A fully elliptic computational method for the analysis of steady viscous flow in high speed subsonic centrifugal compressor impellers with tip leakage, is presented. A generalised curvilinear, non-orthogonal grid is utilised and the timeaveraged Navier-Stokes equations are transformed and expressed in a fully conservative form. The discretisation of the governing equations is performed through finite volume integration. The solution procedure employs a non-staggered variable arrangement and a SIMPLE based method for coupling the velocity and pressure fields. The turbulence effects are simulated with the use of the k-e model, modified to account for rotation and streamline curvature, and the near-wall viscous phenomena are modelled through the wall function method. The numerical model is implemented for the flow prediction in a series of two and three dimensional test cases. Incompressible flow predictions in twodimensional cascades and three-dimensional ducting systems with different geometrical features and inlet conditions are initially performed and the numerical results are compared against available experimental data. The final objective of the present study is achieved through the comparative study of the predictions obtained against the results of Eckardt's experimental investigation of the viscous compressible flow in a high speed radial impeller operating at design condition and in a backswept impeller at design and off-design conditions. In addition, the flow is simulated in the passages of the Rolls Royce GEM impeller which was tested at Cranfield at design and off-design flow rates. A jet/wake pattern was discerned in all the simulated centrifugal compressor cases and a good overall agreement was achieved with the measured wake formation and development; and, encouraging results were obtained on the evolution of the secondary flows. The tip leakage effects influenced the loss distribution, the size and the location of the wake flow pattern at the rotor exit. The effects of the flow mass rate on the detailed flow pattern and on the compressor performance have been well represented. In certain cases, the quality of the present predictions is an improvement over that obtained by other 'state-of-the-art' Navier-Stokes solvers. In conclusion, the developed finite volume flow model has captured a large number of complex flow phenomena encountered in the tested impellers and is expected to provide a useful aerodynamic analysis tool for stationary or rotating, axial or radial turbomachinery components.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this work is to study and characterize aerodynamically a free jet operating at subsonic regime and identify its acoustic signature. This study aims to analyze fundamentally the turbulent structures and the total noise produced at different Mach numbers. This kind of research is crucial to the understanding of these mechanisms of noise generation and propagation, and it is extremely important for aeronautical applications, for instance, the jet engine exhaust. The research is done by analysing the data obtained in experiments using pitot tube, hot-wire anemometer and acoustic measurements. This work also describes the experimental procedures for each step of analysis, as well as the characteristics of jet noise facilities. The data from measurements with a pitot tube was used to study the mean velocity profiles. The average properties are also analyzed with an anemometry system, likewise used to study the turbulent intensity at eleven axial lines, ranging from the centerline to the edge of the nozzle (lipline). These results are compared with literature and has verified the accuracy of hot-wire anemometers for turbulent intensities lower than 15%. The aerodynamic data are obtained for Mach numbers 0.25, 0.50 and 0.75, from the nozzle exit to thirteen diameters in the direction of the jet. The acoustic study is carried out by analyzing the sound pressure level obtained at six positions in the far field, with observer angles ranging from 40 to 110º. In this campaign more velocities are studied with Mach numbers from 0.18 to 1.00 with step of 0.05 are described. A database with the sound pressure level as a function of frequency is constructed from this information. / O objetivo deste trabalho é estudar e caracterizar aerodinamicamente um jato livre operando em regime subsônico e identificar a assinatura acústica do mesmo. Esse estudo busca analisar fundamentalmente as estruturas turbulentas e o ruído total produzido em diferentes números de Mach. Tal estudo é crucial para o entendimento desses mecanismos de geração e propagação, e encontra extrema importância para aplicações aeronáuticas, como, por exemplo, a exaustão de motores a reação (jato). A investigação é feita através da análise dos dados obtidos em experimentos utilizando tubo de pitot, anemômetro de fio-quente e ensaios acústicos. Neste trabalho também são descritos os procedimentos experimentais de cada etapa de análise, bem como as características dos laboratórios utilizados para o estudo do ruído de jato. Com os dados provenientes das medições com tubo de pitot são estudados os perfis de velocidade média. As propriedades médias também são analisadas com o sistema de anemometria, que ainda é utilizado para estudo da intensidade turbulenta em onze linhas axiais, variando da linha de centro até a borda do bocal (lipline). Estes resultados são comparados com a literatura e é constatada a acurácia dos anemômetros de fio-quente para intensidades turbulentas menores que 15%. Os dados aerodinâmicos mencionados são obtidos para números de Mach 0,25, 0,50 e 0,75, a partir da saída do bocal até treze diâmetros na direção do jato. O estudo acústico é feito através da análise do nível de pressão sonora obtido em seis posições no campo distante, com ângulos de observação variando de 40 a 110º. Diferentes velocidades também foram analisadas, desta vez, com números de Mach de 0.18 a 1.00 com passo de 0.05. Um banco de dados com o nível de pressão sonora em função da frequência é construído a partir destas informações. / Mestre em Engenharia Mecânica

Cette thèse est consacrée au calcul et à l’étude du champ acoustique rayonné par un jet fortement supersonique, sur-détendu et chauffé. L’approche numérique utilisée consiste à résoudre simultanément l’écoulement turbulent et le champ proche acoustique par simulation des grandes échelles.Afin de résoudre les équations de Navier-Stokes instationnaires et compressibles, des schémas numériques de dérivation spatiale et d’intégration temporelle peu dissipatifs et peu dispersifs sont utilisés. Pour le système de coordonnées cylindriques, une procédure de déraffinement progressive au voisinage de l’axe du jet est proposée pour augmenter le pas de temps de l’intégration temporelle. Une procédure de capture de choc est finalement développée pour supprimer les oscillations de Gibbs aux voisinages des chocs. Cette procédure est explicite, adaptative et conservative.Un jet rond, sur-détendu et présentant un nombre de Mach d’éjection de 3.30 ainsi qu’une pression et une température de réservoir de 28.6 × 105Pa et 1144K est résolu par simulation des grandes échelles. Ce jet est initialement laminaire et possède un nombre de Reynolds de 0.94 × 105. Les champs aérodynamique et acoustique obtenus sont comparés aux données disponibles dans la littérature. Afin de pouvoir identifier les sources acoustiques,le champ turbulent est caractérisé le long de la couche de mélange, notamment en utilisant une analyse spectrale et une décomposition selon les modes azimutaux. Les champs acoustiques proche et lointain sont enfin étudiés et différentes composantes de bruit sont identifiées à partir de comparaisons avec des mesures et des modèles de la littérature, ainsi qu’en établissant des liens avec les propriétés de l’écoulement turbulent. L’influence des effets de la propagation non linéaire des ondes acoustiques est finalement discutée. / This thesis deals with the computation and the investigation of the noise radiated by a rocket-like jet. A direct noise simulation based on large-eddy simulation is used in this study. Low-dissipation and low-dispersion numerical schemes are implemented in the solver.As the cylindrical Navier-Stokes equations are considered, a procedure to increase the integration time step is derived. To remove Gibbs oscillations near shocks, an explicit, adaptative and conservative shock-capturing procedure is developed for aeroacoustics computations.An over expanded initially laminar jet with an exit Mach number of 3.30 and stagnation pressure and temperature of 28.6 × 105Pa and 1144K is then computed by large-eddy simulation.The jet Reynolds number is 0.94 × 105. Aerodynamic and acoustic results are compared to data available in the literature. In order to identify noise sources, the turbulent flow fluctuations along the shear layer are characterized, especially by using a two dimensional Fourier transform in time and in the azimuthal direction. Acoustic near and far fields are also studied and different noise components are identified using comparisons with models and experimental data, and by establishing links with the turbulent flow field. Non-linear propagation effects of acoustic waves are finally discussed.

No autorizado por el autor para ser publicada a texto completo / El objetivo principal de este trabajo es estudiar los mecanismos de transporte turbulento de calor y masa en una cortina de aire, a fin de proveer antecedentes para la evaluación de cortinas de aire como objetos físicos capaces de confinar calor y/o masa en ambientes cerrados con geometrías tipo corredor, como túneles. El trabajo se enmarca en el proyecto FONDECYT Nº1085015, que apunta a la caracterización experimental y numérica de los fenómenos de transporte, a través de un dispositivo de cortinas de aire doble jet-doble flujo. El estudio se llevó a cabo en un túnel de laboratorio a escala 1:34, dotado de dos dispositivos generadores de cortinas de aire en configuración doble jet-doble flujo, y de un foco de calor constituido por una resistencia eléctrica. La función deseada de las cortinas es evitar la propagación de calor y momentum hacia zonas alejadas de la resistencia. Para analizar los mecanismos de transporte, se midieron los campos de temperatura y velocidad en dos dimensiones, en una de las cortinas de aire y su entorno inmediato. Los datos registrados se utilizaron para determinar términos asociados al transporte turbulento de calor y masa, puesto que las cortinas de aire se caracterizan por tener un régimen fluidodinámico turbulento. Las mediciones de temperatura y velocidad se llevaron a cabo con una termocupla fina de rápido tiempo de respuesta y un sistema de Anemometría Láser Doppler (LDA-2D), respectivamente. Se obtuvieron y analizaron resultados para cuatro casos, con diferentes potencias en la fuente de calor y diferentes velocidades en la salida de los jets. En cada caso, se analizó el comportamiento de los términos asociados al transporte turbulento de calor y momentum en la zona de la cortina y su entorno inmediato. Adicionalmente se estudió el efecto de la fuente de calor sobre la dinámica de la cortina, mediante el cálculo del número de Richardson y el análisis espectral de las señales de velocidad en ciertos puntos en las capas de mezcla de la cortina. Se concluye que existen zonas críticas de transporte turbulento de calor y momentum que es necesario contemplar en la evaluación de las cortinas de aire como dispositivo confinatorio. Para una mejor comprensión del fenómeno, sin embargo, es necesario realizar mediciones en un dominio más fino que el utilizado en este trabajo en el eje longitudinal; en particular, debe analizarse en mayor detalle la zona de impacto de la cortina con el suelo. Se observa, para la mayoría de los casos, un régimen de convección mixta en ciertos sectores de la cortina, verificándose la influencia térmica de la fuente de calor sobre la dinámica de la cortina; este hecho releva la importancia de estudiar configuraciones con potencias más altas que las utilizadas en este trabajo para la fuente de calor.

Controlled cooling is an important part of steel production industry that affects the properties of the outcome steel. Many of the researches done in controlled cooling are experimental. Due to progress in the numerical techniques and high cost of experimental works in this field the numerical work seems more feasible. Heat transfer analysis is the necessary element of successful controlled cooling and ultimately achievement of novel properties in steel. Heat transfer on the surface of the plate normally contains different regimes such as film boiling, nucleate boiling, transition boiling and radiation heat transfer. This makes the analysis more complicated. In order to perform the heat transfer analysis often empirical correlations are being used. In these correlations the velocity and pressure within the fluid domain is involved. Therefore in order to obtain a better understanding of heat transfer process, study of hydrodynamics of the fluid becomes necessary. Circular jet due to its high efficiency has been used vastly in the industry. Although some experimental studies of round jet arrays have been done, yet the characteristics of a single jet with industrial geometric and flow parameters on the surface of a flat plate is not fully understood. Study of hydrodynamics of the jet impingement is the first step to achieve better understanding of heat transfer process. Finite element method as a popular numerical method has been used vastly to simulate different domains. Traditional approaches of finite element method, Lagrangian and Eulerian, each has its own benefits and drawbacks. Lagrangian approach has been used widely in solid domains and Eulerian approach has been widely used in fluid fields. Jet impingement problem, due to its unknown free surface and the change in the boundary, falls in the category of special problems and none of the traditional approaches is suitable for this application. The Arbitrary Lagrangian Eulerian (ALE) formulation has emerged as a technique that can alleviate many of the shortcomings of the traditional Lagrangian and Eulerian formulations in handling these types of problems. Using the ALE formulation the computational grid need not adhere to the material (Lagrangian) nor be fixed in space (Eulerian) but can be moved arbitrarily. Two distinct techniques are being used to implement the ALE formulation, namely the operator split approach and the fully coupled approach. This thesis presents a fully coupled ALE formulation for the simulation of flow field. ALE form of Navier-Stokes equations are derived from the basic principles of continuum mechanics and conservation laws in the fluid. These formulations are then converted in to ALE finite element equations for the fluid flow. The axi-symmetric form of these equations are then derived in order to be used for jet impingement application. In the ALE Formulation as the mesh or the computational grid can move independent of the material and space, an additional set of unknowns representing mesh movement appears in the equations. Prescribing a mesh motion scheme in order to define these unknowns is problem-dependent and has not been yet generalized for all applications. After investigating different methods, the Winslow method is chosen for jet impingement application. This method is based on adding a specific set of partial differential Equations(Laplace equations) to the existing equations in order to obtain enough equations for the unknowns. Then these set of PDEs are converted to finite element equations and derived in axi-symmetric form to be used in jet impingement application. These equations together with the field equations are then applied to jet impingement problem. Due to the number of equations and nonlinearity of the field equations the solution of the problem faces some challenges in terms of convergence characteristics and modeling strategies. Some suggestions are made to deal with these challenges and convergence problems. Finally the numerical treatment and results of analyzing hydrodynamics of the Jet Impingement is presented. The work in this thesis is confined to the numerical simulation of the jet impingement and the specifications of an industrial test setup only have been used in order to obtain the parameters of the numerical model. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Un jet d’azote à basse température et généré à haute pression est utilisé pour le décapage et le traitement de surfaces. Ce procédé est en cours de développement. Il se présente comme une écotechnologie au regard des procédés de décapage conventionnels. L’interaction jet/matière impactée dépend de nombreux paramètres : paramètres liés à la formation et à la nature physique du jet d’une part, paramètres mécaniques et thermiques de la cible d’autre part. Ces différents éléments se composent pour produire une grande variété de modes d’endommagement (rupture par clivage, fissuration, écaillage, fragmentation des grains, expansion de cavités, déformation plastique et rupture ductile). Pour comprendre les mécanismes physiques responsables de ces diverses formes d’endommagement, une étude expérimentale sur quatre matériaux métalliques est présentée. Cette étude a montré que le choc thermo-mécanique et l’effet de souffle dus à l’impact du jet peuvent expliquer la superposition de plusieurs modes d’endommagement dans le même test. Le mécanisme d’endommagement principal est la décohésion du matériau due aux contraintes thermo-élastiques de traction engendrées par le choc thermique. La fragmentation des grains et le transport ultrarapide de l'azote dans une couche profonde sous la surface impactée et leurs relations avec le durcissement de la couche superficielle sont explorés dans le cas de l’acier E24. Les résultats suggèrent qu'un tel traitement de surface pourrait être efficace pour le durcissement du matériau / Nitrogen jets have been used recently for matter removal as well as surface treatment. The process consists in projecting onto a surface a low temperature jet obtained from releasing the liquid nitrogen stored in a high pressure tank through a nozzle. This work is aimed at understanding the highly complex jet/material surface interaction mechanisms. Depending on the impacted material, the thermo-mechanical shock and blast effect induced by the jet can activate a wide range of damage mechanisms, including cleavage, crack nucleation and spalling, as well as plastic deformation, void expansion and localized ductile failure. The test parameters (standoff distance, dwell time, operating pressure) play a role in selecting the dominant damage mechanism, but combinations of these various modes are usually present. The main damage mechanism is the decohesion of the material due to thermo-elastic stress generated by the thermal shock. The fragmentation of grains and high-speed transport of nitrogen in a deep layer below the impacted surface and their relationship with the hardening of a surface layer are explored in the case of the steel E24. The results suggest that such surface treatment may be effective for the hardening of the material surface

The thesis begins with a review of the literature dealing with the incentives and disincentives for pursuing defence co-production policies in Western Europe. Political, economic and military aspects are each dealt with in turn, and their relative importance assessed. Following this section is a case study of the Panavia Multi-Role Combat Aircraft - the 'Tornado' - now in service with the air forces of West Germany, Britain and Italy. The study traces the progress of the MRCA programme from its initial conception through to production. The main theme of the case study is how the concerns of military-operational performance, cost-saving benefits, and programme efficiency were all secondary to government pursuit of wider political objectives. While the general literature was found to focus upon cost-savings in collaborative procurement, such savings are seen to be constrained or even determined by the outcome of frequently unrelated political decisions. Although set within the broad framework of national economic performance and the demands of social needs upon limited public expenditure budgets, these decisions are based upon government preferences rather than industrial or other lobby-group pressures. A cursory evaluation of the MRCA programme and the aircraft itself is included in the conclusion. The project is seen to have achieved mixed success, but with significant problems. / Arts, Faculty of / Political Science, Department of / Graduate

A better understanding and control of internal combustion engine pollutants require more insightful investigation of gasoline oxidation chemistry. An oxidation study has been done on n-heptane, iso-octane, their binary mixtures (Primary Reference Fuel, (PRF)), and nine hydrocarbon mixtures which represent the second generation of gasoline surrogates (multi-component surrogates). This study aims to develop a better understanding of the combustion reaction by studying the oxidation reaction of different fuels inside a jet-stirred reactor and numerically simulating the reaction using different models under the following conditions: pressure 1 bar, temperature 500-1050K, residence time 1.0 and 2.0s, and two fuel-to-oxygen ratios (ϕ=0.5 and 1.0). Intermediate and product species mole fractions versus temperature profiles were experimentally measured using a GC (gas chromatograph). The experiment was performed within the high and low-temperature regions, where the high-temperature oxidation showed similar behavior for different compositions but the low-temperature oxidation showed significant dependence on the composition of the surrogates. Additionally, the effect of octane number on oxidation chemistry has been investigated and it was found that the low octane number surrogates were more reactive than high octane number surrogates during the low temperature regime. Furthermore, Kinetic analysis was conducted to provide insightful understanding of different factors of fuel reactivity. In addition, the pyrolysis of two TPRF, (Toluene primary reference fuels) mixtures (TPRF70 and TPRF97.5), representing low octane (research octane number 70) and high octane (research octane number 97.5) gasoline, was also studied in jet-stirred reactor coupled with gas chromatography (GC) analysis to investigate the formation of soot and polycyclic aromatic hydrocarbons (PAH) formation.

Jet-in-crossflow is an interaction between a fuel jet and air crossflow commonly found in jet engines. The crossflow is used to break up or atomize the fuel jet for downstream combustion. This interaction between fluids while at low speeds, is predictable, varies greatly at higher speeds. This investigation seeks to (1) create a mechanism for jet-in-crossflow, using mechanical pintles, that is independent of velocity to help increase the predictability and reliability of jet engines and (2) identify key design parameters that will lead to flow independence. Parameters investigated in this experiment include pintle height, angle, and percent of pintle coverage into the jet orifice. Pintles that covered 100 percent of the jet showed a strong deviation from the traditional interaction with no pintle. Relationships were also found between the angle, height, and penetration depth although none as ubiquitous as the jet coverage.

No description available.