A computer code is developed using finite volume technique for solving steady twodimensional and axisymmetric compressible Euler and Navier-Stokes equations for internal flows by &ldquo / multi-block&rdquo / technique. For viscous flows, both laminar and turbulent flow properties can be used. Explicit one step second order accurate Lax-Wendroff scheme is used for time integration. Inviscid solutions are verified by comparing the results of test cases of a support project which was supported by ONERA/France for Turkey T-108, named &ldquo / 2-D Internal Flow Applications for Solid Propellant Rocket Motors&rdquo / . For laminar solutions, analytical flat plate solution is used for planar case and theoretical pipe flow solution is used for axisymmetric case for verification. Prandtl turbulent flow analogy is used in a flat plate solution to verify the turbulent viscosity calculation. The test cases solved with single-block code are compared with the ones solved with multi-block technique to verify the multi-block algorithm and good similarity is observed between single-block solutions and multi-block solutions. For the burning simulation of propellant of Solid Propellant Rocket Motors, injecting boundary is used. Finally, a segmented solid propellant rocket motor case is solved to show the multi-block algorithm&rsquo / s flexibility in solving complex geometries.

Orientador: Prof. Dr. Juan Pablo Julca Avila / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia Mecânica, 2015. / Risers são estruturas tubulares cilíndricas usados para transferir petróleo e gás desde um poço de petróleo localizado no fundo do mar até uma plataforma. O presente trabalho de mestrado tem como enfoque o desenvolvimento e implementação de um código computacional para análise plana de vibrações livres de risers dispostos em catenária com escoamento interno. O riser, objeto deste estudo, é visto como uma viga plana curva e extensível com rigidez de tração e de flexão que experimentam grandes deslocamentos. O escoamento interno é visto como uma barra de flexibilidade infinita viajando ao longo do riser com velocidade constante. As equações do movimento do riser são deduzidas em coordenadas cartesianas via a abordagem variacional usando o princípio da energia potencial estacionária. O método de elementos finitos é usado para a análise estática e dinâmica geometricamente não linear do riser. Para a solução das equações não lineares de equilíbrio estático, o método iterativo de Newton-Raphson é utilizado. As frequências naturais e os modos de vibrar de um riser disposto em catenária são determinados para diferentes velocidades de escoamento interno, tensões no topo e velocidade de correnteza. Os resultados obtidos são comparados satisfatoriamente com dados da literatura. Verifica-se a funcionalidade do código desenvolvido que pode ser usado para conduzir pesquisas em vibrações livres de risers em catenária com escoamento interno. / Risers are cylindrical tubular structures used to produce/convey subsea oil and gas from wells located on the seafloor of the sea up to a platform. The focus of the present work of master¿s degree is the development and implementation of a computational code for the plane analysis of riser¿s free vibrations of a riser in catenary configuration under the effects of an internal fluid. The riser under study is seen as a plane extensible beam with axial and of bending stiffness, that experiments big displacements. The internal fluid is consider like a bar of infinite flexibility travelling along of riser with constant velocity. The riser¿s equations of motion are deducted in cartesian coordinates by an variational approach using the concept of total potential energy of a structural system. The finite elements method is used for the analysis dynamic and static non-linear geometrically of the riser. To solve the non-linear equations of static equilibrium, the iterative method of Newton-Raphson is used. The natural frequencies and vibrating modes of riser in catenary configuration are determined for different velocities of internal fluid, top tensions and current velocities. The results obtained are satisfactory when compared with literature data. Is verified the functionality of this code developed that can be used to conduct researches in free vibrations of risers in catenary configuration with internal fluid.

Le couchage rideau est un procédé d'enduction sans contact qui permet un couchage « contour » d'une feuille de papier dont le point clé est la stabilité du rideau. Ce procédé semble devoir se développer dans les années à venir pour la production de papiers impression-écriture et de papiers et cartons d'emballages. Néanmoins, il existe aujourd'hui un écart important entre la stabilité théorique du rideau et les observations. Nous avons donc analysé par CFD l'écoulement interne dans un dispositif de couchage pilote avec différents fluides Newtoniens et Non-Newtoniens ainsi que l'écoulement externe sur le plan incliné de l'appareil. L'étude de l'écoulement interne par CFD a permis de faire ressortir la cause de vortex pouvant apparaître dans le dispositif. Pour avoir un écoulement sans vortex, le nombre de Reynolds à l'entrée doit être inférieur à une valeur critique égale à 20 pour la géométrie étudiée quel que soit le fluide utilisé. De plus la présence d'une seconde cavité permet de filtrer les perturbations pour des fluides peu rhéofluidifiants, ce qui est le cas des sauces de couchages pour des papiers WFC. Ces résultats ont été validés expérimentalement à l'aide de traceurs et de PIV en utilisant une réplique exacte en Plexiglas de la coucheuse rideau. Enfin en ce qui concerne l'étude de l'écoulement externe sur le plan incliné, l'utilisation de la CFD a permis de conclure que, pour les dispositifs de couchage utilisés et les conditions opératoires de nos industries, certains problèmes présentés dans la littérature ne devraient pas exister. / Curtain coating is a contactless coating process which permits a contour coating of the paper and the key parameter of this process is a perfect stable curtain. This technology is expected to spread widely for graphic paper grades and boards in the next few years. Nevertheless, many experimental works revealed some differences between stability theory and results observed on the curtain. In this work, we performed CFD simulations both for Newtonian and Non-Newtonian fluids on the internal flow in a pilot curtain coater and on the flow down the inclined plane. The CFD study of the internal flow revealed the cause of vortex creation into the coater. To maintain vortex-free operation, the Reynolds number at the inlet must remain below a critical value whatever the fluid, which is equal to 20 with the studied geometry whatever the studied fluid. Moreover, a second cavity is useful since instabilities coming from the first cavity could be filtered for low shear-thinning fluids, which is the case of the WFC coating colours. These simulation results were validated thanks to flow visualization experiments with tracers and PIV using a transparent replica of the coater. Finally CFD simulations on the inclined plane were carried out and permitted to conclude that for the range of operating conditions used on the pilot curtain coater, some issues presented in literature should not exist industrially.

Resumen Los sistemas de inyección directa han sido uno de los principales puntos focales de la investigación en motores, particularmente en sistemas Diésel, donde la geometría interna, movimiento de aguja y comportamiento del flujo afectan el spray externo y por tanto determinan completamente el proceso de combustión dentro del motor. Debido a regulaciones medioambientales y al potencial de los (más ineficientes) motores "Otto", grandes esfuerzos se están aportando en investigación sobre sistemas de inyección directa de gasolina. Los motores GDi tienen el potencial de incrementar sustancialmente la economía de combustible y cumplir con las regulaciones de gases contaminantes y de efecto invernadero, aunque aún existen muchos desafíos por delante. Esta tesis estudia en detalle una moderna tobera GDi que fue específicamente diseñada para el grupo de investigación conocido como Engine Combustion Network (ECN). Con metodologías punteras, este inyector ha sido usado en un amplio abanico de instalaciones experimentales para caracterizar el flujo interno y varias características clave de geometría y funcionamiento, y aplicarlo para evaluar cómo se relaciona con los efectos observados del comportamiento del chorro externo. Para la caracterización interna del flujo, el objetivo ha sido determinar la geometría de la tobera y el desplazamiento de aguja, caracterizar la tasa de inyección y el flujo de cantidad de movimiento, y evaluar el flujo cercano. Algunas metodologías nunca antes habían sido empleadas en inyectores GDi, y muchas otras lo han sido solo eventualmente. Para la geometría interna, el levantamiento de aguja y el flujo cercano, varias técnicas avanzadas con rayos-x fueron aplicadas en las instalaciones de Argonne National Laboratory. Para la tasa de inyección y flujo de cantidad de movimiento, las técnicas disponibles en el departamento han sido adaptadas desde Diésel y aplicadas en inyectores GDi multiorificio. Dado lo novedoso de las técnicas aplicadas, las particularidades de las metodologías han sido discutidas en detalle en el documento. Aún con la elevada turbulencia del flujo interno, el inyector se comporta de forma consistente inyección a inyección, incluso cuando el estudio se centra en la variabilidad orificio a orificio. Esto ha sido atribuido al comportamiento repetitivo de la aguja, evaluado en los experimentos. También fue observado que el flujo estabilizado tiene una variación de alta frecuencia que no pude ser explicado por el movimiento de la aguja, sino por el particular diseño de las toberas. El análisis de geometría interna realizado a ocho toberas nominalmente iguales resultó en la obtención de un punto vista único en la construcción de toberas y la variabilidad de dimensiones clave. Las medidas de tasa de inyección permitieron estudiar la respuesta hidráulica del inyector a varias variables como la presión de inyección, presión de descarga, temperatura de combustible y la duración de la señal de comando. Estas medidas fueron combinadas con medidas de flujo de cantidad de movimiento para estudiar el bajo valor del coeficiente de descarga, el cual fue atribuido al bajo levantamiento de aguja y coeficiente L/D de los orificios. Por otro lado, el estudio del spray externo resultó en la identificación de un importante fenómeno específico a este particular hardware, el colapso del spray. Las extensivas campañas experimentales, utilizando Schlieren e iluminación trasera difusa (DBI) permitieron identificar y describir las características macroscópicas del spray y las condiciones bajo las que el colapso ocurre. El colapso del spray se forma por una combinación de interacción de las diferentes plumas (causado por el flujo interno) y determinadas condiciones ambiente que promueven evaporación y entrada de aire. Fue determinado que a niveles de densidad y temperatura moderados se desarrolla el colapso, modificando completamente el comportamiento espera / Abstract Fuel injection systems have been one of the main focal points of engine research, particularly in Diesel engines, where the internal geometry, needle lift and flow behavior are known to affect the external spray an in turn completely determine the combustion process inside engines. Because of environmental regulation and the potential development of the more inefficient Otto engines, a lot of research efforts are currently focused into gasoline direct injection systems. GDi engines have the potential to greatly increase fuel economy and comply with pollutant and greenhouse gases emissions limits, although many challenges still remain. The current thesis studies in detail a modern type of GDi nozzle that was specifically developed for the international research group known as the Engine Combustion Network (ECN). With the objective of employing state-of-the-art techniques, this hardware has been used in a wide range of experimental facilities in order to characterize the internal flow and several geometrical and constructive aspects like needle lift; and assess how it relates to the effects seen external spray. For the internal flow characterization, the goal was to determine the nozzle geometry and needle displacement, to characterize the rate of injection and rate of momentum, and evaluate the near-nozzle flow. Some methodologies applied here have never been applied to a GDi injector before, and many have only been applied rarely. For the internal geometry, needle lift and near-nozzle flow, several advanced x-rays techniques were used at Argonne National Laboratory. For the rate of injection and rate of momentum measurements, the techniques available in CMT-Motores Térmicos have been adapted from Diesel spray research and brought to multi-hole GDi injectors. Given the novelty of the techniques used, the particular methodologies and setups are discussed in detail. Despite the high turbulence of the flow, it was seen that the injector behaves consistently injection to injection, even when studying variation in individual holes. This is attributed to the repetitive behavior of the needle that was observed in the experiments. It was also observed that the stabilized flow has a high frequency variability that could not be explained by random movement of the needle, but rather by the particular design of the nozzle. The geometrical analysis done to eight, nominally equal nozzles, allowed a unique view into the construction of the nozzle and provided insights about the variability of key dimensions. The rate of injection measurements allowed to study the hydraulic response of the injector to the main variables like rail pressure, discharge pressure, fuel temperature and command signal duration. These measurements were combined with the rate of momentum measurements to study the low value of the discharge coefficient, that ultimately was attributed to the low needle lift and low L/D ratio of the orifices. On the other hand, the study of the external spray yielded the identification of very important phenomena specific to this particular hardware, the spray collapse. The extensive experimental campaigns featuring shadowgraph (Schlieren) and Diffused Back Illumination (DBI) visualization techniques allowed identifying and describing the macroscopic characteristics of the spray and the conditions under which the collapse occurs. The spray collapse engenders from a combination of the internal flow that creates plume interaction, and ambient conditions that promote air entrainment and evaporation. At moderate density and temperature levels the collapse develops, completely modifying the expected trends in the behavior of the plumes. / Resum Els sistemes d'injecció directa han sigut un dels principals punts focals de la investigació en motors, particularment en sistemes dièsel, en què la geometria interna, el moviment de l'agulla i el comportament del flux afecten l'esprai extern i per tant determinen completament el procés de combustió dins del motor. Degut a regulacions mediambientals i al potencial dels (més ineficients) motors "Otto", grans esforços s'estan aportant en investigació sobre sistemes d'injecció directa de gasolina. Els motors GDi tenen el potencial d'incrementar substancialment l'economia del combustible i complir les regulacions de gasos contaminants i d'efecte hivernacle, encara que existeixen molts desafiaments per davant. Esta tesi estudia en detall una moderna tovera GDi que va ser especialment dissenyada per al grup d'investigació conegut com a ECN. Amb l'objectiu de desenvolupar metodologies punteres, este injector ha sigut usat en un ampli ventall d'instal·lacions experimentals per tal de caracteritzar el flux intern i diverses característiques clau de la seua geometria i funcionament, per tal d'avaluar com es relacionen amb els efectes observats del comportament de l'esprai extern. Per a la caracterització interna del flux, l'objectiu ha sigut determinar la geometria de la tovera i el desplaçament de l'agulla, caracteritzar la taxa d'injecció i el flux de quantitat de moviment, i avaluar el flux proper. Algunes metodologies no s'havien empleat abans en injectors GDi, i moltes altres ho han sigut únicament de manera eventual. Per a la geometria interna, l'alçament de l'agulla i el flux proper, s'han aplicat diverses tècniques avançades amb raigsx a les instal·lacions d'Argonne National Laboratory. Per a la taxa d'injecció i el flux de quantitat de moviment, les tècniques disponibles al departament han sigut adaptades des de Dièsel i aplicades a injectors GDi multi-orifici. Considerant la novetat de les tècniques aplicades, les particularitats de les metodologies es discuteixen en detall al document. A pesar de l'elevada turbulència del flux intern, l'injector es comporta de manera consistent injecció a injecció, inclús quan l'estudi se centra en la variabilitat orifici a orifici. Aquest fet s'ha atribuït al comportament repetitiu de l'agulla, avaluat als experiments. També es va observar que el flux estabilitzat té una variació d'altra freqüència que no pot ser explicat pel moviment de l'agulla, sinó pel particular disseny de les toveres. L'anàlisi de la geometria interna realitzat a vuit toveres nominalment iguals va permetre obtenir un punt de vista únic en la construcció de toveres i la variabilitat de dimensions clau. Les mesures de taxa d'injecció van permetre estudiar la resposta hidràulica de l'injector a diverses variables com la pressió d'injecció, la pressió de descàrrega, la temperatura del combustible i la duració de la senyal de comandament. Estes mesures van ser combinades amb mesures de flux de quantitat de moviment per tal d'estudiar el baix valor del coeficient de descàrrega, el qual va ser atribuït al baix alçament de l'agulla i al coeficient L/D dels orificis. D'altra banda, l'estudi de l'esprai extern va permetre identificar un important fenomen específic d'aquest hardware particular: el col·lapse de l'esprai. Les extensives campanyes experimentals, utilitzant Schlieren i il·luminació darrera difusa (DBI) van permetre identificar i descriure les característiques macroscòpiques de l'esprai i les condicions sota les quals el col·lapse té lloc. El col·lapse de l'esprai es forma per una combinació d'interacció de les diverses plomes (causat pel flux intern) i determinades condicions ambient que promouen evaporació i entrada d'aire. Es va determinar a quins nivells de densitat i temperatura moderats es desenvolupa el col·lapse, modificant completament el comportament esperat de l'esprai. / Vaquerizo Sánchez, D. (2018). Study on Advanced Spray-Guided Gasoline Direct Injection Systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/99568 / TESIS

Tato práce se zabývá studií Simplex a SR verze původní trysky používané ve spalovací komoře malého proudového motoru. Pro lepší porozumění procesu rozprašování byl vyroben transparentní model obou trysek v měřítku 10:1. Tvorba spreje u tlakové vířivé trysky je komplexní proces dvoufázového proudění. Vnitřní a vnější proudění bylo zkoumáno pomocí Laserového Dopplerovského Anemometru a vysokorychlostní kamery při vstupních tlacích p = 0.5, 1.0 a 1.5 MPa s použitím kerosinu a p-Cymenu. Z hlediska vnitřního proudění byla provedena charakteristika vzdušného jádra a zkoumán vliv různých SFR hodnot na délku a průměr jádra. Dále byly objasněny rychlostní profily společně s jejich fluktuačními složkami vzhledem k Reynoldsovu číslu a použité kapalině. Také jednoduchý numerický model byl vyvinut k odhadu vnitřního proudění pomocí trackování částic. V případě vnějšího proudění byl zkoumán vliv vstupního tlaku na rozpadovou vzdálenost spreje a úhel kužele spreje.

The aim of the thesis is to put a transparent scaled PMMA model of the pressure swirl nozzle into operation, which includes, the selection of working fluids and the preparation of a test set to allow measurements using optical methods (LDA, PDA, PIV, high-speed visualization). The theoretical part describes the basic theory of atomization, optical measurement methods and deals with the problems of optical transition in optically complex systems. It also includes an extensive search for transparent liquids and materials of enlarged models that have been used in experiments, which often aim to match light refractive indices between these materials. In the practical part, attention is paid to the preparation of the test set and tests of chemical effects of several selected liquids on PMMA material are conducted, including a summary of experience with their use, as there was a permanent damage to the material. Several LDA measurements followed, using kerosene, p-cymene, 1-bromonaphthalene and water, evaluated the effect of the refractive index difference on the results. It turned out that no observable influence occurred if the refractive index difference between the nozzle material and the liquid was small. In addition, a visualization of internal flow through a high-speed camera was made. The practical part closes the static pressure measurement in the nozzle chamber, where the pressure ratio was measured on the walls of the chamber as well as on its axis. The measurement confirmed that the pressure on the chamber walls is constant and varies with the distance from the chamber axis.

In the context of an aviation industry whose top priority is to face the sustainability challenge, the growing civil UAV branch is not an exception. Hydrogen-powered UAVs equipped with PEM (Polymer Electrolyte Membrane) fuel cells are more and more frequently identified as the most convincing and promising technology, particularly for long-endurance mission requirements. However, the onboard carriage of a hydrogen fuel cell leads to unexplored internal flow characteristics, including the introduction of water vapour. The purpose of this master thesis is to develop a valid CFD model and methodology for the internal flow simulation of hydrogen-powered UAVs. Given the strict environmental operational requirements of PEM fuel cells, the intended application of the model is to effectively assess the evolution of the internal bay flow temperature and humidity fields. An explicit-time fourth-order Runge-Kutta projection method is tested successfully on a sample 2D case setup. The case geometry and flow conditions are inspired by the Green Raven UAV project conceived by the Department of Aeronautical and Vehicle Engineering at KTH. / I samband med en flygindustri vars högsta prioritet är att bemöta hållbarhetsutma- ningen är den växande civila UAV-sektorn inget undantag. Vätgasdrivna UAV:er utrustade med PEM (Polymer Electrolyte Membrane) bränsleceller betecknas allt oftare som den mest övertygande och lovande teknologin, särskilt för att de ska kunna utföra långvariga uppdrag. Den ombordgående transporten av en vätebränslecell leder emellertid till outforskade inre flödesfenomen, inklusive alstrad vattenånga. Syftet med detta examensarbete är att utveckla en lämplig CFD-modell och metodik för intern flödesimulering av vätgasdrivna UAV. Med tanke på de strikta miljökraven för PEM-bränsleceller är modellens avsedda tillämpning att eektivt utvärdera utvecklingen av de inre flödestemperaturerna och luftfuktighetsfälten. En tidsexplicit Runge-Kutta-projektionsmetod av fjärde ordningen testas framgångsrikt på ett 2D-exempel. Fallets geometri och flödesförhållanden är inspirerade av Green Raven UAV-projektet som utförts på Farkost och Flyg avdelningen på KTH.

The cooling systems in a gas turbine are especially important as the turbine blades and vanes are exposed to extreme temperatures. The relatively cool air is extracted from the compressors and fed to the turbines to cool the turbine blades. The manufacturing of these blades and channels used to cool is especially complicated using conventional manufacturing techniques. Additive Manufacturing (AM) gives the designer much more freedom to design core components. The AM technique currently explored is the Selective Laser Melting process (SLM). The surface area is exposed to the cooling airflow by using lattice structures which can be manufactured at relative ease using AM. This thesis will provide some insights into using AM parts for the cooling, by analyzing the pressure drop that could be expected from superalloys that are manufactured using AM. The surface roughness is an inherent property of the AM components therefore it would be interesting to analyze a turbulent flow through AM channels (CM247LC and INCONEL 939). The thesis deals with turbulent flows as the airflow used for cooling in the gas turbine is most likely turbulent.  The friction factor (Darcy–Weisbach friction factor) is used to relate the impact of the surface roughness to the pressure drop. The results from the previous experiments are contrasted as the flow in the previous experiments was assumed to be fully developed but in reality, it was not. And the accuracy of the previous results to the actual fully developed flow will shed some light on the feasibility of the flow analysis techniques used in the previous experiments. It is found that the previous experimental results for the CM247LC TPs have good agreement with current experimental results but INCONEL 939 exhibits significant deviation. The possible reasons for the deviations are directly linked to the assumptions made to calculate the minor losses. The Test Pieces (TP) analyzed in this thesis have varying length to diameter (L/D) ratios and the impact of the variation of different L/D ratios is analyzed along with varying pressure ratios. Where the flow resistance increases with an increase in L/D and pressure ratio. The technique to accommodate the compressibility of the airflow is also explored in this thesis. Finally, reasons for the manifestation of anomalies are discussed. The probability of the compressibility effects of the airflow on the anomalies was found to be quite high, and concluding remarks are provided.

Cette thèse présente la Simulation des Grandes Echelles (LES) de l’injection, de la pulvérisation et de la cavitation dans un injecteur pour les applications liées aux moteurs à combustion interne. Pour la modélisation de l’atomisation, on utilise le modèle ELSA (Eulerian Lagrangian Spray Atomization). Le modèle résout la fraction volumique du combustible liquide ainsi que la densité de surface d’interface liquide-gaz pour décrire le processus complet d’atomisation. Dans cette thèse, l’écoulement à l’intérieur de l’injecteur est également pris en compte pour une étude ultérieure de l’atomisation. L’étude présente l’application du modèle ELSA à un injecteur Diesel typique, à la fois dans le contexte de RANS et de LES.Le modèle est validé à l’aide de données expérimentales disponibles dans Engine Combustion Network (ECN). Le modèle ELSA, qui est normalement conçu pour les interfaces diffuses (non résolues), lorsque l’emplacement exact de l’interface liquide-gaz n’est pas pris en compte, est étendu pour fonctionner avec une formulation de type Volume of Fluid (VOF) de flux à deux phases, où l’interface est explicitement résolu. Le couplage est réalisé à l’aide de critères IRQ (Interface Resolution Quality), qui prennent en compte à la fois la courbure de l’interface et la quantité modélisée de la surface de l’interface. Le modèle ELSA est développé en premier lieu en considérant les deux phases comme incompressibles. L’extension à la phase compressible est également brièvement étudiée dans cette thèse. Il en résulte une formulation ELSA compressible qui prend en compte la densité variable de chaque phase. En collaboration avec l’Imperial College de Londres, la formulation de la fonction de densité de probabilité (PDF) avec les champs stochastiques est également explorée afin d’étudier l’atomisation. Dans les systèmes d’injection de carburant modernes, la pression locale à l’intérieur de l’injecteur tombe souvent en dessous de la pression de saturation en vapeur du carburant, ce qui entraîne une cavitation. La cavitation affecte le flux externe et la formulation du spray. Ainsi, une procédure est nécessaire pour étudier le changement de phase ainsi que la formulation du jet en utilisant une configuration numérique unique et cohérente. Une méthode qui couple le changement de phase à l’intérieur de l’injecteur à la pulvérisation externe du jet est développée dans cette thèse. Ceci est réalisé en utilisant le volume de formulation de fluide où l’interface est considérée entre le liquide et le gaz; le gaz est composé à la fois de vapeur et d’airambiant non condensable. / This thesis presents Large Eddy Simulation (LES) of fuel injection, atomization and cavitation inside the fuel injector for applications related to internal combustion engines. For atomization modeling, Eulerian Lagrangian Spray Atomization (ELSA) model is used. The model solves for volume fraction of liquid fuel as well as liquid-gas interface surface density to describe the complete atomization process. In this thesis, flow inside the injector is also considered for subsequent study of atomization. The study presents the application of ELSA model to a typical diesel injector, both in the context of RANS and LES. The model is validated with the help of experimental data available from Engine Combustion Network (ECN). The ELSA model which is normally designed for diffused (unresolved) interfaces, where the exact location of the liquid-gas interface is not considered, is extended to work with Volume of Fluid (VOF) type formulation of two phase flow, where interface is explicitly resolved. The coupling is achieved with the help of Interface Resolution Quality (IRQ) criteria, that takes into account both the interface curvature and modeled amount of interface surface. ELSA model is developed first considering both phases as incompressible, the extension to compressible phase is also briefly studied in this thesis, resulting in compressible ELSA formulation that takes into account varying density in each phase. In collaboration with Imperial College London, the Probability Density Function (PDF) formulation with Stochastic Fields is also explored to study atomization. In modern fuel injection systems, quite oftenthe local pressure inside the injector falls below the vapor saturation pressure of the fuel, resulting in cavitation. Cavitation effects the external flow and spray formulation. Thus, a procedure is required to study the phase change as well as jet formulation using a single and consistent numerical setup. A method is developed in this thesis that couples the phase change inside the injector to the external jet atomization. This is achieved using the volume of fluid formulation where the interface is considered between liquid and gas; gas consists of both the vapor and non condensible ambient air.