Coupled Problems and Multi-Physics

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Authors: Fatima Madi Arous, Amina Mataoui, Abdellali Terfous, Abdellah Guenaim
Abstract: The simulation of a turbulent wall jet flow over a rectangular cavity is realised by the low Re stress-omega model. FLUENT 6.3 CFD code was used as the solver. The structured grid was built using Gambit 2.3. A preliminary study of a wall jet flow and a wall jet backward facing step interaction has been undertaken to validate the turbulence model. The numerical approach reproduces fairly the experimental results. A wall jet flow over rectangular cavities of different aspect ratios was investigated. The cavity aspect ratio effect on the flow structure evolution, particularly on the reattachment phenomenon, was examined in this paper. The results of this study show that the flow structure is very sensitive to the cavity aspect ratio. The reattachment length in the wall jet incoming flow case is very short compared to that of the boundary layer incoming flow case.
Authors: R. Allouche, R. Haoui, J.D. Parisse, R. Renane
Abstract: This work consists of the numerical simulation of high enthalpy flows. The numerical model is governed by Euler equations and supplemented by the equations of the chemical kinetics modeling the phenomena of the chemical air components in a non-equilibrium state. The finite differences method is used for numerical simulations, the phenomena of a hypersonic flow one-dimensional reactive, non-viscous, chemical non-equilibrium is developed taking into account the physicochemical phenomena like the vibration, the dissociation of the diatomic molecules, the ionization of molecules and the formed atoms of chemical species to higher temperatures which appear behind a strong shock detached and evolve according to time in a relaxation range until to reach the equilibrium state. We are interesting in particular on the temperature effect in ionization of the atoms and the molecules.
Authors: R. Renane, Olivier Serro-Guillaume, A. Nour, R. Allouche
Abstract: The aim of our work is to contribute to the analysis of the structure of laminar premixed Methane-Air flames using two methods. This allows us to validate the chemical mechanisms, to know the fine structure of the flame front and to get, for a given pressure and temperature of fresh gases, the speed and the mass fractions of all chemical species of the combustion reaction. The first method is based on controlling combustion parameters of laminar premixed flame. The numerical resolution strategy used consist in the discretization of the balance equations completed by the transport properties and the thermodynamic variables expressions, as well as the kinetic mechanisms concepts of chemical reactions and boundary conditions, using the first-order finite difference spatial scheme technique. The final solution is obtained, thereafter, iteratively using a recursive method. The calculations stop when equilibrium is reached. The second method consists in the use of FDS (Fire Dynamics Simulator) in order to simulate the propagation speed of the flame for different equivalence ratio in the cylindrical combustion chamber. This geometry is used by Tahtouh et al. (2009), and Bouvet et al. (2010) in their experimental devices for calculating the flame velocity. This study examines the influence of temperature variation of unburned gases on the structure of the flame front, as well as the effect of equivalence ratio on the flame front speed, combustion products and pollutants formation that allows us to deduce which parameters ensure higher efficiency with less fuel consumption and fewer pollutants.
Authors: Mourad Gareche, Noureddine Zeraibi, Ahmed Allal
Abstract: In this article, we demonstrate how the non ionic polymer, the polyethylene oxide (PEO) with molecular weight 6000 g/mol of varying concentration mass (0.7%, 1%, 2% et 3%) significantly alter the rheological properties (yield stress, viscosity, loss and elastic modulus) of the bentonite suspensions (6%) in the water. The different rheological tests made in simple shear and in dynamic on the ternary system (water-bentonite-PEO), showed the influence of the polymer on the rheological properties of this drilling fluid. The PEO which presents an affinity for the bentonite particles slows down the kinetic of aggregation of the clay particles. Also the analysis by X-rays diffraction on different samples revealed the intercalation of the clay platelets on one hand and the links bridges assured by the chains of polymer between bentonite particles beyond a critical concentration in PEO on the other hand. The Herschel-Bulkley rheological model is used for the correlation and the interpretation of our experimental results.
Authors: I. Boumrar, A. Ouibrahim
Abstract: Experiments were conducted on thin delta wings to investigate, for subsonic flow, the effect of both privileged apex angle values and the wing-fuselage interactions on the aerodynamic characteristics, i.e. the distribution of the defect pressure on the extrados, the drag and the lift coefficients. For this purpose, several delta wing models of various apex angle (β = 75, 80 and 85°) were realized and tested without and with fuselages of cylindrical form, with diameters of 20 and 30 mm, downstream the apex and appropriately disposed on the extrados. The impact of the apex angle as well as the interaction on the defect pressure were specially considered along the apex vortices where the pressure defect is usually maximum. The above mentioned effects were investigated via the variations of the mean velocity in the wind tunnel and the incidence (attack) angle.
Authors: Hamza Gouidmi, Abdelhadi Beghidja, Mohamadi Said, Razik Benderradji
Abstract: We are interested In this study to the interaction between oblique shock wave, induced by a surface of a supersonic nozzle with an angle of inclination of θw=8.5°, by a laminar boundary layer generated by a flat surface (reflection of oblique shock on a flat wall) . We studied also the problem of the development of the interaction zone and its unsteadiness. Our study is based on complex numerical simulation of interaction of shock wave / boundary layer and on their disturbance found within the interaction zone. This is the area of unsteady physical characteristics. This study was conducted under condition that the flow is compressible, of laminar and two-dimensional character. We treated also the point of detachment of the boundary layer by varying the value of the upstream Mach number. We compared our results (obtained by the commercial code FLUENT) with those found numerically and experimentally.
Authors: A. Ghomrassi Hadhri, Hatem Mhiri, G. Lepalec, P. Bournot
Abstract: In the present work, we conducted a numerical simulation of flow and sediment transport and deposition in a meandering river. The corresponding results were compared to experimental data of a physical river that was assumed to have a 0.001 longitudinal slope. A three-dimensional numerical model was simulated by means of the commercial FLUENT code. The latter used the RNG k-ε turbulence closure model whose ability to reproduce the experiments was compared to further models. The lagrangian tracking of particles (DPM) was performed. The adopted grid was non uniform, particularly refined on the wall zones where the sedimentation of particles took place. The hydrodynamic section of the model was checked using experimental data. The comparison of the sediment concentration numerical result gave a satisfying agreement with the experimental data. Once the model validated, we studied the effects of varying longitudinal slope on deposition of particles under a flow velocity of 0.2 m/s. The tested values are 0.001 and 0.0045.
Authors: Amar Berkache, Rabah Dizene
Abstract: A numerical simulation is used to evaluate the curvature effects of the wall on features of the interaction between discrete jets and cross flow, and therefore on the efficiency of the cooling. The injection is realized in a turbulent limit layer through only one row of openings. Our study was especially based on the SST model that is efficient in the capture of the phenomena near and in the wall. Three turbulence models are used; the k-, the RSM and the SST on a flat plate crossed by throw in order to identify which of these models are more capable to capture the near wall interaction phenomena. Discrete jets are arranged across a surface exposed to a wall boundary layer of parallel compressible stream, as occurs in certain discrete-hole cooling systems for turbine blades. Comparisons of the results of this study are presented in the case of a flat plate crossed by throw inclined of 45° with a rate injection Ra=0.6. These results compared to experimental data proved the aptitude of the SST model, in relation to the other models in this case of problems. Applied for a NACA0012 profile, this model (SST) revealed us the distinct difference of features of the interaction in relation to the flat plate.
Authors: Ange Kongo Kondé, Iulian Rosu, F. Lebon, L. Seguin, Olivier Brardo, Florian Troude, Bernard Devésa
Abstract: This paper presents a finite element model for the simulation of aircraft tire rolling. Large deformations, material incompressibility, heterogeneities of the material, unilateral contact with Coulomb friction law are taken into account. The numerical model will allow estimating the forces in the contact patch - even in critical and extreme conditions for the aircraft safety and security. We show the influence of loading parameters (vertical load, velocity, inflating pressure) and slip angle on the Self Aligning torque and on the lateral friction coefficient. A friction coefficient law corresponding to Chichinadze model is considered to take into account thermal effects in the aircraft tire model behaviour.

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