A dynamic forcing method for unsteady turbulent inflow conditions

The present paper aims to provide an efficient and flexible method for the initialization of a zonal RANS/LES type calculation when the resolution of the near wall region is treated in RANS mode. Indeed, when part of the boundary layer must be resolved in LES mode, one generally experiences a very long transient state, which makes this approach inapplicable to industrial applications. The skillful combination of a Zonal Detached Eddy Simulation method (ZDES), a Synthetic Eddy Method (SEM) and a self-adaptative dynamic forcing approach enables this. The two former being taken as framework, while the latter, based on innovative considerations, is the purpose of the paper. The main strength of the dynamic forcing method comes from its local nature, enabling to treat geometrically complex applications.A new definition of the dynamic forcing method, based on v′2¯t error, is derived from the original one. It dramatically increases the efficiency of the inflow generation. Indeed, the dynamic forcing method allows to reduce the transition distance up to 76%, compared to the SEM inflow by itself, when a RANS/LES type resolution is employed. Thus the use of a synthetic turbulence generation method is now affordable for industrial applications both technically and economically. A particular attention is brought to the behavior and the parametrization of such an approach, with regards to the other simulation parameters. The authors will try to give all the information required to successfully apply the present strategy on a particular case.