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Evaluation of turbulence models using direct numerical and large-eddy simulation data / Raiesi, Hassan in Transactions of the ASME . Journal of fluids engineering, Vol. 133 N° 2 (Fevrier 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 2 (Fevrier 2011) . - 10 p. Titre : Evaluation of turbulence models using direct numerical and large-eddy simulation data Type de document : texte imprimé Auteurs : Raiesi, Hassan, Auteur ; Piomelli, Ugo, Auteur ; Pollard, Andrew, Auteur Année de publication : 2011 Article en page(s) : 10 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Boundary  layers  Flow  separation  Flow  simulation  Pipe  flow  Turbulence Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The performance of some commonly used eddy-viscosity turbulence models has been evaluated using direct numerical simulation (DNS) and large-eddy simulation (LES) data. Two configurations have been tested, a two-dimensional boundary layer undergoing pressure-driven separation, and a square duct. The DNS and LES were used to assess the k−epsilon, zeta−f, k−omega, and Spalart–Allmaras models. For the two-dimensional separated boundary layer, anisotropic effects are not significant and the eddy-viscosity assumption works well. However, the near-wall treatment used in k−epsilon models was found to have a critical effect on the predictive accuracy of the model (and, in particular, of separation and reattachment points). None of the wall treatments tested resulted in accurate prediction of the flow field. Better results were obtained with models that do not require special treatment in the inner layer (zeta−f, k−omega, and Spalart–Allmaras models). For the square duct calculation, only a nonlinear constitutive relation was found to be able to capture the secondary flow, giving results in agreement with the data. Linear models had significant error. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...] [article] Evaluation of turbulence models using direct numerical and large-eddy simulation data [texte imprimé] / Raiesi, Hassan, Auteur ; Piomelli, Ugo, Auteur ; Pollard, Andrew, Auteur . - 2011 . - 10 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 133 N° 2 (Fevrier 2011) . - 10 p. Mots-clés : Boundary  layers  Flow  separation  Flow  simulation  Pipe  flow  Turbulence Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : The performance of some commonly used eddy-viscosity turbulence models has been evaluated using direct numerical simulation (DNS) and large-eddy simulation (LES) data. Two configurations have been tested, a two-dimensional boundary layer undergoing pressure-driven separation, and a square duct. The DNS and LES were used to assess the k−epsilon, zeta−f, k−omega, and Spalart–Allmaras models. For the two-dimensional separated boundary layer, anisotropic effects are not significant and the eddy-viscosity assumption works well. However, the near-wall treatment used in k−epsilon models was found to have a critical effect on the predictive accuracy of the model (and, in particular, of separation and reattachment points). None of the wall treatments tested resulted in accurate prediction of the flow field. Better results were obtained with models that do not require special treatment in the inner layer (zeta−f, k−omega, and Spalart–Allmaras models). For the square duct calculation, only a nonlinear constitutive relation was found to be able to capture the secondary flow, giving results in agreement with the data. Linear models had significant error. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA400013 [...]

Wall-modeled large-Eddy simulations of flows with curvature and mild separation / Senthilkumaran Radhakrishnan in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 10 (Octobre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 10 (Octobre 2008) . - 9 p. Titre : Wall-modeled large-Eddy simulations of flows with curvature and mild separation Type de document : texte imprimé Auteurs : Senthilkumaran Radhakrishnan, Auteur ; Piomelli, Ugo, Auteur ; Anthony Keating, Auteur Année de publication : 2009 Article en page(s) : 9 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : wall-modeled  large-eddy  simulation;  Reynolds-averaged  Navier–Stokes  equation;  large-eddy  simulation Résumé : The performance of wall-modeled large-eddy simulation (WMLES) based on hybrid models, in which the inner region is modeled by Reynolds-averaged Navier–Stokes (RANS) equation and the outer region is resolved by large-eddy simulation (LES), can make the application of LES attainable at high Reynolds numbers. In previous work by various authors, it was found that in most cases a buffer region exists between the RANS and LES zones, in which the velocity gradient is too high; this leads to an inaccurate prediction of the skin-friction coefficient. Artificially perturbing the RANS∕LES interface has been demonstrated to be effective in removing the buffer region. In this work, WMLES has been performed with stochastic forcing at the interface, following the previous work by our group on two nonequilibrium complex flows. From the two flows studied, we conclude that the application of stochastic forcing results in improvements in the prediction of the skin-friction coefficient in the equilibrium regions of these flows, a better agreement with the experiments of the Reynolds stresses in the adverse pressure gradient and the recovery region, and a good agreement of the mean velocity field with experiments in the separation region. Some limitations of this method, especially in terms of CPU requirements, will be discussed. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27341 [...] [article] Wall-modeled large-Eddy simulations of flows with curvature and mild separation [texte imprimé] / Senthilkumaran Radhakrishnan, Auteur ; Piomelli, Ugo, Auteur ; Anthony Keating, Auteur . - 2009 . - 9 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 10 (Octobre 2008) . - 9 p. Mots-clés : wall-modeled  large-eddy  simulation;  Reynolds-averaged  Navier–Stokes  equation;  large-eddy  simulation Résumé : The performance of wall-modeled large-eddy simulation (WMLES) based on hybrid models, in which the inner region is modeled by Reynolds-averaged Navier–Stokes (RANS) equation and the outer region is resolved by large-eddy simulation (LES), can make the application of LES attainable at high Reynolds numbers. In previous work by various authors, it was found that in most cases a buffer region exists between the RANS and LES zones, in which the velocity gradient is too high; this leads to an inaccurate prediction of the skin-friction coefficient. Artificially perturbing the RANS∕LES interface has been demonstrated to be effective in removing the buffer region. In this work, WMLES has been performed with stochastic forcing at the interface, following the previous work by our group on two nonequilibrium complex flows. From the two flows studied, we conclude that the application of stochastic forcing results in improvements in the prediction of the skin-friction coefficient in the equilibrium regions of these flows, a better agreement with the experiments of the Reynolds stresses in the adverse pressure gradient and the recovery region, and a good agreement of the mean velocity field with experiments in the separation region. Some limitations of this method, especially in terms of CPU requirements, will be discussed. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27341 [...]