A hybrid RANS/LES approach, based on the Limited Numerical Scales concept, is applied to the numerical simu- lation of the flow around a square cylinder and of a jet in cross-flow. The key feature of this approach is a blending between two eddy-viscosities, one given by the k − ε RANS model and the other by the Smagorinsky LES closure. A mixed finite-element/finite-volume formulation on unstructured grids is used for the numerical discretization. For the square cylinder flow, it is shown that the LNS recovers the LES results when the grid is sufficiently refined and it leads to an improvement of the results with respect to LES and RANS for coarser grids. Conversely, for the simulation of the jet in cross-flow, the results are not completely satisfactory. Indeed, the model works in RANS mode, as wished, in the attached boundary layers but also in the shear layer near the jet orifice and this inhibits the formation of the ring-like vortices, leading to significant errors in the shape and in the mixing characteristics of the jet.

Blended RANS/LES simulations of massively separated flows

CAMARRI, SIMONE;SALVETTI, MARIA VITTORIA
2005

Abstract

A hybrid RANS/LES approach, based on the Limited Numerical Scales concept, is applied to the numerical simu- lation of the flow around a square cylinder and of a jet in cross-flow. The key feature of this approach is a blending between two eddy-viscosities, one given by the k − ε RANS model and the other by the Smagorinsky LES closure. A mixed finite-element/finite-volume formulation on unstructured grids is used for the numerical discretization. For the square cylinder flow, it is shown that the LNS recovers the LES results when the grid is sufficiently refined and it leads to an improvement of the results with respect to LES and RANS for coarser grids. Conversely, for the simulation of the jet in cross-flow, the results are not completely satisfactory. Indeed, the model works in RANS mode, as wished, in the attached boundary layers but also in the shear layer near the jet orifice and this inhibits the formation of the ring-like vortices, leading to significant errors in the shape and in the mixing characteristics of the jet.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11568/203863
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