Development of Fine-Scale Structures in Large-Eddy Simulations over Complex Terrain

Large-eddy simulations over real complex terrain remain difficult to perform due to complications with surface and lateral boundary conditions. These include issues with incorporating fine-scale topography, land-use, vegetation and canopy data, as well as challenges related to grid nesting and turbulence closure scheme choices. Here, simulations of the 2017 Perdigao field campaign are presented using the Weather Research and Forecasting model. A multi-scale domain setup is used with resolutions ranging from the meso-scale to the LES micro-scale. To assist with the transition of turbulent structures across different grid nests, the cell perturbation method is used along inflow boundaries to decrease the fetch required to develop fine scale turbulence on the inner domain. The resolution of the topography used on the finest domains is also found to be crucial to the development of turbulence. In general, a combined approach to incorporate fine-scale surface data and ease the transition across nest boundaries achieves a more realistic representation of turbulence.