EXPERIMENTAL DATA AND MODEL FOR THE TURBULENT BOUNDARY LAYER ON A CONVEX, CURVED SURFACE.

Three experiments were performed to determine how boundary-layer turbulence is affected by strong convex curvature. The data gathered on the behavior of the recover stress suggested the formulation of a simple turbulence model. Three sets of data were taken on two separate facilities. Both rigs had flow from a flat surface, over a convex surface with 90 degree of turning, and then onto a flat recovery surface. Results of the experiments show that, after a sudden introduction of curvature, the shear stress in the outer part of the boundary layer is sharply diminished and is even slightly negative near the edge. The wall shear also drops off quickly downstream. In contrast, when the surface suddenly becomes flat again, the wall-shear and shear-stress profiles recovery very slowly towards flat-wall conditions. Data suggest that as many as forty boundary layer thicknesses may be needed for significant recovery, whereas the curvature effects are dominating the flow in two layer thicknesses after the beginning of the curved flow region. A simple turbulence model, which was based on the theory that the Prandtl mixing length in the outer layer should scale on the velocity-gradient layer, was shown to account for the slow recovery.