Simulation of Bluff-Body Flows Through a Hybrid RANS/VMS-LES Model

A new strategy is proposed for blending RANS and LES approaches in a hybrid model. To this purpose, the flow variables are decomposed in a RANS part (i.e. the averaged flow field), a correction part that takes into account the turbulent large-scale fluctuations, and a third part made of the unresolved or SGS fluctuations. The basic idea is to solve the RANS equations in the whole computational domain and to correct the obtained averaged flow field by adding, where the grid is adequately refined, the remaining resolved fluctuations. To obtain a model which progressively switches from the RANS to the LES mode, a smooth blending function is introduced to damp the correction term. Different definitions of the blending function are proposed and investigated. The capabilities of the proposed hybrid approach are appraised in the simulation of the flow around a square cylinder at a Reynolds number equal to Re = 22,000, and in the simulation of the flow around a circular cylinder at Re = 140,000. Results are compared to those of other hybrid simulations in the literature and to experimental data.