Thèses doctorat

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evolution of the bunrication regine of a cylindrical journal beranig in the starting
(Université des Sciences et de la Technologie D’Oran Mohamed Boudiaf, 2014-05-23) mehala, kada
Etude de l’évolution du régime de lubrification au cours de la phase transitoire dans les paliers hydrodynamiques
(Université des Sciences et de La Technologie d’Oran « Mohammed Boudiaf », 2015-01-22) kada, mehala
L’objectif de ce travail est d’étudier les effets thermiques dans un palier hydrodynamique pendant la période de démarrage. Une approche numérique qui permet de tenir compte la production de la chaleur, des transferts de chaleur et de la variation de la viscosité dans n'importe quel point de film fluide dans l'état transitoire: c’est le modèle thermohydrodynamique (THD). La période limite de démarrage est estimée plus qu'une minute. Une analyse numérique est effectuée en tenant compte de plusieurs paramètres tels que la vitesse de rotation, l'effet thermique, le temps de démarrage. Cette analyse à la possibilité de déterminer les exécutions thermohydrodynamiques d'un palier cylindrique travaille en régime transitoire par la résolution des équations de mouvement en utilisant la méthode volume fini. Pour une vitesse de démarrage de 750, 1000 et 1800 tr/min et une charge appliquée de 1000 N, le régime de lubrification du palier passe du régime hydrodynamique au régime mixte, donc pendant la phase de démarrage, le palier doit déplacer très rapidement ces vitesses, pour éviter le contact de la surface interne du coussinet et de l'arbre.
Parametric study of the performance of a turbocharged compression ignition engine
(University of sciences and technology on Oran, 2015-02-18) Menacer, Brahim; Bouchetara, Mostefa
In this study, the thermodynamic performance of a turbocharged compression ignition engine with heat transfer and friction term losses was analyzed. The purpose of this work was to provide a flexible thermodynamic model based on the filling-and-emptying approach for the performance prediction of a four-stroke turbocharged compression ignition engine.To validate the model, comparisons were made between results from a computer program developed using FORTRAN language and the commercial GT-Power software operating under different conditions. The comparisons showed that there was a good concurrence between the developed program and the commercial GT-Power software. We also studied the influence of several engine parameters on brake power and effective efficiency. The range of variation of the rotational speed of the diesel engine chosen extended from 800 to 2100 rpm. By analyzing these parameters with regard to two optimal points in the engine, one relative to maximum power and another to maximum efficiency, it was found that if the injection timing is advanced, so the maximum levels of pressure and temperature in the cylinder are high.
Simulation des émissions d’aérosols désertiques à l’échelle Régionale : Analyse climatologique des émissions du Nord de l’Afrique
(University of sciences and technology on Oran, 2015-02-23) BENAOUDA, DOUAIBA
Une investigation numérique de la déposition sèche de quatre particules à savoir, le sable, l’argile, petit et grand limon, provoquée par les émissions et le transport de la poussière désertique depuis l’Afrique du Nord, ainsi des conditions météorologiques favorables au cycle de vie des aérosols désertiques au cours de la période du 3 mars 2004 a été effectuée à l’aide d’un modèle régional météorologique (Eta) couplé avec le module décrivant le cycle de la poussière désertique (DREAM). L’analyse de ce phénomène naturel s’appuie sur une étude des conditions dynamiques, elle est axée sur un suivi temporel du nuage de poussière, ce qui a permis de préciser sa trajectoire, son extension spatiale, ainsi que l’allure de sa progression. En 3 mars 2004, un déclenchement d’une masse d’air froide venant de l’Europe vers l’Afrique de l’Ouest provoque une grave tempête de poussière entraînée dans l’atmosphère formant une structure frontale visible de la poussière. Par conséquent, le front de la poussière produit une brume sèche en forme d’un grand arc épais sur les proximités des zones sources et conduise à une grande échelle extraordinaire qu'il accompagne par une quantité significative de la déposition audessus des ils des canaries. En effet, les résultats obtenus par la simulation des conditions météorologiques et de la déposition sèche de quartes particules, ont montré une assez bonne approche numérique de la modélisation des émissions et de la déposition sèche des aérosols désertiques, cela traduit la bonne concordance entre la simulation et l’évolution du phénomène enregistrée sur quelques stations météorologiques sahariennes est conforte les précisions apportées par les images satellitaires, tel que la vitesse de vent surfacique, du 1 à 3 mars 2004 qui tend à soutenir preuve d'un excellent lien entre la vitesse du vent à 10 m simulés et celle mesurée dans la station (OT) située en île de Ténériffe. Suite à la grande quantité de la poussière minérale qui a été déplacée depuis l’Afrique du Nord vers l’île de Grande Canarie, les résultats de la déposition sèche de cet événement ont été en accord avec les analyses de texture des échantillons pris des stations météorologiques situées à la Grande Canarie, ainsi une bonne corrélation a été trouvée entre le résultat concernant la concentration des poussières et celle d’aluminium mesuré.
ENTROPY GENERATION AND NATURAL CONVECTION IN SQUARE CAVITIES WITH WAVY WALLS
(University of sciences and technology in Oran, 2015-03-29) Morsli, Souad; Sabeur-Bendehina, Amina
The aim of the present work is to study the entropy generation in the natural convection process in square cavities with hot wavy walls through numerical simulations for diﬀerent undulations and Rayleigh numbers, while keeping the Prandtl number constant. The results show that the hot wall geometry aﬀects notably the heat transfer rate in the cavity. It has been found in the present numerical study that the mean Nusselt number in the case of heat transfer in a cavity with wavy walls is lower, as compared to heat transfer in a cavity without undulations. Based on the obtained dimensionless velocity and temperature values, the distributions of the local entropy generation due to heat transfer and ﬂuid friction, the local Bejan number, and the local entropy generation are determined and plotted for diﬀerent undulations and Rayleigh numbers. The study is performed for Rayleigh numbers 10e3 < Ra < 10e5 , irreversibility coeﬃcients 10e−4<ϕ<10 , and Prandtl numbers Pr = 0.71. The total entropy generation is found to increase with increasing undulation number.
Coupling of internal and external cooling of gas turbine blades
(University of sciences and technology in Oran, 2015-04-05) Ghezali, Faiza; A. Azzi; A. Bouzidane
Showerhead cooling process which consists of internal convective cooling and external ﬁlm cooling of a turbine blade is investigated using ANSYS-CFX software. The aim of the present investigation is to provide a better understanding of the fundamental nature of showerhead cooling using the three dimensional Reynolds averaged Navier Stokes analysis. A numerical model has been developed to study the eﬀects of coupled internal and external cooling of the leading edge for a semi-elliptical body shape with the SST k-ω model. This model consists of all internal ﬂow passages and cooling hole rows at the leading edge. The numerical results obtained are discussed and compared with experimental data available in the literature. The results show that the cooling eﬃciency increases with the increase of the blowing ratio and the Mach number, therefore, the overall eﬃciency for the steel becomes less important compared to the plexiglas which has a low thermal conductivity.
Inserts thermal coupling analysis in hexagonal honeycomb plates used for satellite structural design
(University of sciences and technology in Oran, 2015-04-16) Boudjemai, Abdelmadjid; A. Mankour; H. Salem; R. Amri; R. Hocine; B. Chouchaoui
Mechanical joints and fasteners are essential elements in joining structural components in mechanical systems. The thermal coupling effect between the adjacent inserts depends to a great extent on the thermal properties of the inserts and the clearance. In this paper the Finite-Element Method (FEM) has been employed to study the insert thermal coupling behaviour of the hexagonal honeycomb panel. Fully coupled thermal analysis was conducted in order to predict thermal coupling phenomena caused by the adjacent inserts under extreme thermal loading conditions. Detailed ﬁnite elements models for a honeycomb panel are developed in this study including the insert joints. New approach of the adhesive joint is modelled. Thermal simulations showed that the adjacent inserts cause thermal interference and the adjacent inserts are highly sensitive to the effect of high temperatures. The clearance and thermal interference between the adjacent inserts have an important inﬂuence on the satellite equipments (such as the electronics box), which can cause the satellite equipments failures. The results of the model presented in this analysis are signiﬁcant in the preliminary satellites structural dimensioning which present an effective approach of development by reducing the cost and the time of analysis.
Close Range Photogrammetry Using Dense Epipolar Matching (DEM)
(University of sciences and technology in Oran, 2015-04-21) Zeroual, Ibrahim; A. Liazid; P. Grussenmeyer
This paper deals with the close numerical photogrammetry applications using several testing objects. The different steps of the metrological process are recalled and discussed according to the obtained results. To get effective geometrical information on objects, automation by stereo matching is needed for proﬁt ability and homogeneity requirements. The qualitative and quantitative evaluation of the 3D accuracy of measurements and the analysis of the resulting dot cloud is done according to a known reference. This study proposes restitution for metrological requirements using the method of dense epipolar matching. Mappings quite redundant and distributed on the images, but also a denser reconstruction are preferable for the application of the surface reconstruction. The use of a digital reﬂex body CANON EOS 5D with focal of 20 and 28 mm enabled us to observe concretely the inﬂuence of the measurements accurately and the step to be planned for a metrology project.
Numerical investigations of AC electrokinetic forces to enhance the rate of transport of reactants in a microchannel
(University of sciences and technology in Oran, 2015-06-02) Khaldi, Abdel Aziz; Driss, Nehari; Aichouni, Mohamed; Sait Eren, San
The present paper presents an investigation to study of AC electrokinetic phenomena in microfluidics. The results show that the variation of the width of electrodes and the gap between electrodes has no effect on the results, but if we change the height of the microcantilver, the concentration of the bonded molecules exchanged with a proportional manner and the width of reaction surface has an effect inversely proportional to the results. The results show also that increasing the length of reaction surface has a negative effect on the attachment of molecules on the surface reaction and changing the width of electrodes or the gap between electrodes changes the concentration of the bonded molecules. The present numerical results can be considered as a contribution to the design of the microchannel used in lab-on-a-chip applications.
Dynamic study of the operation behavior of hydrodynamic coupling by experimental and numerical simulation
(University of sciences and technology in Oran, 2015-06-08) Khatir, Tawfiq; Bouchetara.M; Boutchicha.D
The hydrodynamic clutch is a device of coupling which works according to the principle of the hydrody-namic transmission. Fluid couplings work on the hydrody-namic principle. It consists of a pump-generally known as impeller and a turbine generally known as rotor, both en-closed suitably in a casing. It is a hydrodynamic device used to transmit rotating mechanical power. The Fluid coupling has centrifugal characteristics during starting, thus enabling no load start-up of prime mover, which is of great importance. It has been used in automobile transmis-sions as an alternative to a mechanical clutch. This study aimed at the installation of a test bench of hydrodynamic couplings or clutches, on which it was planned to, analyze the pressing problems of the coupler in its not still regime. One parallel in the experimental part, we made a theoreti-cal study of these phenomena which based itself essentially on the resolution of a system of equations of movement of the wheel-pump, the wheel-turbine and the fluid. For the numerical simulation, a special program is written in FORTRAN 90 were used, we’ll find the values of characteristic of speed and the moments, we compared the two results. They are given in the form of the curves.
Thermodynamic analysis of an HCCI engine based system running on natural gas
(University of sciences and technology in Oran, 2015-06-16) Mohamed Djermouni; Ahmed Ouadha
This paper attempts to carry out a thermodynamic analysis of a system composed of a turbocharged HCCI engine, a mixer, a regenerator and a catalytic converter within the meaning of the ﬁrst and the second law of thermodynamics. For this purpose, a thermodynamic model has been developed taking into account the gas composition resulting from the combustion process and the speciﬁc heat temperature dependency of the working ﬂuid. The analysis aims in particular to examine the inﬂuence of the compressor pressure ratio, ambient temperature, equivalence ratio, engine speed and the compressor isentropic efﬁciency on the performance of the HCCI engine. Results show that thermal and exergetic efﬁciencies increase with increasing the compressor pressure ratio. However, the increase of the ambient temperature involves a decrease of the engine efﬁciencies. Furthermore, the variation of the equivalence ratio improves considerably both thermal and exergetic efﬁciencies. As expected, the increase of the engine speed enhances the engine performances. Finally, an exergy losses mapping of the system show that the maximum exergy losses occurs in the HCCI engine.
Improving cooling effectiveness by use of chamfers on the top of electronic components
(University of sciences and technology in Oran, 2015-07-01) Nemdili Saleha; Nemdili Fadèla; Azzi Abbès
A Computational Fluid Dynamic (CFD) study based on Reynolds Averaged Navier–Stokes (RANS) approach is carried out to predict the mean velocity ﬁeld and the heat transfer rate of an impinging jet in cross-ﬂow conﬁguration on a heated wall-mounted cube. Targeting an electronic cooling conﬁguration, the aim is to investigate the effect of geometrical modiﬁcation of the component on the cooling effectiveness. For the same cross ﬂow Reynolds number Re = 3410, three levels of impinging jets are computed as well as a case without impinging jet that will serve as baseline case for comparison. The results from the RANS computation are compared to experimental data from published scientiﬁc literature. The validation shows qualitatively good agreement and almost all ﬂow structures are well reproduced by the computation. In an attempt to optimize the wall heat ﬂux over the cube surface, a new geometry is proposed without sharp corners on the top cube face. Numerical results show that with minor geometrical modiﬁcation (chamfer), the ﬂuid ﬂow structure around the electronic component is radically transformed and the heat transfer rate can be improved. The highest cooling effectiveness improvement is realize for the highest Reynolds number ratio Re H j /Re = 1.5 and for the chamfer height of 4 mm.H
Turbulent flow computation in a circular U-Bend
(University of sciences and technology in Oran, 2015-07-01) Miloud, Abdelkrim
Turbulent flows through a circular 180° curved bend with a curvature ratio of 3.375, defined as the the bend mean radius to pipe diameter is investigated numerically for a Reynolds number of 4.45×104. The computation is performed for a U-Bend with full long pipes at the entrance and at the exit. The commercial ANSYS FLUENT is used to solve the steady Reynolds-Averaged Navier-Stokes (RANS) equations. The performances of standard k-∊ and the second moment closure RSM models are evaluated by comparing their numerical results against experimental data and testing their capabilities to capture the formation and extend this turbulence driven vortex. It is found that the secondary flows occur in the cross-stream half-plane of such configurations and primarily induced by high anisotropy of the cross-stream turbulent normal stresses near the outer bend. Turbulent flow computation in a circular U-Bend. Available from: http://www.researchgate.net/publication/262983316_Turbulent_flow_computation_in_a_circular_U-Bend [accessed Jul 1, 2015].
Réhabilitation et Renforcement des Canalisations sous pression en présence des défauts de surfaces
(University of sciences and technology in Oran, 2015-07-01) Nateche, Tahar
L’objectif de cette étude est d’augment er la durée de vie des structures en acier API 5L X52 comportant des défauts de surface. La méthode des éléments finis (FEM) est utilisée pour analyser le comportement d’un défaut sous forme d’entaille réparée par deux méthodes, un patch composite en boron/époxy et par la technique de perçage. L'effet de la profondeur du défaut et la méthode de réparation sur la variation du facteur d'intensité de contrainte et la contrainte T à la pointe de l’entaille ont été mises en évidence. La méthode de différence de contrainte SDM est utilisée pour calculer la contrainte T et la méthode volumétrique proposée par Pluvinage est utilisée pour calculer les paramètres de rupture effectives Kρc et T. Les résultats de la réparation ont montrés une chute considérable du facteur d’intensité de contrainte et le confinement T. Un soulagement important de la zone endommagée est remarqué pour les éprouvettes réparées par patch composite. La réparation des structures fissurées a pour conséquence d’augmenter la durée de vie ces structures. Cette augmentation est de l’ordre de 72% pour les éprouvettes renforcées par un patch composite et de 24% pour les éprouvettes réparées par la technique de perçage.
Numerical Investigation of Methane-air Mixture with CO2 Dilution (in Fuel, first air and second air inlet) in a Gas Turbine Combustor Chamber
(University of sciences and technology in Oran, 2015-07-06) Guessab, Ahmed
A numerical study on non-premixed combustion methane/air and biogas/air mixture in swirl combustor is performed. In this study the inlet velocity, NO and temperature of fuel and combustor geometry and size are kept to be the same but the effect on the variation of CO2 dilution is observed. Results of this simulation show as the CO2 dilution rate increases, flame temperature, NO and combustion velocity decreases.
Modelled NO2 tropospheric columns at different resolutions versus OMI satellite data: analysis of a 1-year BOLCHEM simulation over Europe
(University of sciences and technology in Oran, 2015-07-06) Aidaoui, Lakhdar
Model simulations of tropospheric NO2 vertical column density are performed using the online-coupled BOLCHEM model. Model output is compared to ozone monitoring instrument (OMI) data from the Tropospheric Emission Monitoring Internet Service (TEMIS) over Europe for the year 2007. European hot-spots (Po Valley and BeNeLux) are simulated at finer resolution and analysed separately, along with the area of Gibraltar. Standard statistical analysis reveals good model performances, even in highly polluted regions, with spatial correlation 0.90 for the whole of Europe, 0.74 for the Po Valley, 0.85 for BeNeLux and 0.79 for Gibraltar. Seasonal analysis shows some dependency on time, with lowest scores in winter, when the satellite product also suffers weaker statistical significance due to the presence of clouds. The increase in resolution is found to affect the spatial correlation more the Po Valley (+23 %) than in BeNeLux (+5 %). This difference is likely to depend on the very different meteorology of the two hot-spots.
Numerical investigation of a standing-wave thermoacoustic device
(University of sciences and technology in Oran, 2015-07-06) Dar Ramdane, Mohamed Zouhir
A numerical study of a standing-wave thermoacoustic engine is presented. The aim of this work is to study the effect of increasing the heat exchangers length on the acoustic power. The analysis of the flow and the prediction of the heat transfer are performed by solving the non linear unsteady Navier-Stocks equations using the finite volume method implemented in -ANSYS CFX- CFD code. The results show an increase in the limit cycle acoustic pressure and power as well as the specific work per cycle with the increase of heat exchangers length.
CONTROLE NON DESTRUCTIF DES MACHINES TOURNANTES : APLICATION A UNE EOLIENNE A AXE VERTICAL
(University of sciences and technology in Oran, 2015-09-09) Cherif Khelifi
Les structures des machines tournantes modernes sont devenues complexes, légères, résistantes et plus flexibles afin de réduire l'inertie, le processus de fabrication et le coût du système. Ces exigences du consommateur rendent ces structures assujetties aux vibrations indésirables nècessitant l’application des normes de fiabilitè et de sècuritè strictes fixèes par des règlementations. Cette situation, pose un défi aux chercheurs et ingénieurs de la dynamique des structures de mieux comprendre les propriétés dynamiques des structures en utilisant tous les moyens disponibles. Les travaux prèsentès dans cette thése portent sur l’exploitation de la conception assistée par ordinateur CAO/DAO dans le cadre de la méthode des éléments finis dans l'analyse mécanique et vibratoire d'une éolienne à axe vertical de type Savonius de faible puissance, original ou fissuré sous des chargements critiques du vent, fondée sur le code universel SolidWorks Simulation. Le but est de proposer une procédure permettant de simuler rapidement le comportement statique et dynamique de la machine sous des conditions de fixation et de chargements critiques de vent. Les travaux de simulation statique ont permis d'accéder aux contraintes équivalentes maximales fixant les conditions de rupture de la structure et les travaux de simulation dynamique ont permis de déterminer les paramètres structuraux fixant les conditions de résonance et le facteur qualité dynamique du système. La stabilité et la fiabilité de la structure semble montrée car le critère de résistance des matériaux de la structure de VonMises et d'amplification dynamique testés sont dans les normes et tenant compte des défaillances de la conception. Les performances mécaniques de résistance simulées de l'aérogénérateur sont fortement influencées par la diffusion des criques longitudinales surtout dans l’arbre lent et aussi par l'augmentation de la force centrifuge due à la vitesse du vent. Seulement, les shifts prédites sur les paramètres structurels, fréquences propres et déformés modales sont faibles, ils sont indétectables dans la pratique pour surveiller l'état de santé de la machine en temps réel. D'autre part, les travaux de modélisation et de simulation des écoulements d'air ont montré que les centrales cheminées solaires de puissance à base d'aérogénérateur sont une technologie renouvelable faisable et rentable au sud algérien riche en ressources énergétiques solaire et éolienne, hydrique, en terrain plat et en matériaux de construction (sable).
ETUDE NUMERIQUE ET EXPERIMENTALE DU COMPORTEMENT TRIBOLOGIQUE DES CONTACTS GLISSANT - Application aux freins à disques
(University of sciences and technology in Oran, 2015-10-25) DJAFRI, Mohammed
Understanding the physical mechanisms resulting from dry sliding contact disc / pads, require an experimental simulation represented by a disc and a pin, under the influence of a number of braking parameters, such as the nature of the disc material and pin, the load applied by the pin in,and the rotational speed of the disc. On the other hand to apprehend the evolution of the tribological behaviour of braking materials, it is a critic to understand the answer of the brake disc materials in them environments especially in the littoral environment where humidity and salinity rate are very high. However the corrosion of the contact emerges because these environments have a large effect on the friction coefficient and the wear of the brake discs materials.For that purpose,a friction experimental model was carried out by means a tribometer disc-on-pin (SRV4, Optimal Instruments Germany), using as disc brake materials: cast iron (FG25), chromium steel (100Cr6) and an aluminum-based composite Al-MMC (A359/SiC ). The pins in all tests were in friction materials, an organic resin-based brake pads material used in automotive Fabia Skoda 1.4, and a composite semi-metallic brakes pads equipped a transport aircraft. The experimental results showed that friction coefficients and the wear rate for all materials were insensitive to increasing normal load and sliding speed.By increasing humidity it observed a formation of water films which behaved as a lubricant at the sliding interface and reduced the friction coefficient and the wear rate. The corrosion due to salt spray had a larger influence on the tribological behaviour of the cast iron and the chromium steel than it did.The numerical investigation offers significant results as those measured by the tribometer. The Al MMC A359/SiC exhibited a better tribological behavior than the other brake disc materials used in this investigation under the given test conditions.
COMPARAISON RANS-LES DANS LES FLAMMES DE PREMELANGE
(University of sciences and technology in Oran, 2015-11-09) BENSAYAH KHALED
Le sujet de cette th ese porte sur la mod elisation et la simulation num erique des ecoulements turbulents compressibles issues des tuy eres convergentes-divergentes de di erentes formes (coniques ou pro l ees). Les travaux ant erieurs ont montr e que les mod eles de turbulence standard etaient incapables de pr edire correctement les ecoulements compressibles avec gradients de pression adverses. Dans ce travail, on se propose d’introduire le mod ele de turbulence a deux equations SST-V de Menter qui n ecessite pas de fonctions d’amortissements pour am eliorer les pr edictions de tels ecoulements. Ce modele a ensuite et e appliqu e pour etudier les probl emes suivants : La simulation des ecoulements turbulents compressibles dans les tuy eres. La simulation des interactions supersoniques onde de choc/couche limite tur-bulente. La simulation de la transition entre d ecollement libre et d ecollement restreint. L’ etude du transfert de chaleur a travers la paroi d’une tuy ere en ecoulements supersoniques. Ces ph enom enes jouent un r^ole fondamental dans la conception et le fonction- nement dans de nombreuses situations tant en a erodynamiques internes et externes, ainsi l’ echau ement par frottement turbulent en supersonique est important et un refroidissement externe devient n ecessaire pour le maintien de l’int egrit e de la surface de la tuy ere. La comparaison des r esultats obtenus avec l’exp erimentation d egage d’un accord tr es satisfaisant, le mod ele de turbulence SST-V apporte une nette am elioration de pr ediction de tels ecoulements.