Turbulent boundary layers on rough surfaces

The influence of three-dimensional, stochastic roughness on the properties of turbulent boundary layers has been investigated experimentally in order to obtain an improved understanding and description of such effects on the boundary-layer flow over turbomachinery blading. Four rough surfaces were examined: a surface representative of newly-finished turbo-machinery blading, a variant of this surface with different roughness parameters, a sand-cast surface and a mesh surface with a deterministic roughness geometry. A skin-friction correlation has been obtained, and trends in this correlation and the roughness function caused by changes in roughness parameters have been identified.