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Gurson–Tvergaard–Needleman model is widely used to describe the three stages of ductile tearing: nucleation, growth and the coalescence of micro-voids. The aim of this article is to study the relationship between volume fraction of voids and the fracture strain ɛf. The effects of the volume fraction of nucleation, fN, and the critical volume fraction, fc, were analysed. These parameters play crucial roles in the process of ductile damage. A phenomenological analysis is carried out to study the relationship between the different void volume parameters and the fracture strain ɛf. A method is proposed for the determination of fN and fc, knowing the experimental fracture strain ɛf. The experimental parameters are extracted from the load–diametric contraction curve of an axisymmetric notched tensile bar test AN2.

The topic of this study is the numerical simulation of a turbulent non-premixed hydrogen flame with different micromixing models in order to investigate their predictive capability. The two micromixing models are compared. Comparisons with experimental data demonstrate that predictions based on the EMST model are slightly better. The EMST improves largely the precision of the results to the detriment of the RAM and the CPU performances. Overall, profile predictions of mixture fraction, flame temperature and major species are in reasonable agreement with experimental data.

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Dans le présent article, les jets turbulents confinés axisymétriques non réactifs sontétudiés en utilisant le modèle de turbulence de second ordre. L'objectif est de mettre enévidence, dans la région initiale du jet, les effets de la variation de densité, provoquée par unécart de température entre le jet d'air chauffé et l'air ambiant, sur les principaux paramètres caractéristiques de telsécoulements. Les résultats numériques obtenus sont alors discutés en comparaison avec ceux issus des expériences de Djeridane [T. Djeridane, Contributionà l'étude expérimentale de jets turbulents axisymétriquesà densité variable, Thèse de doctorat, Univ. Aix-Marseille II, 1994] (relatifs aux jets air/air et He/air) et d'autres trouvées dans la littérature. Les mesures expérimentales de la vitesse longitudinale, de l'écart-type des tensions de Reynolds et du scalaire, présentent qualitativement le même comportement. L'écart entre la simulation numérique et l'expérience n'est pas important et les résultats numériques obtenus sont en général satisfaisants. Mots clés :Turbulence / jets / effets de densité / modélisation au second ordre Abstract -Numerical simulation of an axisymmetric turbulent jet with variable density using a Reynolds stress model. In this paper, the nonreacting axisymmetric confined turbulent jets are studied by using the second order turbulence model. The aim is to present, in the initial region of the jet, the variable density effects, caused by a difference in temperature between the hot air and the ambient air, on the principal characteristic parameters of such flows. The numerical results obtained are then discussed in comparison with experimental data Djeridane [T. Djeridane, Contributionà l'étude expérimentale de jets turbulents axisymétriquesà densité variable, Thèse de doctorat, univ. Aix-Marseille II, 1994] (relating to the air/air and He/air jets) and other found in the literature. Experimental measurements of the axial velocity, the Reynolds stress and the scalar, present qualitatively the same behaviour. The comparison of the numerical simulation to the experiment does not show large difference and the results obtained are in general satisfactory.