SEMINAR SERIES and COLLOQUIA

In recent decades, large-eddy simulation (LES) has become a popular tool that has been successfully implemented to study neutral and convective atmospheric boundary layer flows. However, the applicability of LES to stably-stratified flows remains unclear and is an ongoing area of research. Many subgrid-scale (SGS) closure schemes have been developed in order to account for the anisotropic and intermittent characteristics of turbulence in a stratified environment, but it is difficult, if not impossible, to identify which scheme is the most appropriate to employ.

Our focus is on LES of a specific class of stably-stratified flows: turbulent katabatic flows. This type of flow not only exhibits strong shear over a shallow layer near the ground, but is also inherently stably-stratified. Multiple simulations of turbulent katabatic flow induced by a constant surface buoyancy flux using LES are undertaken; each with a different SGS closure model. To evaluate the LES output, a posteriori testing is employed. This method compares filtered output from direct numerical simulation (DNS), to the output from each LES. Mean buoyancy and velocity fields, second-order moments, and velocity spectra show that each scheme considered has its own set of successes as well as drawbacks.

Boundary Layer, Urban Meteorology, and Land-Surface Processes Seminar Series website

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