<p> An experimental study of the flow phenomena occurring in jet-driven vortex flows was undertaken. Two vortex chambers were constructed, one using compressed air, the other using water as the working fluid. Temperatures and total and static pressures were measured at several locations in the air-driven vortex chamber, and the wall static pressure, temperature and Mach number distributions for the vortex were presented for different exit geometries and mass flow rates. A comparison of some indicative experimental results was made with the present vortex theory. </p> / Thesis / Master of Engineering (MEngr)

Acoustic sensing provides a possibility of measuring propulsion flow fields non-intrusively, and is of great interest because it may be applicable to cases that are difficult to measure with traditional methods. In this work, some of the successes and limitations of this technique are considered. In the first main result, the acoustic time of flight is shown to be usable along with a calibration curve in order to accurately estimate the thrust of two turbofan engines (1.0-1.5%). In the second, it is shown that acoustic tomography methods that only use the first ray paths to arrive cannot distinguish some relevant propulsion flow fields (i.e., different flow fields can have the same times of flight). In the third result we demonstrate, via the first validated acoustic tomography experiment on a turbofan engine, that a reasonable estimate of the flow can be produced despite this challenge. This is also the first successful use of acoustic tomography to reconstruct a compressible, multi-stream flow. / Doctor of Philosophy / Sound may be used to measure air flows, and has been used for this purpose in studies of the atmosphere for decades. In this work, the extension of the method to measure air flows in aircraft engines is considered. This is challenging for two main reasons. The first challenge is that aircraft engines are very loud, which makes it harder to accurately measure the sounds that are needed to determine the speeds and temperatures. In this work, we show that the thrust (the force made by an engine) may be accurately measured using sound despite this difficulty. The second challenge is that the temperatures and velocities involved are very large compared to those in the atmosphere. We show that these large variations in temperature and velocity can make it impossible to distinguish between two different air flows in certain circumstances. We also show that despite this limitation, sound can be used to produce a reasonable, though imperfect, estimate of the flow. In particular, the technique was successfully used to measure the varying temperatures and velocities in a jet engine, which has not been done successfully before.

Previous experimental and numerical studies focused on incompressible flow interactions with multi-scale fractal structures targeting the generation of turbulence at multiple scales. Depending on various flow conditions, it was found that these fractal structures are able to enhance mixing and scalar transport, and in some cases reduce flow generated sound in certain frequency ranges. The interaction of compressible flows with multi-scale fractal structures, however, did not receive attention as the focus was entirely on the incompressible regime. The objective of this study is to conduct large eddy simulations (LES) of flow interactions with a class of fractal plates in the compressible regime, and to extract and analyze different flow statistics in an attempt to determine the effect of compressibility. Immersed boundary methods (IBM) will be employed to overcome the difficulty of modeling the fractal structures via a bodyitted mesh, with adequate mesh resolution around small features of the fractal shapes.

No description available.

The Air Inlet Method of Characteristics Analysis Tool (AIMCAT), a tool based in Python 3, is developed to model supersonic air inlet geometries during the early phases of design. The method of characteristics (MOC) is used to solve the governing equations for an inviscid, irrotational, isentropic, steady, supersonic flowfield. A comparison is made between modeling shock waves implicitly using Mach wave coalescence and modeling them explicitly using oblique shock relations. Multiple test cases are used to assess the accuracy of the tool by comparing to experimental wind tunnel data. Good general agreement was achieved over the majority of the supersonic portion of the flowfield for all test cases. The implicit shock mesh achieved better accuracy for shock wave positions compared to the explicit shock mesh. However, the explicit shock mesh captured total pressure losses across the shocks which is of value when assessing the efficiency of the inlet. Both approaches show their respective values and their suitability depends on the conditions being studied. AIMCAT has shown initial promise, however further development is need to improve its utility and robustness.

Lubrication theory plays a fundamental role in all mechanical design as well as applications to biomechanics. All machinery are composed of moving parts which must be protected against wear and damage. Without effective lubrication, maintenance cycles will be shortened to impractical levels resulting in increased costs and decreased reliability. The focus of the work presented here is on the lubrication of rotating machinery found in advanced power systems and designs involving micro-turbines. One of the earliest studies of lubrication is due to Osborne Reynolds in 1886 who recorded what is now regarded as the canonical equation governing all lubrication problems; this equation and its extensions have become known as the Reynolds equation. In the past century, Reynolds equation has been extended to include three-dimensional effects, unsteadiness, turbulence, variable material properties, non-newtonian fluids, multi-phase flows, wall slip, and thermal effects. The bulk of these studies have focused on highly viscous liquids, e.g., oils. In recent years there has been increasing interest in power systems using new working fluids, micro-turbines and non-fossil fuel heat sources. In many cases, the design of these systems employs the use of gases rather than liquids. The advantage of gases over liquids include the reduction of weight, the reduction of adverse effects due to fouling, and compatibility with power system working fluids. Most treatments of gas lubrication are based on the ideal, i.e., low pressure, gas theory and straightforward retro-fitting of the theory of liquid lubrication. However, the 21st Century has seen interest in gas lubrication at high pressures. At pressures and temperatures corresponding to the dense and supercritical gas regime, there is a strong dependence on gas properties and even singular behavior of fundamental transport properties. Simple extrapolations of the intuition and analyses of the ideal gas or liquid phase theory are no longer possible. The goal of this dissertation is to establish the correct form of the Reynolds equation valid for both low and high pressure gases and to explore the dynamics predicted by this new form of the Reynolds equation. The dissertation addresses five problems involving our new Reynolds equation. In the first, we establish the form appropriate for the simple benchmark problem of two-dimensional journal bearings. It is found that the material response is completely determined by a single thermodynamic parameter referred to as the "effective bulk modulus". The validity of our new Reynolds equation has been established using solutions to the full Navier-Stokes-Fourier equations. We have also provided analytical estimates for the range of validity of this Reynolds equation and provided a systematic derivation of the energy equation valid whenever the Reynolds equation holds. The next three problems considered here derive local and global results of interest in high speed lubrication studies. The results are based on a perturbation analysis of our Reynolds and energy equation resulting in simplified formulas and the explicit dependence of pressure, temperature, friction losses, load capacity, and heat transfer on the thermodynamic state and material properties. Our last problem examines high pressure gas lubrication in thrust bearings. We again derive the appropriate form of the Reynolds and energy equations for these intrinsically three-dimensional flows. A finite difference scheme is employed to solve the resultant (elliptic) Reynolds equation for both moderate and high-speed flows. This Reynolds equation is then solved using perturbation methods for high-speed flows. It is found that the flow structure is comprised of five boundary layer regions in addition to the main ``core'' region. The flow in two of these boundary layer regions is governed by a nonlinear heat equation and the flow in three of these boundary layers is governed by nonlinear relaxation equations. Finite difference schemes are employed to obtain detailed solutions in the boundary layers. A composite solution is developed which provides a single solution describing the flow in all six regions to the same accuracy as the individual solutions in their respective regions of validity. Overall, the key contributions are the establishment of the appropriate forms of the Reynolds equation for dense and supercritical flows, analytical solutions for quantities of practical interest, demonstrations of the roles played by various thermodynamic functions, the first detailed discussions of the physics of lubrication in dense and supercritical flows, and the discovery of boundary layer structures in flows associated with thrust bearings. / Doctor of Philosophy / Lubrication theory plays a fundamental role in all mechanical design as well as applications to biomechanics. All machinery are composed of moving parts which must be protected against wear and damage. Without eective lubrication, maintenance cycles will be shortened to impractical levels resulting in increased costs and decreased reliability. The focus of the work presented here is on the lubrication of rotating machinery found in advanced power systems and designs involving micro-turbines. One of the earliest studies of lubrication is due to Osborne Reynolds in 1886 who recorded what is now regarded as the canonical equation governing all lubrication problems; this equation and its extensions have become known as the Reynolds equation. In the past century, Reynolds equation has been extended to include three-dimensional eects, unsteadiness, turbulence, variable material properties, non-newtonian uids, multi-phase ows, wall slip, and thermal eects. The bulk of these studies have focused on highly viscous liquids, e.g., oils. In recent years there has been increasing interest in power systems using new working uids, micro-turbines and non-fossil fuel heat sources. In many cases, the design of these systems employs the use of gases rather than liquids. The advantage of gases over liquids include the reduction of weight, the reduction of adverse eects due to fouling, and compatibility with power system working uids. Most treatments of gas lubrication are based on the ideal, i.e., low pressure, gas theory and straightforward retro-tting of the theory of liquid lubrication. However, the 21st Century has seen interest in gas lubrication at high pressures. At pressures and temperatures corresponding to the dense and supercritical gas regime, there is a strong dependence on gas properties and even singular behavior of fundamental transport properties. Simple extrapolations of the intuition and analyses of the ideal gas or liquid phase theory are no longer possible. The goal of this dissertation is to establish the correct form of the Reynolds equation valid for both low and high pressure gases and to explore the dynamics predicted by this new form of the Reynolds equation. The dissertation addresses ve problems involving our new Reynolds equation. In the rst, we establish the form appropriate for the simple benchmark problem of two-dimensional journal bearings. It is found that the material response is completely determined by a single thermodynamic parameter referred to as the eective bulk modulus. The validity of our new Reynolds equation has been established using solutions to the full Navier-Stokes-Fourier equations. We have also provided analytical estimates for the range of validity of this Reynolds equation and provided a systematic derivation of the energy equation valid whenever the Reynolds equation holds. The next three problems considered here derive local and global results of interest in high speed lubrication studies. The results are based on a perturbation analysis of our Reynolds and energy equation resulting in simplied formulas and the explicit dependence of pressure, temperature, friction losses, load capacity, and heat transfer on the thermodynamic state and material properties. Our last problem examines high pressure gas lubrication in thrust bearings. We again derive the appropriate form of the Reynolds and energy equations for these intrinsically threedimensional ows. A nite dierence scheme is employed to solve the resultant (elliptic) Reynolds equation for both moderate and high-speed ows. This Reynolds equation is then solved using perturbation methods for high-speed ows. It is found that the ow structure is comprised of ve boundary layer regions in addition to the main core region. The ow in two of these boundary layer regions is governed by a nonlinear heat equation and the ow in three of these boundary layers is governed by nonlinear relaxation equations. Finite dierence schemes are employed to obtain detailed solutions in the boundary layers. A composite solution is developed which provides a single solution describing the ow in all six regions to the same accuracy as the individual solutions in their respective regions of validity. Overall, the key contributions are the establishment of the appropriate forms of the Reynolds equation for dense and supercritical ows, analytical solutions for quantities of practical interest, demonstrations of the roles played by various thermodynamic functions, the rst detailed discussions of the physics of lubrication in dense and supercritical ows, and the discovery of boundary layer structures in ows associated with thrust bearings.

Les émissions polluantes à l’échappement des véhicules automobiles sont l'une des principales sources de pollution de l'air dans le monde d'aujourd'hui. Par conséquent, la législation a évolué afin de limiter ces émissions. L'un des aspects clés pour répondre consiste à bien maîtriser les échanges gazeux au sein du moteur à combustion interne. Cette amélioration est possible par l'optimisation de répartiteurs d'admission d'air. Dans ces répartiteurs d'admission d'air, la maitrise de l’écoulement de type tumble est une piste de progrès. Des volets sont installés à la sortie du répartiteur afin d'améliorer le rapport de tumble et donc le mélange air-carburant (VTS-Variable Tumble System). Une autre caractéristique de l'écoulement à l'intérieur des répartiteurs est l'effet des écoulements pulsés qui engendrent des fluctuations de pression assez importante. Par conséquent, le but de cette étude consiste à simuler le flux d'air pulsé à l'intérieur des répartiteurs d'admission et à identifier l'effet des pulsations de pression sur les composants actifs tels que les volets. Le travail de simulation dans la présente thèse a été effectué à partir du code open source CFD OpenFOAM. Dans un premier temps, l'effet des pulsations de pression est simulé à l'intérieur d'un tube d'acier et une méthodologie de simulation est développée. Les résultats de la simulation sont validés à partir de résultats expérimentaux obtenus sur un dispositif spécifique, le banc dynamique. Ensuite, des simulations ont été effectuées sur le répartiteur d'admission principal avec des volets. Tout d’abord, les simulations sont effectuées en régime permanent avec cinq positions d'ouverture différentes du clapet. Les forces et les moments agissant sur le volet en régime permanent sont obtenus et analysés. Puis, des simulations en régime transitoire avec des effets de pulsation de pression sont effectuées. Les résultats de la simulation instationnaire sont comparés aux résultats expérimentaux en termes de fluctuations de pression relative. Les effets des pulsations de pression sur les forces aérodynamiques et les moments agissant sur les volets sont analysés et commentés. / The exhaust emissions from automobiles are one of the major sources of air pollution in today’s world. Thence,research and development is the key feature of the modern automotive industries to meet strict emission legislation. One of the key aspects to meet these requirements is to improve the gas exchange process within internal combustion engines. It is possible by the design optimization of the air intake manifolds for internal combustion engines. One of such advancement in air intake manifolds is variable tumble systems (VTS). In VTS system, tumble flaps are installed at the exit of the manifold runner in order to improve tumble ratio and hence air-fuel mixing. Another feature of the flow inside the intake manifolds is pressure pulsation effect. Therefore, the aim of the Ph.D. work is to simulate the pulsating air flow inside the air intake manifolds and to identify the effect of the pressure pulsations on the active components like tumble flaps. The simulation work in the present thesis has been carried out on open source CFD code OpenFOAM. In a first step, the effect of pressure pulsations is simulated inside a steel tube and a simulation methodology is developed. The results of the simulation are validated on a specific experimental device, the dynamic flow bench. Then,simulations have been carried out on the main intake manifold with tumble flaps. Firstly, the simulations are performed with five different opening positions of the tumble flap in a steady state configuration. The forces and moments acting on the flap in steady state are obtained and analyzed. Then, unsteady simulations with pressure pulsation effects are performed. The results of obtained from unsteady simulation are compared with the experimental results in terms of relative pressure fluctuations. The effect of the pressure pulsation on the aerodynamic forces and moments acting on the tumble flaps are analyzed and explained.

La pyrolyse est la décomposition thermochimique de la biomasse en gaz de synthèse valorisables en biocarburants. Cette technologie, propre et renouvelable, nécessite aujourd’hui des efforts de recherche et de développement afin de prouver sa compétitivité par rapport aux autres sources d’énergie. L’objectif de cette thèse est de développer un modèle macroscopique de la pyrolyse en utilisant la méthode de prise de moyenne volumique. Le modèle sera ensuite utilisé pour faire des études numériques afin de caractériser le procédé et améliorer les performances des réacteurs. Une approche en deux temps a été établie afin d’atteindre notre objectif. D’abord, des modèles macroscopiques d’écoulements à masse volumique variable en milieu poreux ont été développés. Ce type d’écoulements est similaire à celui mis en jeu en pyrolyse pour deux deux raisons: la masse volumique varie sous l’effet de gradients forts de température et le réacteur de pyrolyse peut être considéré comme un milieu poreux à double porosité (porosité à l’échelle du lit et porosité à l’échelle de la particule). Les résultats théoriques ont montré que les équations de conservation macroscopiques (continuité, quantité de mouvement et énergie) et les propriétés effectives (masse volumique, perméabilité et diffusivité thermique) font apparaitre de nouveaux termes résultants de la variation de densité. La forme explicite de ces termes a été établie et validée par simulations numériques. Les résultats obtenus ont été utilisés dans un deuxième temps afin de développer un modèle macroscopique de la pyrolyse. / Pyrolysis is a thermo-chemical conversion of biomass into bio-fuels. This technology has not been fully developed and its competitiveness against other sources of energy is yet to be proven. The aim of this work is to derive a macroscopic model of pyrolysis by means of volume averaging method. The obtained macroscopic model can then be used to conduct fast and low-cost numerical simulations to characterize the process and improve the reactor efficiency. To achieve our objective, a two-steps methodology has been established. First, the fundamental problem of variable density flow in porous media has been investigated. The physical phenomena in this kind of problem are very similar to those involved in pyrolysis for two reasons: the fluid density varies due to high temperature gradients and the pyrolysis reactor can be considered as a double porosity medium (porosity at the reactor scale and porosity at the biomass particle scale). The obtained macroscopic conservation equations (continuity, momentum and energy) and the effective properties (density, permeability and thermal diffusivity) contain additional terms resulting from the fluid density variation. The explicit form of these terms has been established and their components have been computed. The resulting models of the first step have then been used to develop a macroscopic model of the pyrolysis in the second part of our study.

La simulation des écoulements cavitants est confrontée à des difficultés de modélisation et de résolution numérique provenant des caractéristiques particulières de ces écoulements : changement de phase, gradient de masse volumique important, variation du nombre de Mach, turbulence diphasique, instationnarités. Dans cette thèse, nous nous sommes appliqués à dériver proprement le modèle de mélange homogène 1-fluide couplé à une modélisation RANS de la turbulence. A partir des termes contenus dans ces équations et de la nature des écoulements cavitants étudiés, plusieurs modèles de turbulence basés sur la notion de viscosité turbulente ont été testés : modèles faiblement non-linéaires (corrections SST et de réalisabilité), ajout des termes de turbulence compressible, application de la correction de Reboud, modèles hybrides RANS/LES (DES, SAS). Ces modèles ont été incorporés dans un code compressible qui fait appel à une résolution implicite en pas de temps dual des équations de conservation avec une technique de pré-conditionnement bas-Mach pour traiter les zones incompressibles. Les simulations 2D et 3D ont porté sur deux géométries de type Venturi caractérisées par la présence d’une poche de cavitation instationnaire due à l’existence d’un jet rentrant liquide/vapeur le long de la paroi. Elles montrent que l’ensemble des modèles sont capables de capturer le jet rentrant. En revanche, la dynamique de la poche varie entre les modèles et le manque de données expérimentales ne permet pas de discriminer les modèles entre eux. Il apparaît à la vue des résultats que les approches avec la correction de Reboud ou les modèles SAS améliorent la simulation des écoulements. / The computation of cavitating flows is a challenging issue due to the characteristics of these flows : phase transition, large density gradient, Mach number variation, interaction between phases and turbulent flow, unsteadiness. In the present study, we performed a derivation of the one-fluid compressible homogenous model coupled with a RANS approach for the turbulent flow. From these equations and the nature of the cavitating flows, several models based on the eddy viscosity assumption have been tested : weakly non-linear models (SST and realisability corrections), compressible turbulence models, hybrid RANS/LES turbulence models (SAS, DES) and the Reboud correction. All the models are implemented in a compressible code, which solves the equations using an implicit dual-time stepping method coupling with a pre-conditionning technique for the incompressible area. 2D and 3D computations are performed on two Venturi geometries characterized by an unsteady cavitation sheet with a liquid/vapor re-entrant jet. All the models are able to capture the re-entrant jet. Nevertheless, the dynamic behaviour differs from one model to another and the lack of experimental data prevents to discriminate the models between them. From the results, the computations with the SAS model and the Reboud correction improve the prediction of the flow.

Grâce à leurs bonnes propriétés mécaniques spécifiques, les matériaux cellulaires architecturés présentent un fort intérêt pour répondre aux problématiques du secteur aéronautique. Cependant, la modélisation d'une structure macroscopique incluant un matériau cellulaire nécessite, soit de modéliser complètement l'architecture à l'échelle mésoscopique - ce qui est coûteux en temps de calcul - soit d'utiliser un Milieu Homogène Equivalent (MHE). Ainsi, cette thèse propose de caractériser un matériau cellulaire modèle constitué d'un empilement de tubes, selon un motif carré ou hexagonal, puis d'identifier un modèle phénoménologique rendant compte du comportement mécanique inélastique du matériau. Dans un premier temps, le matériau est caractérisé sous chargements multi-axiaux à l'aide de simulations éléments finis périodiques en petites déformations. Le comportement homogénéisé en petites déformations est ensuite utilisé pour l'identification d'une Loi Homogène Equivalente (LHE) compressible et anisotrope, qui permet la modélisation de structures sandwichs en remplaçant le coeur cellulaire par son MHE. Une comparaison est réalisée entre les réponses mécaniques des simulations de référence complètement maillées et celles utilisant l'approche par MHE, validant ainsi la pertinence de la méthode multi-échelle de modélisation proposée. La caractérisation en grandes déformations des deux types d'empilement est ensuite menée. D'abord, les effets de bords et les instabilités qui gouvernent le comportement macroscopique sont étudiés. Puis, après une étude du volume élémentaire représentatif des empilements, la caractérisation du comportement inélastique par la technique de l'homogénéisation périodique est réalisée. Le comportement adoucissant en compression de l'empilement hexagonal est ainsi étudié. Finalement, une extension des LHE identifiées en petites déformations est proposée pour rendre compte du comportement en compression du matériau observé en grandes déformations. / Cellular materials have excellent specific properties, which make them attractive for aeronautical applications. However, modelling macroscopic structures including a cellular material is either very costly in terms of computational time if the whole mesoscopic structure is considered or a Homogeneous Equivalent Medium (HEM) has to be used. This Ph.D. dissertation presents, the characterisation of a cellular material built from a stacking of tubes with a square or hexagonal based pattern and the identification of a phenomenological model of their inelastic mechanical behaviour. First, the material is characterised for multi-axial loadings through a periodic finite element model in small deformations for each tube stacking pattern. The macroscopic behaviour is then used to identify a compressible anisotropic Homogeneous Equivalent Law (HEL). Within the infinitesimal strain hypothesis, a comparison is carried out between reference full scale models and HEM based ones of sandwich structures with a cellular core, confirming the relevance of the proposed multi-scale method. Then, the mechanical behaviour of each tube stacking is characterised for large deformations in order to study the influence of the boundary size effects and the instabilities in the core on the macroscopic behaviour of sandwich structures. After a study on the representative volume element, the macroscopic inelastic behaviour is characterised through the periodic homogenisation technique, especially the softening observed in compression for the hexagonal pattern. Finally, an extension of the HELs identified in small deformations is proposed to model the behaviour observed in large deformations.