Large Eddy Simulation of Stratified Flow over Hills

山丘上的分层流动在大气和海洋中都很常见。这些流动是广泛研究的主题，应用包括数值天气预报、海洋混合、风工程或预测复杂地形中空气污染源的浓度分布。分层流动与孤立山丘的相互作用会给流动带来许多扰动，包括尾流中的内波和湍流涡旋(也可以在没有分层的情况下发生)。我们对地形上分层流动的大部分知识来自实验室实验，这些实验通常是定性的。数值模拟，特别是大涡模拟(LES)，可以提供详细的定量答案，因此非常适合于研究雷诺数较高的复杂地形中的分层流动。这项研究的主要目的是加深对层化对山坡流动影响的了解：分离尾流如何受浮力影响，产生哪些弗劳德数内重力波，层化如何影响大尺度涡旋结构的产生、演变和相互作用，层化如何影响山坡上的阻力，污染物的扩散和稀释。为此，将进行若干次大涡模拟，改变进场流动和分层(弗劳德数)。该项目的另一个目的是证明大涡模拟是研究地形上分层流动的一种合适的预测工具。

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.