RANS Modeling of Stably Stratified Turbulent Boundary Layer Flows in OpenFOAM^®

Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, CO 80523-1372, USA

^a Corresponding author: wilsonjm@lipscomb.edu
^b Current affiliation: Department of Mechanical Engineering, Lipscomb University, 1 University Park Drive, Nashville, TN 37204, USA

Abstract

Quantifying mixing processes relating to the transport of heat, momentum, and scalar quantities of stably stratified turbulent geophysical flows remains a substantial task. In a stably stratified flow, such as the stable atmospheric boundary layer (SABL), buoyancy forces have a significant impact on the flow characteristics. This study investigates constant and stability-dependent turbulent Prandtl number (Pr_t) formulations linking the turbulent viscosity (ν_t) and diffusivity (κ_t) for modeling applications of boundary layer flows. Numerical simulations of plane Couette flow and pressure-driven channel flow are performed using the Reynolds-averaged Navier-Stokes (RANS) framework with the standard k-ε turbulence model. Results are compared with DNS data to evaluate model efficacy for predicting mean velocity and density fields. In channel flow simulations, a Prandtl number formulation for wall-bounded flows is introduced to alleviate overmixing of the mean density field. This research reveals that appropriate specification of Pr_t can improve predictions of stably stratified turbulent boundary layer flows.