Jamel Chahed

Jamel Chahed
University of Tunis El Manar | FST · Ecole Nationale d'Ingénieurs de Tunis

PhD
I am interested in issues related to Scientific Integrity, Research Ethics, and Higher Education Deontology

About

196
Publications
87,387
Reads
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738
Citations
Citations since 2017
75 Research Items
448 Citations
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
Introduction
My research relates to theoretical and applied fluid mechanics and focuses on the modeling of hydrodynamics and transfers in single and multiphase flows; with the perspective of application to industrial systems and environmental fluids. I also contributed to the development of a water security conceptual model of the arid region, based on a holistic vision of water resources. In this regard, have been involved in a number of national and international academic research and technical programs.
Additional affiliations
September 2005 - January 2006
Institut National des Sciences Appliquées de Toulouse
Position
  • Senior Researcher
April 1991 - February 1992
Institut de Mécanique des Fluides de Toulouse
Position
  • Researcher
September 1981 - present
École Nationale d'Ingénieurs de Tunis
Position
  • Professor (Full)

Publications

Publications (196)
Article
Full-text available
The Eulerian–Eulerian two-fluid model presented in this paper emphasizes two aspects of the dynamic interactions between phases. First, the turbulent correlations associated with the added mass force are taken into account in the expression of the force exerted by the liquid on the bubbles, thus proving that the turbulent contributions of the inter...
Article
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This paper envisions a comprehensive balance for water management that takes into account all kinds of water resources: withdrawal (blue) water, (green) water in rainfed agriculture and the net contribution of "virtual water" to the food import-export balance. In countries where water resources are limited, this leads to a better understanding of t...
Article
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The role of the turbulence in the void,fraction distribution in bubbly pipe flow under microgravity condition is evaluated on the basis of numerical simulations using a Eulerian-Eulerian two-fluid model. In microgravity, the average relative velocity is weak and the void fraction distribution is mainly governed by the turbulence. The simulations sh...
Article
Full-text available
Related topics are discussed within the following threads: https://www.researchgate.net/post/Scientific_Watch_on_Turbulence_Closure_for_Two-Fluid_RANS_Modeling https://www.researchgate.net/post/Scientific_Watch_on_Transfer_Closure_for_Two-Fluid_RANS_Modeling We apply a two-fluid model with second-order closure of the turbulence in the simulations...
Article
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Many experiments demonstrate that the bubble relative (slip) velocities in vertical turbulent sheared bubbly flows are significantly lower than those in quiescent infinite fluid. Moreover, vertical bubbly jet experiments performed by Sun and Faeth (1986, "Structure of Turbulent Bubbly Jets-1. Methods and Centerline Properties," Int. J. Multiphase F...
Chapter
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Introduction to Fluid Mechanics: Introduction à la Mécanique des Fluides
Chapter
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Chapter 7: Navier Stokes equations and reference flows VII.1 Navier Stokes equations VII.2 Reference flows and simplifications of the NS equations VII.3 Reynolds number VII.4 Introduction to the theory of irrotational flows VII.5 Introduction to creeping flow theory VII.6 Introduction to plane flows established in one direction
Chapter
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Bilan de quantité de mouvement - Théorème d’Euler
Chapter
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Chapitre 5: Ecoulements de Fluide Parfait
Chapter
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Chapitre 5 : Ecoulement mono-dimensionnel stationnaire et idéal
Research
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Jamel CHAHED is a Hydraulics Engineer, PhD and Doctor es Sciences, Professor at the National Engineering School of Tunis, University of Tunis El Manar. His work focuses on transfers in industrial and environmental fluid systems, atmospheric dispersion, water management and governance. His research has appeared as articles, books, book chapters, con...
Article
The paper studies one-way and two-way coupling interactions between the liquid turbulence and bubbles' presence in bubbly jets. One-way coupling focuses on jet with low void fraction in which the bubbles have no significant effect on the hydrodynamic liquid fields in comparison to the single-phase jet. It sets out to model the interfacial momentum...
Article
The paper studies one-way and two-way coupling interactions between the liquid turbulence and bubbles' presence in bubbly jets. One-way coupling focuses on jet with low void fraction in which the bubbles have no significant effect on the hydrodynamic liquid fields in comparison to the single-phase jet. It sets out to model the interfacial momentum...
Chapter
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Ideal compressible fluid flow. We analyze the case of stationary compressible one-dimensional flows of ideal fluids. The results obtained will however be very instructive by their simplicity for the knowledge of the essential effects of compressibility in a flow. They have the advantage of highlighting the major phenomena which are the consequence...
Chapter
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Chapter 3: Thermodynamics of ideal gases Ideal Gas – Real Gas Consequences of the ideal gas equation Isentropic transformations Sound celerity Compressibility
Chapter
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Mechanics of Compressible Fluids. Chapter 2: Elements of thermodynamics The problems studied concern fluids in compressible flows for which the thermal effects are important. This chapter is devoted to reminders of thermodynamics, in particular the notions that are needed in the rest of the presentation. We avoid going into details but we endeavor...
Chapter
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Mécanique des Fluides Compressibles Chapitre 1 : Introduction Générale Rappels de Mécanique du Fluide Classique
Chapter
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Recall the fundamental notions and basic equations of the Continuous Medium
Chapter
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Equations of Classical Fluid Mechanics: Kinematics of Continuous Media
Chapter
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Equations of Classical Fluid Mechanics: General Equations of the Classical Fluid
Chapter
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Equations of Classical Fluid Mechanics: Statics of Fluids, Hydrostatic Forces and Stability of Floating Bodies
Data
Related topics are discussed within the following threads: https://www.researchgate.net/post/National_Water_Security_in_Water-Scarce_Countries https://www.researchgate.net/post/Water_Footprint_Water_Colors_Blue_Water_Green_Water_Grey_Water_Virtual_Water https://www.researchgate.net/post/Scientific_Watch_on_Water_Scarcity_Indicators
Data
Related topics are discussed within the following threads: https://www.researchgate.net/post/National_Water_Security_in_Water-Scarce_Countries https://www.researchgate.net/post/Water_Footprint_Water_Colors_Blue_Water_Green_Water_Grey_Water_Virtual_Water https://www.researchgate.net/post/Scientific_Watch_on_Water_Scarcity_Indicators
Chapter
Full-text available
Turbulence et Dispersion dans la Couche Limite Atmosphérique : 5.1 Considérations générales sur la Couche Limite (CL) 5.2 Equation de l écoulement homogène dans une direction 5.3 Etude asymptotique à grand nombre de Reynolds 5.4 Propriétés de similitude et profils de vitesse 5.5 Applications aux écoulements internes 5.6 Turbulence dans la Couche Li...
Chapter
Full-text available
Academic Resources on Single Phase and Multiphase Turbulent Flows in Nature and in Industry. Turbulent jets, plumes, and floating jets
Preprint
Related topics are discussed within the following threads: https://www.researchgate.net/post/Scientific_Watch_on_Turbulence_Closure_for_Two-Fluid_RANS_Modeling https://www.researchgate.net/post/Scientific_Watch_on_Transfer_Closure_for_Two-Fluid_RANS_Modeling The major focus of the present work is to develop an adequate closure model for the turbule...
Presentation
Full-text available
Academic Resources on Single Phase and Mulltiphase Turbulent Flows in Nature and in Industry. Head losses in two-phase pipe flows
Article
The major focus of the present work is to develop an adequate closure model for the turbulent contribution of the interfacial momentum transfer term in turbulent bubbly flow. For this purpose, numerical simulations have been conducted on bubbly pipe flows under microgravity conditions. With no buoyancy effect, the average interfacial forces are neg...
Presentation
Full-text available
Academic Resources on Single Phase and Multiphase Turbulent Flows in Nature and in Industry. Scales in Turbulent Flows
Chapter
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Academic Resources on Single Phase and Mulltiphase Turbulent Flows in Nature and in Industry. Dynamics and thermodynamics of Geo-Fluids
Chapter
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Single Phase and Multiphase Turbulent Flows in Nature and in Industry: Structure of the atmosphere and scales of atmospheric movements
Chapter
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Academic Resources on Single Phase and Multiphase Turbulent Flows in Nature and in Industry. Introduction to Single phase and Multiphase Turbulent Flows
Presentation
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Academic Resources on Single Phase and Multiphase Turbulent Flows in Nature and in Industry. Fundamental aspects of multiphase flows
Chapter
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Estimating and quantifying in an accurate way, the distribution of pollutant concentrations plays a crucial role in the emergency response management in major nuclear accidents. As in many areas of the environmental studies, air quality models are used to simulate atmospheric dispersion phenomena, although they lack accuracy due to the uncertainty...
Article
The present research aims to assess and analyze one-dimensional two-fluid models used in simulating gas-liquid dynamics and interphase transfers in degassing columns. The assessment of two-fluid models is based on benchmark measurement data carried out over a long period of time, both on dissolved gas concentrations in Lake Nyos at different depths...
Presentation
Full-text available
Academic Resources on Single Phase and Mulltiphase Turbulent Flows in Nature and in Industry. Balance equations in 1D two-phase flows
Presentation
Full-text available
Academic Resources on Single Phase and Mulltiphase Turbulent Flows in Nature and in Industry. 1D models in two-phase gas-liquid flows
Chapter
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Academic Resources on Single Phase and Mulltiphase Turbulent Flows in Nature and in Industry. Atmospheric Boundary Layer (ABL): Dynamic and thermal aspects
Presentation
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Academic Resources on Single Phase and Multiphase Turbulent Flows in Nature and in Industry. Statistical Description of Turbulence
Presentation
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Academic Resources on Single Phase and Mulltiphase Turbulent Flows in Nature and in Industry. Turbulence modeling
Chapter
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Modèles Gaussiens pour l'étude de la dispersion et des retombées atmosphériques 6.1 Diffusion à partir d'une source ponctuelle 6.2 Le Modèle Gaussien Rectiligne 6.3 Dispersion à partir d'une source continue : Le Modèle de Bouffée 6.4 Calcul des concentrations d’effluents issus d’une cheminée 6.5- Paramétrisation de la stabilité de la CLA
Article
Full-text available
A two-fluid model with second order turbulence closure is used for the simulation of a turbulent bubbly boundary layer. The turbulence model is based on the decomposition of the Reynolds stress tensor in the liquid phase into two parts: a turbulent part and a pseudo-turbulent part. The reduction of second order turbulence closure in the near-wall r...
Article
Full-text available
The paper presents an investigation of the drag force coefficient modification in homogenous turbulent two-phase bubbly flows at moderate volume fractions (less than 10%). We focus in this investigation on the analysis of aptitude of the bubble surrounding flow confinement at moderate volume fraction assumption to explain the evolution of the drag...
Thesis
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La prévision opérationnelle des conséquences de la pollution radioactive dans l'atmosphère fait appel aux modèles de dispersion atmosphérique fournissant des solutions numériques ou analytiques de l'équation d'advection-diffusion. Les champs météorologiques influent énormément le transport de radionucléides car il contrôlent principalement la stabi...
Technical Report
Full-text available
Article
Full-text available
The paper presents a one-dimensional two-fluid model for the simulation of gas–liquid flow in vertical degassing devises used in extracting dissolved gases for energy production or for protection against lake overturns. The inter-phase mass transfer is determined assuming gas–liquid phase equilibrium with a gas mixture comprising two gases (CO2, CH...
Article
The paper presents an assessment of turbulence models in dispersed bubbly flows based on an analysis of their application to uniform and uniformly sheared homogeneous turbulence. This analysis leads to the development of a five-equation model where the total turbulent fluctuations in bubbly flow is submitted to a double decomposition : At first,...
Thesis
Full-text available
This thesis work analyses interfacial interactions and turbulence in dispersed two-phase flows at different density contrasts. In these flows, the mean interfacial forces are directly associated with a negligible, low or fairly important mean slip velocity and a turbulent contribution of interfacial exchange, including that of the mass added force...
Thesis
Full-text available
The work presents, firstly, a study for the evaluation of turbulence models in dispersed bubbly flows based on an analysis of their application in uniform and uniformly sheared homogeneous turbulence. Then presents an analysis of the three equations model based on turbulent viscosity derived from the reduction of the second-order model. The numeric...
Technical Report
Full-text available
SEMINAIRES: ECOLE POLYTECHNIQUES DE MONTREAL (EPM) & UNIVERSITE QUEBEQOISE A MONTREAL (UQAM) N0VEMBRE 1999
Thesis
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Many vertical bubbly flows experiments show a reduction in slip velocities compared to the limit velocity of bubble rise in a liquid at rest. Some experiments note even a vertical slip inversion giving rise to negative values of the relative velocity. The work led in this thesis concerns the numerical study of gas-liquid jet flows with low and high...
Article
Full-text available
Related topics are discussed within the following threads: https://www.researchgate.net/post/National_Water_Security_in_Water-Scarce_Countries https://www.researchgate.net/post/Water_Footprint_Water_Colors_Blue_Water_Green_Water_Grey_Water_Virtual_Water https://www.researchgate.net/post/Scientific_Watch_on_Water_Scarcity_Indicators Water securit...
Article
Full-text available
Numerous uncertainty factors in dispersion models should be taken into account in order to improve the reliability of predictions. The ability of a mesoscale meteorological model to assimilate observational data is an efficient way to improve operational air quality model forecasts. In this study, local weather data assimilation based on a flux-adj...
Article
Regional-scale atmospheric circulations play a critical role in air pollutants transport. The planetary boundary layer height, in conjunction with other components, is a key factor in atmospheric dispersion. In this study, planetary boundary layer parameters over two coastal locations (Skhira and Marsa-Dhouiba) in Tunisia were simulated using the W...
Article
Full-text available
First and second turbulence models for turbulent bubbly flows are implemented in the CFD code. In the second order turbulence closure, the Reynolds stress tensor of the continuous phase is split into two parts: a turbulent part produced by the gradient of the mean velocity and a pseudo-turbulent part induced by the bubbles displacements; each part...
Article
A new formulation of the interfacial momentum transfer in two-fluid model for bubbly flows is presented and implemented in a CFD code. The main feature of the interfacial momentum closure lies in an explicit formulation of the turbulent contribution of the added mass force. The two-fluid model with the proposed closure of the momentum interfacial t...
Chapter
Full-text available
The chapter considers the detailed water balance related to food needs of Tunisia. The water footprint of agricultural production, including rainfed crop production, irrigated agriculture and animal production is estimated on average at 12 km³/year. Overall, the green water contribution, including rangelands, represents three quarters of the agricu...
Chapter
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After a preamble devoted to water demand management (WDM) principles in Tunisia, the chapter examines aspects relating to water supply and management conditions, and major challenges in water use key areas: drinking water and agriculture. Use of non conventional waters: desalination and treated wastewater reuse, are considered as an extension to de...
Chapter
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The chapter introduces to concepts and debates that dominate the water issue at the global scale. First, the world water balance outlines contributions made to the development of understanding renewable freshwater resources on Earth, as well as withdrawals and impact of human actions on the hydrological cycle. The water footprint concept applied at...
Chapter
Full-text available
Water requirements for food demand in Tunisia have more than tripled over the past four decades, and amount to more than 16 km³ in 2010. As the population has nearly doubled during the same period, water requirements for individual dietary recorded an increase from about 1050 m³/year/capita in the early 1970s to nearly 1600 m³/year/capita in the la...
Chapter
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Tunisia has implemented a network of hydraulic facilities allowing to ensure safety about drinking water supply of the whole urban population and a large part, although unequally, of rural regions. Irrigation has been developed on 420,000 ha, or 8% of arable land which contribute nearly a third of the agricultural production value. The water facili...
Chapter
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The Tunisian case provides a conceptual model of the National water security paradigm with its multiple dimensions. The main idea that emerges from the holistic view of water resources is that water scarce countries should cope with all water resources: improvement of water use efficiency, valorization of rainfed agriculture, development of alterna...
Chapter
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Tunisia’s rainfall resource is 36 km³/year, generating flows for 4.8 km³/year as blue water. Groundwater withdrawals are 2 km³, and many aquifers are overexploited: the national groundwater overexploitation is 20%. The chapter presents updated information on water facilities: large dams, hill lakes and hill dams, water-table and deep aquifers, with...
Book
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This book shows how the change of water paradigm has become urgent, and provides evidence for new policies that expand water balance to green and virtual water. The issue of water security concerns drinking water supply but also food safety, linked to agricultural policy. Both rain-fed and irrigated agriculture play complementary roles in food secu...
Chapter
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Dans un contexte de rareté de l'eau, les pays de l’Afrique du Nord Ouest (NWA) consomment 70% de leurs ressources en eau renouvelables. La surexploitation des eaux souterraines, estimée à près de 50%, est devenue un défi majeur pour la conception et la mise en oeuvre de politiques durables d'allocation et de gestion de l'eau dans la région. Cette s...
Chapter
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Northwest African countries (NA) consume 70 percent of their renewable water resources, and groundwater overdraft has become a major problem. Blue water irrigation represents 17 percent of overall water resources and is economically significant. Green water represents 83 percent, but is not yet well evaluated, and is not considered in national wate...
Thesis
Full-text available
This Ph.D. thesis focuses on the evaluation of turbulence and mass transfer closures of two-fluid models applied to gas-liquid bubbly flows. Turbulence models in bubbly flow are based on the decomposition of turbulent fluctuations into fluctuations induced by the velocity gradients and fluctuations induced by the bubbles. Experimentally, it is diff...
Chapter
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This chapter attempts to place the reader in tune with current trends, debates and sometimes contradictions that dominate the issue of water on a global scale. A historical overview traces the progress of water status, describes the international community action in addressing the water issue and analyzes the implementation of the right to water. I...
Article
Separating “shear induced turbulence” and “bubble induced turbulence” contributions in gas-liquid bubbly flows is still experimentally difficult to characterize. Numerical simulations were investigated in order to isolate the turbulence produced by the mean velocity gradient of the continuous phase which comprises the turbulence generated in bubble...
Article
Full-text available
We applied an Eulerian-Eulerian two-fluid model on an upward dispersed oil-water flow in vertical pipe with 80 mm diameter and 2.5 m length. The numerical profiles of the radial distribution of the oil drops at 1.5 m from the inflow are compared to the experimental data of Lucas et al.1 This paper analyzes the roles of turbulence and interfacial fo...
Poster
Full-text available
Realistic simulation of atmospheric dispersion requires accurate representation of flow fields in time and space in the region of the source release and its environment. In this study, weather is simulated using the WRF-ARW v3.8 mesoscale model (Skamrock et al. 2008), and pollutant dispersion is run using the ADMS v4.1 model (CERC, 2008). The new f...
Article
Full-text available
Bubbles’ dynamics in the near-wall region of turbulent bubbly flows can significantly influence transfer mechanisms. The present paper is devoted to an analysis of the interfacial momentum transfer in the turbulent bubbly pipe flows under different gravity conditions, in particular in the near-wall region where the void fraction and turbulent shear...
Conference Paper
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(1) Water resources in Tunisia are scares, not uniformly distributed, and highly withdrawn; (2) Water withdrawal has reached the water potential, especially for groundwater; (3) The direct demand (drinking water, industry, tourism) is incompressible and increases with the population but still moderate; (4) An important part of «Blue Water» is used...
Conference Paper
Full-text available
(1) Water resources in Tunisia are scares, not uniformly distributed, and highly withdrawn; (2) Water withdrawal has reached the water potential, especially for groundwater; (3) The direct demand (drinking water, industry, tourism) is incompressible and increases with the population but still moderate; (4) An important part of «Blue Water» is used...
Chapter
Full-text available
The Chapter is devoted to the development of water balance related to the food demand of Tunisia. A linear regression model relating annual rainfall to crop yields is developed to estimate the water-equivalent of agricultural production. Its implementation is based on national data on crop and animal productions and leads to quantification of food...
Thesis
Full-text available
Wall turbulence and head losses in bubbly flows: The work presented in this thesis is interested in two-phase flows and the developments that we bring relate, in particular to the modeling of gas-liquid bubble flows in various configurations in order to develop a methodology for the prediction of the pressure drop, in two-phase flows.
Thesis
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Experimental study and modeling of the hydrodynamics induced by a plume of bubbles under controlled aeration conditions: This thesis work concerns the analysis of the hydrodynamics induced by a plume of bubbles under controlled aeration conditions. It is based on local experiences and on the implementation of two-fluid modeling. The originality of...
Conference Paper
Full-text available
This paper presents a numerical study of axisymmetric bubbly jet flow using an eulerian-eulerian two-fluid model. The model presented in [1], focuses on two aspects of the interaction between phases: first, the turbulent correlations associated to the added mass force are taken into account in the expression of the force exerted by the liquid on th...
Data
LMHE: Scientific Report of Research Teams (2012 - 2015) Project 2: Transfers in mono and multiphase fluid systems
Conference Paper
Full-text available
One of the most important issues in the closure of Eulerian two-fluid models is related to the adequate formulation of the momentum interfacial transfer. In gas-liquid dispersed flows, the interfacial momentum transfer is usually modeled as the density of the force exerted by the continuous phase on the bubble where only the average contribution is...
Conference Paper
Full-text available
Le papier présente une étude numérique d’un écoulement de jet axisymétrique à bulles à l’aide d’un modèle eulérien-eulérien à deux fluides implanté dans le code CFX. Le modèle à deux fluides présentés dans Chahed et al (2003), met l’accent sur deux aspects des interactions entre phases : d’une part, dans la formulation de la force interfaciale moye...
Conference Paper
Full-text available
On s'appuie sur des simulations d'écoulements uniformément cisaillés sur une sphère immobile afin d'évaluer des fermetures de la turbulence développées à partir d'une modélisation au second ordre de la turbulence en écoulement à bulles. La sphère est placée dans la zone d'équilibre production-dissipation d'un écoulement monophasique uniformément ci...
Conference Paper
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La présente étude concerne l'analyse de la distribution des phases dans un écoulement diphasique liquide-liquide dispersé ascendant en conduite cylindrique. On s'intéresse en particulier au rôle des contributions turbulentes du transfert interfacial dans la distribution des phases. On se base sur des simulations numériques pour évaluer les rôles re...