Habib Ben Aissia

HYDROMAGNETIC DOUBLE-DIFFUSIVE LAMINAR NATURAL CONVECTION IN A RADIATIVELY PARTICIPATING FLUID

ABSTRACT Two-dimensional hydromagnetic double-diffusive convection of a radiatively participating fluid confined in a rectangular enclosure is studied numerically for fixed Prandtl, Rayleigh, and Lewis numbers, Pr = 13.6, Ra = 105, Le = 2. Uniform temperatures and concentrations are imposed along the vertical walls, while the horizontal walls are assumed to be adiabatic and impermeable. The damping and stabilization effects of an external horizontal magnetic field are studied for three different optical thicknesses of the semitransparent fluid as well as for an opaque medium. For moderate optical thickness, a steady compositionally dominated flow is observed for all values of Hartmann number considered, and the magnetic damping is remarkably lower than in the opaque medium, for which the flow is always thermally dominated. For optically thin and optically thick media, the thermally dominated flow is stabilized and becomes compositionally dominated as soon as the Hartmann number is increased.

NUMERICAL STUDY OF THE INFLUENCE OF DYNAMIC AND THERMAL EXIT CONDITIONS ON AXISYMMETRIC LAMINAR BUOYANT JET

We propose in our article numerical solutions of the Navier-Stokes equations governing the buoyant round laminar jet. The purpose of this work is to study the influence of the exit conditions at the nozzle exit on the dynamic and thermal parameters of the vertical jet flow. Two emission cases have been considered: Velocity and temperature are uniform or parabolic. The numerical code developed uses a finite difference scheme. The numerical results have been compared with those given by Martynenko, who considered in his analysis only two integration constraints: the momentum at the nozzle exit and the conservation of the energy transported by the jet flow. The obtained results are in good agreement with those proposed in the literature in the plume zone, in which the emission conditions are ignored, and the jet flow is governed mainly by the buoyancy forces. We propose in this paper a correlation to predict the axial virtual origin Xp of the plume zone. Experiments were conducted to validate the numerical model using a nonintrusive method, namely, laser doppler velocimetry.

Prediction of unsteady natural convection within a horizontal narrow annular space using the control-volume method

ABSTRACT Oscillatory natural convection in a narrow horizontal space is investigated numerically using the control-volume method. A parametric study for Rayleigh number is carried out using the power-law scheme and a confrontation with the central-difference scheme is developed. At intermediate values of the Prandtl number, complex interaction between hydrodynamic and thermal instabilities exists. For Pr = 0.2, gradual transitions from monocellular to three-top cell regimes are registered, the phenomenon of coalescence and separation of like-rotating cells is observed, and a subharmonic instability, followed by an early chaotic flow, is depicted. A disagreement between the power-law and the central-difference schemes results exists; the latest ones are in good agreement with the finite-difference method computations. However, the central-difference scheme results suffer from the false diffusion phenomenon.

Interaction of two plane parallel jet

In the present work, a numerical simulation of two plane parallel turbulent jets was performed. The simulations were carried out by using the k-e standard, the k-w standard and the RSM models. A parametric study was also presented to determine the effect of the nozzles spacing and velocity ratio on the axial and transverse positions of the merge and combined points. Correlations between the various parameters governing this type of flow were also provided in this study.