Modelling of Wind Flows over Complex Terrain Using a DES Method

Abstract

This study focuses on the application of detached eddy simulation (DES) for siting of wind turbines in complex terrain. The DES method uses a SST k-ω model as the Reynolds-averaged Navier-Stokes (RANS) model in the near-wall regions. The model switches to large eddy simulation (LES) mode if the dynamic length scale is greater than the local length scale. Therefore, in flow separation zones where the turbulent kinetic energy is large, the flow field is simulated with LES mode. This method is a standard practice in DES and many commercially available computational fluid dynamics (CFD) codes use it to determine the model behaviours. In contrast to traditional RANS studies, a significant advantage of DES is its capability of resolving a time-dependent flow field. One can observe the transient flow behaviours instead of a stationary mean value. This is useful if we want to understand the scale of fluctuating wind and the unsteadiness of the wind across the rotor area of a wind turbine. Applying this DES method can distinguish flow separation zones in complex terrain and this has been helpful to identify wind problems which may cause difficulties in operation of wind turbines.