Simulating effects of a wind turbine array using LES and RANS

Growth in wind power production has motivated investigation of wind-farm impacts on in-situ flow fields and downstream interactions with agriculture and other wind farms. These impacts can be simulated with both large-eddy simulations (LES) and mesoscale wind farm parameterizations (WFP). The Weather Research and Forecasting (WRF) model offers both approaches. We used the validated generalized actuator disk (GAD) parameterization in WRF-LES to assess WFP performance. A four-turbine array was simulated using the GAD model and the WFP in WRF. We examined the performance of each scheme in both convective and stable conditions (see Figure). The GAD model and WFP produced similar wind speed deficits and turbulent kinetic energy (TKE) production across the array in stable conditions, while wind speed deficits were underestimated by the WFP in convective conditions. Sensitivity tests of various WFP settings were also performed. Increased horizontal resolution degraded WFP estimates of TKE generation by the turbines, perhaps indicating resolution dependence within the scheme. Turning off explicit addition of TKE by the WFP resulted in turbulence levels within the array well below those produced by the GAD in both stable and unstable conditions. Finally, the variability in downwind turbine power deficits due to wakes from upstream turbines is lower in WFP simulations, resulting from smoother flow evolution in the RANS output compared to the LES.