Key words: jet, vortex, instability, excitation, frequency, mode.

Abstract: A numerical study of the instabilities is realized for 2D incompressible, isothermal and plane jet. The eulerian numerical finite volume method is used. Numerical parameters and boundary conditions are optimized for the studied configuration. This study was operated for moderate Reynolds numbers. The flow is perturbated at the entry of the nozzle. The excitation frequency is a harmonic or sub-harmonic of the natural instability. The instability amplification depends on the excitation frequency. A response mode inherent to the shear flows was detected. The vortex energy is amplified allowing to know their sinuous or varicose behavior. The vortex dissociation and pairing phenomena are highlighted.

Key words: Natural convection, heating obstacle, Rayleigh number, unsteady state, heat transfer.

Abstract: The present work deals with the prediction of a natural convection flow in a square cavity, partially heated by an obstacle placed at the bottom wall. The two transverse walls and the top wall of the cavity are supposed to be cold, the remaining walls are kept insulated. The main parameter of numerical investigations is the Rayleigh number (engine convection) varying from 10³ to 10⁵. When Ra is fixed at 10⁷, the flow and thermal fields bifurcate and undergoes an unsteady behavior at critical positions.
Flow patterns corresponding to the unsteady state are presented and analyzed in the current study. The simulations were conducted using a numerical approach based on the finite volume method and the projection method, which are implemented in a computer code in order to solve the Navier-Stokes equations.

Key words: FEM, ECAE , molecular orientation

Abstract: The behavior of molecularly orientated polycarbonate (PC) sheets was investigated numerically. In the present contribution finite element simulations, using a physically-based viscohyperelastic-viscoplastic constitutive model, were carried out in order to evaluate the degree and distribution of molecular chain anisotropy in polycarbonate and the effect of strain rate on distribution of plastic deformation when it is extruded by the ECAE process at 135°.

Key words: Heat transfer; Natural convection; Non-Newtonian fluids; Numerical study; Square cavity.

Abstract: Study of buoyancy driven convection of thermo-dependent a shear-thinning power-law fluid confined in a square cavity, submitted to cross uniform heat fluxes is conducted numerically using a finite difference method. The combined effects of the ratio between the cross heat fluxes and the thermo-dependency parameter on the flow and thermal fields, and the resulting heat transfer are examined and discussed.

Key words: Natural convection, finite volume, parallelepiped, k-epsilon.

Abstract: The heat transfer by convection is, so far, a basic principle of many industrial applications. This study led to the analysis of turbulent convection. Ra > 10⁹ in a rectangular three-dimensional cavity filled with air, the two opposite vertical walls are differentially heated a constant temperature at cold wall and the heat flux at the hot wall, the other walls are hot wall except ceiling wall is cold according to fig. 2. The finite volume method has been used to discretize the equations of flow in turbulent convection. The model of turbulence used is κ-ε. The results obtained are suitable, because they show that for a number of Pr = 0.71 and while varying the heat flow, generating consequently a great influence on the transfer of heat inside the field of study, the numerical results of the heat flux at the hot wall are over predicted. The strong influence of the undulation of the cavity and its orientation is well shown, and the release of the instability due to the interactions of the swirling structures with the boundary layer.