Strategies for RANS/VMS-LES coupling
Résumé
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 $k-\varepsilon$ RANS model and the other by the Smagorinsky VMS-LES (variational multiscale LES) closure. The blending is set by a parameter $\theta$: VMS-LES mode is active when $\theta=0$, RANS mode if $\theta=1$, 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.