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1.
《Comptes Rendus Mecanique》2017,345(10):706-711
The study presented in the present paper deals with the modeling of the rotation effects on a homogeneous turbulence evolving without a mean velocity gradient. The developed model results from a modification of the second order model of Haworth and Pope. This modification is expressed as a function of the rotation rate, of the component of the Reynolds tensor and of the characteristic length scale in the direction of the rotation axis. The obtained results have evidenced the great capacity of the present model to describe the rotation effects on the time evolution of the homogeneous decaying turbulence.  相似文献   

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This work deals with transient laminar boundary layer along a vertical surface and system of equations is solved using finite difference implicite scheme. We show that the nature of the plate influence thermal and dynamical boundary layer thicknesses as well as the flow velocity. Moreover, we observe that a small perturbation of the velocity implies to flow laminar instabilities.  相似文献   

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A homogeneous and isotropic turbulence is suddenly subjected to a rigid body rotation, whose influence on the turbulent vorticity field is studied. It is shown that only the odd statistical moments are influenced by the rotation at the first order in time. This effect is shown in particular for triple correlations and should be more important for a small Rossby number.  相似文献   

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From kinematic observations by granularity in whiting light mode based on a technique of digital speckle images correlation, the behaviour in tension of a reactive powders concrete is studied. The measures show several localisation areas of the deformation fields and the role of the fibres in the transmission of the stresses in the neighbourhood of a damaged area.  相似文献   

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An original reformulation of the viscous stress tensor is proposed for the motion equations dedicated to an incompressible fluid. Four different tensors appear in this decomposition, associated with viscosities of compression, elongation, shearing and rotation. This new model allows us to build a numerical solver of the Navier–Stokes equations based on a technique of tensorial penalization which is generalized with all the stresses acting on a flow. The processing of incompressibility and the rotation of a rigid body in a flow are described thanks to the model. Several numerical applications are proposed to illustrate the abilities of the new penalization method.  相似文献   

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《Comptes Rendus Mecanique》2002,330(12):893-898
This Note is devoted to the experimental verification of the Onsager's reciprocal relations in the particular case of electro-osmosis and electro-filtration. A special set up has been designed to carry out the measurements of both the electro-osmotic permeability and the streaming potential. This has been performed by using a natural material i.e., saturated kaolinite. To cite this article: K. Beddiar et al., C. R. Mecanique 330 (2002) 893–898.  相似文献   

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Résumé Ce travail porte sur l'étude de solutions diluées d'un polymère de l'acide acrylique dans l'eau (concentration en poids 0,1%). Ce fluide présente des effets de seuil. La mesure du champ de vitesse par vélocimétrie laser permet une détermination précise de l'indice rhéologique,n, étant un paramètre essentiel de la loi de comportement proposée: . Les autres constantes peuvent être déduites d'essais rhéologiques classiques, à fort taux de cisaillement. Il est possible de corriger le gradient de pression mesuréP/L, afin d'obtenir la valeur véritable de ce gradient, notéedp/dz. L'analyse de l'écoulement dans un élargissement brusque montre que le seuil a une forte influence sur les zones de recirculation.
This work deals with the study of very dilute solutions of polyacrylic acid in water (weight concentration about 0.1%). These fluids seem to exhibit a yield effect. The determination of the fully developed velocity field by laser velocimetry allows us an accurate determination of the rheological indexn which is an essential parameter for the proposed rheological relationship: . Other constants can be determined from classical rheological experiments (high shear strain). It is possible to correct the experimental pressure gradientP/L so as to get the real value, noted asdp/dz. An analysis of the flow in an abrupt expansion shows that the yield effect strongly influences the recirculation zones.

D, d m diamètre intérieur d'une conduite cylindrique - C % concentration en poids - s Pa seuil de contrainte - K consistance - gradient de vitesse axiale - gradient pariétal de vitesse axiale - Pa s viscosité pour - Pa contrainte de cisaillement - m/s vitesse débitante - n indice de structure - dp/dz Pa/m gradient longitudinal de pression - z m abscisse longitudinale - u m/s vitesse axiale - écart entre le gradient de pression effectif et le gradient mesuré en Pa - P Pa différence de pression mesurée - L m distance entre 2 prises de pression - A Pa constante intervenant dans l'expression de - B 10–3 Pa s constante intervenant dans l'expression de  相似文献   

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F. Campus  K. Gamski 《Rheologica Acta》1961,1(4-6):491-494
Résumé Le fluage des aciers doux, demi-durs et durs possédant une limite apparente d'élasticité se présente sous la forme particulière d'un écoulement rapide et différé, lorsque ces aciers ont été d'abord soumis à un étirage sous une tension atteignant la limite apparente d'élasticité et lorsqu'ils ont été soumis immédiatement après décharge à l'effet d'une charge permanente de fluage réalisant une tension inférieure à la limite apparente d'élasticité.Plusieurs essais de fluage et de relaxation ont été réalisés dans ces conditions pour déterminer l'ordre de grandeur de la tension la plus basse susceptible de provoquer cet écoulement caractéristique.
Summary The creep of different kinds of steels with a yield point has the particular form of a delayed yield when the bars have previously been strained at a stress equal to the yield point and afterwards submitted to creep under a constant stress lower than the yield point.Several creep and relaxation tests have been performed under these conditions in order to appreciate the lower stress which is able to produce the delayed yield.

Zusammenfassung Das Kriechen der Stähle von verschiedener Güte mit natürlicher Streckgrenze stellt sich dar in charakteristischer Form eines verspäteten Fließens, wenn diese Stähle zuerst beim Zuge bis zur Streckgrenze verformt werden und dann nach Entspannung dem Kriechversuch übergeben werden unter eine Zugspannung kleiner als die Streckgrenze.Mehrere Kriech- und Relaxationsversuche wurden in diesen Angelegenheiten durchgeführt, um die kleinste Zugspannung zu bestimmen, welche noch geeignet ist, das verspätete Fließen zu bewirken.


Professeur à l'Université de Liège, directeur des Laboratoires d'Essais des Constructions du Génie Civil.

Agrégé à l'Université de Liège, chef de section aux Laboratoires d'Essais des Constructions du Génie Civil.  相似文献   

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Double scale homogenization is used to average stationary equation or inequalities in which both highly oscillating variables and parameters appear. We demonstrate how the limit is obtained using a two-stage procedure , firstly by carrying out a classical homogenization process by freezing the oscillating parameter, then by averaging the result with respect to this parameter. These results allow us to average the pressure for a newtonian fluid in a narrow gap between two rough unstationnary surfaces.  相似文献   

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Two color laser-induced fluorescence technique is able to measure mean temperature of flying droplets, in the evaporation regime without combustion. This paper presents preliminary results about the use of this technique in reactive media.  相似文献   

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The time integration of strain rate tensor D? is a central problem in large transformations even if it is often an underlying one. The cumulated tensorial strains, obtained by the time integration of strain rate tensor D?, allow the tackling of this problem from a geometrical point of view, and independently of material behaviour considerations. The time integration here takes place in the local objective frame defined by the logarithmic spin proposed by Lehmann et al. and Xiao et al. The numerical results obtained in a closed deformation path are presented here. The advantages and drawbacks of this novel integration for the development of behaviour laws are described. To cite this article: V. Mora et al., C. R. Mecanique 332 (2004).  相似文献   

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A horizontal saltation layer of glass particles in air was investigated experimentally in a wind tunnel. Particle concentrations are measured by light scattering diffusion and image processing and all the statistical characteristics were evaluated and thus the probability density function. Our experimental results confirm that the mean concentration decreases exponentially with height, the mean Eulerian dispersion height H being a characteristic lengthscale and that the instantaneous concentration distribution c?(x,t) is a random variable following quite well a lognormal distribution. To cite this article: X. Zhang et al., C. R. Mecanique 334 (2006).  相似文献   

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