APPLICATION OF TURBULENCE MODELS TO SEPARATED FLOW OVER ROUGH SURFACES

Principal results of classical experiments on the effects of sandgrain roughness are briefly reviewed, along with various models that have b een proposed to account for these effects in numerical solutions of th e fluid-flow equations. Two models that resolve the near-wall flow are applied to the flow in a two-dimensional, rough-wall channel. Compari sons with analytical results embodied in the well-known Moody diagram show that the k-omega model of Wilcox performs remarkably well over a wide range of roughness values, while a modified two-layer k-epsilon b ased model requires further refinement. The k-omega model is applied t o water flow over a fixed sand dune for which extensive experimental d ata are available. The solutions al-e found to be in agreement with da ta, including the flow in the separation eddy and its recovery after r eattachment. The results suggest that this modeling approach may be ex tended to other types of surface roughness, and to more complex flows.