The stringing regulation on greenhouse gases emissions coupled with the rising fuel price and the growth in aviation transportation have imposed increasing demands on the aircraft industry to develop revolutionary technologies to meet such challenges. Methods of delaying flow separation on aircraft high lift systems have been sought which can lead to an increase in the aircraft performance and ultimately a reduction in aircraft operational costs and its impact on the environment. Synthetic jet actuators are a promising method of delivering flow control for aircraft applications due to their ability to inject momentum to an external flow without net mass flux and their potential in being integrated in MEMS through micro-fabrication with relative ease. It has been demonstrated in many laboratory experiments that synthetic jets are capable of delaying flow separation on aerodynamic bodies of various shapes. However, currently the operating conditions of synthetic jets are mostly chosen by trial-and-error, and thus the flow control effectiveness varies from one experiment to another. In order to deliver an effective flow separation control which achieves a desired control effect at minimum energy expenditure, a better understanding of the fluid mechanics of the behaviour of synthetic jets and the interaction between synthetic jets and a boundary layer are required. The aims of the present research were to achieve such a goal through a series of purposely designed numerical simulations. Firstly, synthetic jets issued from a circular orifice into quiescent air were studied to understand the effect of dimensionless parameters on the formation and the extent of roll-up of vortex rings. The computational results confirmed that the Stokes number determines the strength of vortex roll-up of a synthetic jet. Based on the computational results, a parameter map was produced in which three different operational regimes of synthetic jets were indentified and a criterion for vortex roll-up was also established. A circular synthetic jet issued into a zero-pressure-gradient laminar boundary layer was then investigated. The capability of FLUENT in modelling the key characteristics of synthetic jets was validated using experimental data. The formation and evolution of coherent structures produced by the interaction between synthetic jets and a boundary layer, as well as their near-wall effect in terms of the wall shear stress, were examined. A parameter map illustrating how the appearance of the vortical structures and their corresponding shear stress patterns vary as the synthetic jet operating condition changes was established. In addition, the increase in the wall shear stress relative to the jet-off case was calculated to evaluate their potential separation control effect.Finally, the study moved one step forward to investigate the flow separation control effect of an array of three circular synthetic jets issued into a laminar boundary layer which separates downstream on an inclined plate. The impact of synthetic jets on the boundary layer prior to separation and the extent of flow separation delay on the flap, at a range of synthetic jet operating conditions, were examined and the correlation between them was investigated. Furthermore, the optimal operating conditions for this synthetic jet array in the current study were identified by considering both the flow control effect and the actuator power consumption. The characteristics of the corresponding vortical structures were also examined.The findings from this work have produced some further insights of the behaviour and the interaction between synthetic jets and a boundary layer, which will be useful for ensuring an effective application of synthetic jets in practical settings.

The introduction of phase change material fluid and nanofluid in micro-channel heat sink design can significantly increase the cooling capacity of the heat sink because of the unique features of these two kinds of fluids. To better assist the design of a high performance micro-channel heat sink using phase change fluid and nanofluid, the heat transfer enhancement mechanism behind the flow with such fluids must be completely understood. A detailed parametric study is conducted to further investigate the heat transfer enhancement of the phase change material particle suspension flow, by using the two-phase non-thermal-equilibrium model developed by Hao and Tao (2004). The parametric study is conducted under normal conditions with Reynolds numbers of Re=600-900 and phase change material particle concentrations ¡Ü0.25 , as well as extreme conditions of very low Reynolds numbers (Re < 50) and high phase change material particle concentration (0.5-0.7) slurry flow. By using the two newly-defined parameters, named effectiveness factor and performance index, respectively, it is found that there exists an optimal relation between the channel design parameters, particle volume fraction, Reynolds number, and the wall heat flux. The influence of the particle volume fraction, particle size, and the particle viscosity, to the phase change material suspension flow, are investigated and discussed. The model was validated by available experimental data. The conclusions will assist designers in making their decisions that relate to the design or selection of a micro-pump suitable for micro or mini scale heat transfer devices. To understand the heat transfer enhancement mechanism of the nanofluid flow from the particle level, the lattice Boltzmann method is used because of its mesoscopic feature and its many numerical advantages. By using a two-component lattice Boltzmann model, the heat transfer enhancement of the nanofluid is analyzed, through incorporating the different forces acting on the nanoparticles to the two-component lattice Boltzmann model. It is found that the nanofluid has better heat transfer enhancement at low Reynolds numbers, and the Brownian motion effect of the nanoparticles will be weakened by the increase of flow speed.

Moderate or Intense Low-oxygen Dilution (MILD) combustion is one of combustion technologies which can improve efficiency and reduce emissions simultaneously. This combustion type is characterised by the highly preheated reactant temperature and the relatively small temperature rise during combustion due to the intense dilution of the reactant mixture. These unique combustion conditions give MILD combustion very attractive features such as high combustion efficiency, reduction of pollutant emissions, attenuation of combustion instabilities and flexibility of the flow field. However, our understanding of MILD combustion is not enough to employ the MILD combustion technology further for modern combustion devices. In this thesis, Direct Numerical Simulation (DNS) has been carried out for turbulent MILD combustion under four MILD and classical premixed conditions. A two-phase strategy is employed in the DNS to include the effect of imperfect mixing between fresh and exhaust gases before intense chemical reactions start. In the simulated instantaneous MILD reaction rate fields, both thin and distributed reaction zones are observed. Thin reaction zones having flamelet like characteristics propagate until colliding with other thin reaction zones to produce distributed reaction zones. Also, the effect of such interacting reaction zones on scalar gradient has to be taken into account in flamelet approaches. Morphological features of MILD reaction zones are investigated by employing Minkowski functionals and shapefinders. Although a few local reaction zones are classified as thin shape, the majority of local reaction zones have pancake or tube-like shapes. The representative scales computed by the shapefinders also show a typical volume where intense reactions appear. Given high temperature and existence of radicals in the diluted reactants, both reaction dominated and flame-propagation dominated regions are locally observed. These two phenomena are closely entangled under a high dilution condition. The favourable conditions for these phenomena are investigated by focusing on scalar fluxes and reaction rate. A conditional Probability Density Function (PDF) is proposed to investigate flamelet/non-flamelet characteristics of MILD combustion. The PDF can be obtained by both numerically and experimentally. The PDF shows that MILD combustion still has the direct relationship between reaction rate and scalar gradient, although the tendency is statistically weak due to the distributed nature of MILD reaction zones. Finally, based on the physical aspects of MILD combustion explained in this work, a representative model reactor for MILD combustion is developed. The model reactor is also used in conjunction with the presumed PDF for a mean and filtered reaction rate closure. The results show a good agreement between the modelled reaction rate and the DNS results.

Technical textiles are increasingly being engineered and used in challenging applications, in areas such as safety, biomedical devices, architecture and others, where they must meet stringent demands including excellent and predictable load bearing capabilities. They also form the bases for one of the most widespread group of composite materials, fibre reinforced polymer-matrix composites (PMCs), which comprise materials made of stiff and strong fibres generally available in textile form and selected for their structural potential, combined with a polymer matrix that gives parts their shape. Manufacturing processes for PMCs and technical textiles, as well as parts and advanced textile structures must be engineered, ideally through simulation, and therefore diverse properties of the textiles, textile reinforcements and PMC materials must be available for predictive simulation. Knowing the detailed geometry of technical textiles is essential to predicting accurately the processing and performance properties of textiles and PMC parts. In turn, the geometry taken by a textile or a reinforcement textile is linked in an intricate manner to its constitutive behaviour. This thesis proposes, investigates and validates a general numerical tool for the integrated and comprehensive analysis of textile geometry and constitutive behaviour as required toward engineering applications featuring technical textiles and textile reinforcements. The tool shall be general with regards to the textiles modelled and the loading cases applied. Specifically, the work aims at fulfilling the following objectives: 1) developing and implementing dedicated simulation software for modelling textiles subjected to various load cases; 2) providing, through simulation, geometric descriptions for different textiles subjected to different load cases namely compaction, relaxation and shear; 3) predicting the constitutive behaviour of the textiles undergoing said load cases; 4) identifying parameters affecting the textile geometry and constitutive behaviour under evolving loading; 5) validating simulation results with experimental trials; and 6) demonstrating the applicability of the simulation procedure to textile reinforcements featuring large numbers of small fibres as used in PMCs. As a starting point, the effects of reinforcement configuration on the in-plane permeability of textile reinforcements, through-thickness thermal conductivity of PMCs and in-plane stiffness of unidirectional and bidirectional PMCs were quantified systematically and correlated with specific geometric parameters. Variability was quantified for each property at a constant fibre volume fraction. It was observed that variability differed strongly between properties; as such, the simulated behaviour can be related to variability levels seen in experimental measurements. The effects of the geometry of textile reinforcements on the aforementioned processing and performance properties of the textiles and PMCs made from these textiles was demonstrated and validated, but only for simple cases as thorough and credible geometric models were not available at the onset of this work. Outcomes of this work were published in a peer-reviewed journal [101]. Through this thesis it was demonstrated that predicting changes in textile geometry prior and during loading is feasible using the proposed particle-based modelling method. The particle-based modelling method relies on discrete mechanics and offers an alternative to more traditional methods based on continuum mechanics. Specifically it alleviates issues caused by large strains and management of intricate, evolving contact present in finite element simulations. The particle-based modelling method enables credible, intricate modelling of the geometry of textiles at the mesoscopic scale as well as faithful mechanical modelling under load. Changes to textile geometry and configuration due to the normal compaction pressure, stress relaxation, in-plane shear and other types of loads were successfully predicted. During simulation, particles were moved randomly until a stable state of minimum strain energy in the system was reached; as particles moved upon iteration, the configuration of fibres in the textile changed under constant boundary conditions. Then boundary conditions were altered corresponding to strains imposed on the textile, and the system was iterated again towards a new state of minimum strain energy. The Metropolis algorithm of the Monte Carlo method was adopted in this specific implementation. The method relies on a statistical approach implemented in computational algorithms. In addition to geometrical modelling, the proposed particle-based modelling method enables the prediction of major elements of the constitutive behaviour of textiles and textile reinforcements. In fact, prediction of the constitutive behaviour is integral to the prediction of the meso-scale geometry. Simulation results obtained from the proposed particle-based modelling method were validated experimentally for yarns, single-layer textiles and multi-layer textiles undergoing compaction. Validation work showed that the particle-based modelling method replicates reality very faithfully, and it also showed the suitability of including Gutowski's function along with Hertz' function for representing lateral compaction of yarns. The procedure and results were accepted in final form for publication in a peer reviewed journal [104]. The capability of the proposed particle-based modelling method towards replicating the time-dependent relaxation and reconfiguration of woven textiles subjected to compaction loading was investigated. The capability, which was demonstrated for single and double-layers of plain woven textiles, is intrinsic to the modelling method. The method is unique in the fact that in contrary to work previously reported in the literature, it models the compaction and the relaxation seamlessly in the same simulations and environment. This work is being finalised towards submission for publication in a peer reviewed journal [103]. The proposed particle-based modelling method was also used for modelling in-plane shear in woven textiles. Simulation results were validated experimentally for a single-layer plain woven textile. Validation work showed that the particle-based modelling method reproduces experimental data and published trends very well. A novel algorithm for modelling friction was introduced, leading to results being obtained from a significantly less computationally demanding procedure in these simulations. This work was submitted for publication in a peer reviewed journal [102]. Finally the thesis discusses early work towards the application of the method to carbon fibre fabrics through the description of expansion algorithm (EA) to be used in modelling textiles made of yarns featuring very large numbers of fibres. Furthermore, additional modelling work is presented towards further manufacturing process involving technical textiles, namely textile bending and punching. The latter part is presented as early steps towards future work.

Ce travail de thèse porte sur la modélisation du procédé de sertissage de contacts électriques sur des câbles à destination d'applications aéronautiques et de la tenue à l'arrachement des contacts sertis. Le sertissage est un assemblage par déformation plastique du contact électrique (composant) sur un câble multibrin. Deux types de technologies de sertissage sont traités. La technologie cuivre, couramment utilisée chez les industriels, met en jeux un contact de cuivre et un câble de cuivre composé de 19 brins. La technologie aluminium, mise au point ces dernières années pour limiter le poids des aéronefs, est caractérisée par l'assemblage d'un câble de 7 brins avec un contact en cuivre au travers d'une liaison électrique et d'une liaison d'étanchéité. Dans un premier temps, la caractérisation des paramètres de loi de comportement élastoplastique des matériaux est faite. La détermination des moyens d'essais appropriés, directement impactée par la faible dimension (ordre millimétrique) de nos échantillons, est suivie d'une analyse détaillée des résultats. Le recours à l'analyse inverse d'essais non normalisés est privilégié. Les résultats des différentes analyses sont validés indépendamment du sertissage. Dans un second temps, les étapes de mise au point des simulations de sertissage sont abordées de façon précise. Pour ce type de modèles fortement multi domaines, l'étude de l'influence des interactions est conduite. La détermination des paramètres de profondeur de sertissage est développée pour chaque technologie. Les premiers résultats de simulation sont discutés pour réduire les temps de calculs. Finalement, le modèle numérique développé est utilisé pour simuler le sertissage de contacts et l'arrachement de contacts sertis dans différentes configurations. L'étude de paramètres géométriques (diamètre des brins, diamètres des contacts, pas de torsadage des câbles), rhéologiques (cuivre standard, ayant subi un recuit insuffisant ou trop important) ou mécaniques (sous-sertissage, sur-sertissage) est faite pour vérifier l'influence sur les efforts de sertissage et les mécanismes de rupture à l'arrachement. Cette étude complète a pour objectif de valider des domaines de validité du sertissage. Celles-ci permettront aux industriels de vérifier la validité d'un sertissage en temps réel, en les comparant aux courbes d'efforts expérimentales par l'intermédiaire d'une pince électronique / This thesis focuses on the modeling of the aeronautical electrical contact crimping process for aircraft applications and the crimped contact mechanical holding. Electrical crimping is a plastic deformation process of a contact (component) on a multi-strand wire. Two types of crimping technologies are studied. The copper technology, widely used in the industry, is characterized by the assembly of a copper contact and a 19 strands copper cable. The aluminum technology, which has been recently developed to reduce the aircraft weight, is characterized by the assembly of a copper contact with a 7 strands cable through two electrical and sealing crimpings. At first, the elastoplastic parameters characterizations of the materials constitutive laws are made. The appropriate testing facilities determination, directly impacted by the small size (millimeter order) of our samples, is followed by a detailed results analysis. The non-standard tests inverse analysis use is preferred. The whole analyzes results are validated, regardless of the process itself. In a second step, the crimping simulation development steps are accurately performed. For this highly multi-model fields type, the study of the interactions influence is conducted. Determining the crimping indentation depth parameters is developed for each technology. The first simulation results are discussed to reduce computation time. Finally, the developed numerical model is used to simulate the contacts crimping and the mechanical holding over various configurations. The geometrical (strands diameter, contact diameter, twisting thread cables), rheological (standard copper having been insufficiently or excessively annealed) or mechanical (under-crimping, over-crimping) parameters study are made to check their influences on the crimping forces and the failure mechanisms while pulling. This study aims to validate the crimping efficiency. The manufacturers could be able to check in real time the crimping validity by comparing the experimental crimping force curves to validity curves integrated in an electronic crimping tool.

Aujourd’hui, l’accès à l’espace constitue un enjeu scientifique, technologique et politique d’importance. Il est primordial de pouvoir garantir le succès de la mise sur orbite des satellites pour un coût de transport minimal. Les lanceurs tels qu’Ariane 5 sont soumis à des fluctuations de pression pouvant induire des efforts instationnaires repris par les vérins du moteur Vulcain. Ces efforts s’exercent notamment dans la zone décollée du culot du lanceur normalement à l’axe de la poussée et sont qualifiés de charges latérales. Du point de vue de la simulation numérique, l’étape de discrétisation des éléments technologiques du lanceur rend la génération de maillages structurés particulièrement complexe. Cette constatation conduit à la présente étude. Dans le but d’évaluer l’influence des effets technologiques sur la prévision des charges latérales pour des configurations réalistes de lanceur, la thématique des frontières immergées est étudiée. L’objectif est de développer une stratégie numérique permettant d’accroître le niveau de complexité de la géométrie considérée tout en conservant la précision des résultats des études antérieures sur des configurations simplifiées. Cette stratégie s’inscrit dans le cadre de simulations numériques ZDES d’écoulements massivement décollés d’arrière-corps, à haut nombre de Reynolds et en régime compressible. Les capacités de la méthodologie développée sont évaluées sur des cas tests numériques canoniques avant d’être éprouvées sur des configurations simplifiées de lanceur. Enfin, l’effet de cette stratégie sur la prévision des charges latérales est étudié. / Nowadays, access to space has become a great issue in scientific, technological and political framework. It is essential to ensure the success of the placing of orbiting satellites with a minimal flight cost. Launchers, as the Ariane 5 space launcher, are subject to pressure fluctuations which can lead to unsteady loads on the actuators of the Vulcain engine. These loads occur especially in the separated zone of the launcher base flow and act normally to the thrust axis. They are referred to as side loads. From the numerical simulation perspective, the launcher technological elements discretization process makes the generation of structured mesh particularly difficult. The present study lies within such a framework. In order to assess the influence of the technological effects on the side loads prediction for realistic launcher configurations, immersed boundaries are studied. The aim is to develop a numerical strategy able to increase the level of geometrical complexity of the geometry at stake while maintaining the accuracy of the results of previous studies on simplified configurations. This strategy fits into numerical simulations of ZDES type of separating/reattaching flows at high Reynolds number and compressible regime. The abilities of the methodology are first assessed on canonical numerical test cases. Then, the strategy is applied on simplified launcher configurations. Finally, the effect of this strategy on the side loads prediction is assessed.

Concrete-Filled Steel Tubular (CFST) columns are increasingly being used because of their many advantages, including high strength, high ductility, and higher fire resistance than conventional steel or concrete columns of the same size. In order to maximise the advantages of CFST column, composite action of the column should be ensured. In realistic structures, the load is not directly applied to the entire CFST column section and is introduced from the beam-column connection. Simple shear connections, which are usually preferred in constructions, are only connected to the external face of the steel tube and there is an issue about how this load is introduced to the concrete core, through the bond at the steel/concrete interface. There are fundamental errors in the load introduction mechanism assumed in various current design methods. Furthermore, based on this erroneous load introduction mechanism, construction methods, such as placing shear connectors inside the steel tube or using through-column plates, are recommended to ensure complete load introduction. However, these methods are either impractical or uneconomical. The aim of this project, therefore, is to develop a thorough understanding of the load introduction mechanism and to use the new insights to assess design implications, for both ambient temperature and fire safety design. The research has been conducted through physical testing, extensive numerical modelling and detailed analytical derivations. A series of new load introduction tests, in which square CFST columns are loaded through simple fin plate connections, are carried out. These tests are designed to investigate the effects of changing column lengths below and above the connection, the effectiveness of using shear connectors inside the steel tube below the connection (according to Eurocode 4) and using a cap plate on the column top for load introduction into the concrete core. The test results indicate that the connection load is introduced to the concrete core through the column length above and within the connection or the cap plate on top of the column. This is different from the currently assumed mechanism of load introduction which assumes that load introduction occurs from underneath the connection. Below the connection, there is transfer of forces from the steel tube to the concrete core, but the total force in the column remains unchanged. Consequently, using shear connectors below the connection is ineffective in increasing CFST column strength, as has been demonstrated by the tests. The physical tests are supplemented by an extensive numerical parametric study to check whether the conclusions are applicable to different design conditions and to provide data for development of a new design method. The parameters include: section geometry (square, circular, and rectangular), position of load application to CFST column, dimensions of the square column cross-section, steel tube thickness, connection length, column length above the connection, column length below the connection, and maximum bond stress at the steel-concrete interface. The numerical simulation results confirm the experimental observations. Furthermore, the numerical simulation results indicate that the entire column length and the entire perimeter of the steel-concrete interface above and within the connection are engaged in load introduction. Based on the experimental and numerical simulation results, a simple calculation method has been proposed to calculate the column cross-section resistance under compression. According to this equation, the concrete compression resistance to the composite column is the minimum of the plastic resistance or the bond strength within and above the connection. This gives rise to a “concrete strength reduction factor” to account for incomplete load introduction, being the ratio of the load introduced to the concrete core through the interface bond to the concrete plastic resistance. Based on the new load introduction calculation method and using representative values of column dimensions and concrete cylinder strength, it has been demonstrated that complete load introduction can be achieved in almost all practical arrangements of concrete-filled tubular construction. For slender CFST column design, this concrete strength reduction factor should also be used to calculate the CFST column cross-section flexural stiffness. For a CFST column under combined axial compression and bending, the concrete strength reduction factor should be used when calculating the compression force, but should be ignored when calculating the bending resistance because composite action is not necessary for bending of the CFST column. The new load introduction mechanism induces additional compression in the concrete core and possible tension in the steel tube above the connection. Therefore, the concrete core of the column above the connection in multi-storey construction should be designed to resist the additional compression force. For the steel tube, in ambient temperature design, the steel contribution ratio (steel section resistance/plastic resistance of composite cross-section) of the top floor column should be at least 0.25. For fire resistance design, the steel contribution ratio of the top floor columns, those on the floor below the top floor, and those two floors below the top floor, should not be less than 0.5, 0.33, and 0.25 respectively.

Les suspensions de grains rigides dans un fluide constituent une classe de fluides complexes présentant une rhéologie riche. Même dans les cas simples où le fluide est Newtonien, et les grains sphériques, non Browniens et non colloïdaux, les comportements macroscopiques observés restent mal compris, en particulier dans le cas de suspensions concentrées. Dans ces matériaux, la complexité de la dynamique provient de l'équilibre subtil qui se met en place entre les interactions de nature hydrodynamiques portées par le fluide interstitiel et les forces de contact entre les grains. Dans ce travail, nous abordons ces questions sous l'angle de la simulation numérique discrète, dans le cadre du cisaillement simple de suspensions concentrées 2D. Nous modélisons les efforts hydrodynamiques par des interactions de lubrification de paires, couplées à un modèle de contact éventuellement frottant. L'inertie des grains n'est pas négligée. Nous accédons à tous les coefficients du tenseur des contraintes, ce qui permet de mesurer pression, contrainte de cisaillement, et différence des contraintes normales, ainsi que les viscosités associées. L'étude du cisaillement à volume constant nous permet de mettre en évidence l'existence d'une transition de rhéo-épaississement entre un régime visqueuse à bas taux de cisaillement (contrainte proportionnelle au taux de cisaillement) et un régime inertiel à haut taux de cisaillement (contrainte proportionnelle au carré du taux de cisaillement), selon que la contrainte soit dominée par les interactions de lubrification ou par l'inertie des grains. Le taux de cisaillement de transition mesuré est compatible avec un argument d'échelle pour la contrainte, tenant compte de sa divergence avec la fraction volumique. Des simulations du cisaillement à pression constante nous permettent ensuite d'explorer le comportement de suspensions très concentrées (jusqu'à 1% de la fraction volumique de blocage théorique) dans leur domaine d'écoulement visqueux. Nous montrons que la rhéologie du mélange peut se décrire sous la forme d'une loi d'écoulement dépendante du seul nombre visqueux, construit comme le rapport entre un temps caractéristique de réarrangement local des grains sous l'effet des forces visqueuses et un temps typique de convection imposé par l'écoulement. Cette description nous permet de caractériser précisément la divergence de la contrainte avec la concentration en particules. Enfin, nous mesurons la microstructure stationnaire développée dans l'écoulement. Nous mettons en évidence une anisotropie importante des contacts générés, et discutons l'évolution de cette distribution avec la concentration du mélange / Suspensions of rigid grains in a fluid constitute a class of complex fluids that present a rich rheology. Even simpler cases of non-Brownian, non-colloidal spherical grains suspended in a Newtonian fluid feature macroscopic behaviours that are still not completely understood, especially when the concentration of particles is high. In these materials, the complexity of the dynamic is the result of the subtle balance that occurs between hydrodynamic interactions mediated by the interstitial fluid, and contact forces between grains. In this work, we tackle those questions from the point of view of discrete numerical simulations, in the context of the simple shear of 2D concentrated suspensions. Hydrodynamic interactions are modelled by pair lubrication, coupled with a possibly frictional contact law. Grains inertia is not neglected. We have access to the whole stress tensor, allowing the measure of pressure, shear stress, and normal stress difference, as well as their associated viscosities. The study of constant volume simple shear shows the existence of a shear-thickening transition between a viscous regime at low shear rate (stress proportional to the shear rate) and an inertial regime at high shear rate (stress proportional to the shear rate squared), depending on whether the stress is dominated by lubrication interactions or grains inertia. The position of the measured transition shear rate is consistent with a scaling argument for the stress that takes its divergence with concentration into account. Constant pressure simple shear simulations then let us explore the behaviour of very concentrated suspensions (up to 1% to the theoretical jamming fraction) in their viscous flow domain. We show that the rheology of the mix can then be described by a flow law that is only function of the viscous number, constructed as the ratio of a typical time for the local rearrangement of grains subjected to viscous forces, and a convection time consistent with the imposed flow. This allows a precise characterization of the divergence of stress with particles concentration. At last, we measure the stationary microstructure that develops within the flow. We show an important anisotropy of contacts, and discuss the evolution of this distribution with the concentration of the suspension

Este trabalho tem como propósito analisar o modelo matemático baseado na Teoria Elementar da Plasticidade (TEP) para o Forjamento em Matriz Aberta (FMA) de tarugos cilíndricos com o intuito de obter um eixo vazado para a utilização em aerogeradores. Foram realizadas simulações computacionais pelo Método dos Elementos Finitos (FEM) com efeito de comparação, utilizando o software Simufact.Forming 11.0. Foi exposto a sequência de cálculos e as interações realizadas para a construção de um modelo matemático a partir da TEP. Esse modelo matemático foi aplicado para os dois primeiros recalques em um tarugo cilíndrico vazado. Ambos os recalques foram executados no processo de Forjamento em Matriz Aberta. Tanto com o procedimento matemático baseado na TEP, quanto na simulação numérica baseado no FEM, foram obtidos os valores de distribuição de deformações, de distribuição de tensões e de forças de compressão requeridos pela prensa de forjamento para ambos os recalques. Com a conclusão dos experimentos físicos foi constatado que os valores das forças obtidos pela Teoria Elementar da Plasticidade (TEP) e pelo Método dos Elementos Finitos (FEM) variaram aproximadamente entre 5 a 15% em relação aos valores experimentais, possibilitando fazer comparações com variações e alterações na metodologia do processo. Observou-se que as regiões que apresentaram maiores concentrações de deformações equivalentes e tensões na direção z pelo modelo matemático (TEP) coincidiram com as regiões de maiores concentrações encontradas no software de simulação numérica (FEM). Desta forma, estima-se para a geometria estudada que a TEP pode ser empregada como uma ferramenta de simulação eficiente no processo de Forjamento em Matriz Aberta. / This paper aims to analyze the mathematical model based on the Plasticity Elementary Theory (TEP) for the Open Die Forging of cylindrical billets in order to get a hollow shaft for using in wind generator. Computer simulations were performed by the Finite Element Method (FEM) with purpose of comparison, using the software Simufact.Forming 11.0. It was exposed the calculations sequence and performed interactions to make a mathematical model from the TEP. This mathematical model was applied for the first two upsetting in a hollow cylindrical billet. Both upsetting were executed in the process of Open Die Forging. Both the mathematical method based in the TEP as the numerical simulation based in the FEM, it were obtained the value of the strains distribution, the stresses distribution and the compressive force required by the forging press for both upsetting. With the physical experiments concluded, it was found that the forces values obtained by the TEP and by the FEM ranged approximately between 5 and 15% compared to the experimental values, allowing make comparisons with variations and changes in the process methodology. It was observed that regions where showed higher concentrations of equivalent strains and stresses in the z direction by the mathematical model (TEP) coincided with the regions of higher concentrations found numerical simulation software (FEM). It’s demonstrated for the geometry studied that the TEP can be employed as a simulation efficient tool in the process of Open Die Forging.

Escoamentos sobre superfícies côncavas, como os que ocorrem no intradorso de uma pá de turbina, estão sujeitos à instabilidade centrífuga. A esse tipo de configuração atribui-se possibilidade de transição à turbulência devido a formação dos vórtices de Görtler. Estudos são propostos no sentido de identificar possível influência do gradiente de pressão nos mecanismos de desenvolvimento desses vórtices e sua interação com outras perturbações na transição. O processo de investigação dá-se numericamente por meio do desenvolvimento e uso de um código numérico paralelizado e de alta ordem de precisão. Resultados obtidos caracterizam o gradiente de pressão adverso como mais instável se comparado ao caso neutro ou favorável. Variações no gradiente de pressão não se mostram eficientes no processo de controle da instabilidade. Ao gradiente adverso atribui-se antecipação da região de saturação dos vórtices. Ressalta-se ainda a natureza desestabilizadora do gradiente adverso quanto aos mecanismos de amplificação dos modos varicoso e sinuoso associados à instabilidade secundária. / Flows over concave surfaces are subjected to centrifugal instability and may transition to turbulence. Studies are conducted to identify the role of the external pressure gradient on the development of the Görtler vortices and their interaction with other flow disturbances. Numerical simulations are carried out by the development and use of an in-house parallel code with highorder of accuracy. Adverse pressure gradient configurations are observed to be more unstable than the neutral and favourable ones. Pressure gradient variations do not prove to be an efficient way to control the centrifugal instability. The destabilizing behaviour that is observed by the adverse pressure gradient justifies its influence on the anticipation of the saturation of the primary vortices and growth of the sinuous and varicose secondary modes.