k–l based hybrid LES/RANS approach and its application to heat transfer simulation

SUMMARY To improve the compatibility of a k-l based hybrid LES=RANS approach, a controllable transitional zone is introduced to bridge the RANS and LES zones. This allows blending of the very dierent modelled turbulence length scales in these regions. To obtain a smooth variation of the length scales and transitional zone parameters dierent weighting functions are proposed. Results show the 'RANS' region has signicant coherent unsteadiness. For Unsteady RANS (URANS) theoretical correctness, a favourable spectral gap between the modelled and resolved scales is required. The use of unsteadi- ness damping and time stepltering to ensure this is explored. Approaches are tested for a plane channelow and theow over a matrix of surface mounted cubes. The capability of the new hybrid LES=RANS method in improving heat transfer prediction in a conjugate heat transfer problem is exam- ined. Numerical tests show that, compared to the RANS simulation, the proposed hybrid LES=RANS scheme performs well for theow with large scale unsteadiness. It is also eective for improving the prediction of heat transfer. Copyright ? 2004 John Wiley & Sons, Ltd.

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