Large eddy simulations of Rayleigh-Benard convection using subgrid scale estimation model

The subgrid scale estimation model, which has been previously studied for l arge eddy simulations of turbulent channel flow, was extended to convective flows. The estimation procedure involves expanding the temperature and vel ocities to scales smaller than the grid size using the properties of the to p-hat filter, Fourier expansions, and nonlinear interactions among the reso lved scales. An expanded field, which contains subgrid scales two times sma ller than the grid size, is used to calculate the subgrid scale stresses di rectly from the definition. In an a priori analysis, the exact quantities c omputed from the direct numerical simulation data are compared with results from the estimation model and the Smagorinsky model applied without wall f unctions. The subgrid scale stresses from the estimation model agree well w ith the exact quantities, but the Smagorinsky model results do not. The sam e conclusions are reached after both models are implemented in actual large eddy simulations. For both the velocities and temperature, the estimation model produces a more realistic distribution of subgrid scale stresses acro ss the convective layer, does not require wall functions for correct behavi or near the boundary, and does not contain any arbitrary constants, in cont rast to the Smagorinsky model. Additionally, numerically stable backscatter is inherent in the estimation model. (C) 2000 American Institute of Physic s. [S1070-6631(00)00501-8].