CFD simulation of flow and dispersion around an isolated building: Effect of inhomogeneous ABL and near-wall treatment

This paper presents a study of the effect of the inhomogeneous atmospheric boundary layer (ABL) and near-wall treatment on a computational fluid dynamics (CFD) simulation of the flow and dispersion around an isolated building. Based on a revised k−ɛ model (MMK), the effect of the inhomogeneous ABL is studied by comparing several sets of inhomogeneous inlet conditions with a homogeneous one, while the roughness-adapted standard wall functions and two-layer model are compared to examine the effect of the near-wall treatment of rough ground. Wind tunnel experimental data from previous investigations are used to validate the numerical simulations. The inhomogeneous ABL has a significant effect on the prediction of the flow and dispersion fields, depending on the percentage deviation of the incident from the inlet conditions. A decreased incident k profile results in a longer reattachment length on the roof and a larger recirculation region in the wake, which in turn produce decreased and increased nondimensional velocity and concentration fields, respectively. An increased incident U profile enlarges the reattachment lengths and raises the k field, which has a similar effect on the nondimensional velocity and concentration fields as decreased k. It is observed that the use of the two-layer model to solve the near-wall viscous sublayer clearly improves the prediction of flow and dispersion, depending on the role of the low-Reynolds-number effect of the near-wall region on the entire wall-bounded turbulent flow.