Large Eddy Simulation of Stratified Flow over Hills

在大气和海洋中，越过山丘的分层流是很常见的。这些流动是广泛研究的主题，其应用包括数值天气预测、海洋混合、风力工程或预测复杂地形中空气污染源的浓度分布。分层流与孤立山丘的相互作用可将许多扰动引入流中，包括尾流中的内波和湍流涡流（也会在没有分层的情况下发生）。我们对地形上的分层流的知识大多来自实验室实验，而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，非常适合在相对较高的雷诺数复杂地形的分层流动的调查。拟议的研究的主要目标是提高对分层的效果的理解，在山上流：分离的尾流是如何受到浮力的影响，弗劳德数的值产生内部重力波，分层如何影响的产生，演变和大规模的旋涡结构的相互作用，分层如何影响阻力的山，污染物的扩散和稀释。为此，将进行一系列LES，改变进场流量和分层（弗劳德数）。该项目的另一个目的是表明，大涡模拟是一个合适的，预测工具的地形分层流的研究。

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.