Large eddy simulation of canonical urban geometries*

Forecasts of wind energy potential at the hub height of wind turbines are important for optimizing the siting and layout of wind turbines in a distributed wind scenario where the generated electrical power is fed directly to buildings/farms in an urban/semi-urban setting. However, the effect that an array of buildings would have on the turbulence characteristics near the terrain surface, and at hub height, continues to challenge attempts to model the flow. Therefore, information about the mean flow velocity and turbulence structures of canonical urban layouts are important for the efficient design and layout of wind turbines. In our work, high-fidelity, high-order spectral element (Nek5000) simulations of flow in the atmospheric surface layer, at the lower hub heights, were performed to understand the influence of urban geometry on the turbulence characteristics. A comparison of our results, with the limited experimental data available from open literature, shows good agreement with our LES predictions, and sets the stage for the development of low-order (macro-scale) models.  We present the results of our simulations and also discuss their importance in parametrizing the effects of the urban canopy in meso-scale and macro scale models.