Modelling of stably-stratified atmospheric boundary layers with commercial CFD software for use in risk assessment

Abstract : One the of the significant challenges faced in simulating atmospheric boundary layers (ABLs) with standard computational fluid dynamics (CFD) models is to preserve the correct ABL profiles throughout the flow domain. Appropriate ABL profiles may be imposed at the inlet to the CFD domain but they are often progressively modified downwind by the CFD model until they are no longer representative of the correct stability class and/or wind speed. To address this issue, this paper reviews solutions proposed in the literature with respect to the choice of turbulence model and CFD boundary conditions (inlet profiles, wall conditions, outlet and top boundary conditions). The main focus is on modelling stable ABLs which often produce the largest dispersion distances in hazard analyses. CFD results are presented for a 2 km long domain with flat terrain using ANSYS-CFX with standard and modified k-ε turbulence models and two different choices of inlet profiles. The results show that improvements in the ABL profiles are obtained using a modified turbulence model with a consistent choice of inlet profile.