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A FINITE DIFFERENCE APPROXIMATION TO THE HYBRID RANS/LES FILTER

Fujihiro Hamba
Institute of Industrial Science, University of Tokyo Komaba, Meguro-ku, Tokyo 153-8505, Japan

Abstrakt

Hybrid approach combining large eddy simulation (LES) with the Reynolds-averaged Navier-Stokes equation (RANS) is expected to be useful for simulating wall-bounded turbulent flows at high Reynolds numbers. It is known that log-layer mismatch, or unphysical buffer layer near the RANS/LES interface appears in hybrid RANS/LES simulations of channel flow. Although several methods including additional filtering at the interface have been proposed to eliminate the mismatch, there is no obvious physical justification for the methods and some ad-hoc tuning is necessary. In this work, a hybrid RANS/LES filter formulated theoretically is investigated to justify the method of the additional filtering. It is shown that the additional filtering can be considered as a finite difference approximation to the hybrid RANS/LES filter. An expression determining the filter width and its location for the additional filtering is obtained and applied to hybrid simulations of channel flow.