including an allowance for the power required for the suction) was reduced slightly, but still remains fairly high. No hysteresis was observed in the change of drag with suction quantity. The flap was essential to stabilise the flow : without it, the flow with suction was unsteady and the wake drag was appreciable. When the flap was deflected 20 deg there was no increase in the suction quantity required to prevent separation.