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Published January 9, 2012 | public
Book Section - Chapter

Explicitly Filtered LES of Single-Phase Compressible Flow

Abstract

In Large Eddy Simulation (LES), it is often assumed that the filter width is equal to grid spacing. Predictions from such LES are grid-spacing dependent since any Subgrid Scale (SGS) model used in the LES equations is dependent on the resolved flow field which itself varies with grid spacing. Moreover, numerical errors affect the flow field, especially the smallest resolved scales. Thus, predictions using this approach are affected by both modeling and numerical choices. However, grid-spacing independent LES predictions unaffected by numerical choices are necessary to validate LES models through comparison with a trusted template. First, such a template is here created through Direct Numerical Simulation (DNS). Then, simulations are conducted using the conventional LES equations and also LES equations which are here reformulated so that the small-scale producing nonlinear terms in these equations are explicitly filtered (EF) to remove scales smaller than a fixed filter width; this formulation is called EFLES. The conventional LES solution is both grid-spacing and spatial discretization-order dependent, thus showing that both of these numerical aspects affect the flow prediction. The solution of the EFLES equations is grid independent for a high-order spatial discretization on all meshes tested. However, low order discretizations require a finer mesh to reach grid independence. With an eighth order discretization, a filter-width to grid-spacing ratio of two is sufficient to reach grid-independence, while a filter-width to grid-spacing ratio of four is needed to reach grid independence when a fourth or a sixth order discretization is employed. On a grid fine enough to be utilized in a DNS, the EFLES solution exhibits grid independence and does not converge to the DNS solution.

Additional Information

© 2012 by California Institute of Technology. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.

Additional details

Created:
August 19, 2023
Modified:
October 18, 2023