Experiments on the Flow past a Porous Circular Cylinder fitted with a Thwaites Flap

Abstract

This paper describes wind-tunnel experiments on a porous circular cylinder of 3 in. diameter fitted with a Thwaites Flap. Measurements were made Of the pressure distribution at mid-span, together with a number of wake traverses, over a,range of suction quantity, flap size, wind speed and flap setting. The distributed suction effectively prevented boundary-layer separation and enabled a close approximation to potential flow to be achieved. The flap was essential to the attainment of steady flow conditions with suction; without a flap the pressure recovery at the rear Of the cylinder was incomplete and the pressure distribution fluctuated. In view of this unsteadiness in the flow without a flap, the circulation could scarcely be expected to remain, as had previously been conjectured, when the flap was withdrawn.