La législation sur les émissions de polluants des Moteurs à Combustion Interne (ICEs) est de plus en plus contraignante et représente un gros défi pour les constructeurs automobiles. De nouvelles stratégies de combustion telles que la Combustion à Allumage par Compression Homogène (HCCI) et l’exploitation de stratégies d’injections multiples sont des voies prometteuses qui permettent de respecter les normes sur les émissions de NOx et de suies, du fait que la combustion a lieu dans un mélange très dilué et par conséquent à basse température. Ces aspects demandent la création d’outils numériques adaptés à ces nouveaux défis. Cette thèse présente le développement d’un nouveau modèle 0D de combustion Diesel HCCI : le dual Combustion Model (dual - CM). Le modèle dual-CM a été basé sur l’approche PCM-FPI utilisée en Mécanique des Fluides Numérique (CFD) 3D, qui permet de prédire les caractéristiques de l’auto-allumage et du dégagement de chaleur de tous les modes de combustion Diesel. Afin d’adapter l’approche PCM-FPI à un formalisme 0D, il est fondamental de décrire précisément le mélange à l’intérieur du cylindre. Par consequent, des modèles d’évaporation du carburant liquide, de formation de la zone de mélange et de variance de la fraction de mélange, qui permettent d’avoir une description détaillée des proprietés thermochimiques locales du mélange y compris pour des configurations adoptant des stratégies d’injections multiples, sont proposés. Dans une première phase, les résultats du modèle ont été comparés aux résultats du modèle 3D. Ensuite, le modèle dual-CM a été validé sur une grande base de données expérimentales; compte tenu du bon accord avec l’expérience et du temps de calcul réduit, l’approche présentée s’est montrée prometteuse pour des applications de type simulation système. Pour conclure, les limites des hypothèses utilisées dans dual-CM ont été investiguées et des perspectives pour les dévélopements futurs ont été proposées. / More and more stringent restrictions concerning the pollutant emissions of Internal Combustion Engines (ICEs) constitute a major challenge for the automotive industry. New combustion strategies such as Homogeneous Charge Compression Ignition (HCCI) and the implementation of complex injection strategies are promising solutions for achieving the imposed emission standards as they permit low NOx and soot emissions, via lean and highly diluted combustions, thus assuring low combustion temperatures. This requires the creation of numerical tools adapted to these new challenges. This Ph.D presents the development of a new 0D Diesel HCCI combustion model : the dual Combustion Model (dual−CM ). The dual-CM is based on the PCM-FPI approach used in 3D CFD, which allows to predict the characteristics of Auto-Ignition and Heat Release for all Diesel combustion modes. In order to adapt the PCM-FPI approach to a 0D formalism, a good description of the in-cylinder mixture is fundamental. Consequently, adapted models for liquid fuel evaporation, mixing zone formation and mixture fraction variance, which allow to have a detailed description of the local thermochemical properties of the mixture even in configurations adopting multiple injection strategies, are proposed. The results of the 0D model are compared in an initial step to the 3D CFD results. Then, the dual-CM is validated against a large experimental database; considering the good agreement with the experiments and low CPU costs, the presented approach is shown to be promising for global engine system simulations. Finally, the limits of the hypotheses made in the dual-CM are investigated and perspectives for future developments are proposed.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Diseases and environment are closely related, especially with regard to air temperature and relative humidity. The weather data tend to follow a daily pattern of temporal variation, which derives mainly from the daily variation of the surface radiation balance. Based on this, this study aimed to make a qualitative and quantitative description of the database of the Automatic Meteorological Station of the Instituto Nacional de Meteorologia (INMET) in Santa Maria, RS, determine the hours of greatest frequency of occurrence of daily extreme air temperatures in Santa Maria, develop models to estimate hourly values of air temperature (T) and relative humidity (RH), based on values measured in "UTC standard times" and on the daily minimum air temperature and to determine the risk of fungal diseases occurrence during the developmental cycle of potato in different planting dates, using the Blitecast forecasting system. Models were fitted to estimate air T and partial vapor pressure of water at different times of the day. RH was indirectly obtained from partial vapor pressure of water and saturation vapor pressure, calculated from estimated T values. The database of Principal Climatological Station of Santa Maria was transformed to an hourly estimated T and RH database and the Blitecast's calculated severity values (CSV) were obtained for 14 planting dates in 43 years. The automatic weather station of Santa Maria, RS, belonging to INMET, shows 90.1% of the days of flawless data records in 10 years, from 2002 to 2011. The minimum daily air temperature in Santa Maria occurs more frequently at 09AM UTC, corresponding to 6AM on local official time, from September to February. From March through August, this time is delayed, and its occurrence to be more frequent at 10 h UTC. The precision of the estimates ranged from 0.7 ºC to 1.5 ºC, with average deviation of 0.65 °C for T and 0.7 % to 1.2 %, with average deviation of up to 4% for RH depending on the time. Potato crops during the Fall growing season require on average 54% more fungicide applications compared to the Spring season. In the Spring growing season the most probable number of sprayings ranged from two to four and from six to seven in the Fall growing season. Potato crops planted in August and March were demanded a lower economic, ecological and farmer health cost in crop protection against late blight than earlier crops (July and February). / Doenças e ambiente estão intimamente relacionados, especialmente no que se refere à temperatura e umidade relativa do ar. Os elementos meteorológicos tendem a seguir um padrão de variação temporal diária, que deriva principalmente da variação diária do balanço de radiação da superfície. Com base nisso, o objetivo desse trabalho foi descrever qualitativa e quantitativamente do banco de dados da Estação Meteorológica Automática do Instituto Nacional de Meteorologia de Santa Maria (INMET), determinar os horários de maior frequência de ocorrência das temperaturas extremas diárias do ar em Santa Maria, desenvolver modelos para estimativa dos valores horários de temperatura (T) e umidade relativa do ar (UR) e determinar o risco de ocorrência de requeima no ciclo de desenvolvimento da batata, em diferentes datas de plantio. Foram ajustados modelos analíticos para estimativa da T e da pressão parcial de vapor no ar nos diferentes horários do dia. A UR foi obtida indiretamente, com base nos valores de pressão parcial de vapor no ar estimados e nos valores de pressão de saturação de vapor no ar, calculados com base na T estimada. O banco de dados da Estação Climatológica Principal de Santa Maria foi transformado em um banco de dados horários estimados de T e UR e foram obtidos os valores de severidade calculada (VSC) pelo sistema Blitecast em 14 datas de plantio da batata em 43 anos agrícolas. A estação meteorológica automática de Santa Maria, RS, pertencente ao INMET, apresenta 90,1% dos dias sem falhas de registros de dados em 10 anos, de 2002 a 2011. A temperatura mínima diária do ar em Santa Maria ocorreu com maior frequência às 09 h UTC, correspondendo às 06 h no horário oficial local, nos meses de setembro a fevereiro. De março até agosto, esse horário é atrasado, sendo a sua ocorrência mais frequente às 10 h UTC. A precisão das estimativas variou de 0,7 oC a 1,5 oC, com desvio médio de até 0,65oC para T do ar e de 0,7 % a 1,2 %, com desvio médio de até 4 %, para UR, dependendo do horário. Cultivos de batata no período de safrinha necessitam, em média, de um número 54 % maior de aplicações de fungicida em relação ao período de safra. Na safra o número mais provável de pulverizações oscila entre duas e quatro e na safrinha entre seis e sete. Plantios de batata realizados em agosto e em março exigiram um menor custo econômico, ecológico e de saúde do produtor na proteção da cultura contra a requeima do que plantios mais precoces (julho e fevereiro).

The phenomenon of spray in crossflow is of relevance in gas turbine combustor development. The current work focuses on spray in crossflow rather than liquid jet in crossflow from the standpoint of enhancing fuel dispersion and mixing. Specifically, the first part of the work involves study of spray structure, droplet sizing, and velocimetry for sprays of water and ethanol in a crossflow under ambient conditions. Laser-based diagnostic techniques such as Particle/Droplet Image Analysis (PDIA) and Particle Tracking Velocimetry (PTV) are utilized. Using spray structure images, trajectory equations are derived by multi-variable regression. It is found that the spray trajectory depends only on the two-phase momentum ratio and is independent of other flow parameters. A generalized correlation for the spray trajectory is proposed incorporating the liquid surface tension, which is found to be effective for our data, with water and ethanol, as well as data on Jet-A from the literature for a wide variety of operating conditions. An interesting phenomenon of spatial bifurcation of the spray is observed at low Gas-to-Liquid ratios (GLRs). The reason for this phenomenon is attributed to the co-existence of large and highly deformed ligaments along with much smaller droplets at low GLR conditions. The smaller droplets lose their vertical momentum rapidly leading to lower penetration, whereas the larger ligaments/droplets penetrate much more due to their larger momentum leading to a spatial separation of the two streams. The second part of the study focuses on evaporating sprays in preheated crossflow. Experiments are conducted using ethanol, decane, Jet-A1 fuel, and a two-component surrogate for Jet-A1 fuel. The crossflow air is heated up to 418 K and the effect of evaporation is studied on spray trajectory and droplet sizes. Measured droplet sizes and velocities at two successive locations are used to estimate droplet evaporation lifetimes. Evaporation constant for the d2 law derived from the droplet lifetimes represents the first-ever data for the above-mentioned liquids under forced convective conditions. This data can be used to validate multi-component droplet evaporation models. The last part of the study focuses on Large Eddy Simulations (LES) of the spray in crossflow. The near-nozzle spray structure is investigated experimentally to obtain droplet size and velocity distributions that are used as inputs to the computational model. For the spray in crossflow under ambient conditions, trajectory and droplet sizes at different locations are compared with experimental results. While the predicted trajectory is found to be in good agreement with data, the predicted droplet sizes are larger than the measured values. This is attributed to the implicit assumption in the secondary breakup model that the droplets are spherical, whereas the experimental data in the near-nozzle region clearly shows presence of mostly ligaments and non-spherical droplets, especially for the low GLR cases. A modified breakup model is found to lead to improved agreement in droplet sizes between predictions and measurements. Overall, the experiments and computations have provided significant insight into spray in crossflow phenomenon, and have yielded useful results in terms of validated spray trajectory correlations, droplet evaporation lifetimes under forced convective conditions, and a methodology for simulation of airblast sprays.

The work presented here pertains to investigations on gas-on-liquid type of impinging injectors with a generic approach with prospective applications in several areas, and at places with particular emphasis on cryogenic or semi-cryogenic liquid propellant rockets. In such rockets, one of the components arrives at the injector in a gaseous phase after passing through the regenerative coolant passages or a preceding combustion stage. Most often, the injectors in such systems are of shear coaxial type. The shear coaxial injectors suffer from several disadvantages like complexity in design, manufacture and quality control. Adoption of impinging jet configuration can alleviate these problems in addition to providing further benefits in terms of cost, robustness in high temperature environment and manifolding. However, there is very little literature on gas-on-liquid injectors either in this context or in any other Even for the simplest form of impinging injectors such as like-on-like doublets, literature provides no conclusive direction at describing a spray from the theoretical models of physical mechanisms. Empirical approach is still the prime mode of obtaining a proper understanding of the phenomena. Steady state spray characterization includes mainly of describing the spatial distribution of liquid mass and drop size distribution as a function of geometric and injection parameters. The parameters that are likely to have an impact on spray characteristics are orifice diameter, ratio of orifice length to diameter, pre-impingement length of individual jets, inter orifice distance, impingement angle, jet velocity and condition of the jet just before impingement. The gas-on- liquid configuration is likely to experience some qualitative changes because of the expansion of the gas jet. The degree to which each one of the above variables influences the drop size and mass distribution having implication to combustion performance forms the core theme of the thesis. A dedicated experimental facility has been built, calibrated and deployed exhaustively. While spray drop size measurement is done largely by a laser diffraction instrument, some of the cases warranted an image processing technique. Two different image processing algorithms are developed in-house for this purpose. The granulometric image processing method developed earlier in the group for cryogenic sprays is modified and its applicability to gas-on-liquid impinging sprays are verified. Another technique based on the Hough transform which is feature extraction technique for extracting quantitative information has also been developed and used for gas-on-liquid impinging injectors. A comparative study of conventional liquid-on-liquid doublet with gas-on-liquid impinging injectors are first made to establish the importance of studying gas-on-liquid impinging injectors. The study identifies the similarities and differences between the two types and highlights the features that make such injectors attractive as replacements to coaxial configuration. Spray structure, drop-size mass distributions are quantified for the purpose of comparison. This is followed by a parametric study of the gas-on-liquid impinging injectors carried out using identified control variables. Though momentum ratio appeared to be a suitable parameter to describe the spray at any given impingement angle, the variations due to impingement angle had to be factored in. It was found that normal gas momentum to liquid mass is an apt parameter to generalize the spray characteristics. It was also found that using identical nozzles for desired mass ratio could lead to rather large deflection of the spray which may not be acceptable in combustion chamber design. One way of overcoming this is to work with unequal orifice sizes for gas and liquid. It was found that using smaller gas orifice for a given liquid orifice resulted in lower SMD (Sauter Mean Diameter of the spray) for constant gas and liquid mass flow rates. This is attributable to the high dynamic pressure of gas in the case of smaller gas orifices for the same mass flow rate. The impinging liquid jets with unequal momentum in the doublet configuration would result in non-uniform mass and mixture ratio distribution within the combustion chamber which may have to operate under varying conditions of mass flow rates and/or mixture ratio. The symmetrical arrangement of triplet configuration can eliminate this problem at the same time generating finely atomized spray and a homogeneous mixture ratio. In view of the scanty literature available in this field, the atomization characteristics of the spray generated by liquid centered triplet jets are examined in detail. It was found that as in the case of gas-on-liquid impinging doublets, normal gas momentum to liquid mass is an ideal parameter in describing the spray. Variants of this configuration are studied recently for many other applications too. As done in the case of doublets, efforts have also been made to compare gas centered triplet to liquid-liquid triplet. It was found that the trend of SMD of gas centered triplet is different from that of liquid-liquid triplets, thus pointing to a different mechanism in play. The SMD in the case of liquid-liquid triplets decreases monotonically with increasing specific normal momentum. It is to be noted that specific normal momentum is an ideal parameter for describing the spray characteristics of liquid-liquid triplets and doublets. In the case of gas centered triplet the SMD first increases and then decreases with specific normal momentum, the inversion point depends on the gas mass flow rate for a constant specific normal momentum. The thesis concludes with a summary of the major observations of spray structures for all the above injector configurations and quantifies the parametric dependencies that would be of use to engineering design

No description available.

yes / The NLW database illustrates the extensive and eclectic literature regarding NLWs which covers the last few decades. It currently contains over 250 entries. It is important to have access not only to the more recent material, but also to earlier sources since many of the general debates and controversies have already been rehearsed, and lessons learnt from them are still relevant today. Yet, it is also vital to follow new developments of NLWs closely because rapidly changing technology is producing weapons whose implications for integration into military and civil police forces have yet to be clearly defined and understood. Of particular interest are not only NLW applications for war fighting, but opportunities for deployment in peace enforcement and peace keeping missions. These technologies span many bases including: psycho-chemicals; unmanned weapons platforms and delivery systems; biogenetics; acoustic and microwave weapons; biological and chemical weapons; laser systems; kinetic energy ballistics; dual purpose (lethal/non-lethal) weapons; and, sprays and foams which inhibit movement. The database will keep up to date on these developments and future reports will highlight new issues and debates surrounding them. With these rapid technological advances come a series of associated dangers and concerns including: the ethics of use; implications for weapons control and disarmament treaties; military doctrine; public accountability and guidelines; dangers of misuse and proliferation; and, research and development strategies. Using the database, and drawing from military and non-military sources, this report will select the main current issues and debates within the non-lethal community. Bearing in mind that many operations undertaken by military forces are now more akin to policing actions (such as peace support operations) there are lessons to be learnt by military units from civil police experience. There still remains a tension between perceived benign and malign intent both in NLW operational use and non-lethal research and development.

yes / Non-lethal weapons (NLWs) are explicitly designed and primarily employed to incapacitate personnel or material whilst minimising collateral damage to property and the environment. Existing NLWs include rubber and plastic bullets, entangling nets, chemical sprays such as OC and CS gas, and electrical stunning devices such as the `Taser¿ gun. New NLWs are on the way, which will include acoustic and microwave weapons, non-lethal landmines, malodorants, and sophisticated weapons developed through rapid advances in neuroscience and the genomics revolution. Most analysts would agree that there is a `legitimate¿ role for non-lethal weapons, both for civil and military applications. However there is considerable disagreement as to the operational effectiveness of NLWs, and the threat such weapons pose to arms conventions and international law. As usual, a balance has to be achieved where the benign advantages of developing and deploying non-lethal weapons are not outweighed by their more malign effects. In particular, emerging non-lethal technologies offer an increasing opportunity for the suppression of civil dissent and control of populations ¿ these are sometimes referred to as the `technologies of political control¿. There is a continuing need for sustained and informed commentary to such developments which highlights the impact and threats that these technologies pose to civil liberties and human rights. Because the last BNLWP Report was produced in August 2001, this edition is somewhat longer than usual so that key developments since then can be highlighted and summarised. Future BNLWRP reports will be published three times a year, and we welcome material to be considered for inclusion.

yes / Two recent detailed reports, by the U.K Northern Ireland Office (NIO) - January 2004 1 and the U.S. Council on Foreign Relations (CFR) - February 2004 2, provide further insights into current policy and technology developments in the U.K. and U.S. The NIO report is the 4th and final report of a U.K wide Steering Group set up by the Secretary of State for Northern Ireland in Summer 2000, with the objective: To establish whether a less potentially lethal alternative to baton rounds is available; and to review the public order equipment which is presently available, or could be developed, in order to expand the range of tactical options available to operational commanders. 3 In her foreword to the report Jane Kennedy, Minister of State for Northern Ireland notes that: Despite a protracted and international search for a commercially available product, we have been unable to find anything that meets the criteria of an acceptable, potentially less lethal alternative to the baton round currently in service which provides an effective capability that does not expose officers and the public to greater risk in violent public disorder.4 The NIO Report has sections looking at the Defence Science and Technology Laboratory (DSTL) programme on the development of less lethal technologies (particularly the Attenuating Energy Projectile and the Discriminating Irritant Projectile); commercial off the shelf product evaluations and update (12 Gauge Sock Round Assessment); Water Cannon; the U.K. use of less lethal technologies (with a focus on L21A1 baton rounds, CS sprays and the Taser). The report also contains a section entitled `The Management of Conflict¿ which discusses the dynamics of crowd behaviour. For a critical response to the NIO report see that from Dr. Brian Rappert.5 The CFR report provides a strong endorsement for non-lethal weapons. A key finding states: Wider integration of nonlethal weapons into the U.S. Army and Marine Corps could have reduced damage, saved lives, and helped to limit the widespread looting and sabotage that occurred after the cessation of major conflict in Iraq. Incorporating NLW capabilities into the equipment, training and doctrine of the armed services could substantially improve U.S. effectiveness in conflict, post-conflict, and homeland defense. 6 Interestingly, in describing the nonlethal capability sets (NLCS) which have been deployed in Kosovo and Iraq, and which help to provide a continuum of force between ¿don¿t shoot¿ and ¿shoot¿ 7, the CFR seems to distinguish between NLWs (rubber balls [grenades and shotgun munitions], bean bags, riot shields, Tasers, net entanglers, and caltrops), and equipment such as flash-bang grenades, laser dazzlers, and bullhorns of which it states ¿It is important to note that these are not weapons but non-lethal capabilities¿ 8 The CFR recommends expanded deployment of NLWs in the armed services, longer ranges for non-lethal payloads using precision delivery and fusing systems, and further development of millimetre-wave area-denial system (HPM weapons such as VMADS) and the advanced tactical laser (ATL). The report also argues for the need to have a bigger Joint Non-Lethal Weapons Directorate (JNLWD) or a new Non-lethal Joint Program Office (NLJPO) and for Bradford Non-Lethal Weapons Research Project (BNLWRP) ¿ Research Report 5 (May 2004) 2 closer links with the Joint Forces Command (JFCOM). In the opinion of the authors the JNLWD should also have more access into classified programmes throughout all branches of the armed services so as not to duplicate non-lethal development initiatives. To stimulate incorporation of NLWs throughout the U.S. Armed Services the CFR advocates two approaches: (1) top-down planning in the Defense department and (2) creation of demand for these [NLWs] weapons from the field as personnel gain experience with prototype equipment. 9 They argue there is a need for the top-level military and civilian leadership to be educated about NLW capabilities, not only for warfighting and peacekeeping, but also in `homeland defence in isolating a hot zone in the aftermath of a biological attack' 10. We will be referring again to both the NIO and CFR publications in other sections of this report.

L’injection directe à haute pression du carburant dans les moteurs à combustion interne permet une atomisation compacte et efficace. Dans ce contexte, la simulation numérique de l’injection est devenue un outil fondamental pour la conception industrielle. Cependant,l’écoulement du carburant liquide dans une chambre occupée initialement par l’air est un écoulement diphasique très complexe ; elle implique une très large gamme d’échelles. L’objectif de cette thèse est d’apporter de nouveaux éléments de modélisation et de simulation afin d’envisager une simulation prédictive de ce type d’écoulement avec un coût de calcul abordable dans un contexte industriel. En effet, au vu du coût de calcul prohibitif de la simulation directe de l’ensemble des échelles spatiales et temporelles, nous devons concevoir une gamme de modèles d’ordre réduit prédictifs. En outre, des méthodes numériques robustes, précises et adaptées au calcul de haute performance sont primordiales pour des simulations complexes.Cette thèse est dédiée au développement d’un modèle d’ordre réduit Eulérien capable de capter tant la polydispersiond’un brouillard de goutte dans la zone dispersée,que la dynamique de l’interface dans le régime de phases séparées. En s’appuyant sur une extension des méthodes de moments d’ordre élevé à des moments fractionnaires qui représentent des quantités géométriques de l’interface, et sur l’utilisation de variables géométrique sen sous-échelle dans la zone où l’interface gaz-liquide ne peut plus être complètement résolue, nous proposons une approche unifiée où un ensemble de variables géométriques sont transportées et valides dans les deux régimes d’écoulement [...]. / Direct fuel injection systems are widely used in combustionengines to better atomize and mix the fuel withthe air. The design of new and efficient injectors needsto be assisted with predictive simulations. The fuel injectionprocess involves different two-phase flow regimesthat imply a large range of scales. In the context of thisPhD, two areas of the flow are formally distinguished:the dense liquid core called separated phases and thepolydisperse spray obtained after the atomization. Themain challenge consists in simulating the combinationof these regimes with an acceptable computational cost.Direct Numerical Simulations, where all the scales needto be solved, lead to a high computational cost for industrialapplications. Therefore, modeling is necessaryto develop a reduced order model that can describe allregimes of the flow. This also requires major breakthroughin terms of numerical methods and High PerformanceComputing (HPC).This PhD investigates Eulerian reduced order models todescribe the polydispersion in the disperse phase andthe gas-liquid interface in the separated phases. First,we rely on the moment method to model the polydispersionin the downstream region of the flow. Then,we propose a new description of the interface by usinggeometrical variables. These variables can provide complementaryinformation on the interface geometry withrespect to a two-fluid model to simulate the primary atomization.The major contribution of this work consistsin using a unified set of variables to describe the tworegions: disperse and separated phases. In the case ofspherical droplets, we show that this new geometricalapproach can degenerate to a moment model similar toEulerian Multi-Size Model (EMSM). However, the newmodel involves fractional moments, which require somespecific treatments. This model has the same capacityto describe the polydispersion as the previous Eulerianmoment models: the EMSM and the multi-fluid model.But, it also enables a geometrical description of the interface...].

[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