Turbulence characteristics of a boundary layer over a two-dimensional bump

Abstract

The turbulent flow development was examined for a two-dimensional boundary layer over a bump. The upstream boundary layer had a momentum-thickness. Reynolds number of approximately 4030. The ratios of upstream boundary layer thickness to bump height and convex radius of curvature were 1.5 and 0.06, respectively. The bump was defined by three tangential circular arcs, which subjected the flow to alternating signs of pressure gradient and surface curvature. The boundary layer grew rapidly on the downstream side of the bump but did not separate. The mean velocity profiles deviated significantly from the law of the wall above the bump. The change from concave to convex surface curvature near the leading edge triggered an internal boundary layer, as shown by knee points in the turbulent stress profiles. The internal layer grew rapidly away from the wall on the downstream side of the bump owing to the adverse pressure gradient. The effect of convex surface curvature was considered small since the flow behaviour was generally explained by the effects due to streamwise pressure gradient. A second internal layer was triggered by the change from convex to concave curvature near the trailing edge. The boundary layer recovered rapidly in the downstream section and approached typical flat-plate boundary layer behaviour at the last measurement location.