The accuracy of CFD simulations of atmospheric boundary layer (ABL) flow can be seriously compromised when wall-function roughness modifications based on experimental data for sand-grain roughened pipes and channels are applied at the bottom of the computational domain. This type of roughness modification is currently present in many CFD codes including Fluent 6.2 and Ansys CFX 10.0. The problems typically manifest themselves as unintended changes (streamwise gradients) in the vertical mean wind speed and turbulence profiles as they travel through the computational domain. They can-at least partly-be held responsible for the discrepancies that are sometimes found between CFD simulations and the corresponding measurements. This paper discusses this problem by focusing on a relatively simple situation: the simulation of a neutrally stratified, fully-developed, horizontally homogeneous ABL over uniformly rough, flat terrain. (author abst.)
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