HYBRID RANS/LES SIMULATIONS OF BLUFF-BODY FLOWS

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A new hybrid RANS/LES approach is proposed. The key feature of this approach is a blending between two eddy-viscosities, one given by the k-epsilon RANS model and the other by the Smagorinsky VMS-LES (variational multiscale LES) closure. The blending is set by a parameter teta: VMS-LES mode is active when teta=0, RANS mode if teta=1, a hybrid mode for 0<theta<1. The proposed hybrid model has been applied to the numerical simulation of the flow around a square cylinder at Re_L=22000. Three different parameters (based on viscosity ratio, time ratio and length ratio) are tested. The results obtained with this new hybrid approach are compared with those obtained using the LNS approach for two different grid resolutions; comparisons with experimental data in the litterature are also provided. The sensitivity of the model to some setting parameters (the inflow value of the turbulent kinetic energy, k_0 and the parameter delta in the approximate wall treatment) is also analysed. The hybrid model has been also applied to the simulation of the flow around a circular cylinder at Re_D=140000.The results are compared with those obtained using the DES approach. Also for this case, comparisons with experimental data in the litterature are provided.