Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta uma família de novos métodos numéricos euleriano-lagrangeanos localmente conservativos para leis de conservação hiperbólicas escalares. Estes métodos não utilizam soluções analíticas de problemas de Riemann e são bastante precisos na captura de saltos nas soluções. Estes métodos foram introduzidos, implementados computacionalmente e testados para leis de conservação em uma e duas dimensões espaciais. Foram consideradas as equações de Burgers e Buckley-Leverett. Nossos experimentos numéricos indicaram que os métodos são pouco difusivos e que as soluções não apresentam oscilações espúrias.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este trabalho apresenta uma família de novos métodos numéricos euleriano-lagrangeanos localmente conservativos para leis de conservação hiperbólicas escalares. Estes métodos não utilizam soluções analíticas de problemas de Riemann e são bastante precisos na captura de saltos nas soluções. Estes métodos foram introduzidos, implementados computacionalmente e testados para leis de conservação em uma e duas dimensões espaciais. Foram consideradas as equações de Burgers e Buckley-Leverett. Nossos experimentos numéricos indicaram que os métodos são pouco difusivos e que as soluções não apresentam oscilações espúrias.

Lie-detection has been an evergreen and evolving subject. Polygraph techniques have been the most popular and successful technique till date. The main drawback of the polygraph is that good results cannot be attained without maintaining a physical contact, of the subject under test. In general, this physical contact would induce extra consciousness in the subject. Also, any sort of arousal in the subject triggers false positives while performing the traditional polygraph based tests. With all these drawbacks in the polygraph, also, due to rapid developments in the fields of computer vision and artificial intelligence, with newer and faster algorithms, have compelled mankind to search and adapt to contemporary methods in lie-detection. Observing the facial expressions of emotions in a person without any physical contact and implementing these techniques using artificial intelligence is one such method. The concept of magnifying a micro expression and trying to decipher them is rather premature at this stage but would evolve in future. Magnification using EVM technique has been proposed recently and it is rather new to extract these micro expressions from magnified EVM based on HOG features. Till date, HOG features have been used in conjunction with SVM, and generally for person/pedestrian detection. A newer, simpler and contemporary method of applying EVM with HOG features and Back-propagation Neural Network jointly has been introduced and proposed to extract and decipher the micro-expressions on the face. Micro-expressions go unnoticed due to its involuntary nature, but EVM is used to magnify them and makes them noticeable. Emotions behind the micro-expressions are extracted and recognized using the HOG features \& Back-Propagation Neural Network. One of the important aspects that has to be dealt with human beings is a biased mind. Since, an investigator is also a human and, he too, has to deal with his own assumptions and emotions, a Neural Network is used to give the investigator an unbiased start in identifying the true emotions behind every micro-expression. On the whole, this proposed system is not a lie-detector, but helps in detecting the emotions of the subject under test. By further investigation, a lie can be detected. / This thesis uses a magnification technique to magnify the subtle, faint and spontaneous facial muscle movements or more precisely, micro-expressions. This magnification would help a system in classifying them and estimating the emotion behind them. This technique additionally magnifies the color changes, which could be used to extract the pulse without a physical contact with the subject. The results are presented in a GUI. / Gautam: +46(0)739528573, +91-9701534064 Tushal: +46(0)723219833, +91-9000242241 Venu: +46(0)734780266, +91-9298653191 Sai: +91-9989410111

Problems governed by partial differential equations (PDEs) in deformable domains, t Rd; d = 2; 3; are of fundamental importance in science and engineering. They are of particular relevance in the design of many engineering systems e.g., aircrafts and bridges as well as to the analysis of several biological phenomena e.g., blood ow in arteries. However, developing numerical scheme for such problems is still very challenging even when the deformation of the boundary of domain is prescribed a priori. Possibility of excessive mesh distortion is one of the major challenge when solving such problems with numerical methods using boundary tted meshes. The arbitrary Lagrangian- Eulerian (ALE) approach is a way to overcome this difficulty. Numerical simulations of convection-dominated problems have for long been the subject to many researchers. Galerkin formulations, which yield the best approximations for differential equations with high diffusivity, tend to induce spurious oscillations in the numerical solution of convection dominated equations. Though such spurious oscillations can be avoided by adaptive meshing, which is computationally very expensive on ne grids. Alternatively, stabilization methods can be used to suppress the spurious oscillations. In this work, the considered equation is designed within the framework of ALE formulation. In the first part, Streamline Upwind Petrov-Galerkin (SUPG) finite element method with conservative ALE formulation is proposed. Further, the first order backward Euler and the second order Crank-Nicolson methods are used for the temporal discretization. It is shown that the stability of the semi-discrete (continuous in time) ALE-SUPG equation is independent of the mesh velocity, whereas the stability of the fully discrete problem is unconditionally stable for implicit Euler method and is only conditionally stable for Crank-Nicolson time discretization. Numerical results are presented to support the stability estimates and to show the influence of the SUPG stabilization parameter in a time-dependent domain. In the second part of this work, SUPG stabilization method with non-conservative ALE formulation is proposed. The implicit Euler, Crank-Nicolson and backward difference methods are used for the temporal discretization. At the discrete level in time, the ALE map influences the stability of the corresponding discrete scheme with different time discretizations, and it leads to schemes where conservative and non-conservative formulations are no longer equivalent. The stability of the fully discrete scheme, irrespective of the temporal discretization, is only conditionally stable. It is observed from numerical results that the Crank-Nicolson scheme induces high oscillations in the numerical solution compare to the implicit Euler and the backward difference time discretiza-tions. Moreover, the backward difference scheme is more sensitive to the stabilization parameter k than the other time discretizations. Further, the difference between the solutions obtained with the conservative and non-conservative ALE forms is significant when the deformation of domain is large, whereas it is negligible in domains with small deformation. Finally, the local projection stabilization (LPS) and the higher order dG time stepping scheme are studied for convection dominated problems. The analysis is based on the quadrature formula for approximating the integrals in time. We considered the exact integration in time, which is impractical to implement and the Radau quadrature in time, which can be used in practice. The stability and error estimates are shown for the mathematical basis of considered numerical scheme with both time integration methods. The numerical analysis reveals that the proposed stabilized scheme with exact integration in time is unconditionally stable, whereas Radau quadrature in time is conditionally stable with time-step restriction depending on the ALE map. The theoretical estimates are illustrated with appropriate numerical examples with distinct features. The second order dG(1) time discretization is unconditionally stable while Crank-Nicolson gives the conditional stable estimates only. The convergence order for dG(1) is two which supports the error estimate.

Les écoulements diphasiques jouent un rôle prépondérant dans les moteurs-fusées à ergols liquides cryogéniques, équipant par exemple les lanceurs de la famille Ariane. L'étude expérimentale de tels engins propulsifs étant complexe et onéreuse, disposer d'outils numériques à même de simuler fidèlement leur fonctionnement se révèle être un objectif aussi important qu'ambitieux. La difficulté majeure réside dans le caractère fortement multi-échelles du problème, si bien qu’aucune approche numérique existante n'est capable à elle seule de décrire parfaitement l'ensemble des échelles liquides. Partant de ce constat, les travaux présentés dans cette thèse visent à mettre en place une stratégie de couplage entre des modèles bien adaptés aux différentes topologies d'écoulement diphasique, et ce dans le cadre de la plateforme logicielle multi-physique CEDRE développée par l'ONERA. La démarche adoptée consiste précisément à coupler un modèle à interface diffuse de type ``4 équations'' pour les zones à phases séparées, et un modèle cinétique eulérien pour la phase dispersée, rendant ainsi possible la description de l’atomisation primaire. Par ailleurs, les conditions sévères qui règnent dans les moteurs cryotechniques, où de forts gradients de température, vitesse et densité sont rencontrés, mettent à l'épreuve la robustesse des méthodes numériques. Une nouvelle méthode MUSCL multipente pour maillages non structurés généraux a ainsi été développée, permettant d’améliorer la robustesse et la précision des schémas de discrétisation spatiale. L’ensemble de la stratégie de couplage est finalement appliquée à la simulation du banc Mascotte de l'ONERA pour la combustion cryotechnique. / Two-phase flows play a significant role for the proper functioning of cryogenic liquid-propellant rocketengines, such as those that equip the launchers of the Ariane family. Since the experimental investigationof such propulsion devices is complex and expensive, developing numerical tools able to accuratelysimulate their functioning, is a crucial but nonetheless ambitious objective. The major difficulty is due tothe multiscale nature of the problem, as a result of which there is currently no numerical approach ableto perfectly describe all the liquid scales on its own. Based on this observation the work presented in thisthesis aims at setting up a coupling strategy between models well-adapted to each two-phase flowtopology, in the framework of the ONERA’s multiphysics CEDRE software. The approach adoptedprecisely consists in coupling a 4-equation diffuse interface model for the separated phases and aeulerian kinetic model for the dispersed phase, thus making it possible to describe primary atomization.Besides, the harsh conditions within cryogenic rocket engines, where large temperature, velocity anddensity gradients are encountered, severely challenge the robustness of numerical methods. A newmultislope MUSCL method for general unstructured meshes is thus developed in order to improve therobustness and accuracy of space discretization schemes. The whole coupling strategy is finally appliedto the numerical simulation of the ONERA’s Mascotte test bench for cryogenic combustion research.

In power plants using large utility coal-fired boilers for generation of electricity the coal is pulverised in coal mills and then it has to be pneumatically transported and distributed to a larger number of burners (e.g. 30-40) circumferentially arranged in several rows around the burning chamber of the boiler. Besides the large pipework flow splitting devices are necessary for distribution of an equal amount of pulverised fuel (PF) to each of the burners. So called trifurcators (without inner fittings or guiding vanes) and ''riffle'' type bifurcators are commonly used to split the gas-coal particle flow into two or three pipes/channels with an equal amount of PF mass flow rate in each outflow cross section of the flow splitting device. These PF flow splitting devices are subject of a number of problems. First of all an uneven distribution of PF over the burners of a large utility boiler leads to operational and maintenance problems, increased level of unburned carbon and higher rates of NOX emissions. Maldistribution of fuel between burners caused by non uniform concentration of the PF (particle roping) in pipe and channel bends prior to flow splitting devices leads to uncontrolled differences in the fuel to air ratio between burners. This results in localised regions in the furnace which are fuel rich, where insufficient air causes incomplete combustion of the fuel. Other regions in the furnace become fuel lean, forming high local concentrations of NOX due to the high local concentrations of O2. Otherwise PF maldistribution can impact on power plant maintenance in terms of uneven wear on PF pipework, flow splitters as well as the effects on boiler panels (PF deposition, corrosion, slagging). In order to address these problems in establishing uniform PF distribution over the outlet cross sections of flow splitting devices in the pipework of coal-fired power plants the present paper deals with numerical prediction and analysis of the complex gas and coal particle (PF) flow through trifurcators and ''riffle'' type bifurcators. The numerical investigation is based on a 3-dimensional Eulerian- Lagrangian approach (MISTRAL/PartFlow-3D) developed by Frank et al. The numerical method is capable to predict isothermal, incompressible, steady gas- particle flows in 3-dimensional, geometrically complex flow geometries using boundary fitted, block-structured, numerical grids. Due to the very high numerical effort of the investigated gas-particle flows the numerical approach has been developed with special emphasis on efficient parallel computing on clusters of workstations or other high performance computing architectures. Besides the aerodynamically interaction between the carrier fluid phase and the PF particles the gas-particle flow is mainly influenced by particle-wall interactions with the outer wall boundaries and the inner fittings and guiding vanes of the investigated flow splitting devices. In order to allow accurate quantitative prediction of the motion of the disperse phase the numerical model requires detailed information about the particle-wall collision process. In commonly used physical models of the particle-wall interaction this is the knowledge or experimental prediction of the restitution coefficients (dynamic friction coefficient, coefficient of restitution) for the used combination of particle and wall material, e.g. PF particles on steel. In the present investigation these parameters of the particle-wall interaction model have been obtained from special experiments in two test facilities. Basic experiments to clarify the details of the particle-wall interaction process were made in a test facility with a spherical disk accelerator. This test facility furthermore provides the opportunity to investigate the bouncing process under normal pressure as well as under vacuum conditions, thus excluding aerodynamically influences on the motion of small particles in the near vicinity of solid wall surfaces (especially under small angles of attack). In this experiments spherical glass beads were used as particle material. In a second test facility we have investigated the real impact of non-spherical pulverised fuel particles on a steel/ceramic target. In this experiments PF particles were accelerated by an injector using inert gas like e.g. CO2 or N2 as the carrier phase in order to avoid dust explosion hazards. The obtained data for the particle-wall collision models were compared to those obtained for glass spheres, where bouncing models are proofed to be valid. Furthermore the second test facility was used to obtain particle erosion rates for PF particles on steel targets as a function of impact angles and velocities. The results of experimental investigations has been incorporated into the numerical model. Hereafter the numerical approach MISTRAL/PartFlow-3D has been applied to the PF flow through a ''riffle'' type bifurcator. Using ICEM/CFD-Hexa as grid generator a numerical mesh with approximately 4 million grid cells has been designed for approximation of the complex geometry of the flow splitting device with all its interior fittings and guiding vanes. Based on a predicted gas flow field a large number of PF particles are tracked throughout the flow geometry of the flow-splitter. Besides mean quantities of the particle flow field like e.g. local particle concentrations, mean particle velocities, distribution of mean particle diameter, etc. it is now possible to obtain information about particle erosion on riffle plates and guiding vanes of the flow splitting device. Furthermore the influence of different roping patterns in front of the flow splitter on the uniformness of PF mass flow rate splitting after the bifurcator has been investigated numerically. Results show the efficient operation of the investigated bifurcator in absence of particle roping, this means under conditions of an uniform PF particle concentration distribution in the inflow cross section of the bifurcator. If particle roping occurs and particle concentration differs over the pipe cross section in front of the bifurcator the equal PF particle mass flow rate splitting can be strongly deteriorated in dependence on the location and intensity of the particle rope or particle concentration irregularities. The presented results show the importance of further development of efficient rope splitting devices for applications in coal-fired power plants. Numerical analysis can be used as an efficient tool for their investigation and further optimisation under various operating and flow conditions.

The transport or the separation of solid particles or droplets suspended in a fluid flow is a common task in mechanical and process engineering. To improve machinery and physical processes (e.g. for coal combustion, reduction of NO_x and soot) an optimization of complex phenomena by simulation applying the fundamental conservation equations is required. Fluid-particle flows are characterized by the ratio of density of the two phases gamma=rho_P/rho_F, by the Stokes number St=tau_P/tau_F and by the loading in terms of void and mass fraction. Those numbers (Stokes number, gamma) define the flow regime and which relevant forces are acting on the particle. Dependent on the geometrical configuration the particle-wall interaction might have a heavy impact on the mean flow structure. The occurrence of particle-particle collisions becomes also more and more important with the increase of the local void fraction of the particulate phase. With increase of the particle loading the interaction with the fluid phase can not been neglected and 2-way or even 4-way coupling between the continous and disperse phases has to be taken into account. For dilute to moderate dense particle flows the Euler-Lagrange method is capable to resolve the main flow mechanism. An accurate computation needs unfortunately a high number of numerical particles (1,...,10^7) to get the reliable statistics for the underlying modelling correlations. Due to the fact that a Lagrangian algorithm cannot be vectorized for complex meshes the only way to finish those simulations in a reasonable time is the parallization applying the message passing paradigma. Frank et al. describes the basic ideas for a parallel Eulererian-Lagrangian solver, which uses multigrid for acceleration of the flow equations. The performance figures are quite good, though only steady problems are tackled. The presented paper is aimed to the numerical prediction of time-dependend fluid-particle flows using the simultanous particle tracking approach based on the Eulerian-Lagrangian and the particle-source-in-cell (PSI-Cell) approach. It is shown in the paper that for the unsteady flow prediction efficiency and load balancing of the parallel numerical simulation is an even more pronounced problem in comparison with the steady flow calculations, because the time steps for the time integration along one particle trajectory are very small per one time step of fluid flow integration and so the floating point workload on a single processor node is usualy rather low. Much time is spent for communication and waiting time of the processors, because for cold flow particle convection not very extensive calculations are necessary. One remedy might be a highspeed switch like Myrinet or Dolphin PCI/SCI (500 MByte/s), which could balance the relative high floating point performance of INTEL PIII processors and the weak capacity of the Fast-Ethernet communication network (100 Mbit/s) of the Chemnitz Linux Cluster (CLIC) used for the presented calculations. Corresponding to the discussed examples calculation times and parallel performance will be presented. Another point is the communication of many small packages, which should be summed up to bigger messages, because each message requires a startup time independently of its size. Summarising the potential of such a parallel algorithm, it will be shown that a Beowulf-type cluster computer is a highly competitve alternative to the classical main frame computer for the investigated Eulerian-Lagrangian simultanous particle tracking approach.

Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-German / Teil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch

Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-German / Teil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch

[ES] El proceso de atomización primaria es el mecanismo por el cual una vena líquida se disgrega en un ambiente gaseoso. Este proceso está presente en muchas aplicaciones de ingeniería realizando diferentes tareas. En ocasiones es un paso previo antes de ser quemado, como en la industria energética o de propulsión, donde el objetivo es extraer la energía específica del líquido. En otros sectores, como el revestimiento o la extinción de incendios, el objetivo es maximizar el área cubierta por el chorro. Sin embargo, aunque la atomización es una parte fundamental de varios procesos industriales, está lejos de comprenderse por completo. El proceso de atomización es una mezcla de fenómenos de interacción gas-líquido dentro de un campo turbulento que tiene lugar en el campo cercano, que es la región más densa del chorro. Cuando se trata de arrojar luz sobre el proceso de atomización primaria, el problema principal es la falta de teorías físicas definitivas capaces de vincular los complejos eventos de ruptura con la turbulencia. El principal obstáculo que impide investigar el proceso de atomización primaria es la incapacidad de las técnicas ópticas clásicas para proporcionar información de la región densa del chorro. Solo en los últimos años, las nuevas técnicas basadas en rayos X podrían proporcionar nueva información sobre las características de la atomización cerca de la salida de la tobera. Esto también afecta a los modelos computacionales de atomización primaria que, al no disponer de información experimental sobre la región densa, requieren una calibración precisa de sus constantes para proporcionar resultados fiables en el campo lejano. Esta tesis se centra en mejorar el conocimiento del proceso de atomización primaria, especialmente en cómo las condiciones de inyección afectan el desarrollo del chorro en el campo cercano desde dos puntos de vista diferentes. Por un lado, con un enfoque computacional usando Direct Numerical Simulations y, por otro lado, experimentalmente usando Near-Field Microscopy. El estudio computacional se centra en variar los números de Reynolds y Weber de inyección. Los resultados muestran que aumentar el número de Reynolds mejora la desintegración del líquido, mostrando un aumento de las gotas generadas y una nube de gotas más fina. Sin embargo, la falta de un perfil turbulento de flujo de entrada completamente desarrollado conduce a comportamientos inesperados en la longitud de ruptura de la vena líquida que también aumenta con el número de Reynolds. El número de gotas también aumenta cuando aumenta el número de Weber, pero los tamaños característicos de las gotas siguen siendo los mismos. La longitud de ruptura no varía, lo que sugiere que las variaciones de la tensión superficial afectan la ruptura de las gotas y los ligamentos, pero no la desintegración del núcleo líquido en sí. Con los resultados obtenidos de ambos estudios, se propone un modelo fenomenológico que predice la distribución del tamaño de gota en función de las condiciones de inyección. Además, también se ha estudiado el efecto de usar toberas elípticas. Se ha obtenido que el número de gotas detectadas aumenta en comparación con el chorro redondo manteniendo ángulos de apertura del chorro similares. Sin embargo, cuando se utilizan toberas extremadamente excéntricas, la disminución de la turbulencia del flujo de entrada contrarresta los beneficios de este tipo de inyectores. En cuanto al análisis experimental, usar Near-Field Microscopy permite magnificar la región densa y analizar las características macroscópicas del chorro. Por lo tanto, se varían las presiones de inyección y descarga, centrándose en el ángulo de apertura del chorro. Se observa el aumento esperado en el ángulo al aumentar tanto la presión de inyección como la de descarga. Sin embargo, adicionalmente, se realiza un análisis de las perturbaciones del contorno del chorro, concluyendo que, al aumentar la presión de inyección, y por lo tanto la turbulencia del flujo de / [CA] El procés d'atomització primària és el mecanisme pel qual una vena líquida es disgrega en un ambient gasós. Aquest procés és present en moltes aplicacions d'enginyeria fent diferents tasques. De vegades és un pas previ abans de ser cremat, com ara en la indústria energètica o de propulsió, on l'objectiu és extraure l'energia específica del líquid. En altres sectors, com ara el revestiment o l'extinció d'incendis, l'objectiu és maximitzar l'àrea coberta pel doll. No obstant això, tot i que l'atomització és una part fonamental de diversos processos industrials, està lluny de comprendre's per complet. El procés d'atomització és una barreja de fenòmens d'interacció gas-líquid dins d'un camp turbulent que té lloc en el camp pròxim, que és la regió més densa del doll. Quan es tracta de donar llum sobre el procés d'atomització primària, el problema principal és la falta de teories físiques definitives capaces de vincular els complexos esdeveniments de trencament amb la turbulència. El principal obstacle que impedeix investigar el procés d'atomització primària és la incapacitat de les tècniques òptiques clàssiques per a proporcionar informació de la regió densa del doll. Només en els últims anys, les noves tècniques basades en raigs X podrien proporcionar nova informació sobre les característiques de l'atomització prop de l'eixida de la tovera. Això també afecta els models computacionals d'atomització primària que, en no disposar d'informació experimental sobre la regió densa, requereixen un calibratge precís de les seues constants per a proporcionar resultats fiables en el camp llunyà. Aquesta tesi se centra a millorar el coneixement del procés d'atomització primària, especialment en com les condicions d'injecció afecten el desenvolupament del doll en el camp pròxim des de dos punts de vista diferents. D'una banda, amb un enfocament computacional usant Direct Numerical Simulations i, d'altra banda, experimentalment usant Near-Field Microscopy. L'estudi computacional se centra a variar els nombres de Reynolds i Weber d'injecció. Els resultats mostren que augmentar el nombre de Reynolds millora la desintegració del líquid, tot mostrant un augment de les gotes generades i un núvol de gotes més fi. No obstant això, la falta d'un perfil turbulent de flux d'entrada completament desenvolupat condueix a comportaments inesperats en la longitud de ruptura de la vena líquida que també augmenta amb el nombre de Reynolds. El nombre de gotes també augmenta quan creix el nombre de Weber, però les grandàries característiques de les gotes continuen sent les mateixes. La longitud de ruptura no varia, la qual cosa suggereix que les variacions de la tensió superficial afecten la ruptura de les gotes i els lligaments, però no la desintegració del nucli líquid en ell mateix. Amb els resultats obtinguts de tots dos estudis, es proposa un model fenomenològic que prediu la distribució de la grandària de gota en funció de les condicions d'injecció. A més, també s'ha estudiat l'efecte d'usar toveres el·líptiques. S'ha obtingut que el nombre de gotes detectades augmenta en comparació amb el doll redó tot mantenint angles d'obertura del doll similars. No obstant això, quan s'utilitzen toveres extremadament excèntriques, la disminució de la turbulència del flux d'entrada contraresta els beneficis d'aquesta mena d'injectors. Quant a l'anàlisi experimental, usar Near-Field Microscopy permet magnificar la regió densa i analitzar les característiques macroscòpiques del doll. Per tant, es varien les pressions d'injecció i descàrrega, tot centrant-se en l'angle d'obertura del doll. S'observa l'augment esperat en l'angle en augmentar tant la pressió d'injecció com la de descàrrega. No obstant això, addicionalment, es realitza una anàlisi de les pertorbacions del contorn del doll i es conclou que en augmentar la pressió d'injecció, i per tant la turbulència del flux d'entrada, augmenten les pertorbacions en el contorn del ruixat, especialment a pressions de descàrrega mé / [EN] The primary atomisation process is the mechanism by which a liquid vein breaks into droplets in a gaseous ambient. This process is present in many engineering applications accomplishing different tasks. Sometimes it is a previous step before being burned, as in the energy or propulsion industry, where the objective is to extract the specific energy of the liquid. In other sectors, such as the coating or fire extinction, the objective is to maximise the area covered by the droplet cloud. However, although atomisation is a fundamental part of several industrial processes, it is far from fully understood. The atomisation process is a mixture of gas-liquid interaction phenomena within a turbulent field that takes place in the near-field, which is the denser region of the spray. When trying to shed light on the primary atomisation process, the main issue is the lack of definitive physical theories able to link the complex breakup events and the turbulence. The principal impediment that prevents the investigation from breaking through the atomisation process is the inability of the classic optical techniques to provide information from the dense region of the spray. Only in the last years, newer techniques based on X-Ray could provide new information on spray characteristics near the nozzle outlet. This also affects the computational primary atomisation models that, as there is no available experimental information on the dense region, require an accurate calibration of their constants to provide reliable results on the far-field. This thesis focuses on improving the knowledge of the primary atomisation process, especially on how the injection conditions affect the spray development in the near field from two different standpoints. On the one hand, with a computational approach using Direct Numerical Simulations and on the other hand, experimentally using Near-Field Microscopy. The computational study is focused on varying the inflow Reynolds and Weber numbers. Results show that increasing the Reynolds number improves the liquid disintegration, exhibiting an increase of generated droplets and a finer droplet cloud. However, the lack of a fully developed inflow turbulent profile leads to characteristic behaviours on the breakup length of the spray that also increases with the Reynolds number. The number of droplets increases when the Weber number increases, but the characteristic droplet sizes remain the same. The breakup length does not vary, suggesting that the surface tension variations affect the droplet and ligament breakup but not the core disintegration itself. With the results obtained from both studies, a phenomenological model is proposed to predict the droplet size distribution depending on the injection conditions. Additionally, using elliptical nozzles, the number of detected droplets increases compared with the round spray and maintain similar spray apertures. However, when using extremely eccentric nozzles, the inflow turbulence decrease counteracts the elliptical sprays' benefits. Regarding the experimental analysis, the Near-Field Microscopy magnifies the dense region and analyses the macroscopic features on the spray. So the injection and discharge pressure are varied, and the spotlight is put on the spray angle. The expected increase in the spray angle when increasing both the injection and discharge pressure is observed. Nevertheless, additionally, an analysis of the spray contour perturbations is performed, concluding that increasing the injection pressure, and thus the inflow turbulence, increases the perturbations on the spray contour, especially at lower discharge pressures. / González Montero, LA. (2022). Computational and Experimental Study of the Primary Atomisation Process under Different Injection Conditions [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/190635