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

Numerical simulation and LDV measurements are performed for laminar inlet flow condition in a vortex exchange chamber with isothermal conditions. Newtonian and non-Newtonian fluids were used. Experimental measurements are compared to results of numerical computations with good agreement. Both show the existence of a secondary flow generated by hydrodynamical instabilities due to streamline curvature. The main vortex flow appears then to be restricted by this secondary flow.

In recent years it was observed that chaotic behaviour can occur in some infinite–dimensional linear systems. An example of this type, related to a kinetic model (death process), has been previously reported. In this paper we generalize these earlier results to the case of variable coefficients, showing that the property of being chaotic can be in a certain sense stable. On the other hand the ‘opposite’ birth process cannot be chaotic.

In this paper, we propose a new class of algorithms to solve large scale linear algebraic equations. This method is based on homotopy, perturbation technique and Padé approximants.

The first part of this paper dealt with the conceptual issues encountered in the definition of the interfacial area and in the derivation of a transport equation. The second part has the following objectives: 1. to address the closure issues for the source terms appearing in the transport equation when dealing with a bubbly flow in a vertical pipe; 2. to provide a list of open questions to be answered before introducing a transport equation for the interfacial area concentration in a thermal–hydraulic computer code.

Within the framework of nonlinear elasticity, we study the behaviour of a bonded joint formed by two adherends and a joint of thickness $\text{εh}$. When the stiffness of the adhesive is of order $\text{ε}$ with respect to the adherends, the analysis gives us a limit model where the constitutive equations of the adherend are only linear. We show existence of solutions of the model and discuss the unicity.

A thermal modelling of a solid–fluid interface is proposed. The developed procedure is based on a numerical identification, in a dimensionless space, of a unique transfer function, associated with a recurrent relation. The method is usable for direct or inverse problems and well fit for control–command applications. An inverse numerical simulation example is presented for a random thermal excitation.

This article presents a numerical study of a non-isothermal axisymmetric turbulent jet by two $\text{k}$–$\text{ε}$ closure models based on Favre or Reynolds averaging, respectively. The numerical results are in good agreement with the experimental ones found in the literature. We show, in particular, the advantage of treating separately the turbulent mass flux terms and their contribution to predicting variable density effects. A mixing efficiency definition is finally introduced. It is observed that the mixing efficiency increases when the density ratio between the turbulent jet and the ambient gas is reduced.

A stability analysis of detonation waves is carried out at strong overdrive and in the Newtonian limit (small difference between the specific heats at constant pressure and at constant volume). The instability threshold is determined. An analytical expression of the dispersion relation and a linear integral-differential equation for the evolution of the detonation front, both valid at onset of the instability, are obtained. The analysis is valid for an arbitrary chemistry compatible with stable or weakly unstable gaseous detonations.

In this note we discuss the generalization of a Lagrange multiplier based fictitious domain method to the simulation of migration of neutrally buoyant particles in plane Poiseuille flow of a Newtonian fluid. The migration away from the center of the channel is believed to be an effect of the curvature of the velocity profile. We found this effect is not weakened by the presence of many particles, but instead by the collisions among the particles. Experiments and simulations show that the particles concentrate in the central region where the shear rate is low.

We describe the formation of spatial structures generated by diffusive instabilities in bistable systems. It is shown that the coupling between the different spatial modes emanating from the two homogeneous states can give rise to self-parametric instabilities favoring the occurrence of resonant quasiperiodic structures such as superlattices or quasipatterns.