Scale-similar models employ multiple filtering operations to identify the smallest resolved scale... more Scale-similar models employ multiple filtering operations to identify the smallest resolved scales, which have been shown to be the most active in the interaction with the unresolved subgrid scales. They do not assume that the principal axes of the strain-rate tensor are aligned with those of the subgrid-scale stress (SGS) tensor, and allow the explicit calculation of the SGS energy. They can provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses in regions that are well correlated with the locations where large Reynolds stress occurs. In this paper, eddy viscosity and mixed models, which include an eddy-viscosity part as well as a scale-similar contribution, are applied to the simulation of two flows, a high Reynolds number plane channel flow, and a three-dimensional, nonequilibrium flow. The results show that simulations without models or with the Smagorinsky model are unable to predict nonequilibrium effects. Dynamic models provide a...
ABSTRACT The separated flow behind a sharp corner has been the object of several numerical studie... more ABSTRACT The separated flow behind a sharp corner has been the object of several numerical studies that have used both large-eddy (LES) and direct numerical simulations (DNS). In the present study, a mixed SGS model including a scale-similar formulation and a dissipative part is applied to the calculation of a backward-facing step and a shallow cavity. Mixed models have been shown to be the most active in the interaction with the unresolved, subgrid scales. Their ability to provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses that are well correlated with the locations where large Reynolds stress occurs allows them to give accurate prediction of the local flow structure in strongly non-equilibrium flows such as the ones under consideration, a capability required if the noise generated in these flows is desired.
ABSTRACT Scale-similar models employ two filtering operations to identify the smallest resolved s... more ABSTRACT Scale-similar models employ two filtering operations to identify the smallest resolved scales, which have been shown to be the most active in the interaction with the unresolved, subgrid scales. They do not assume that the principal axes of the strain-rate tensor are aligned with those of the SGS stress tensor, and allow the explicit calculation of the SGS energy, can provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses that are well correlated with the locations where large Reynolds stress occurs. A comparative evaluation of several mixed model formulations is carried out by performing the LES of two non-equilibrium flows, an accelerating channel flow and a three-dimensional boundary layer. Mixed models including the scale-similar formulation and a dissipative part, give improved results over the standard Smagorinsky model, especially in the three-dimensional boundary layer, in which they predict the recovery after the minimum in the turbulent kinetic energy more accurately than the Smagorinsky model.
Scale-similar models employ multiple filtering operations to identify the smallest resolved scale... more Scale-similar models employ multiple filtering operations to identify the smallest resolved scales, which have been shown to be the most active in the interaction with the unresolved subgrid scales. They do not assume that the principal axes of the strain-rate tensor are aligned with those of the subgrid-scale stress (SGS) tensor, and allow the explicit calculation of the SGS energy. They can provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses in regions that are well correlated with the locations where large Reynolds stress occurs. In this paper, eddy viscosity and mixed models, which include an eddy-viscosity part as well as a scale-similar contribution, are applied to the simulation of two flows, a high Reynolds number plane channel flow, and a three-dimensional, nonequilibrium flow. The results show that simulations without models or with the Smagorinsky model are unable to predict nonequilibrium effects. Dynamic models provide a...
ABSTRACT The separated flow behind a sharp corner has been the object of several numerical studie... more ABSTRACT The separated flow behind a sharp corner has been the object of several numerical studies that have used both large-eddy (LES) and direct numerical simulations (DNS). In the present study, a mixed SGS model including a scale-similar formulation and a dissipative part is applied to the calculation of a backward-facing step and a shallow cavity. Mixed models have been shown to be the most active in the interaction with the unresolved, subgrid scales. Their ability to provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses that are well correlated with the locations where large Reynolds stress occurs allows them to give accurate prediction of the local flow structure in strongly non-equilibrium flows such as the ones under consideration, a capability required if the noise generated in these flows is desired.
ABSTRACT Scale-similar models employ two filtering operations to identify the smallest resolved s... more ABSTRACT Scale-similar models employ two filtering operations to identify the smallest resolved scales, which have been shown to be the most active in the interaction with the unresolved, subgrid scales. They do not assume that the principal axes of the strain-rate tensor are aligned with those of the SGS stress tensor, and allow the explicit calculation of the SGS energy, can provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses that are well correlated with the locations where large Reynolds stress occurs. A comparative evaluation of several mixed model formulations is carried out by performing the LES of two non-equilibrium flows, an accelerating channel flow and a three-dimensional boundary layer. Mixed models including the scale-similar formulation and a dissipative part, give improved results over the standard Smagorinsky model, especially in the three-dimensional boundary layer, in which they predict the recovery after the minimum in the turbulent kinetic energy more accurately than the Smagorinsky model.
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Papers by Fabrizio Sarghini