A RANS/LES hybrid model based on local flow structure

In order to overcome the inherent deficiency of the traditional Reynolds Averaged Navier-Stokes/large eddy simulation (RANS/LES) hybrid model, i.e., 'the bridging problem of RANS and LES', a discriminating function extracted from Vreman's subgrid-scale (SGS) model, which is used to describe flow regimes, is employed to formulate a new RANS/LES hybrid model. The model coefficients are calibrated by incompressible turbulent channel flows. The test cases include incompressible turbulent channel flows, stable-state supersonic boundary layers over a flat plate, flow past NACA4412 airfoil and flow past a circular cylinder at subcritical Reynolds numbers. This new model is not only able to solve the modeled-stress-depletion problem, but also greatly raises the accuracy when compared with the traditional RANS/LES hybrid approach, such as detached eddy simulation (DES) in predicting large-scale unsteadiness. Furthermore, the model can also solve the log-layer mismatch (LLM) problem when RANS/LES hybrid is employed as wall modeled LES, thus extending the ability of Vreman's LES model in dealing with coarse meshes. The accuracy is greatly improved.