Large-eddy simulation of turbulent separated flow over rough hills

Large-eddy simulations (LES) have been performed of neutral turbulent flow over two-dimensional ridges steep enough to cause separation. Both periodic and isolated ridges have been considered. The results are compared with wind-tunnel observations and with the predictions of various turbulence closure models. For the periodic case the LES results are qualitatively reasonable, although the depth of the separated region appears to be sensitive to the use of a distributed drag near the lower boundary. The isolated ridge results compare very favourably with the experimental data, with the LES performance appearing to be at least as good as that of the closure models.