Small two-dimensional surface excrescences on aircraft wings approaching separation

Abstract

When studying the performance of aircraft wings at high-lift configurations it is important to appreciate the effects that discontinuities in the surface can cause in promoting premature flow separation. Having caused two-dimensional incompressible fluid flow to separate from the floor of a specially-designed wind tunnel in an experimental research program, the authors introduced small two-dimensional surface excresences on the windtunnel floor, some distance upstream of this flow separation region. The techniques used to establish that the clean-surface flow was separating, to measure its gross characteristics, and then to make the necessary measurements when the excrescences were present, are described. Provided that the excrescences were small, having y+ values that were less than 500, and were as far upstream of the separation region as at least 14 excrescence heights, the investigation that the downstream separation process was unaffected by their upstream presence. An appropriate lag-entrainment integral boundary-layer-prediction technique supported this conclusion.