Simulations of Flow Over an Axisymmetric Hill

Abstract

In this report, high-Reynolds number turbulent flow around an axisymmetric hill is studied using large-eddy and unsteady Reynolds-averaged Navier-Stokes simulations and the results are extensively compared against experiment. The boundary-layer thickness of the incoming flow is about half of the height of the hill. In the process, the dynamic Smagorinsky sub-grid scale eddy-viscosity model and a precursor forcing technique to match the experimental mean velocity profile is implemented in the computational toolbox for wind engineering, windOF which is based on the open source computational fluid dynamic solver OpenFOAM. The results show that the windOF is capable of producing reliable results with large-eddy simulation (LES) for this complex flow which includes complicated flow topography due to smooth-wall separation, lee-side separation, reattachment and recovery behind the hill, etc. However, Unsteady Reynolds-Averaged Navier-Stokes (URANS) predictions demonstrate significant discrepancies in several flow features, specifically in the lee-side separation and recovery that are characteristic of the Reynolds-Averaged Navier-Stokes (RANS) models which only consider much smaller scale turbulence compared to the mean flow distortion scales relevant to this flow.