

Artikel
Taking largeeddy simulation of wallbounded flows to higher Reynolds numbers by use of anisotropyresolving subgrid models
AbstractProperly resolved largeeddy simulations (LES) of wallbounded high Reynolds number flows using standard subgridscale (SGS) models require high spatial and temporal resolution. We have shown that a more elaborated SGS model taking into account the SGS Reynolds stress anisotropies can relax the requirement for the number of grid points by at least an order of magnitude for the same accuracy. This was shown by applying the recently developed Explicit Algebraic subgridscale model (EAM) (Marstorp et al., J. Fluid Mech. 639, 2009) to fully developed high Reynolds number channel flows with friction Reynolds numbers of 550, 2000 and 5200. The nearwall region is fully resolved, i.e. no explicit wall modelling or wall functions are applied. A dynamic procedure adjusts the model at the wall for both low and high Reynolds numbers. The resolution is reduced, from the typically recommended 50 and 15 wall units in the stream and spanwise directions respectively, with up to a factor of five in each direction. It was shown by comparison with direct numerical simulations that the EAM is much less sensitive to reduced resolution than the dynamic Smagorinsky model. Skin friction coefficients, mean flow profiles and Reynolds stresses are better predicted by the EAM for a given resolution. Even the notorious overprediction of the streamwise fluctuation intensity typically seen in poorly resolved LES is significantly reduced when EAM is used on coarse grids. The improved prediction is due to the capability of the EAM to capture the SGS anisotropy, which becomes significant close to the wall.

