Cette thèse porte sur l’étude expérimentale de la réduction de traînée par injection de bulles. Le contexte de l’étude est lié à la propulsion navale. Les bulles peuvent, lorsqu’elles sont injectées dans la couche limite en développement le long des carènes de navires, contribuer à réduire significativement la résistance de frottement, en allégeant d’une part le fluide le long de la coque et d’autre part en interagissant avec les structures turbulentes de proche paroi. La configuration expérimentale retenue pour cette étude est l’écoulement de Taylor-Couette, avec cylindre extérieur fixe et injection de bulles calibrées. Nos investigations portent sur les régimes de transition, de turbulence naissante et turbulent avec persistance des cellules de Taylor (Re≤20.104). La taille des bulles varie avec le capillaire et le mélange utilisés, entre 0,05 et 0,12 fois la largeur de l’entrefer. Une méthode originale de suivi de la phase dispersée dans un plan méridien, couplée à des mesures de couple global appliqué au cylindre intérieur ont permis de mettre en évidence deux régimes de réduction de traînée et plusieurs types d’arrangements des bulles, en fonction de leur taille et du nombre de Reynolds. Les bulles peuvent avoir une trajectoire glissante, oscillante, être capturées par les cellules de Taylor ou en proche paroi du cylindre intérieur dans les zones de jets sortants. La caractérisation par PIV des vitesses de la phase liquide en monophasique et diphasique a permis d’étudier les modifications induites par les bulles sur la phase liquide et de discuter des mécanismes impliqués dans la modification du couple global par la présence des bulles. Il ressort de cette étude que pour les nombres de Reynolds en deçà de la capture, les bulles contribuent à stabiliser l’écoulement en accord avec une réduction du couple visqueux pouvant atteindre -30% pour des taux de vide très faible (< 1%). Pour des nombres de Reynolds plus élevés, la capture dans les cellules conduit à une réduction de la longueur d’onde axiale et une augmentation de la vorticité des cellules, associée à une augmentation des vitesses rms. Cette configuration est favorable à une augmentation du couple visqueux. A l’inverse, la capture des bulles dans le jet sortant conduit à une augmentation de la longueur d’onde axiale, associée à une diminution de la vorticité. Cette configuration est favorable à une réduction du couple visqueux, moins marquée qu’en absence de capture. / This work presents experimental study of drag reduction by injection of bubbles. Injection of bubbles into the developing boundary layer along the hulls of ships could help to reduce significantly the frictional resistance by lowering a fluid along the hull and interacting with the near-wall turbulent structures. We investigate the interactions between bubbles, the coherent motion and the viscous torque in a Taylor-Couette flow for outer cylinder at rest, while bubbles are injected constantly through a needle. The Reynolds number ranges up to Re≤20.104, for these values of the Reynolds number, Taylor vortices are persistent leading to an axial periodicity of the flow. Bubbles size varies between 0.05 and 0.12 times the width of the gap, depending on the needle and the liquid used. An original method for tracking bubbles in a meridian plane coupled with measures of overall torque applied to the inner cylinder helped to highlight two regimes of drag reduction and various types of arrangements of bubbles, depending on their size and Reynolds number. Bubbles could have a sliding motion, wavering, be captured by the Taylor cells or in the outflow areas near the inner cylinder. Characterization of the liquid velocity by PIV both in single phase and two-phase flow helped to study the modifications induced by the bubbles on the liquid phase and to discuss about the mechanisms involved in the changes induced by the bubbles in the overall torque. The study show that for the Reynolds number before the capture, bubbles could help to stabilize the flow in agreement to the reduction of the viscous torque up to -30% for lowest void fraction (<1%). For the Reynolds number after the capture, bubbles trapped by the Taylor cells lead to a reduction of the axial wavelength and increasing of the vorticity of the cells, associated to an increasing of the rms. This configuration leads to an increasing of the viscous torque. However, bubbles trapped in the outflow areas near the inner cylinder lead to an increasing of the axial wavelength, associated to a decreasing of the vorticity. The configuration supports a smaller reduction of the viscous torque than in the case without captured.

La turbulence est connue pour sa capacité à disperser efficacement de la matière, que ce soit des polluantes dans les océans ou du carburant dans les moteurs à combustion. Deux considérations essentielles s’imposent lorsqu’on considère de telles situations. Primo, l’écoulement sous-jacente pourrait avoir une influence non-négligeable sur le comportement des particules. Secundo, la concentration locale de la matière pourrait empêcher le transport ou l’augmenter. Pour répondre à ces deux problématiques distinctes, deux dispositifs expérimentaux ont été étudiés au cours de cette thèse. Un premier dispositif a été mis en place pour étudier l’écoulement de von Kàrmàn, qui consiste en une enceinte fermé avec de l’eau forcé par deux disques en contra-rotation. Cette écoulement est connu pour être très turbulent, inhomogène, et anisotrope. Deux caméras rapides ont facilité le suivi Lagrangien des particules isodenses avec l’eau et petites par rapport aux échelles de la turbulence. Ceci a permis une étude du bilan d’énergie cinétique turbulente qui est directement relié aux propriétés de transport. Des particules plus lourdes que l’eau ont aussi été étudiées et montrent le rôle de l’anisotropie de l’écoulement dans la dispersion des particules inertielles. Un deuxième dispositif, un écoulement de soufflerie ensemencé avec des gouttelettes d’eau micrométriques a permis une étude de l’effet de la concentration locale de l’eau sur la vitesse de chute des gouttelettes grâce à une montage préexistant. Un modèle basé sur des méthodes théorique d'écoulements multiphasiques a été élaboré enfin de prendre en compte les effets collectifs de ces particules sedimentant dans un écoulement turbulent. Les résultats théoriques et expérimentaux mettent en évidence le rôle de la polydispersité et du couplage entre les deux phases dans l’augmentation de la sédimentation des gouttelettes. / Turbulence is well known for its ability to efficiently disperse matter, whether it be atmospheric pollutants or gasoline in combustion motors. Two considerations are fundamental when considering such situations. First, the underlying flow may have a strong influence of the behavior of the dispersed particles. Second, the local concentration of particles may enhance or impede the transport properties of turbulence. This dissertation addresses these points separately through the experimental study of two different turbulent flows. The first experimental device used is the so-called von K\'arm\'an flow which consists of an enclosed vessel filled with water that is forced by two counter rotating disks creating a strongly inhomogeneous and anisotropic turbulence. Two high-speed cameras permitted the creation a trajectory data base particles that were both isodense and heavier than water but were smaller than the smallest turbulent scales. The trajectories of this data base permitted a study of the turbulent kinetic energy budget which was shown to directly related to the transport properties of the turbulent flow. The heavy particles illustrate the role of flow anisotropy in the dispersive dynamics of particles dominated by effects related to their inertia. The second flow studied was a wind tunnel seeded with micrometer sized water droplets which was used to study the effects of local concentration of the settling velocities of these particles. A model based on theoretical multi-phase methods was developed in order to take into account the role of collective effects on sedimentation in a turbulent flow. The theoretical results emphasize the role of coupling between the underlying flow and the dispersed phase.

De nos jours, l’énergie délivrée par la combustion dépasse 80% de l‟énergie totale dans le monde, et ce pourcentage restera probablement élevé le long des 100 prochaines années. La plupart des systèmes réactifs qui génèrent la combustion turbulente sont utilisés dans la fabrication, le transport et l‟industrie pour la génération des puissances. Comme résultat, l‟émission des polluants est parmi les problèmes majeurs qui sont devenus des facteurs critiques dans notre société. Dans ce cadre, une étude détaillée des systèmes réactifs est alors nécessaire pour la conception de systèmes de haute performance qui s‟adaptent aux technologies modernes. L'optimisation des performances de ces systèmes énergétiques permet d‟une part d‟économiser l'énergie et d‟autre part de réduire la pollution. Les jets turbulents sont impliqués dans l'efficacité de ces divers systèmes. Dans le cas isotherme, la complexité des écoulements turbulents résulte principalement de la coexistence des structures de tailles très différentes et de l‟interaction non linéaire entre ces structures. Les plus grandes structures dépendent fortement de la géométrie du domaine considéré, elles sont donc anisotropes. De plus, elles ont une grande durée de vie et elles sont responsables du transport de la quasi-totalité de l'énergie. Les plus petites structures, quant à elles, ont souvent un caractère beaucoup plus "universel" (dû à leur comportement relativement isotrope) et sont à l'origine du processus de dissipation visqueuse. Prédire numériquement la dispersion et le mélange d‟un scalaire non réactif dans un écoulement turbulent est considéré comme un problème primordial et reste toujours actuel. Plusieurs recherches sont attachés à ce sujet afin d‟approfondir de plus à la connaissance de différents phénomènes pour pouvoir les mieux prédire. La prédiction numérique du mélange turbulent existant dans plusieurs applications industrielles et environnementales, a un important intérêt en génie chimique. Il est nécessaire donc de bien comprendre la majorité de propriétés du mélange et de l‟écoulement. En combustion, la complication du comportement des jets résulte de l‟interaction entre le dégagement de la chaleur, les processus de mélange, l'entraînement et la recirculation des gaz. Pour bien comprendre la complexité de ce phénomène, il est nécessaire de connaître parfaitement l'évolution dynamique et scalaire des jets turbulents isothermes en présence d'importantes différences de densité, comme elles peuvent lors de la combustion. Cette optimisation passe par la compréhension de l'effet de la variation des conditions d'entrée sur les processus de mélange dans le cas non réactif et sur la stabilité et la nature de la flamme dans le cas réactif. Ainsi, des études théoriques, expérimentales et numériques, doivent être menées en parallèle pour mieux identifier les effets d'une telle intervention. Bien des questions demeurent ouvertes dans le but de mieux caractériser les différents écoulements turbulents réactifs. Les objectifs des études menées dans ce domaine sont la réduction des émissions de polluants et l‟amélioration du rendement de combustion. Une compréhension du mélange et leur interaction avec les différents processus chimiques traduit donc un enjeu majeur. Elle est considéré alors comme un facteur déterminant la qualité des variétés des procèdes. Ce travail de thèse se base sur les jets coaxiaux qui constituent un cas particulier de jet axisymétrique. Ils sont communément rencontrés dans des différents brûleurs industriels qui assurent le contact entre le comburant et le carburant sous une forme de jets coaxiaux. Cette technique est le siège d‟une amélioration du mélange et de la stabilité des flammes. / Résumé non fourni

Im Rahmen des Transferprojektes T01 „Textilbeschichtung mit hochviskosen Massen“ des Sonderforschungsbereiches 532 (SFB 532) wird die Realisierung und Bewertung eines integrierten Beschichtungskonzeptes zur nachhaltigen Verbesserung der Tragfähigkeit von textilbewehrten Betonbauteilen an der RWTH Aachen University untersucht. Dazu wird eine neue Auftragstechnik für hochviskose Beschichtungsmassen entwickelt, die eine vollständige Penetration von Multifilamentgarnen mit großen Garntitern und einer hohen Anzahl an Filamenten in textilen Gelegen erzielt. Des Weiteren werden aktive Beschichtungsmassen auf der Basis von Polyvinylalkohol-Zement-Compositen, die eine homogene Anbindung aller Einzelfilamente an die Zementmatrix ermöglichen, erforscht.

This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow. The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated. The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated. Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods. The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature. / QC 20120425

<p>    </p> <p>Cerebral aneurysms are presented in 3-5% of the population and account for approximately 10% of all strokes. The clinical decision on treating unruptured aneurysms should not be taken lightly because a majority of the asymptomatic cerebral aneurysm will not rupture, while both endovascular and microsurgical treatments carry the risk of morbidity and mortality. Thus, there is a need for objective risk assessment to reliably predict the high-risk aneurysms to intervene. Recent studies have found that the blood flow hemodynamic metrics such as pressure and wall shear stress (WSS) are related to the growth and rupture of the aneurysms. 4D flow magnetic resonance imaging (MRI) measures time-resolved three-dimensional velocity fields in the aneurysms <em>in vivo</em>, allowing for the evaluation of hemodynamic parameters. This work presents the developments of flow-physics constrained data enhancement and augmentation methods for 4D flow MRI to assist the risk stratification of cerebral aneurysms. First, a phase unwrapping and denoising method is introduced to enhance the dynamic range and accuracy of 4D flow MRI velocity measurement by incorporating the divergence-free constraint of incompressible flow. Moreover, methods are developed to improve the estimation of hemodynamic parameters from 4D flow data including pressure and WSS. The pressure reconstruction method is also applied to the flow data acquired using particle imaging velocimetry (PIV) and particle tracking velocimetry (PTV) and shows superior performance as compared to the existing methods by solving the pressure Poisson equation. We also proposed a framework to estimate the uncertainty of the PIV/PTV based pressure estimation by propagating the velocity uncertainty. In addition, a multi-modality approach is introduced to enhances the resolution and accuracy of 4D flow data with sparse representation, which improves the reliability of the hemodynamic evaluation. Finally, we present a method to measure the left ventricular flow propagation velocity from cardiac imaging to help in assessing the diastolic function. </p>

Cette thèse concerne l’aérodynamique de pales d'extrémité transsonique. Ces pales sont conçues pour maximiser le rendement en croisière, tout en générant la traction requise au décollage. Elles ont des profils fins et peu cambrés, travaillant à forte incidence au décollage, ce qui peut entraîner l’apparition d’un tourbillon de bord d’attaque (TBA). Or ce TBA présente des similitudes avec les tourbillons d’apex d’aile Delta, connus pour leur capacité à générer de la portance tourbillonnaire.Cette étude consiste à examiner l’intérêt du TBA pour les performances aérodynamiques.La démarche a consisté dans un premier temps à caractériser la topologie du TBA sur une maquette représentative d’une pale d’ Open Rotor, à l'aide d'essais PIV résolus en temps et de calculs RANS k-omega SST, et à évaluer la capacité de la simulation RANS à reproduire les caractéristiques d’intérêt pour cette étude. Un algorithme a été développé afin d'estimer la contribution de ce TBA à la portance à partir du champ de pression pariétal RANS.Afin d'expliciter l'influence des paramètres géométriques et de fonctionnement de la pale sur la portance tourbillonnaire, un modèle 1D de la portance tourbillonnaire a été développé puis couplé à la méthode de l'élément de pale.Les premières comparaison de géométries à iso-traction ont montré que la portance tourbillonnaire permet de générer la traction requise au décollage avec une surface alaire plus faible. Ces résultats ouvrent de nouvelles perspectives pour la conception de géométries avec un meilleur rendement en croisière. / This thesis deals with the aerodynamic properties of propeller blades. Those blades are designed to maximise cruise efficiency, while achieving the target thrust at take-off. Their thin, low-cambered profiles must work at high incidence at take-off, which may give rise to a leading-edge vortex (LEV).The topology of this LEV looks similar to Delta wing LEVs, which are known to generate vortex lift.the aim of this study is to explore the probable impact of the LEV on lift at take-off in order to reconsider propeller blade designs. The approach first consisted in caracterising the LEV topology on a model blade representative of an Open Rotor front blade, using both Time-Resolved PIV and RANS k-omega SST calculations. The comparison between both methods demonstrated the ability of RANS calculations to reproduce the LEV characteristics of interest to this study.Then, the LEV contribution to lift was evaluated thanks to an algorithm developed to estimate vortex lift contribution from RANS wall pressure fields.In order to explicit the influence of the blade's geometrical and functioning parameters on vortex lift, a 1D vortex lift model was developed and coupled to the Blade Element Momentum Theory.The first blade geometry comparative studies at iso-thrust showed that vortex lift enables to generate target thrust at take-off with a lower blade surface. This opens new perspectives for the design of blade geometries with enhanced cruise efficiency.

Master of Science / Department of Grain Science and Industry / Kingsly Ambrose / Consistent and reliable flow of bulk wheat from hoppers and silos is very significant in wheat handling and processing. Bulk wheat flow challenges such as inconsistent flow, arching, etc., are common during handling. The irregular size and non-uniformity of physical properties, the presence of impurities affects the flow behavior during discharge. Chaff and insects infested kernels are the two most common impurities present in wheat. In this research, the effect of these two impurities on their physical and flow properties of wheat were studied. Physical and flow indicators, such as bulk, tapped, particle densities, angle of repose, Hausner’s ratio, Carr index, and porosity measures the flowability of uncompacted bulk solids. Meanwhile, flow properties tested by shear testing principle based on Jenike’s method, simulated bulk wheat under pressure in bins/hoppers. The dynamic properties tested quantify the energy required to flow, compressibility and permeability at dynamic handling situations. Due to the presence of impurities and moisture content differences, bulk density and angle of repose of wheat varied from 801.54kg/m3 to 718.36kg/m3, and 23.6° to 38.4°, respectively. Angle of internal friction and wall friction angle that reflect interaction between particles and particle with bins/hopper walls, ranged from 23.95° to 43.13° and 15.46° to 20.33°, respectively. In addition to instrumental flow property evaluation, the flow profile, discharge rate, and particle velocity during hopper flow of bulk wheat was studied using Particle Image Velocimetry method. Mass flow and funnel flow hopper dimensions were used for this flow profile analysis. The discharge rate decreased from 1.67 to 1.12 kg/s for mass flow and 1.42 to 0.86 kg/s for funnel flow when the chaff in bulk wheat increased from 0% to 7.5% (weight basis). Analysis of the active flow zone indicated that bulk wheat without chaff had a uniform flow compared to wheat with chaff in the bulk. The findings from this study will be useful for design of hopper bottom bins and handling equipment based on the wheat quality and percent moisture content.

This research will investigate the problem of position estimation for planetary rovers. Diverse algorithmic filters are available for collecting input data and transforming that data to useful information for the purpose of position estimation process. The terrain has sandy soil which might cause slipping of the robot, and small stones and pebbles which can affect trajectory. The Kalman Filter, a state estimation algorithm was used for fusing the sensor data to improve the position measurement of the rover. For the rover application the locomotion and errors accumulated by the rover is compensated by the Kalman Filter. The movement of a rover in a rough terrain is challenging especially with limited sensors to tackle the problem. Thus, an initiative was taken to test drive the rover during the field trial and expose the mobile platform to hard ground and soft ground(sand). It was found that the LSV system produced speckle image and values which proved invaluable for further research and for the implementation of data fusion. During the field trial,It was also discovered that in a at hard surface the problem of the steering rover is minimal. However, when the rover was under the influence of soft sand the rover tended to drift away and struggled to navigate. This research introduced the laser speckle velocimetry as an alternative for odometric measurement. LSV data was gathered during the field trial to further simulate under MATLAB, which is a computational/mathematical programming software used for the simulation of the rover trajectory. The wheel encoders came with associated errors during the position measurement process. This was observed during the earlier field trials too. It was also discovered that the Laser Speckle Velocimetry measurement was able to measure accurately the position measurement but at the same time sensitivity of the optics produced noise which needed to be addressed as error problem. Though the rough terrain is found in Mars, this paper is applicable to a terrestrial robot on Earth. There are regions in Earth which have rough terrains and regions which are hard to measure with encoders. This is especially true concerning icy places like Antarctica, Greenland and others. The proposed implementation for the development of the locomotion system is to model a system for the position estimation through the use of simulation and collecting data using the LSV. Two simulations are performed, one is the differential drive of a two wheel robot and the second involves the fusion of the differential drive robot data and the LSV data collected from the rover testbed. The results have been positive. The expected contributions from the research work includes a design of a LSV system to aid the locomotion measurement system. Simulation results show the effect of different sensors and velocity of the robot. The kalman filter improves the position estimation process.

Cardiovascular disease, mostly atherosclerosis, is responsible for one third of all deaths globally, rising to more than 50% in the Western World. Risk factors include smoking, diet, and familial history. Doppler ultrasound can provide estimates of blood velocity and wall shear rate. Clinically, maximum velocity is used to categorise patients for surgery, although Doppler velocity measurement is prone to errors and in need of validation. Wall shear stress—which can be derived from wall shear rate—plays a role in disease initiation and progression, although its clinical utility is unclear due to difficulties associated with its measurement. This thesis investigates the use of Doppler ultrasound as a tool to estimate blood velocity and wall shear rate. A simplified method for estimation of wall shear rate in healthy arteries is developed that uses spectral Doppler ultrasound. This method is based upon the theory of oscillatory flow in rigid pipes, requiring two measurements that are readily available with clinical ultrasound machines. This method is compared to a similar method based on colour flow imaging. The spectral Doppler method underestimated the theoretic value of wall shear rate by between 7 and 22%, with results varying between phantoms. Errors for the colour method were on average 35% greater. Test measurements from one healthy volunteer demonstrated that this method can be applied in-vivo. In more advanced stages of disease, peak velocity distal to a stenosis is of clinical interest and the simplified method for wall shear rate estimation is invalid. Steady flow in a series of simplified stenosis geometries was studied using a dual-beam Doppler system to obtain velocity vectors. These measurements were compared with data from an equivalent system that used particle image velocimetry (PIV) and was considered the gold standard. For Reynolds numbers at the stenosis throat of less than 800, flow remained laminar over the region studied, although distal flow separation did occur. For higher throat Reynolds numbers—corresponding to more severe stenoses or increased flow rates—asymmetric recirculation regions developed; the transition to turbulence occurred more proximally, with a corresponding reduction in stenotic jet and recirculation length. Qualitative agreement was observed in the velocity profile shapes measured using ultrasound and PIV at throat Reynolds numbers less than 800. Above this threshold the qualitative agreement between the velocity profiles became poorer as both downstream distance and the degree of stenosis increased. Peak axial velocity distal to the stenosis was underestimated, on average, by 15% in the ultrasound system. Estimation of shear rate remained difficult with both experimental techniques. Under a Newtonian approximation, the normalised wall shear stresses agree qualitatively. Under pulsatile flow conditions using an idealised flow waveform, superior qualitative agreement was observed in the velocity profiles at diastole than at systole. Similar to the steady flow behaviour, this agreement deteriorated with stenosis severity. The current generation of clinical ultrasound machines are capable of estimating the wall shear rate in healthy arteries. In the presence of significant arterial disease, errors in the peak velocity may result in mis-selection of patients for surgery, while estimation of the wall shear stress remains extremely problematic; particularly with identifying the wall location and measuring velocities close to the wall.