A SUBGRID-SCALE MODEL-BASED ON THE ESTIMATION OF UNRESOLVED SCALES OFTURBULENCE

A new method for large eddy simulations is described and evaluated. In the proposed method the primary modeled quantity is the unfiltered ve locity field appearing in the definition of the subgrid-scale stress t enser. An estimate of the unfiltered velocity is obtained by expanding the resolved large-scale velocity held to subgrid-scales two times sm aller than the grid scale. The estimation procedure consists of two st eps, The first step utilizes properties of a filtering operation and t he representation of quantities in terms of basis functions such as Fo urier polynomials. In the second step, the phases associated with the newly computed smaller scales are adjusted In order to correspond to t he small-scale phases generated by nonlinear interactions of the large -scale field. The estimated velocity field is expressed entirely in te rms of the known. resolved velocity field without any adjustable const ants. The modeling procedure is evaluated in a priori analyses using d irect numerical simulation results of channel flow at low Reynolds num ber and in actual large eddy simulations of channel flow at two differ ent Reynolds numbers. In all cases, the new model performs better than or comparable to classical eddy viscosity models for the majority of physical quantities. Ln particular, all components of the subgrid-scal e stress tensor are predicted accurately and the procedure naturally a ccounts for backscatter without any adverse effects on the numerical s tability. (C) 1997 American Institute of Physics.