Comptes Rendus de l'Académie des Sciences - Series IIB - Mechanics-Physics-Astronomy最新文献

In case of a two components material with a matrix reinforced by a large number of inclusions, we describe explicitely the dependence of the homogenized coefficients in function of the inclusions shape.

In order to determine the pressure drop equation and the minimum fluidization velocity of a 2D bed of monodispersed particles, an experimental setup has been devoloped. The first results show clearly that the well-known equations for 3D bed are not reliable for this configuration. In particular, the minimum fluidization velocity is underestimated. A new pressure drop law is proposed which allows the determination of the minimum fluidization velocity, and is in good agreement with the experimental measurements.

Recent visualisations have shown the instabilities that develop at low Reynolds numbers in a closed cavity formed by a rotating disc, a fixed disc and a fixed outer cylinder. The origin of the spiral structures located near the fixed corner of the cavity is still not well understood. A numerical scheme associating a finite volume method and a pseudo-spectral method is used. The velocity and pressure fields are analysed. A description of this complex structure is proposed.

A theoretical study of the radiative heat transfer inside an uniaxial dichroic non optically active crystal is presented. The general equations which govern the thermal problem are established for absorbing moderately crystals. The temperature and radiative flux fields at radiative equilibrium show the thermal effects due to the anisotropy inside the medium.

This note is concerned with the speed of propagation of a chemical reaction in a fast, steady and nonuniform flow which may apply to flame propagation in some instances. The structure of the flow is: (1) a parallel shear flow with velocity perpendicular to the average front, where the flame speed is close to the maximum flow speed toward the fresh gases; (2) a periodic cellular structure where the speed of propagation of the reaction grows like the fourth root of the fluid speed.

The meeting of a jet and a cross flow generates unstationary vortices at the boundaries of the jet. This paper describes, with the help of flow visualizations, the evolution of these structures. One of the possible evolution is particularly detailed: the pairing process between two consecutive vortices.

The objective of this experience is to study an exemple of complex turbulent flow produced by two coflows with the same velocity which presents a mixing of scales. This type of flow produces spectral perturbations with interactions between structures with different sizes. The experimental system produces the mixing of a primary flow into two secondary flows, these flows are supplied by two types of honeycombs producing turbulence and that can be differently combined. The motivation of this study is the development of turbulence models applicable in non-equilibrium situations. The experimental contribution presented here is aimed at describing the effects of the honeycombs on spectral distributions.

The aim of this contribution is to elaborate a general framework for modelling flows of two-ionic species electrolytes through porous piezoelectric media.

By using the method of two-scale asymptotic expansions, the macroscopic phenomenological equations describing electrokinetics of such a structure are derived and the formulae for the effective mechanical and nonmechanical coefficients are given. Natural jump conditions are assumed on the interfaces between the piezoelectric skeleton and conductive fluid.

Within the framework of finite deformations and using an approach to the kinematics of contact due to A. Curnier, Q.C. He and J.J. Téléga, we propose a spatial thermodynamic formulation for the problem coupling unilateral condition, friction and adhesion. The adhesion is characterized by its intensity introduced by M. Frémond. In the case of frictionless contact between an hyperelastic body and a plane rigid support, with a particular `static' law for the evolution of the intensity of adhesion, the problem can be reduced to a minimization one for which we can show the existence of a solution.

This note presents an adaptive wavelet method to compute two-dimensional turbulent flows. The Navier–Stokes equations in vorticity–velocity form are discretized using a Petrov–Galerkin scheme. The vorticity field is developed into an orthogonal wavelet series where only the most significant coefficients are retained. The testfunctions are adapted to the linear part of the equation so that the resulting stiffness matrix turns out to be the identity. The nonlinear term is evaluated on a locally refined grid in physical space. This numerical scheme is applied to simulate a temporally developing mixing layer. A comparison with a classical pseudo-spectral method is used for validation of the new method. The results show that the formation of Kelvin–Helmholtz vortices is well captured and all scales of the flow are well represented.