The research activity carried out by our group towards the accurate numerical prediction of complex flows is summarized. The large-eddy simulation (LES) and variational multiscale (VMS) LES approaches are adopted to simulate massively separated, three-dimensional, unsteady flows. The numerical discretization is based on a mixed finite-element/finite-volume formulation on unstructured grid. The application of the LES and VMS-LES approaches to the flow around a square cylinder at a Reynolds number equal to Re = 22000 is presented and analyzed. Furthermore, in order to simulate high Reynolds number flows, a new strategy for blending RANS and LES approaches in a hybrid model is described. 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. This approach is applied to the simulation of the flow around a square cylinder and of the flow around a circular cylinder at Re = 140000. Results are compared to those of other hybrid simulations in the literature and to experimental data. The sensitivity to different parameters, such as the blending function definition, the grid refinement and the closure model for the LES part, is analyzed.
LES and hybrid RANS/LES simulation of complex flows on unstructured grids
SALVETTI, MARIA VITTORIA;CAMARRI, SIMONE;
2007-01-01
Abstract
The research activity carried out by our group towards the accurate numerical prediction of complex flows is summarized. The large-eddy simulation (LES) and variational multiscale (VMS) LES approaches are adopted to simulate massively separated, three-dimensional, unsteady flows. The numerical discretization is based on a mixed finite-element/finite-volume formulation on unstructured grid. The application of the LES and VMS-LES approaches to the flow around a square cylinder at a Reynolds number equal to Re = 22000 is presented and analyzed. Furthermore, in order to simulate high Reynolds number flows, a new strategy for blending RANS and LES approaches in a hybrid model is described. 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. This approach is applied to the simulation of the flow around a square cylinder and of the flow around a circular cylinder at Re = 140000. Results are compared to those of other hybrid simulations in the literature and to experimental data. The sensitivity to different parameters, such as the blending function definition, the grid refinement and the closure model for the LES part, is analyzed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
