Reynolds and dispersive shear stress contributions above highly skewed roughness

Abstract

The roughness functions induced by irregular peak- and/or pit-dominated surfaces in a fully developed turbulent channel flow are studied by direct numerical simulation. A surface generation algorithm is used to synthesise an irregular Gaussian height map with periodic boundaries. The Gaussian height map is decomposed into 'pits-only' and 'peaks-only' components, which produces two additional surfaces with similar statistical properties, with the exception of skewness, which are equal and opposite . While the peaks-only surface yields a roughness function comparable to that of the Gaussian surface, the pits-only surface exhibits a far weaker roughness effect. Analysis of results is aided by d..