An anguilliform swimming robot replicating an idealized motion is a complex marine vehicle necessitating both a theoretical and experimental analysis to completely understand its propulsion characteristics. The ideal anguilliform motion within is theorized to produce ``wakeless'' swimming (Vorus, 2011), a reactive swimming technique that produces thrust by accelerations of the added mass in the vicinity of the body. The net circulation for the unsteady motion is theorized to be eliminated. The robot was designed to replicate the desired, theoretical motion by applying control theory methods. Independent joint control was used due to hardware limitations. The fluid velocity vectors in the propulsive wake downstream of the tethered, swimming robot were measured using Particle Image Velocimetry (PIV). Simultaneously, a load cell measured the thrust (or drag) forces of the robot via a hydrodynamic tether. The measured field velocities and thrust forces were compared to the theoretical predictions for each. The desired, ideal motion was not replicated consistently during PIV testing, producing off-design scenarios. The thrust-computing method for the ideal motion was applied to the actual, recorded motion and compared to the load cell results. The theoretical field velocities were computed differently by accounting for shed vortices due to a different shape than ideal. The theoretical thrust shows trends similar to the measured thrust over time. Similarly promising comparisons are found between the theoretical and measured flow-field velocities with respect to qualitative trends and velocity magnitudes. The initial thrust coefficient prediction was deemed insufficient, and a new one was determined from an iterative process. The off-design cases shed flow structures into the downstream wake of the robot. The first is a residual disturbance of the shed boundary layer, which is to be expected for the ideal case, and dissipates within one motion cycle. The second are larger-order vortices that are being shed at two distinct times during a half-cycle. These qualitative and quantitative comparisons were used to confirm the possibility of the original hypothesis of ``wakeless'' swimming. While the ideal motion could not be tested consistently, the results of the off-design cases agree significantly with the adjusted theoretical computations. This shows that the boundary conditions derived from slender-body constraints and the assumptions of ideal flow theory are sufficient enough to predict the propulsion characteristics of an anguilliform robot undergoing this specific motion.

Cette thèse présente une étude expérimentale du problème de mélange dans les fluides complexes, étude menée en partenariat avec l’entreprise Sanofi Pasteur. Le mélange est un acte des plus fréquents dans la vie courante et aussi dans l’activité industrielle. On trouve dans la littérature de nombreuses études s’intéressant aux cuves de mélange pour en améliorer les performances à partir d’observations faites à grande échelle. Par contre, à notre connaissance, il y a peu de recherche sur l’hydrodynamique du mélange dans les fluides complexes. Dans notre travail, on étudie des fluides non-Newtoniens formés de solutions diluées de polymères caractérisés par leurs propriétés rhéofluidifiante et viscoélastique. Il s’agit de solutions aqueuses de Polyacrylamide (PAA) ou de la gomme de Xanthan (XG). Afin d’identifier la différence de comportement avec les fluides Newtoniens, une étude expérimentale avec de l’eau est effectuée dans les mêmes conditions que celles pour les fluides non-Newtoniens. Cette étude a été menée, en premier, sur un modèle réduit d’une cuve de mélange de Sanofi Pasteur. Les résultats obtenus, non représentés dans ce mémoire de thèse, nous ont amenés à mettre en place une étude fondamentale de l’écoulement dans un mélangeur de géométrie plus simple. Il s’agit alors de pouvoir contrôler les conditions initiales et de s’affranchir des effets secondaires de l’agitation pour ne s’intéresser qu’au mélange. Pour cela, la géométrie retenue est celle d’un mélangeur en T avec deux entrées perpendiculaires. L’exploration en 2D des champs de vitesse et de concentration de scalaire dans cette jonction en T est assurée simultanément aux moyens des techniques optiques (PIV et PLIF). Les observations montrent un effet non négligeable sur l’hydrodynamique et le mélange lié à la présence de polymères dans l’écoulement. De plus, les résultats obtenus permettent de calculer la tension de Reynolds uv et les flux de masse vc et uc. Ils seront utilisés par la suite pour vérifier leur conformité avec le modèle k epsilon couramment utilisé dans l’industrie. / This thesis presents an experimental study of the mixing in complex fluids which is conducted in partnership with Sanofi Pasteur. The mixture is one of the most common act in everyday life and also in industrial activities. We found in the literature many studies focusing on the mixing tanks with objective to improve performance based on observation of large scale. By cons, in our knowledge, there is few or no research on the hydrodynamics of a mixture in complex fluides. In our work, we study non-Newtonian fluids formed of diluted solution of polymer which characterized by their viscoelastic and shear thinning properties. We used in this study aqueous solutions of polyacrylamide (PAA) or xanthan gum (XG). To identify the difference in behavior with Newtonian fluid, an experimental study with water is carried out under the same conditions as those non-Newtonian fluids. At first, this study was on a reduced mixing tank of Sanofi Pasteur. The results, which not shown in this thesis, led us to develop a fundamental study of flow in a mixer with a simple geometry. The objective is to be able to control the initial conditions and to avoid the side effects of agitation to focus on the mixture. For this, we chose a mixer in a T shape with two perpendicular inputs. Exploring 2D velocity and scalar concentration fields in this T-junction is provided simultaneously of optical techniques (PIV and PLIF). Observations show a significant effect on the hydodynamic and mixture related to the presence of polymers in the flow. In addition, results are used to calculate the Reynolds stress uv and the scalar flux vc and uc. They will be used to check their compliance with the k epsilon model that commonly used in industry.

La présente étude s'intéresse à un écoulement d'acoustic streaming, c'est-à-dire un écoulement généré par la propagation d'une onde acoustique dans un fluide. Le travail consiste à comparer deux approches: expérimentale et numérique. Les ultrasons sont émis à 2MHz par un transducteur piézo-électrique de 28.5mm de diamètre. Ce dernier est plongé dans une cuve d'eau équipée de deux parois absorbantes: l'une sert à séparer le champ proche du champ lointain et l'autre est placée à l'extrémité du domaine fluide afin d'éviter toutes réflexions. On réalise ainsi une étude en champ proche et une étude en champ lointain. Les mesures sont de deux types: champ de pression acoustique (hydrophone) et champ de vitesse (PIV). En parallèle, on effectue des simulations numériques directes avec le logiciel StarCCM+TM. Il s'agit de résoudre les équations de Navier-Stokes en fluide incompressible complétées d'un terme source de force acoustique. L'expression de ce dernier est obtenue par séparation des échelles de temps, ce qui consiste à négliger à l'échelle de temps acoustique les variations temporelles lentes, de l'écoulement généré. La démarche est ensuite analogue à celle utilisé en turbulence pour le calcul des tenseurs de Reynolds. On obtient finalement un bon accord entre les résultats expérimentaux et ceux de la modélisation numérique. / Acoustic streaming, i.e. the flow induced by a propagating acoustic wave, is investigated here with both experiental and numerical approaches. The ultrasound source is a 2MHz transducer with a 29mm diameter. The transducer is introduced inside a water tank with two absorbing walls. An intermediate absorbing wall is used to separate the near field from the far field. An other absorbing wall is placed in the opposite side to teh source to avoid reflective waves. Both near field and far field are studied. The measurements concern the acoustic pressure field (hydrophone) and the velocity field (PIV). Numerical simulations are also performed with the software STARCCM+TM. They solve the incompressible Navier-Stokes equations with an acoustic force source term. Ths term is obtained by time scale separation: the slow variations of the flow are neglected on an acoustic time scale with regard to the fast variations of the acoustic field. The procedure is then similar to that used in turbulence for Reynolds stress calculation. A good agreement is eventually obtained between the experimental and numerical results.

Les plasmas froids d’air à pression atmosphérique sont très utiles pour un grand nombre d’applications grâce à leur chimie hors-équilibre et leur souplesse d’utilisation. Leur intérêt réside dans la production de certaines espèces réactives ou chargées avec un coût énergétique plus avantageux que la chimie à l’équilibre. L’objectif de cette thèse est de combiner les décharges nanosecondes répétitives pulsées (NRP) avec une géométrie micrométrique. Par cette combinaison, nous souhaitons palier au chauffage excessif des étincelles qui génèrent pourtant des fortes densités d’espèces. Notre étude se concentre en trois points principaux. Dans un premier temps la phase de claquage est étudiée ; c’est pendant cette étape que l’énergie est déposée et que les espèces sont produites. La combinaison des diagnostics électriques et de spectroscopie d’émission optique montrent que l’air est presque complètement dissocié et ionisé. Ensuite, nous nous intéressons à la phase de recombinaison qui conditionne la durée de vie de ces espèces. Les résultats mettent en évidence une réaction à trois corps comme mécanisme de recombinaison principal. Et enfin, le dernier point concerne le transport des espèces vers un substrat conducteur. En lui appliquant une tension, celui-ci nous permet de générer un écoulement de vent ionique provenant de la décharge. L’écoulement est étudié par vélocimétrie d’images de particules et imagerie Schlieren. Ce travail a permis de démontrer la capacité des NRP micro-plasmas dans la production contrôlée d’espèces réactives et chargées, mais aussi dans leur transport vers une surface par panache électro-aérodynamique. / Non-thermal plasmas generated in air at atmospheric pressure have numerous potential applications due to their non-equilibrium chemistry and ease of use. Their main advantages lie in the cost-efficient production of reactive and charged species compared to that of equilibrium chemistry. The aim of this thesis is to combine nanosecond repetitively pulsed discharges (NRP) with a microscale geometry. Using this combination, we seek to reduce the excessive heat release of NRP sparks, while nonetheless reaching high densities of reactive species and electrons. This work is comprised of three main parts. Our first goal is to study the breakdown phase, in which energy is deposited and charged species are produced. We employ both electrical characterization and optical emission spectroscopy in order to show that the NRP microplasma fully ionizes and dissociates the gas. The second part consists of the study of the recombination phase, in which the produced species recombine or survive. Results show that three-body recombination can explain the electron lifetime in this phase. Finally, we study the transport of plasma chemical species from the microplasma to a DC-biased conductive plate representing a substrate. By applying a voltage to this third electrode, we drive an electro-thermal plume via an ionic wind from the microplasma to the plate. This flow is investigated mainly by particle image velocimetry as well as Schlieren imaging. This work shows the capability of NRP microplasmas to produce high densities of reactive and charged species and transport them to a surface using an electrohydrodynamic plume.

Les caméras infrarouges modernes permettent d’accéder à la mesure de champs thermiques et de leur évolution temporelle. Le traitement d’images obtenues permet d’analyser la signature thermique d’objets mobiles ou de fluides en écoulement. Dans ce contexte nous avons fait l’étude de trois expériences différentes. La première consiste à suivre des billes mobiles et à évaluer leurs coefficients d’échanges thermiques avec l’environnement par l’estimation de temps caractéristiques. Dans le deuxième cas, nous faisons une comparaison entre deux fluides qui s’écoulent dans un microcanal, afin de déterminer les variations relatives des propriétés thermiques. La dernière application consiste à réaliser une cartographie de diffusivité thermique avec une source de chaleur mobile. / The modern infrared cameras allow the measurement of thermal fields and their temporal evolution. Infrared images processing is suitable to analyze the thermal signature of moving objects or fluid flows. In this context, we made the study of three different experiments. The first one is relative to infrared tracking of randomly moving balls and then estimate their thermal exchanges with the environment by the estimation of some characteristic time. In the second case we made a comparison between two fluids which flow inside a microchannel in order to determine the relative changes of thermal properties. The last application was to estimate a thermal diffusivity field with a mobile heat source.

Le travail de thèse présenté dans ce manuscrit propose une analyse expérimentale du dé-veloppement spatio-temporel d’une zone de mélange (air/hélium) initiée par instabilité deRichtmyer-Meshkov (IRM). Cette étude s’appuie sur la mise en oeuvre d’un tube à chocspositionné verticalement et sur le développement d’un nouveau protocole expérimental associéà un système innovant de génération de l’interface initiale entre les deux espèces gazeuses enprésence. Ce système est basé sur un dispositif d’obturation/ouverture composé d’un rideau rigiderétractable et d’une série volets mobiles. La caractérisation de l’interface initiale et de l’évolutionspatio-temporelle de la zone de mélange ainsi obtenue est effectuée en exploitant les résultats dedifférentes techniques de mesures telles que la visualisation strioscopique (Schlieren) résolue entemps, la tomoscopie plan laser (TPL) et la Vélocimétrie par Imagerie de Particules (PIV). Enpremier lieu, différentes campagnes de mesures visant à caractériser l’interface initiale ont permisde quantifier la répétabilité du système et de démontrer ses capacités à générer une interfacepériodique faiblement diffuse. Dans un second temps, une étude du mélange gazeux obtenu pourun jeu de paramètres expérimentaux donné, est proposée. L’analyse s’intéresse en particulieraux mécanismes d’initiation et de transition a la turbulence de la zone de mélange produite parl’IRM. L’interaction entre cette zone de mélange en cours de développement et le choc réfléchisur l’extrémité supérieure du tube (phénomène de rechoc) est également étudiée dans l’optique deconfirmer la transition turbulente de la zone de mélange. / This work proposes an experimental analysis of the spatio-temporal development of an air/heliummixing zone promoted by the Richtmyer-Meshkov instability (RMI). This study relies on the useof a vertical shock tube and on the development of a new experimental protocol associated with aninnovative device for the generation of an initial interface between two gazeous species. This deviceconsists a rigid retractable curtain and of a series of rotating shutters. The characterization ofthis initial interface and the spatio-temporal evolution of the RMI-induced mixing zone is carriedout by exploiting the results of various experimental methods such as time resolved Schlierenvisualizations, planar laser mie scattering and Particle Image Velocimetry (PIV). In a first step,various measurement campaigns have made it possible to quantify the repeatability of the newdevice and to demonstrate its ability to generate a periodic, weakly diffused interface. In a secondstep, a study of the gaseous mixing for a given set of experimental parameters is proposed. Theanalysis focuses on the understanding of the underlying mechanisms driving the gaseous interfaceformation and the transition to turbulence of the RMI-induced mixing. The interaction betweenthis mixing zone and the reflected shock from the upper end of the tube (re-shock phenomenon)is also studied in order to confirm the turbulent transition of the mixing zone.

This thesis reports on an experimental study of slow viscoelastic flow through models of fibrous porous media. The models were square arrays of parallel cylinders, with solid volume fractions or ‘solidities’ of 2.5%, 5.0%, and 10%. An initial study using a Newtonian fluid provided a baseline for comparison with results for two Boger fluids, so that the effects of fluid elasticity could be determined. Boger fluids are elastic fluids that have near constant viscosities and can be used in experiments without having to account for shear-thinning effects. The experimental approach involved measurements of pressure loss through the three arrays and interior velocity measurements using particle image velocimetry (PIV). For the Newtonian flows, pressure loss measurements were in good agreement with the analytical predictions of Sangani and Acrivos (1982). PIV measurements showed velocity profiles which were symmetrical and independent of flow rate. Pressure loss measurements for the Boger fluid flows revealed that the onset of elastic effects occurred at a Deborah number of approximately 0.5, for both fluids and the three arrays. Flow resistance data collapsed for the two Boger fluids, and increased with solidity. For all three models, the flow resistance increased monotonically with Deborah number, reaching values up to four times the Newtonian resistance for the 10% model. PIV measurements showed that the transverse velocity profiles for the Newtonian and Boger fluids were the same at Deborah numbers below the elastic onset. Above onset, the profiles became skewed. The skewness, like the flow resistance, was observed to increase with both Deborah number and solidity. In the wake regions between cylinders in a column, periodic flow structures formed in the spanwise direction. The structures were staggered from column to column, consistent with the skewing. As either Deborah number or solidity increased, the flow structures became increasingly three-dimensional, and the stagger became more symmetric. An analysis of fluid stresses reveals that the elastic flow resistance is attributed to additional normal stresses caused by shearing, and not by extension.

This thesis reports on an experimental study of slow viscoelastic flow through models of fibrous porous media. The models were square arrays of parallel cylinders, with solid volume fractions or ‘solidities’ of 2.5%, 5.0%, and 10%. An initial study using a Newtonian fluid provided a baseline for comparison with results for two Boger fluids, so that the effects of fluid elasticity could be determined. Boger fluids are elastic fluids that have near constant viscosities and can be used in experiments without having to account for shear-thinning effects. The experimental approach involved measurements of pressure loss through the three arrays and interior velocity measurements using particle image velocimetry (PIV). For the Newtonian flows, pressure loss measurements were in good agreement with the analytical predictions of Sangani and Acrivos (1982). PIV measurements showed velocity profiles which were symmetrical and independent of flow rate. Pressure loss measurements for the Boger fluid flows revealed that the onset of elastic effects occurred at a Deborah number of approximately 0.5, for both fluids and the three arrays. Flow resistance data collapsed for the two Boger fluids, and increased with solidity. For all three models, the flow resistance increased monotonically with Deborah number, reaching values up to four times the Newtonian resistance for the 10% model. PIV measurements showed that the transverse velocity profiles for the Newtonian and Boger fluids were the same at Deborah numbers below the elastic onset. Above onset, the profiles became skewed. The skewness, like the flow resistance, was observed to increase with both Deborah number and solidity. In the wake regions between cylinders in a column, periodic flow structures formed in the spanwise direction. The structures were staggered from column to column, consistent with the skewing. As either Deborah number or solidity increased, the flow structures became increasingly three-dimensional, and the stagger became more symmetric. An analysis of fluid stresses reveals that the elastic flow resistance is attributed to additional normal stresses caused by shearing, and not by extension.

The present thesis is an experimental study of some aspects of unsteady two dimensional boundary layers subject to adverse pressure gradient. An adverse pressure gradient usually leads to boundary layer separation or an instability which may result in transition to turbulence. Unsteady boundary layer separation is not yet fully understood and there is no specific criterion proposed in literature for its occurrence. The details of separation depend on the Reynolds number, the geometry of the body (streamlined or bluff) and the type of imposed unsteady motion (impulsive, oscillatory etc.). Similarly there are many unknowns with respect to instability and transition in unsteady boundary layers, especially those having a streamwise variation. For unsteady flows it is useful to break up the pressure gradient term in the unsteady boundary layer equation into two components:(Formula) is the velocity at the edge of the boundary layer. The first term of the right hand side of this equation may be called the temporal component (Πt) which signifies acceleration or deceleration in time of the free stream and the second term is the spatial component (Πx) which represents the spatial or convective acceleration of the free stream. Many of the studies on instability in unsteady flows found in literature are carried out in straight tubes or channels, where the Πx term is absent. However, in many cases, especially in biological systems both terms are present. An example is the unsteady flow over the moving body of a fish. To study the effects of Πt and Πx on unsteady separation and instability we have built an unsteady water tunnel where the two components can be systematically varied. The flow is created by a controlled motion of a piston. By a suitable combination of the geometry of the model and the piston motion, different types of separation bubbles may be generated. In our studies the piston motion follows a trapezoidal variation: constant acceleration from rest, followed by constant velocity and then deceleration to zero velocity. We have chosen two geometries. One is a bluff body and thus has a high value of Πx and other is a small angle diffuser with a divergence angle 6.2° and thus having a small value of Πx. Upstream and downstream of the diffuser are long lengths of constant cross section. We have performed experiments with the above mentioned geometries placed in the tunnel test section. Flow is visualized using the laser induced fluorescence technique by injecting a thin layer of fluorescein dye on the test wall. Numerical simulations have been done using the software FLUENT. Boundary layer parameters like boundary layer, displacement and momentum thicknesses are calculated from the simulations and used to analyze the experimental results. For the flow in the diffuser, quasi-steady stability analysis of the instantaneous velocity profiles gives a general idea of stability behavior of the flow. Two types of experiments have been done with the bluff body. One is the unsteady boundary layer separation and the formation of the initial vortex for a flow that is uniformly accelerated from rest. We have found some scalings for the formation time (tv) of the separation vortex. The second type of experiment was to study the vortex shedding from the separating shear layer after the boundary layer has fully separated. At high enough Reynolds number shear layer vortices are seen to shed from the separation bubble. The Strouhal number based on the momentum thickness and the velocity at the edge of the boundary layer just upstream of the separation point is found to vary between 0.004 and 0.008. This value is close to the Strouhal number value of 0.0068 found in laminar separation bubbles on a flat plate. The second part of the study concerns with the evolution of the flow in the small angle diffuser with a mild variation of the spatial component of the pressure gradient. From the experimental visualizations we have found that the ratio of Πx and Πt at the start of the deceleration phase of the piston motion is an important parameter that determines the type of instability. This value of Πx/Πt is controlled by controlling the piston deceleration: a large deceleration gives a low Πx/Πt value and a low deceleration gives a large Πx/Πt value. Three types of instabilities have been observed in our experiments. In Type I, the first vortex forms at the maximum pressure gradient point (MPGP) and which grows disproportionately with time. However, instability vortices are seen later at other locations around the MPGP. In type II an array of vortices over a certain length are observed; the vortices grow with time. In Type III, which we observe for low decelerations, we observe initial vortices only in the diffuser section in the deceleration phase of the piston motion. Type III instability is similar to the one observed in dynamic stall experiments. In all cases the instability is very localized - it occurs only over some length of the boundary layer. Transition to turbulence, which is also localized, is observed at higher Reynolds numbers. The non-dimensional time for vortex formation is not very different from that found in straight channel experiments. Quasi-steady linear stability analyses for the boundary layer at the MPGP both for the top and the bottom walls show that the flow is absolutely unstable for some cases. In summary, the thesis looks at in a unified way the separation and instability of unsteady boundary layers with reverse flow. It is hoped that the results will be useful in predicting and understanding onset of separation and instability in practically occurring unsteady flows.

Die vorwiegend experimentelle Arbeit befasst sich mit der systematischen Untersuchung von Parametervariationen bei der aktiven Strömungskontrolle mit elektromagnetischen Kräften. An einer angestellten Platte und einem NACA0015-Profil wurde die saugseitige abgelöste Strömung durch das Einbringen einer periodischen wandparallelen Lorentzkraft an der Vorderkante beeinflusst und experimentell mittels zeitaufgelöster Particle Image Velocimetry (PIV) untersucht. Dabei wurde für verschiedene Anstellwinkel und Reynoldszahlen die Frequenz der Anregung, deren Impulseintrag und der zeitliche Kraftverlauf variiert. Strömungsmechanische Untersuchungen experimenteller und numerischer Natur wurden für eine elektrochemische Zelle und den Fall der Elektrolyse an Millieelektroden unter dem Einfluss externer Magnetfelder durchgeführt. Die Übereinstimmung der gemessenen und berechneten Geschwindigkeitsfelder war dabei sehr gut. Entgegen der Annahme, dass im Falle homogener Magnetfelder keine Strömungen induziert werden, konnte nachgewiesen werden, dass durch die lokale Krümmung der elektrischen Feldlinien in Elektrodennähe starke Lorentzkräfte generiert werden. Dies führt zu sehr komplexen Primär-und Sekundärströmungen. Die gleichen Effekte bewirken ebenfalls in der Nähe von Millieelektroden starke Lorentzkräfte in homogenen magnetischen Feldern. Die experimentellen Beobachtungen an Millieelektroden von Leventis et. al (2005), welche zum Beweis der Konzentrationsgradientenkraft herangezogen wurden, konnten alle auf das Wirken lokaler Lorentzkräfte zurückgeführt werden. Der experimentelle Nachweis der Konzentrationsgradientenkraft steht damit weiterhin aus. Zur Messung der Konzentrationen in elektrochemischen Systemen wurde erstmals das Hintergrundschlierenverfahren angewendet. Dieses Verfahren erlaubt die Bestimmung der räumlichen Konzentrationsgradienten mit erheblich weniger messtechnischen Aufwand gegenüber spektroskopischen Methoden und der Schlierentechnik.