Large Eddy Simulation of Stratified Flow over Hills

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Stratified flows over hills are common in both the atmosphere and the oceans. These flows are the subject of extensive research with applications like numerical weather prediction, mixing in the oceans, wind engineering or the prediction of concentration distribution from sources of air pollution in complex terrain. The interaction of a stratified flow with an isolated hill can introduce numerous disturbances into the flow, including internal waves and turbulent eddies (which also occur without stratification) in the wake. Most of our knowledge of stratified flows over topography comes from laboratory experiments which are usually rather qualitative in nature. Numerical simulations, in particular Large Eddy Simulations (LES), can provide detailed quantitative answers, and are, therefore, highly suited for the investigation of stratified flow in complex terrain at relatively high Reynolds number. The main objective of the proposed research is to improve the understanding of the effect of stratification on flow over hills: how the separated wake flow is affected by buoyancy forces, for which values of the Froude number internal gravity waves are produced, how stratification affects the generation, evolution and interaction of large-scale vortical structures, how stratification affects the drag on the hill, pollutant spreading and dilution. For this, a number of LES will be carried out varying the approach flow and the stratification (Froude number). Another aim of the project is to show that Large Eddy Simulation is a suitable, predictive tool for the study of stratified flows over topography.