Turbulent flow in rough wall channels: Validation of RANS models

Two kinds of a generic roughness on plane channel walls have been investigated by standard RANS turbulence models. The objective was to accurately predict mean flow quantities for steady incompressible flows through rough wall channels. Seven turbulence models have been used in a special validation procedure based on direct numerical simulation (DNS) results for several values of the roughness spacing and the Reynolds number (which here are the free parameters). In addition to single RANS solutions also a parameter expansion method (PEM) is examined with respect to its capability to accurately predict rough wall channel flows for an extended range of parameters, i.e. for various roughness heights and Reynolds numbers. Those methods that could be validated were then used to predict results for parameters beyond the validation range. Their accuracy can be assessed by comparison with reasonably extended DNS results. The final conclusion is that RANS solutions only with certain turbulence models and over some parameter ranges can be used to predict turbulent channel flows influenced by wall roughness.