The effect of inlet conditions on flow over backward facing step

Abstract

The objectives of this paper are to present measurements of physical phenomena associated with two-dimensional separation of a turbulent boundary layer over a backward-facing step (B.W.F.S.). Two flow conditions were studied: Sharp leading edge (S.E.) with flow underneath (Case I) and blunt leading edge (B.E.) with flow underneath (Case II). The comparisons between the two cases are discussed with reference to changes in: (i) The potential flow. (ii) The free shear layer surrounding the bubbles. (iii) The separation condition (separation point, shape of bubbles, reattachment point, etc.). All the experiments on the full scale model were carried out inside an open-circuit low-speed wind tunnel. The experiments were carried out at a Reynolds number of Re H =7.9×10 4 based on step height H . Measurements were made of the longitudinal, U ̄ , and vertical, V ̄ , components of the mean velocity, the two normal stress components u ̄ 2 and, v ̄ 2 and the shear stress uv . These data were obtained using the Flying Hot-Wire (F.H.W.) anemometer. The F.H.W. anemometer can be used with minimal flow interference. The experimental investigations have shown significant differences between the recirculating regions associated with the two conditions studied due to different inlet conditions.