Implementation and Evaluation of Dynamic Subfilter Scale Models in WRF for Improved Large-Eddy Simulation over Complex Terrain

Performance of dynamic subfilter scale (SFS) models for predicting turbulent flow statistics in Large Eddy Simulations (LES) of atmospheric boundary layers is evaluated using the Weather Research and Forecasting (WRF) numerical weather prediction model. Dynamic SFS models compute the Smagorinsky constant in the eddy viscosity equation as a function of both space and time, thereby improving the prediction of atmospheric flows over complex geometries such as those frequently encountered in wind parks. Several dynamic models are evaluated and compared with other SFS stress models over idealized simple and complex terrain surfaces, and under various forcing scenarios, including neutral, stable and unstable conditions. Various approaches to augmenting the dynamic SFS stresses near the surface are also examined, including a hybrid RANS/LES simulations where RANS is used in thin boundary region above the surface, with LES used above. This work is performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-416486