An Analysis of LES models in Stably Stratified Flows

Large eddy simulations (LES) of complex turbulent flows, such as for the simulation of wind farms, are limited by resolution requirements in boundary layers and modeling assumptions for subgrid stress (SGS) models which are inconsistent with flow characteristics. In this talk, we discuss limitations of standard SGS models based on a scalar eddy viscosity and their performance in anisotropic turbulence. A set of DNS simulations of homogeneous stratified turbulence is used to inform current efforts to develop an improved SGS model for anisotropic turbulence. A priori and a posteriori error analysis for a set of LES models is conducted using the DNS data. As expected, it is found that these models are insufficient, especially under stronger levels of stratification. Anisotropic filtering, which is necessary as a result of both the natural meshing of boundary layers as well as the dynamics of the flow, interacts poorly with these models. This emphasizes the need for the formulation of LES models to naturally handle anisotropies present in both the grid and the underlying turbulence. We provide a brief overview of current modeling efforts using a tensorial eddy viscosity and other design choices to develop a more robust LES model.