Implementation of a nonlinear subfilter turbulence stress model for large-eddy simulation in the Advanced Research WRF model

The new models were evaluated against the WRF model's standard Smagorinsky and 1.5-order turbulence kinetic energy (TKE) linear eddy-viscosity SFS stress models in simulations of geostrophically-forced, neutral boundary-layer flow over both flat terrain and a shallow, symmetric transverse ridge.

Comparisons of simulation results with similarity profiles indicate that the nonlinear models significantly improve agreement with the expected profiles near the surface, reducing the over-prediction of near-surface stress characteristic of linear eddy-viscosity models with no near-wall damping. Comparisons of simulations conducted using different mesh sizes indicate that the nonlinear model simulations at coarser resolutions agree more closely with the higher resolution results than corresponding lower-resolution simulations using the standard WRF SFS stress models.