RANS simulation of horizontal homogeneous atmospheric boundary layer over rough terrains by an enriched canopy drag model

Abstract

Atmospheric boundary layer (ABL) is generated due to frictions induced by obstacles on the Earth’s surface, such as terrains, vegetation, buildings, etc … Inspired by this physical mechanism, horizontally homogeneous ABL flow in computational fluid dynamics is achieved by proposing an enriched canopy drag (ECD) model, which is more flexible in reproducing the effects of various physical roughness ground, not limited to vegetation types. The multi-objective evolutionary algorithm is employed to determine the appropriate near-ground drag and the acting height of the proposed ECD model. Furthermore, the evolutionary algorithm is adopted to minimize the discrepancies of mean wind velocity and turbulence kinetic energy (TKE) between the inflow condition and the flow at a target downstream location. A set of simulations using logarithmic- and power-law inlet flows over rural, suburban, and urban terrains based on the shear-stress transport k-ω turbulence model are conducted to demonstrate the effectiveness of the ECD model. The results show that the proposed ECD model is capable of reproducing the Earth’s roughness numerically and improving the homogeneities of mean velocity and TKE in streamwise direction and applicable to different mesh resolutions, near-wall treatment methods, standard k-ε turbulence model and simulation dimension.