Improving Simulation of Turbulence in WRF-LES of Stable Condition Using Velocity Fluctuations

In coupled simulations of real-world case, turbulence develops slowly near the inflow boundary region and the spin up of turbulence is dependent on the atmospheric stability. The turbulence usually develops over a relatively small fetch in convective conditions, whereas it many not develop at all in the entire domain in stable conditions. To increase turbulence in the entire domain, we apply velocity fluctuations to background flow at the inflow boundary over the depth of the boundary layer in WRF-LES framework. The inflow of velocity fluctuation is prepared from the vertical profile of observed wind data and coherence functions derived from empirical relations and using simulated data. The background flow is obtained from the flow field of WRF-LES . The initial results show that adding velocity fluctuations helps significantly to develop turbulence, particularly during stable conditions. Similarly, the spectral energy is improved significantly when the update frequency at the inflow boundary approaches the corresponding time-scale of the grid spacing. This offline method could be useful to assimilate the realistic turbulence (observed) as well as to pass the mesoscale features of the atmosphere into a stand-alone highly resolved wind simulation.