Role of subgrid-scale modeling in large eddy simulation of wind turbine wake interactions

A series of simulations are carried out to evaluate specific features of the Large Eddy Simulation (LES) technique in wind turbine wake interactions. We aim to model wake interactions of two aligned model rotors. The effects of the rotor resolution, actuator line force filter size, and Reynolds number are investigated at certain tip speed ratios. The numerical results are validated against wind tunnel measurements in terms of the mean velocity, turbulence intensity and the power and thrust coefficients. Special emphasis is placed on the role played by subgrid scale (SGS) models in affecting the flow structures and turbine loading, as this has been studied less in prior investigations. It is found that, compared with the effects of rotor resolution and force kernel size, the SGS models have only a minor impact on the wake and predicted power performance. These observations confirm the usual expectations in the field of LES about insensitivity of wake-dominated flows to SGS modeling. However, the observed insensitivity of the near-rotor tip vortices, the thin shear layer structures, and their respective instability phenomena to SGS models are surprising and encouraging as far as accuracy levels to be expected from LES results for wind energy applications, are concerned.