Turbulence modelling for large-eddy simulation of the atmospheric boundary layer

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• Rica Enriquez (DAMTP)
• Monday 04 November 2013, 13:00-14:00
• MR5, Centre for Mathematical Sciences.

If you have a question about this talk, please contact Doris Allen.

Large-eddy simulation (LES) resolves the large eddies in the flow while modeling the effects of smaller motions (turbulence) on those larger eddies. Although the turbulence model can significantly affect the accuracy of the LES , simple turbulence models, which are known to be less accurate, are widely used. The Generalized Linear Algebraic Subgrid-Scale (GLASS) model, that actively couples momentum and heat transport, is an alternative. GLASS is more complete than conventional subgrid-scale (SGS) models because it accounts for additional transport processes, including production, dissipation, pressure redistribution, and buoyancy.

With the inclusion of an actively coupled turbulent heat flux model, GLASS is applicable to a range of atmospheric stability conditions for the unsaturated atmosphere. LES at various resolutions in a neutral boundary layer flow demonstrate that the more physically complete GLASS model provides near-wall anisotropies and yields proper velocity profiles in the logarithmic layer. Its performance is consistent with that of other sophisticated SGS models. LES of the moderately convective boundary layer demonstrated that GLASS predicted the evolution of resolved quantities at least as well as the LESs with simple models, while including additional physics. Additional simulations of the stable boundary layer and the transitioning boundary layer highlight that GLASS can be applied to various stability conditions without the need of tuning model coefficients. Finally, at a given resolution, both snapshots of the spatial variations of vertical velocity and correlograms show that GLASS captured the same large-scale structures, but allowed better representation of smaller structures, than a dynamic eddy viscosity model.

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