Anisotropic turbulence modeling of the atmospheric surface layer: Validation of novel model settings and comparison with traditional two-equation models in flows over complex terrain

Abstract

For atmospheric flows, the limitations of the eddy viscosity assumption are even more critical in cases involving complex terrain and features, where secondary strains are influential. Reynolds Stress Models (RSMs) can account for these effects, but their numerical stiffness and crucially the lack of established guidelines for modelers regarding the appropriate boundary conditions and model settings, as exist for eddy-viscosity models (EVMs), have led to limited adoption. In order to circumvent the shortcomings of EVMs, the focus has been directed at large eddy simulations (LES), which have greater computational requirements that can be prohibitive. Thus, this work aims to extend the traditional methodology that has been applied to adapt EVMs to atmospheric flows to an RSM that incorporates near-ground effects. This results in suggestions for new model constants and novel boundary conditions, which can easily be adapted according to local atmospheric parameters and employed by modelers. The performance of the proposed RSM is compared with four distinct EVMs through real-life cases representing two distinct complex terrain configurations. The results showed that the RSM indeed outperformed the EVMs, and it was found that only its anisotropic formulation could capture more complex flow features that were observed experimentally.