Coupling mesoscale-microscale models for characterising the wind flow in complex terrain

Coupling a mesoscale model to a microscale model which presents a more detailed representation of the topography is one of the promising approaches for wind energy assessment in complex terrain. In our study, the mesoscale flow is simulated by the Weather Research and Forecasting (WRF) model. Then, the microscale simulations are conducted with inflow conditions acquired from the mesoscale model. The latter provides data such as temperature, pressure, velocity or humidity at the lateral and top boundaries of the microscale domain (10 km x 10 km x 2 km) every 1 minute. The microscale model, implemented into the open source toolbox OpenFOAM, is based on an unsteady Reynolds averaged Navier-Stokes (URANS) approach with a modified version of the standard k-ε model. The proposed coupling method is applied to the Wind Science and Engineering in Complex Terrain (WINSENT) field-test site in the Swabian Alps in Southern Germany. The main feature of the site is a vegetated escarpment up to 200 m height with respect to the valley. The site shows a predominant yearly wind direction westward making the test site interesting in the sense that the wind is perpendicular to the escarpment. The WINSENT test site is equipped with several measurement systems, like eddy-covariance micro-meteorological stations, towers equipped with sonic and propeller anemometers. The numerical simulations are compared to tower data and measurements performed by an unmanned aircraft systems (UAS). Preliminary results from the numerical simulations show the potential of the coupling method and satisfactory results in reproducing some interesting flow features