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Fifth International Symposium on Turbulence and Shear Flow Phenomena
August, 27-29, 2007, Technische Universität München, Munich, Germany

DOI: 10.1615/TSFP5

HYBRID LES-RANS: INLET BOUNDARY CONDITIONS FOR FLOWS INCLUDING RECIRCULATION

pages 689-694
DOI: 10.1615/TSFP5.1080
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SINOPSIS

The paper evaluates a new method for prescribing synthesized turbulent inlet boundary conditions. When making LES, DES or hybrid LES-RANS, a precursor channel DNS is often used. The disadvantage of this method is that it is difficult to re-scale the DNS fluctuations to higher Reynolds numbers. In the present work, synthesized isotropic turbulent fluctuations are generated at the inlet plane with a prescribed turbulent length scale and energy spectrum. A large number of independent realizations are generated. A correlation in time between these realization is introduced via an asymmetric, non-truncated time filter. In this way the turbulent time scale of the synthesized isotropic turbulent fluctuations is prescribed.
The method has previously been validated for DNS at Reτ = 500 (Davidson 2007). In that study it was found that the present approach is at least as good as using inlet boundary conditions from a pre-cursor DNS. This method has also been employed using hybrid LES-RANS for channel flow at Reτ = 2000 (Davidson 2007).
In the present study it is employed in hybrid LES-RANS of the flow in an asymmetric diffuser, the flow around a three-dimensional hill and the flow over the downstream part of a bump.

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