Simulation of the Askervein flow.: Part 1:: Reynolds averaged Navier-Stokes equations (k-ε turbulence model)

The neutrally stratified flow over the Askervein Hill was simulated using a terrainfollowing coordinate system and a two-equation (k-epsilon) turbulence model. Calculations were performed on a wide range of numerical grids to assess, among other things, the importance of spatial discretization and the limitations of the turbulence model. Our results showed that a relatively coarse grid was enough to resolve the flow in the upstream region of the hill; at the hilltop, 10 m above the ground, the speed-up was 10% less than the experimental value. The flow's most prominent feature was a recirculating region in the lee of the hill, which determined the main characteristics of the whole downstream flow. This region had an intermittent nature and could be fully captured only in the case of a time-dependent formulation and a third-order discretization of the advective terms. The reduction of the characteristic roughness near the top of the hill was also taken into account, showing the importance of this parameter, particularly in the flow close to the ground at the summit and in the downstream side of the hill. Calculations involving an enlarged area around the Askervein Hill showed that the presence of the nearby topography affected the flow neither at the top nor downstream of the Askervein Hill.