# Modélisation de la turbulence par approches URANS et hybride RANS-LES. Prise en compte des effets de paroi par pondération elliptique.

Abstract : The aim of this work is to take into account the natural large-scale unsteadiness in separated flows at a lower cost than a LES, and to model the wall effects on turbulence using second moment closures. Following Durbin's approaches, the elliptic blending model EB-RSM reproduces the non-local blocking effect of the wall, by solving a differential equation on the pressure term. The two-component limit of turbulence is well predicted in a channel flow. This model is applied to the backstep flow using URANS methodology. We have shown that the numerical errors at the step corner can be sufficient to excite the natural mode of the shear layer, leading to an unsteady solution. Actually, the solution is steady when the mesh is refined, suggesting that URANS is not reliable. Recently, Schiestel \& Dejoan have proposed the seamless hybrid model PITM. The coefficient $C_{\e_2}$ of the dissipation equation becomes a function of the spectral cutoff, and the value $C_{\e_1}=3/2$ is deduced by these authors. We have given a more general formulation where the coefficient $C_{\e_1}$ can take any value. To provide a more consistent formalism for the seamless hybrid models in near-wall flows, an approach based on temporal filtering is proposed. Finally, an elliptic blending model is developped in a hybrid framework, using PITM methodology. Results in channel flow are encouraging: the seamless transition from a RANS model near the wall, to a LES in the centre of the channel is observed. The energy transfer between modelled and resolved scales is well reproduced when the mesh is refined.
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https://tel.archives-ouvertes.fr/tel-00163592
Submitted on : Tuesday, July 17, 2007 - 4:48:23 PM
Last modification on : Friday, October 23, 2020 - 4:37:13 PM
Long-term archiving on: : Thursday, April 8, 2010 - 11:29:48 PM

### Identifiers

• HAL Id : tel-00163592, version 1

### Citation

Atabak Fadai-Ghotbi. Modélisation de la turbulence par approches URANS et hybride RANS-LES. Prise en compte des effets de paroi par pondération elliptique.. Analyse de données, Statistiques et Probabilités [physics.data-an]. Université de Poitiers, 2007. Français. ⟨tel-00163592⟩

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