Salem El Golli

Three-Dimensional Numerical Calculations of a Jet in an External Cross Flow: Application to Pollutant Dispersion

We present a three-dimensional numerical simulation of a circular turbulent jet issuing transversely into a uniform air stream. In the first part an air-helium jet is considered and the three-dimensional structure of the flow field is discussed. Then, a comparison between the numerical results of four turbulence closure models (three first-order models and a second-order one) are presented and compared with the experimental data given by Crabb et al. , and Andreopoulos et al.

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.

Influence des conditions d'émission sur un écoulement de type jet plan laminaire isotherme ou chauffé

Abstract We propose numerical solutions for a laminar jet, accounting for emission conditions at the exit of the nozzle. Two emission cases are considered in this study: velocity and temperature profiles are uniform or parabolic, respectively. A finite difference scheme is developed for the resolution of the equations governing the isothermal and non-isothermal free jet and wall jet developing tangentially along an adiabatic flat plate. The analysed results are the centerline velocity and centerline temperature for the free jet, and wall temperature and shear stress for the wall jet. The results obtained are compared to another method that is based on two constraints of integration, i) conservation of momentum and ii) conservation of energy, to replace the emission conditions at the exit of the nozzle for the resolution of equations. Our results of the velocity and temperature profiles compare well with those obtained by the latter method solely in the plume region, where buoyancy forces are responsible for flow.

Étude numérique des conditions d'émission sur un écoulement de type jet plan turbulent isotherme ou chauffé

Abstract We intend to solve equations governing turbulent plane-vertical isotherm and non isotherm jets by taking into account inflow conditions at the exit of the nozzle. The analysis is focused on the influence of these conditions on this type of flow. Two cases are considered (uniform and parabolic velocity and temperature profiles). A finite difference scheme is developed to solve the governing equations. This numeric model allows us to show that the region of fully developed regime begins much nearer the nozzle for the turbulent case than for the laminar flow case. Indeed, the turbulence increases the mixing between the incoming gas from the nozzle and the ambient fluid, and consequently the size of the potential core zone decreases. The results are compared to other works introducing mathematical variables based on the energy conservation for the case of the mixed convection and the momentum conservation for the forced convection, which allows the validation of our results.

Etude d'un réfrigérateur solaire à adsorption solide avec le couple charbon actif-méthanol

Abstract Study of a solar refrigerator of solid adsorption with carbon active-methanol pair . A solar refrigerator with 4m 2 collection surface was studied to build an industrial refrigerator. It is an adsorption machine with an intermittent daily cycle that uses the active carbon AC35-methanol pair. The system management consists only in actuating the ventilation ports for the heating and cooling of the collectors and valves to change the circuit. The results show that, with a collection efficiency comprised between 0.5 and 0.6, it is possible to obtain a high solar COP comprised between 0.14 and 0.2.

Numerical study of momentum and heat transfer in a pulsed plane laminar jet

Abstract In this paper, we propose numerical solutions for a two-dimensional pulsed plane jet in unsteady laminar regime. At the exit of the nozzle, the pulsating flow is imposed with a uniform temperature T 0 and a velocity u = u 0 (1+ A sin( ωt )). Two cases are considered: the free and the wall pulsed plane jet. For the wall jet case, the wall may either be considered adiabatic or subjected to a uniform temperature. Equations are treated with an appropriate finite difference method. The effect of the important governing parameters, such as the amplitude and the frequency of the pulsation, the Reynolds and Grashof numbers on the flow behavior are also investigated in detail. The results obtained show that the pulsation affects the flow in a vicinity region of the nozzle to reach the same asymptotic regime than the steady jet. The results also indicate that the initial development of the jet is considerably accelerated and the entrainment in the first diameters is enhanced.

NUMERICAL STUDY OF A HEATED PULSED AXISYMMETRIC JET IN LAMINAR MODE

In this work, we have studied numerically the influence of a pulsation on the flow generated by an axisymmetric immerged jet in a laminar mode. A finite-difference method is used to solve the dimensionless equations governing the flow. The simulation enabled us to determine the space-time evolution of the flow variables, such as the velocity components, temperatures, length of the potential core, and both the dynamic and thermal half-thicknesses. The results obtained are the outcome of various factors such as the pulsation amplitude, the frequency which affects the Strouhal number value, and the Reynolds and the Grashof numbers. All of them show that a pulsed jet reaches an asymptotic mode identical to that of the steady one. On the other hand, the pulsation considerably accelerates the expansion of the jet and clearly improves the entrainment at the nozzle exit for distances of some diameters. The results reached in this work are validated with those obtained for a steady jet in its various aspects.

Numerical study of a heated cavity insulated by a horizontal laminar jet

Abstract In this work, we present a numerical study of the thermal insulation of a heated two dimensional cavity limited on its superior part by a horizontal plane air jet. The lower horizontal wall is isothermal, while the two vertical walls are adiabatics. A finite difference method based on the stream function–vorticity formulation is developed to solve the dimensionless Navier–Stokes and energy equations resulting from some assumptions. The results allowed us to point out two flow configurations: if natural convection prevails, the hot jet issuing from the nozzle diffuses upwards, and consequently, the cavity cannot be insulated correctly. However, the use of an aspiration zone can then improve the insulation. When forced convection predominates, the hydrodynamic barrier is conserved, and the enclosure is also thermally well confined.