Segregated coupling of large-eddy simulations with downstream Reynolds-Averaged Navier–Stokes calculations

A technique is proposed for zonal coupling of Large Eddy Simulation (LES) with a downstream Reynolds-Averaged Navier–Stokes (RANS) calculation. At a pre-defined interface, mean velocities are coupled and velocity fluctuations of the LES zone are removed by employing a convective boundary condition. For incompressible flow, the handling of pressure at the interface is crucial to the success of the method. Global coupling as well as decoupling of the pressure are investigated. The latter is more robust and therefore more generally applicable, but it requires an additional mass flux correction at the interface. The resulting approach is used to explain observed short-comings of the so-called enrichment strategy when applied to downstream LES–RANS coupling and it represents an improved and more generally valid method without the need for calibration constants. The performance of the proposed method is scrutinised for turbulent flow in a channel and over periodic hills. The results corroborate the predicted increase in accuracy and robustness.