Foi construído um arranjo experimental para estudar o comportamento dos jatos evaporativos. Um injetor foi projetado para controlar e manter constantes a pressão e temperatura de reservatório durante a injeção. Um bocal cônico convergente de seção reta com diâmetro de saída de 0,30 mm e ângulo entre sua geratriz e seu eixo simetria igual à 10º forma o elemento principal do injetor. O jato é descarregado em uma câmara de baixa pressão de dimensões suficientemente grandes para manter a pressão constante durante o curto período de ensaio, igual à 1 s. Quando injetado, o líquido sofre uma repentina queda de pressão ocasionando sua evaporação. Os fluidos utilizados são os combustíveis querosene e óleo diesel, e a substância n-dodecano, os quais se caracterizam pela possibilidade de uma evaporação completa, de forma adiabática. Utilizou-se o método \"schlieren\" para a visualização do escoamento. A análise dos jatos é feita de forma qualitativa através dos registros fotográficos. Foram observados os seguintes tipos de jato: (1) contínuo, (2) pulverizante e (3) evaporação na superfície. O primeiro jato não implica em imediata mudança de fase tornando o jato de líquido emergente intacto. Com o aumento da temperatura de injeção, existe o espalhamento e a evaporação do jato, formando o segundo tipo de jato, onde é possível visualizar o campo do gradiente de densidade do escoamento e a formação de ondas de evaporação e de choque que pode ocorrer a uma distância proporcional a vários diâmetros à jusante. Em jatos com evaporação completa, foram constadas a formação de ondas de choque tanto de formas elipsóide como de esferóide para elevadas temperaturas. As fotografias digitais são submetidas à filtragem e processamento matemático para melhor destacar tais fenômenos do escoamento. / An experimental apparatus has been built to study the behaviour of flashing jets. An injector was designed to control and maintain the jet pressure and temperature at constant values during the injection process. A conical convergent nozzle whose main dimensions are 0,30 mm of exit diameter, 8 mm long, and a convergence half-angle of 10º is the central component of the injection system. The jet is discharged into a low-pressure chamber large enough to keep the reservoir pressure constant during the short test period of about 1 s. As the testing liquid expands in the nozzle it undergoes a sudden pressure drop causing its evaporation. The fluids are usual fuels, such as kerosene and diesel oil, and the substance ndodecane, which are distinguishable by the possibility of a complete evaporation in an isoentropic expansion process. The photographic method \"schlieren\" is used for flow visualisation. A qualitative analysis is made of the photographic documentation of the images obtained using a CCD camera. The images can be grouped into three categories of jets: (1) continuous, (2) shattering, and (3) with surface evaporation. The first regime has an undisturbed a liquid column, which remains more or less intact during the injection process. In the second type, the existing liquid jet is shattered by vapour nucleation and, in some cases, shock waves are clearly visible. It happens at higher temperature than the preceding evaporation mode. Finally, in special situations, the jet undergoes an evaporation at its surface and the two-phase mixture expands at a high speed followed by a shock wave before the mixture attains the pressure reservoir.

Dans cette thèse, nous nous sommes intéressés à la statique et la dynamique du mouillage de gouttes d’eau sur des substrats mous tels que des gels, encore connu sous le nom d’élastomouillage. Pour ce faire, nous avons d'abord développé une méthode quantitative de visualisation par strioscopie permettant de mesurer la déformation de la surface d'un film de gel transparent avec une précision élevée. Nous montrons que la déformation superficielle de films mous de silicone (PDMS) dépend de la taille des gouttelettes déposées ainsi que de l'épaisseur et de l’élasticité de ces films. Nous avons construit un modèle basé sur la théorie de l'élasticité linéaire tenant compte de la tension superficielle des gels qui prédit bien la forme et l’amplitude de la déformation de surface. Nous apportons aussi la preuve expérimentale et l'analyse théorique de l’importance de l'hystérèse de l’angle de contact dans la description de la déformation en démontrant que la force tangentielle due à la tension superficielle entre liquide et vapeur à la ligne de contact, souvent négligé, contrôle la déformation de la surface. La dynamique de mouillage est étudiée en dégonflant des gouttelettes sur des films de PDMS avec une épaisseur bien contrôlée. Il est démontré que la dissipation d'énergie dans le gel dépend fortement de l'épaisseur lorsque cette dernière est inférieure à 100 μm). L'effet de freinage viscoélastique et l'effet d'épaisseur sont bien rationalisés avec un modèle basé sur la viscoélasticité linéaire et une simple loi l'échelle qui tient compte de l'effet d'épaisseur capture très bien nos expériences. Enfin, nous démontrons que nous pouvons dériver et guider les gouttelettes en mouvement avec la conception de surfaces couvertes de couches de gels ayant des gradients d'épaisseur. / In this thesis, we aim at obtaining a better understanding of the statics and dynamics of the wetting of liquids on soft gels, otherwise known as elastowetting. First, we develop a quantitative Schlieren optics to measure the surface deformation of a transparent gel film with a high precision over large areas in real time. The long-range surface deformation of soft PDMS films is found to be dependent on the sessile droplet size, and the thickness and elasticity of the soft films. We build a model based on linear elasticity theory with the integration of the surface tension of soft materials that predicts the long-range surface deformation in excellent agreement with the data. We also bring the experimental proof and theoretical analysis of the importance of contact angle hysteresis in the description of the deformation of the surface of the gel. We demonstrate that the tangential component of the liquid-vapor surface tension at the contact line, whose contribution are often neglected, significantly affects the surface deformation. Wetting dynamics is investigated by deflating droplets on PDMS films with well-controlled thickness. It is shown that energy dissipation in the soft gel depends on the thickness when the latter is smaller than 100 μm. The viscoelastic braking effect and the thickness effect are both well rationalized with a model based on the theory of linear viscoelasticity and a simple scaling law accounting for the thickness effect captures very well our experiments. Finally, we demonstrate that we are able to guide moving droplets with coatings having a gradient of their thickness.

This thesis proposed and demonstrated a new all-polymer based fabrication process for an all-polymer flexible and parallel optical interconnect cable having a vertical light coupler, which can not only cut down the cost by eliminating metallization process for alignment but also facilitate both in production and application. Throughout the process, polyimide was used as the substrate, coated by Epoclad as claddings, then AP2210B and WPR 5100 were used to fabricate waveguides and 45 degree mirror couplers, respectively. In addition, precisely aligned mirror couplers to waveguides are fabricated by using polymer-based, non-metallic, and transparent alignment marks. Conventional and metallic alignment marks are easy to be detected by camera, when a layer of high reflective material, generally Cr metal, is patterned. However, transparent polymer material is used in this process, as alignment marks made of it which are actually buried phase structures. Therefore, it is hardly to be observed by conventional microscopy system. Hence, to increase the contrast of the alignment marks, I proposed and tested a feature specific alignment camera system for which the shape and depth of the alignment marks are optimized for phase-based imaging, such as phase contrast and Schlieren imaging. The results showed a contrast enhancement of alignment marks image compared to that of a conventional microscopy system. By using the fabrication and alignment process, process for adding waveguides to the structure is identified by using the polymer based alignment marks on the WPR 5100 layer. Mask was made by etch down process using fused silica wafer plate, Cr and AZ 3312 photoresist. At last, the developed and proposed process provides means of all-polymer based fabrication process for a flexible and parallel optical interconnect.

Escoamentos de alta velocidade, sejam eles pertencentes à classe supersônica ou hipersônica, são sistemas intrinsecamente ligados às tecnologias aplicáveis ao setor aeroespacial. A capacidade de se determinar a velocidade de um escoamento ganha particular importância se considerada sua aplicação como informação crítica na validação de códigos computacionais de dinâmica de fluidos. O objetivo do presente trabalho é a caracterização das velocidades de escoamentos produzidos por uma câmara de expansão. Para tanto, foram utilizadas três técnicas para medidas de velocidades supersônicas e subsônicas. Uma técnica intrusiva, que utiliza um Detector por Ionização Rápida, para caracterização de escoamentos supersônicos e duas técnicas ópticas, schlieren e um método modificado do schlieren que foi combinado com a absorção molecular do iodo. Com o uso do Detector por Ionização Rápida foi possível estudar escoamentos produzidos em uma pressão de 10-6 mbar e com velocidades que variaram de 21 até 726 ms-1. Usando o método das características para calcular a temperatura e o número de Mach, foi possível obter escoamentos com temperatura mínima de 29 K e com número de Mach máximo de 12. Com a velocimetria schlieren foi possível visualizar escoamentos sob um vácuo de até 200 mbar e com velocidades que variaram de 5,2 até 66,5 ms-1. A temperatura do escoamento variou de 300,0 a 297,6 K e o número de Mach máximo foi de 0,2. A partir da modificação do método schlieren, foi possível visualizar escoamentos em pressões de até 15 mbar, equivalente a uma ordem de grandeza inferior ao método schlieren convencional. Com o método foram medidas velocidades do escoamento que variaram de 92,0 a 190,0 ms-1. A temperatura variou de 295,3 a 280,1 K e o número de Mach máximo foi de 0,6.

The geometrical characteristics of acoustical radiation are of great importance in instrument design and synthesis, and multiple simplified models have been developed in the past to describe them. In this work two experimental methodologies are proposed and carried out, studying the frequency-dependent radiation in a collection of popular brass instruments with different grades of flaring, and making use of the axis-symmetry of these instruments. The first method uses a scanning linear array and is carefully designed to extract the linear properties of the radiation field. The results of this experimental method are a database of impulse responses distributed in space, and effectively covering a bidimensional on-axis section of the radiation field approximately 0.6 m by 0.9 m. These data can then be used for the validation of a number of simplified physical models used to describe the radiation of these types of instruments. The second method aims at visualising radiation for high amplitude excitation, where shock waves are generated inside the instrument due to non-linear propagation of the plane wave. In this case, the experimental methodology used, taking advantage of the strong density and temperature gradients generated in the air, is an on-axis schlieren optical system. General results of this visualisation show a strong increase in focused directivity at high frequencies and loud playing dynamics, due to the spectral enrichment typical of this family of instruments. The second section of this thesis focuses on the study of playing gestures in the trombone, and could also be applicable to other slide instruments. During glissando playing in the trombone the length of the cylindrical slide section within the bore is altered while waves are propagating. Slide velocities of 2 metres per second are not unusual and result in a (small but measurable) Doppler shift in the wave coming from the mouthpiece before it arrives at the bell. An additional effect is observed in terms of the volume of air within the instrument changing telescopically, leading to a localised change in DC pressure and a resulting flow, which generates infrasound components within the bore. The effects of these playing gestures are investigated in two different setups; one with a high frequency sinusoidal excitation generated by a compression driver, and another one using an artificial mouth to play the instrument. In both experiments the pressures at the mouth or mouthpiece, water key and bell were tracked using microphones and the position of the slide was tracked using a laser distance sensor. Both Doppler shifting and infrasound components were detected for both experimental setups, although the effect on a soft termination such as the artificial lips requires further examination.

In 21 century finned surfaces are used in almost all condensers to enhance their heat transfer capabilities. A lot of different models are presented in the literature: on horizontal and vertical finned tubes, inside finned tubes. The validation method of the theoretical models is based on comparison between measurement of average heat transfer coefficient and one calculated by the model. But in this case it is impossible to validate all approaches made in the theory. The presented work aims to understand the real relation between assumptions made in the theory and flow of the condensate film along a fin. Therefore a comprehensive investigation of the film condensation phenomena on curvilinear surfaces has been done. This investigation has been done in the framework of the preparation of “SAFIR” and “EMERALD” space experiments aboard International Space Station. A special attention has been given to clarify some technical and technological problems that could eventually have a positive feedback for industrial applications. The model of the fin shape optimization has been developed. It takes into account surface tension forces and finite heat conductivity of the fin material. Developed model allows to significantly increase the condensate outflow as compared with the case of the optimal isothermal fin shape at the finite heat transfer conductivity. Enhancement coefficient increases with fin heat conductivity decreasing. The experimental and theoretical investigation of film condensation on a disk-shaped fin has been done under groun condition. 3D condensation model at different gravity levels has been developed. This model allows to reveal the area of dominant influence of surface tension forces. First prototype of experimental cell for the space experiments has been developed and tested. The temperature distribution along the curvilinear fin surface has been measured. The measurements of the film thickness at the fin top shows that the film thickness does not equal to zero as was assumed in some previous theoretical models. Developed model is in a good agreement with experimental results. In the ground set-up the measurement techniques as in future space experiments were realized: local temperature measurement of the fin surface, measurement of non-condensable gas mole fraction, optical system for local film thickness measurement and system of average heat transfer coefficient measurement. Experimental results approve the usefulness of these systems. Optical system based on schlieren technique for film surface deformation has been investigated and developed. This system was used for the investigation of shear driven liquid film on the mirror like substrate under microgravity condition. The microgravity condition was simulated during ESA Parabolic Flight Campaign of October-November 2009. The experimental results show the high capabilities of this system. In the framework of the space experiments preparation the analysis of appropriate liquid has been done. Three candidates have been compared: Water, Ethyl alcohol and FC-72. Third liquid has been chosen as applicable liquid for the “SAFIR” and “EMERALD” experiments. The optimal fin shapes and film thickness distribution have been calculated for the working liquid. Using obtained results requirements for space experiments have been prepared.

The purpose of this study was to investigate the thermochemical properties of a transient supersonic flame. Creation of the transient flame was controlled by pulsing air in 200 millisecond intervals into a combustor filled with flowing methane. The combustor was designed following well-known principles of jet engine combustors. A flame holder and spark plug combination was used to encourage turbulent mixing and ignition of reactant gases, and to anchor the transient flame. Combustion created a high temperature and pressure environment which propelled a flame through a choked de Laval nozzle. The nozzle accelerated the products of combustion to a Mach number of 1.6, creating an underexpanded transient flame which burned for approximately 25 milliseconds. Qualitative information of the flame was gathered by two optical systems. An intensified charge-coupled device (ICCD) was constructed from constitutive components to amplify and capture the chemiluminescence generated by the transient flame, as well as the spatial structure of the flame at specific phases. To gather temporal data of a single transient event as it unfolded, a z-type schlieren optical system was constructed for use with a high speed camera. The system resolves the data in 1 millisecond increments, sufficient for capturing the transient phenomenon. The transient system was modeled computationally in Cantera using the GRI-3.0 reaction mechanism. Experimental conditions were simulated within the zero- dimensional computation by explicit control of the reacting gas mass flow rates within the system. Results from the computational model were used to describe the ignition process. The major limitation of the zero-dimensional reactor model is homogeneity and lack of spatial mixing. In this work a Lagrangian tracking model was used to describe the flame behavior and properties as it travels within the zero-dimensional reactor towards the nozzle. Following this, the flow expansion through the de Laval nozzle was calculated using one-dimensional isentropic relations. The computed reactor model data was then contrasted to experimental results from the ICCD and high speed schlieren images to fully describe the events in the transient supersonic flame.

Detonation waves are supersonic combustion waves that have a multi-shock front structure followed by a spatially non-uniform reaction zone. During propagation, a de-coupled shock-flame complex is periodically re-initiated into an overdriven detonation following a transient Mach reflection process. Past researchers have identified mechanisms that can increase combustion rates and cause localized hot spot re-ignition behind the Mach shock. But due to the small length scales and stochastic behaviour of detonation waves, the important mechanisms that can lead to re-initiation into a detonation requires further clarification. If a detonation is allowed to diffract behind an obstacle, it can quench to form a de-coupled shock-flame complex and if allowed to form a Mach reflection, re-initiation of a detonation can occur. The use of this approach permits the study of re-initiation mechanisms reproducibly with relatively large length scales. The objective of this study is to experimentally elucidate the key mechanisms that can increase chemical reaction rates and sequentially lead to re-initiation of a de-coupled shock-flame complex into an overdriven detonation wave following a Mach reflection. All experiments were carried out in a thin rectangular channel using a stoichiometric mixture of oxy-methane. Three different types of obstacles were used - a half-cylinder, a roughness plate along with the half-cylinder and a full-cylinder. Schlieren visualization was achieved by using a Z-configuration setup, a high speed camera and a high intensity light source. Results indicate that forward jetting of the slip line behind the Mach stem can potentially increase combustion rates by entraining hot burned gas into unburned gas. Following ignition and jet entrainment, a detonation wave first appears along the Mach stem. The transverse wave can form a detonation wave due to rapid combustion of unburned gas which may be attributed to shock interaction with the unburned gas. Alternatively, the Kelvin-Helmholtz instability can produce vortices along the slipline that may lead to mixing between burned-unburned gases and potentially increase combustion rates near the transverse wave. However, the mechanism(s) that causes the transverse wave to re-initiate into a detonation wave remains to be satisfactorily resolved.

Circulation control involves tangentially blowing air around a rounded trailing edge in order to augment the lift of a wing. The advantages of this technique over conventional mechanical controls are reduced maintenance and lower observability. Despite the technology first being proposed in the 1960s and well-studied since, circulation control is not in widespread use today. This is largely due to the high mass flow requirements. Increasing the jet velocity increases both the efficiency (in terms of mass flow) and effectiveness. However, as the jet velocity exceeds the speed of sound, shock structures form which cause the jet to separate. Recent developments in the field of fluidic thrust vectoring (FTV) have shown that an asymmetrical convergent-divergent nozzle capable of producing an irrotational vortex (IV) has the potential to prevent separation through eliminating stream-wise pressure gradients. In this study, the feasibility of preventing separation at arbitrarily high jet velocities through the use of asymmetrical nozzle geometries designed to maintain irrotational (and stream-wise pressure gradient free) flow is explored. Furthermore, the usefulness of an adaptive nozzle geometry for the purpose of extending circulation control device efficiency and effectiveness is defined. Through a series of experiments, the flow physics of supersonic curved wall jets is characterised across a range of nozzle geometries. IV and equivalent area ratio symmetrical convergent-divergent nozzles are compared across three slot height to radius ratios (H/R): H/R = 0.1, H/R = 0.15, H/R = 0.2. The conclusion of this study is that at low H/R (0.1 and 0.15), there is no significant difference in behaviour between IV and symmetrical nozzles, whilst at high H/R (0.2), the IV nozzles begin separating whilst correctly expanded due to the propagation of pressure upstream from the edge of the reaction surface via the boundary layer. Consequently, it is shown that symmetrical nozzles of equivalent mass flow at high H/R have a higher separation NPR compared to IV nozzles. Specifically, the elimination of favourable, in addition to adverse stream-wise pressure gradients contradicts the expected behaviour of IV nozzles. The separation NPR for nozzles tested in this study, in addition to past studies is subsequently plotted against the throat height to radius ratios (A*/R). This shows that in fact, no previous experiments have shown a higher separation NPR for IV nozzles compared to symmetrical nozzles of equivalent mass flow. The overall outcome is that neither fixed geometry IV, nor adaptive nozzles are justified to maintain attachment, or to improve efficiency. This is because fixed nozzle geometries designed for higher separation NPR do not show any performance deficit when operating at lower NPRs. However, the throat height could be varied to maximise effectiveness (at the expense of mass flow). The contributions to new knowledge made by this study are as follows: the development of a new method of combining shadowgraph and schlieren images to simplify and enhance visualisation of supersonic flows; the use of pressure sensitive paint (PSP) to study the structure of the supersonic curved wall jet before and after separation; the identification of a clear mechanism for the separation of supersonic curved wall jets, valid over a broad range of nozzle geometries (including a clarification of previously unexplained behaviour witnessed in prior studies); the explanation that reattachment hysteresis occurs due to the upstream movement of the point of local separation at full separation (specifically, this explains why certain geometries such as backward-facing steps prevent reattachment hysteresis).

(EN) Carbon dioxide (CO2) sequestration in deep saline aquifers is one of the technologies considered to reduce the accumulation of this greenhouse gas in the atmosphere. The injection of CO2 into these deep geological formations and its dissolution in salt water lead to a buoyantly unstable stratification of denser CO2-enriched brine on top of less dense brine, which can give rise to buoyancy-driven convective fingering in the fluid. This convective dissolution of CO2 in brine is a favourable process for its sequestration as it accelerates the mixing of CO2 into the aqueous phase and therefore enhances the safety of the storage in the saline aquifer. The influence of chemical reactions between species and CO2 dissolved in the brine and hence of the physico-chemical characteristics of the geological reservoir on the development of this instability is still not completely understood. In this context, our goal is to determine experimentally whether chemical reactions in the aqueous phase can improve the efficiency of CO2 convective dissolution. To do so, we have developed an experimental device consisting of a vertical Hele-Shaw cell in which gaseous CO2 dissolves from above in aqueous solutions containing chemical reactants of various nature and concentration. The convective dynamics occurring within the transparent fluid are visualised with the help of a schlieren technique. First, we show that the presence of a color indicator in the aqueous solution can affect the fingering dynamics and that such indicators should therefore be used with caution in this kind of studies. We then study the stabilising effect of an increase in the salt concentration on CO2 convective dissolution in brine. In the reactive case, we show that the fingering instability develops faster in basic solutions of MOH (where M+ is an alkali metal cation) than in pure water and that convection is enhanced if the reactant concentration is increased. In addition, a change of the counter-ion M+ changes the density profile, not only through solutal effects, but also through differential diffusivity effects, which impacts the development of the convective instability. Finally, we explore the changes in the convective dynamics induced by precipitation reactions due to CO2 dissolution in aqueous solutions of Ca(OH)2 and CaCl2 in variable concentrations. Diverse precipitation and convective patterns develop in the aqueous solution depending on the nature and concentration of the reactant in the aqueous phase. Our results show that the convective dissolution of CO2 can be strengthened by chemical reactions and that this effect depends on the nature of the reactants and their concentrations. We conclude that chemical reactions can be favourable to the CO2 sequestration process and that a detailed analysis of the chemical composition of a potential storage site should be a prerequisite to assess its efficiency in dissolving CO2. / (FR) La séquestration du dioxyde de carbone (CO2) dans les aquifères salins profonds est l’une des technologies envisagées afin de réduire l’accumulation de ce gaz à effet de serre dans l’atmosphère. L'injection de CO2 dans ces formations géologiques profondes et sa dissolution dans l'eau salée génèrent une stratification de densité instable d’une saumure dense enrichie en CO2 au-dessus d’une saumure moins dense, pouvant donner naissance à une instabilité de digitation de densité dans la phase aqueuse. Cette dissolution convective du CO2 accélère le mélange de CO2 dans le réservoir et donc améliore la sécurité du stockage dans l’aquifère salin. L’influence des réactions chimiques entre les espèces et le CO2 dissous dans l’eau salée et donc des caractéristiques physico-chimiques du réservoir géologique sur le développement de cette instabilité est aujourd’hui encore peu connue. Dans ce cadre, notre objectif est de déterminer expérimentalement si une réaction chimique dans la phase aqueuse peut améliorer l’efficacité de la dissolution convective du CO2. Pour ce faire, nous avons mis au point un dispositif expérimental consistant en une cellule de Hele-Shaw verticale dans laquelle du CO2 gazeux se dissout par le haut dans des solutions aqueuses contenant des réactifs chimiques de nature et concentration variées. La dynamique convective est visualisée dans les solutions aqueuses transparentes à l’aide d’une technique schlieren. Tout d’abord, nous montrons que la présence d’un indicateur coloré dans la solution aqueuse peut affecter la dynamique de digitation et que ces indicateurs doivent être utilisés avec prudence dans ce genre d’études. Nous étudions ensuite l’effet stabilisateur d’une augmentation de la concentration en sel sur la dissolution convective de CO2 dans la saumure. Dans les cas réactifs, nous montrons que l’instabilité de digitation se développe plus vite dans des solutions basiques de MOH (où M+ est un cation de métal alcalin) que dans l’eau pure et que la convection est renforcée si la concentration du réactif est augmentée. De plus, un changement du contre-ion M+ de la base modifie le profil de densité, non seulement par le biais d’effets solutaux, mais aussi par des effets de diffusivité différentielle, ce qui modifie le développement de l’instabilité convective. Enfin, nous explorons les changements de dynamiques convectives induits par des réactions de précipitation dues à la dissolution de CO2 dans des solutions aqueuses de Ca(OH)2 et de CaCl2 de concentrations variables. Divers motifs de précipitation et de convection peuvent être obtenus selon la nature et la concentration du réactif dans la phase aqueuse. Nos résultats montrent que la dissolution convective de CO2 peut être renforcée par des réactions chimiques et que cet effet dépend de la nature des réactifs et de leur concentration. Nous concluons que les réactions chimiques peuvent favoriser le processus de séquestration du CO2 et qu’une analyse détaillée de la composition chimique d’un site potentiel de stockage devrait être un préalable à l’évaluation de son efficacité à stocker le CO2. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished