Séance Séminaire

Séminaire des Doctorant·e·s

Simulation of massively separated flows using hybrid turbulence models

The simulation of unsteady flows characterized by large separations induced by adverse pressure gradient is still a challenge at high Reynolds numbers. In this talk, we propose to numerically predict the characteristics of a flow around a non-profiled body, the circular cylinder, at low Mach number and high Reynolds number. This benchmark, which contains many characteristics encountered in industrial flows, is challenging due to the complex physics of the flow and the considered high Reynolds number. The mathematical modelling of viscous Newtonian compressible fluids is expressed by the compressible Naviers-Stokes equations. However, the direct simulation of these equations is limited by increasing Reynolds numbers. That’s why turbulence models are developed. Among these models, we can mention the RANS models which are not well adapted to massively detached flows, and the LES approach which is still too expensive for this type of application. We will then introduce hybrid approaches such that Delayed Detached Eddy Simulation [1]. The second approach combines a RANS model with a multi-scale variational dynamic model called DVMS [2], the DVMS mode being activated in particular in the wake in order to convect the turbulent structures with small damping thanks to the low dissipation that the model introduces. Finally, the DDES/DVMS [3] zonal approach with a smooth transition between the two models allows to correctly take into account the near-wall flow with the generation of vortices and their downstream convection in the wake with a low dissipation. The numerical resolution of these models is performed using a mixed finite ele- ment/finite volume spatial discretization, the convective terms will be approximated by higher order reconstruction schemes based on the edges with a numerical viscosity that can be weighted. The resulting scheme is thus low-dispersive and low-dissipative in order to preserve the turbulent structures. REFERENCES [1]Spalart, P., Deck, S., Shur, M., Squires, S., Strelets, M., and Travin, A. A new version of detached-eddy simulation, resistant to ambiguous grid densities. Theory and Computational Fluid Dynamics, 20:181–195, 2006. [2]Moussaed, C., Wornom, S., Salvetti, M.V., Koobus, B. and Dervieux, A. : Impact of dynamic subgrid-scale modeling in variational multiscale large-eddy simulation of bluff body flows, Acta Mechanica, 225, 3309—3323 (2014). [3]E. Itam, S. Wornom, B. Koobus, and A. Dervieux, Combining a DDES model with a dy- namic variational multiscale formulation, 12th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements (ETMM12), 2018.