Etude de l'influence de l'amplitude et la fréquence de pulsation sur le taux de mélange d'un jet libre plan à densité variable

International audienceOn se propose d'étudier un jet plan pulsé à masse volumique variable en régimes laminaire et in stationnaire. A la sortie de la buse, l'écoulement est soumis à une perturbation périodique de la vitesse d'éjection de la forme : u = uo(1 + A sin(&#969t)) . La résolution numérique des équations régissant l'écoulement est effectuée à l'aide d'un code de calcul basé sur une méthode aux différences finies. Les résultats obtenus montrent que la pulsation affecte le mélange au voisinage de la buse d'éjection, plus loin les résultats du régime in stationnaire rejoignent ceux du jet permanent non pulsé. Les résultats indiquent aussi que le nombre de Strouhal n'influe pas beaucoup sur le degré de mélange de l'écoulement, alors que l'amplitude de pulsation affecte d'une manière remarquable le mélange

Etude numérique de la structure et la dynamique d'un jet coaxial turbulent

Dans ce travail, on se propose d'étudier numériquement un écoulement de type jet coaxial turbulent de l'air dans l'air pour des rapports des vitesses compris entre 1 et 10. 0n s'intéresse particulièrement à l'effet de ce dernier paramètre sur la structure de l'écoulement. Les équations régissant l'écoulement ont été résolues à l'aide d'un code de calcul numérique personnel basé sur une méthode aux volumes finis. Le modèle de fermeture adopté est le modèle de premier ordre k-epsilon standard. Les résultats obtenus montrent l'apparition d'une zone tourbillonnaire au voisinage de l'axe du jet pour des rapports des vitesses r égal à 3. La structure de l'écoulement dépend étroitement de la présence de ces tourbillons

Modeling of chemical composition in the melt pool during laser welding of Aluminum / Magnesium alloys

Joining dissimilar metals is very difficult due to the formation of brittle intermetallic phases which may be detrimental to mechanical properties. The present work aims to investigate the transport phenomenon in the weld bead and to understand the materials mixing during laser welding process of dissimilar Aluminum-Magnesium alloys. A three-dimensional transient model based on fluid flow, heat and mass transfer has been developed to predict the formation of the weld and to study numerically and experimentally the diffusion of alloying elements in the melted zone. SEM analysis of chemical composition has been realized to map elements distribution in the melted zone. The results of simulation show the formation of a heterogeneous mixture in the melt pool. The elements distribution map and the presence of brittle intermetallic phases in the fusion zone were analysed. The formation of intermetallic compounds, comprising Al3Mg2 and Al12Mg17 phases were predicted by studying the chemical elements distribution in the weld pool. A good tendency between experimental and numerical results is noticed for the weld

A parametric study of microjet assisted methane/air turbulent flames

International audienc

The effect of air velocity on slugs in a confined channel

International audienceThe present work focuses on the study of slugs occurring in a two-phase flow of a confined rectangular channel: conditions of appearance and effect on the flow behavior. Three-dimensional numerical simulations have been carried out to examine the effect of superficial air velocity on flow behavior. The Volume Of Fluid model (VOF) is used to track the air-water interface. Validation of the numerical model is obtained by comparing the results of the simulated axial velocity with experimental data determined using the Laser Doppler Anemometry (LDA) technique. The numerical results revealed that for a fixed water level and superficial water velocity, higher superficial air velocities generate a slug flow that causes channel blockage. The position of these slugs and the timing of their occurrence were correlated in terms of air and water superficial Reynolds number

Contours of Air and Brick Temperatures inside a Tunnel Kiln

International audienceWe present, in this work, the main results obtained from a two-dimensional numerical modeling of a tunnel kiln used for production hollow bricks. The results obtained made it possible to present contours of the temperature inside a tunnel kiln using a home-made two-dimensional code written with the open-source software SCILAB. The results showed the existence of a vertical temperature gradient in the brick stacks which can affect the final quality of the baked products

Improvements of mixing process in a rapidly tubular flame burner

International audienceA three-dimensional simulation of a steady non-reactive mixing process in a rapidly mixed type tubular flame burner is carried out in order to examine the effects of the injectors' number (N= 2, 3, 4 and 6), the swirl number (Sw=0.46, 0.68, 1.05 and 1.83) and the injector arrangements (3-3 and 4-2). The mixing process is investigated by focusing on the following criterions: Particles trajectory, Central reverse zone (CRZ) and mixing layer thickness. The particles are tracked using a Lagrangian Discrete Phase Model (DPM). The numerical solutions are validated by comparing with previous experimental results. It is pertinent to note that the model predicts properly the flow field and the mixing in a rapidly tubular flame. The obtained results have generally shown, that for the same swirl number and same average axial velocity, the increase of injectors' number generates a larger reverse flow and decreases the mixing layer thickness. It is also shown that a high swirl number and same distribution of the injectors' number could significantly promote the mixing in rapidly tubular flame

Swirl generator effect on a confined coaxial jet characteristics

International audienc

A novel ventilation method to prevent obstruction phenomenon within sewer networks

The phenomenon of blockage is a widely encountered issue in industrial applications with multiphase flows such as sewer networks. This paper proposes a solution to eliminate the blocking phenomenon in such confined horizontal channels. The study presents alternative longitudinal ventilation using inclined jets. Numerical simulations were performed to evaluate several parameters such as the position of the jets, their orientation and the velocity ratio between the main air inlet and the jets. The Volume of Fluid model (VOF) is used to follow the evolution of the interface between the air and water phases. Numerical results of the axial velocity were confronted to the experimental data obtained by the Laser Doppler Anemometry (LDA) technique and gave good agreement. The parametric study shows that the lateral injection has a direct effect on the dynamic of the air-water flow inside channels. With the optimal depicted position and orientation of the injectors, the obstruction is avoided for low air velocities and is moved away from the entrance for the higher ones. Results show also that side-by-side lateral injection all over the channel with an optimal ventilation ratio fully avoid the occurrence of slug flow and thus the obstruction of the channel

Numerical investigations of cooling holes system role in the protection of the walls of a gas turbine combustion chamber

International audienceNumerical simulations in a gas turbine Swirl stabilized combustor were conducted to investigate the effectiveness of a cooling system in the protection of combustor walls. The studied combustion chamber has a high degree of geometrical complexity related to the injection system as well as the cooling system based on a big distribution of small holes (about 3,390 holes) bored on the flame tube walls. Two cases were considered respectively the flame tube without and with its cooling system. The calculations were carried out using the industrial CFD code FLUENT 6.2. The various simulations made it possible to highlight the role of cooling holes in the protection of the flame tube walls against the high temperatures of the combustion products. In fact, the comparison between the results of the two studied cases demonstrated that the walls temperature can be reduced by about 800A degrees C by the mean of cooling holes technique