Investigation of the separation bubble formed behind the sharp leading edge of a flat plate at incidence

Abstract

Detailed measurements of the separation bubble formed behind the sharp leading edge of a flat plate at low speeds and incidence are reported. The Reynolds number based on chord length ranged from 0.1 × 105 to 5.5 × 105. Extensive use of laser Doppler anemometry allowed detailed velocity measurements throughout the bubble. The particular advantages of laser Doppler anemometry in this application were its ability to define flow direction without ambiguity and its non-intrusiveness. It allowed the mean reattachment point to be accurately determined. The static pressure distribution along the plate was also measured. The length of the separation bubble was primarily determined by the plate incidence, although small variations occurred with Reynolds number because of its influence on the rate of entrainment and growth of the shear layer. Above about 105, the Reynolds number effect was no longer evident. The reverse flow boundary layer in the bubble exhibited signs of periodic stabilization before separating close to the leading edge, forming a small secondary bubble rotating in the opposite sense to the main bubble.