LES study of a large wind farm within a diurnal ABL

With the increasing role of wind harvesting on the mix of clean renewable energies, wind farms are covering increasingly larger surfaces. At such scales, wind farm dimensions become important and interactions between wind farms and the ABL might have significant implications.

A relevant question, yet to be fully understood is whether large wind farms alter the surface energy fluxes and if so, by how much. Past field observations together with mesoscale simulations seem to indicate the existence of a small change on the surface temperature and the surface energy fluxes when wind farms are present. To conclusively answer this question, recent large eddy simulation (LES) studies including large wind farms have been performed to better comprehend the interaction between the wind farms and the ABL at finer scales. These simulations are nonetheless constrained by the capacity of the wind turbine parameterisation to adapt to the time-changing incoming flow conditions. At present, turbine models must be fixed on to the LES cartesian grid and correspondingly adapt the incoming flow, thus limiting the number of study cases that one can consider.

A new wind turbine algorithm will be presented which permits wind turbines to timely-adjust to the varying wind vector. This algorithm is used to simulate a geostrophic wind driven ABL with two active scalars, temperature and specific humidity, in the presence of Coriolis forces with an embedded wind farm. Imposing a time-varying surface temperature, multiple ‘synthetic' diurnal cycles are simulated. The simulations clearly illustrate the importance of the time-adjustment of the turbines when considering the interaction between a thermal-ABL and a large wind farm. Results show clear changes in sensible and latent heat flux as well as in the Bowen ratio during the different stratification regimes.