Subgrid-scale dissipation in the atmospheric surface layer: Effects of stability and filter dimension

F. Porte-Agel, M. Parlange, C. Meneveau*, W.E. Eichinger+ and M. Pahlow
Department of Geography and Environmental Engineering, *Department of Mechanical Engineering, The Johns Hopkins University, Baltimore MD 21218, + University of Iowa.

ABSTRACT: Field measurements are undertaken with the specific purpose of addressing open issues in subgrid-scale (SGS) modeling of turbulence for large-eddy simulation. Wind velocity and temperature signals are obtained using a horizontal linear array of six three-dimensional sonic anemometers placed at a height of 2.15 m in the surface layer over a grass field. From these data the SGS heat flux and a two dimensional surrogate of the SGS dissipation of temperature variance are computed by means of two-dimensional horizontal filtering and invoking Taylor's hypothesis. Conditional averaging is used to isolate the effects of large-scale structures (sweeps and ejections) of the flow on the SGS dissipation under different stability conditions. Ejections are associated with large negative values of , indicative of transfer of temperature variance from the small scales to the resolved field (backscatter), regardless of atmospheric stability. Sweeps are associated with large positive values of the SGS dissipation. The two dimensional SGS dissipation is compared with a one-dimensional surrogate based on a single sensor used in earlier work. The one and two dimensional results show qualitatively the same trends. Quantitative differences underscore the advantages of a two-dimensional approach based on the sensor array utilized in this work.

J. of Hydromet. 1, p. 75 (2000).

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