Alignment trends of velocity gradients and subgrid-scale fluxes in the turbulent atmospheric boundary layer

Chad Higgins(1), Marc B. Parlange(1,3), C. Meneveau(2,3)

1 Department of Geography and Environmental Engineering 2 Department of Mechanical Engineering 3 Center for Environmental and Applied Fluid Mechanics, The Johns Hopkins University, Baltimore MD 21218

ABSTRACT: Field experimental data in the atmospheric surface layer are analyzed using tools from statistical geometry. The data consist of velocity measurements from sonic anemometer arrays which permit spatial filtering needed to separate large from small scales in the context of Large Eddy Simulations. Time series of various quantities relevant to LES are evaluated from the data. Results show that the preferred filtered fluid deformation is axisymmetric extension and the preferred subgrid stress state is an axisymmetriccally contracting force. The filtered fluctuating vorticity shows preferred alignments with the mean vorticity, with streamwise vortices, and with the intermediate strain-rate eigenvector. The alignment between eigenvectors of the SGS stress and filtered strain rate is used to test eddy viscosity and mixed model formulations. In qualitative agreement with prior laboratory measurements at much lower Reynolds numbers, a bimodal distribution is observed, which can be reduced to good alignment with eddy viscosity closure using the mixed model. Results suggest some level of universality of observed qualitative trends but non-universality of quantitative features.

Boundary Layer Met.(2003), 109, pp. 59-83,

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