Reynolds Averaged Navier-Stokes (RANS) model is a numerical model for a turbulent flow solving time-averaged Navier-Stokes equations, proposed by Osborne Reynolds. The accuracy is lower than DNS and LES, but it is possible to resolve a turbulent flow efficiently when used in a low-resolution grid region. Representative turbulence models for solving the closure terms in RANS include k-e, SA and SST models. Unsteady flow can also be resolved using the unsteady RANS (URANS) equation with a time advancement term added.
Large Eddy Simulation(LES) model is a numerical model for a turbulent flow solving filtered Navier-Stokes equations, propsed by Smagoinsky. The accuracy is lower than DNS but higher than RANS, that is, the compromise of high accuracy of DNS and fast computation of RANS. We developed the LES code based on Lagrangian model, which tracks the particles in the past to resolve the flow well.