L'hélium solide métastable est un candidat possible pour la supersolidité. Notre équipe a démontré en 2011 qu'on pouvait obtenir de l'hélium solide métastable à des pressions inférieures à la pression de fusion à l'aide d'une onde acoustique focalisée. Cependant, une instabilité inattendue apparaît lorsque la pression locale du crystal atteint 21 bar c'est à dire 4 bar sous la pression de fusion. J'ai donc commencé ma thèse en étudiant le temps d'apparition de l'instabilité, et j'ai confirmé qu'elle apparaît toujours dans des phases de décompression de l'onde sonore, c'est à dire à une pression inférieure à la pression de fusion. Ensuite, j'ai étudié la limite de cavitation de l'hélium superfluide à pression négative. En utilisant une méthode interférométrique développée par mon prédécesseur Fabien Souris, j'ai mesuré directement la densité de cavitation de l'hélium superfluide métastable. J'ai trouvé que, à 1 K, l'hélium superfluide cavite lorsque sa densité locale a diminué de 8.4%. En utilisant une équation d'état bien établie théoriquement, on peut convertir ce résultat en pression de cavitation pour le comparer avec ceux obtenus par d'autres groupes. À ma grande surprise, mon résultat n'est pas compatible avec ces derniers. Cette incompatibilité soulève des questions intéressantes quant à la possibilité de nucléation de la bulle sur des vortex quantifiés. Enfin, j'ai étudié la dynamique de la bulle d'hélium déclenchée par la cavitation. En analysant l'équation du mouvement de la bulle et le transfert de chaleur correspondant, j'ai expliqué avec succès pourquoi la durée de vie de la bulle a une transition dramatique quand l'hélium passe de liquide normal à superfluide. / Metastable solid helium is a possible candidate for supersolidity. In 2011, our group has demonstrated that we could obtain the metastable solid helium at pressures below the melting pressure using a focused acoustic wave. However, an unexpected instability occurs when the local pressure of the crystal reaches 21 bar which is 4 bar below the melting pressure. So I started my thesis by studying the appearance time of the instability, and I confirmed that it always appears at the low pressure swing of the acoustic wave. Then, I studied the cavitation limit of superfluid helium at negative pressure. Using an interferometric method developed by my predecessor Fabien Souris, I directly measured the cavitation density of metastable superfluid helium. I found that at 1 K, superfluid helium cavitates when its local density is lowered by 8.4%. Using a theoretically well-established equation of state, this result can be converted to a cavitation pressure in order to compare our results with those obtained by others groups. To my surprise, my result is not consistent with the others'. This incompatibility raises interesting questions about the possibility of nucleation of the bubble on quantified vortices. Finally, I studied the dynamics of the helium bubble triggered by cavitation. By analyzing the equation of motion of bubble and the corresponding heat transfer, I have successfully explained why the bubble's lifetime has a dramatic transition as the helium passes from normal liquid to superfluid.

La conversion de l’énergie mécanique en énergie de pression (transportée par un fluide) -ou inversement-, est nécessaire dans de nombreux domaines de l’industrie : transport, production d’électricité, ventilation... Pour cela, des machines tournantes sont très souvent utilisées. Dans le cas des pompes, elles sont constituées d’au moins une partie rotative contenant des aubes transmettant l’énergie au fluide (la roue), laquelle est liée à un arbre, lui-même mis en rotation par un moteur. La méthode de design de telles machines a évolué depuis le début du siècle dernier jusqu’à aujourd’hui. De nos jours, les composants sont optimisés par l’utilisation de calculs numériques à l’échelle locale de type Computational Flow Dynamics (CFD). La simulation à l’échelle locale apporte des informations sur l’écoulement à l’intérieur des éléments de la machine tournante en trois dimensions. Toutefois, la qualification locale des résultats de calcul à l’échelle CFD reste un challenge, notamment en termes de techniques de mesures expérimentales. Par ailleurs, les temps de calcul sont conséquents même à l’échelle de la machine seule, ce qui permet difficilement la simulation de scénarii transitoires accidentels longs à l’échelle d’un réacteur entier, lesquels sont étudiés dans le cadre de la sûreté nucléaire en particulier. Et d’autant plus s’il est nécessaire de réaliser un grand nombre de calculs (études de propagation d’incertitudes). Dans ce contexte, un modèle d’une échelle intermédiaire entre l’étude globale de la machine par les triangles des vitesses et la modélisation CFD a été développé au cours de cette thèse. L’approche choisie consiste à considérer une ligne de courant moyenne adoptée par l’écoulement dans chaque partie de la pompe et un maillage unidimensionnel (ie. 1D) le long de cette ligne. Il permet, par la description géométrique de la pompe, de prédire ses performances (pression produite, énergie transmise au fluide). Plusieurs machines tournantes ont pu être représentées avec le modèle 1D développé : des pompes centrifuges et hélico-centrifuges et un compresseur. Différents fluides ont été simulés (eau, sodium, air). Des régimes d’écoulement monophasiques et diphasiques dans ces machines ont été représentés lors de calculs permanents et transitoires. Le modèle est capable de prédire les performances de machines de géométries variées en conditions monophasiques quasi-stationnaires avec une erreur relative maximale de l’ordre de 15% sur une large gamme de débit. Le modèle permet également de détecter l’occurrence de la cavitation pour une pompe centrifuge à différentes conditions de débit. Il est capable de prédire la dynamique d’un transitoire de démarrage rapide d’une pompe centrifuge en conditions monophasiques. Il subsiste des difficultés numériques lors de la simulation d’un transitoire comparable où un régime de cavitation s’installe dans la roue de la pompe. Une pompe ainsi modélisée peut être intégrée à la modélisation d’une installation complexe telle qu’un réacteur nucléaire. Ceci ouvre des possibilités en termes d’études de transitoires accidentels dans le cadre d’études de sûreté. Les perspectives d’application du modèle envisagées sont la modélisation des turbines ou de machines multi-étagées et la simulation d’autres fluides. / Conversion of mechanical energy into pressure inside a fluid -or inversely-, is necessary in numerous industries: transport, electricity production, air circulation... Rotating machineries are often used in these frames. They are constituted of at least one bladed rotating part giving energy to the fluid (the impeller) and connected to a shaft, which is entrained by a motor in the case of a pump. The design method of such turbomachines has evolved from the begining of the last century to these days. Nowadays Computational Flow Dynamics (CFD) local scale computations are used to optimize the pump components. Local simulation allows to obtain information on what is happening inside the machine in three dimensions. However, qualification of the local results of such simulations remains a challenge, mostly due to constraints on experimental technics. Additionally, computation cost of such local simulations is heavy even at the scale of the machine alone. That hardly allows the simulation of transient scenarii on whole and complex systems such as a reactor, which are studied in the frame of nuclear safety in particular. And even more when uncertainty propagation studies are intended, which involve a large number of simulations. In such a context, a model of an intermediate scale -between the global study of the machine using velocity triangles and local CFD computations- has been developed during this PhD thesis. The proposed approach consists in considering a mean stream line that is adopted by the flow inside each part of the machine, associated to a one-dimensional (1D) meshing. By defining main geometrical characteristics of the machine, it can predict its performances in terms of pressure rise and energy given to the fluid. Several turbomachines have been modelled using this 1D model: centrifugal pumps, mixed flow pumps and a radial compressor. Various working fluids have been simulated, such as water, liquid metal sodium and air non-condensable gas. Single-phase and two-phase flow regimes have been represented in those machines in steady and transient conditions. The model is able to predict performances of machines of various geometries in steady single-phase conditions with a relative error globally less than 15% for a large range of flow rates. The model allows also to detect the occurrence of cavitation for a centrifugal pump in various conditions of flow rate. It catches also pump fast startup transient dynamics in single-phase conditions. It subsists numerical difficulties when simulating the same transient in cavitating conditions. A pump modelled as described here can be included into the modelling of closed experimental loops or complex facilities such as nuclear reactors. This work opens up new possibilities to study accidental transient in the frame of safety analysis. Intented application prospects of the model are the modelling of turbines or multi-stage machines and the use of other fluids.

Noise pollution threatens marine ecosystems, where animals rely heavily on sound for navigation and communication. The largest source of underwater noise from human activity is shipping, and propeller-induced cavitation is the dominant source of noise from ships. Mitigation strategies require accurate methods for predicting cavitation-induced noise, which remains challenging. The present thesis explores prediction and modelling strategies for cavitation-induced noise from marine propellers, and provides insight into models that can be used both during propeller design and to generate intelligent vessel control strategies. I examined three distinct approaches to predicting cavitation-induced noise, each of which is discussed in one of the three main chapters of this thesis: a high-fidelity computational fluid dynamics scheme, a parametric mapping procedure, and the use of field measurements. Each of these three chapters presents different insight into the acoustic behaviour of cavitating marine propellers, as well both real and potential strategies for mitigating this critical environmental emission. A combined experimental and numerical study of noise from a cavitating propeller, focused on both the fundamental importance of experimental findings and the effectiveness of the numerical modelling strategy used, is detailed in the first main chapter of this thesis. The experimental results highlighted that loud cavitation noise is not necessarily associated with high-power or high-speed propeller operation, affirming the need for intelligent vessel operation strategies to mitigate underwater noise pollution. Comparison of the experimental measurements and simulations revealed that the simulation strategy resulted in an over-prediction of sound levels from cavitation. Analysis of the numerical results and experiments strongly suggested that the cavitation model implemented in the simulations, a model commonly used for marine propeller simulations, was responsible for the over-prediction of sound levels. Ships are powered primarily by combustion engines, for which it is possible to generate "maps" relating the emission of pollutants to the engine’s speed and torque; the second main chapter of this thesis presents the methodology I developed for generating similar "maps" relating the level of cavitation-induced noise to the speed and torque of a ship's propeller. A proof-of-concept of the method that used the model propeller from the first main chapter is presented. To generate the maps, I used a low-order simulation technique to predict the cavitation induced by the propeller at a range of different speed and torque combinations. A pair of semi-empirical models found in the literature were combined to provide the framework for predicting noise based on cavitation patterns. The proof-of-concept map shows a clear optimal operating regime for the propeller. The final main chapter of this thesis presents an analysis of field noise measurements of coastal ferries in commercial operation, the data for which were provided by an industrial partner. The key finding was the identification of cavitation regime changes with variation in vessel speed by their acoustic signatures. The results provide a basis for remotely determining which vessels produce less noise pollution when subject to speed limits, which have been implement in critical marine habitats, and which vessels produce less noise at a specific optimum speed. / Graduate

This diploma thesis deals with cavitation flow in the microscale, which remains an area with a lack of sufficient description of this phenomenon. At the same time, microfluidics is a field experiencing a dramatic rise in numerous biochemical applications, which underlines the relevance of researches of this type. In theoretical part of the thesis, cavitation was described in detail. In the practical part, a microfluidic device with a cavitation orifice was designed and manufactured. The ANSYS program was used for this design. An experiment was performed with the designed microchip, the aim of which was to observe a cavitating flow on the orifice. This measurement took place at the microfluidic laboratory at Victor Kaplan Department of Fluid Engineering. Due to the failure of the experiment, a CFD model of two-phase cavitation flow was built. The conclusions of the thesis were compiled from the findings of measurement and the results of modeling.

This diploma thesis contains three parts. The first part is a background research which deals with notions such as cavitation and cyanobacteria. It also contains current phase in the use of cavitation. The second part deals with design, composition and constructional solution of hydraulic circuit on the riverboat. The third part deals with experimental certification of the cavitation effect on the cyanobacteria in the water. Design of the riverboat with the hydraulic circuit including the circuit itself and the cavitation tube was created in SolidWorks program, calculations, it’s processing and graphs were created in Microsoft Excel.

Avoiding cavitation and especially cavitation erosion are tasks, which have to be considered when working with hydraulics. State of the art is the assessment of the risk of erosion by component testing or to completely avoid cavitation by means of CFD. Another reliable method to assess the risk of cavitation erosion is until now not available. This paper deals with this problem and delivers comparative values for a later method development. In a first step the cavitation of a poppet valve, which controls a methanol flow, is visualized. The resulting three cavitation appearances are deeply examined. After that the results of long-term tests at different operation conditions are presented. A poppet surface analysis following each experiment has shown different types of surface attacks. As a result of this work it is shown that both cavitation appearance and surface attack are strongly influenced by the temperature dependent air solubility of the liquid.

Cette étude sur la stabilité d’une bulle unique de cavitation acoustique s’inscrit dans le cadre d’un projet ANR démarré en septembre 2009 (SONONUCLICE ANR-09-BLAN-0040-02). Elle se situe dans la continuité des travaux sur l’optimisation du procédé de lyophilisation de produits pharmaceutiques menés par l’équipe « Transferts couplés de matière et de chaleur » du laboratoire LAGEP (ESCPE/UCB, Lyon), équipe porteuse du projet, et des travaux sur la cristallisation assistée par ultrasons du laboratoire RAPSODEE. L’application des ultrasons de puissance dans un liquide produit des milliards de bulles. Ce phénomène est appelé cavitation acoustique. Les bulles formées ne font pas toutes la même taille, leurs oscillations ne sont pas en phase, et leur densité dans le fluide est très inhomogène : ce phénomène très complexe implique donc de nombreuses variables difficiles à isoler. Même si le phénomène est chaotique, la cavitation permet d’observer des effets macroscopiques notables sur la nucléation et la croissance des cristaux de glace dans une solution sous-refroidie. Ces effets sont d’une importance capitale pour des applications de congélation ou de lyophilisation. Bien que les effets des ultrasons présentent des intérêts certains sur la cristallisation, leur origine reste mal connue. L’observation directe des milliards de bulles ne fournit aucune piste sur les mécanismes microscopiques mis en jeu. Afin d’isoler l’acteur essentiel de ces effets, l’étude menée vise à isoler une bulle de cavitation acoustique. Pour cela, une cellule de lévitation carrée en verre a été conçue. Le verre a été retenu comme matériau pour sa rigidité et sa transparence. Dans cette cellule, une onde de pression acoustique est imposée par un piézoélectrique collé à la base de la cellule. Il a été possible de reconstruire la dynamique de la bulle. Les étapes d’expansion, d’implosion et de rebonds sont clairement visibles. En vue de l’étude de la cristallisation, un principe de détection des cristaux a été spécifiquement élaboré. Il repose sur le suivi de la modification de la périodicité de la bulle (mesurée par un microphone) provoquée par l’apparition d’un corps étranger à son voisinage. Une méthode utilisant la corrélation de signaux acoustiques du microphone filtré à la fréquence d’excitation du PZT et les harmoniques du signal du microphone directe a été développée. Elle permet de connaître le régime d’oscillation de la bulle et de détecter toutes les modifications de sa dynamique. Des expériences de perturbation de la bulle ont été menées à l’aide d’une micro fibre de 7 μm. Le principe de détection est alors mis en oeuvre pour déclencher l’enregistrement d’images par une caméra rapide lors des derniers instants d’existence de la bulle. Cette méthode devrait permettre de détecter l’apparition des premiers cristaux au voisinage de la bulle. Autour de la cellule de lévitation, différents systèmes ont été développés. Un système de dégazage et de remplissage de la cellule de cavitation ont permis de travailler avec de l’eau ayant des teneurs en gaz dissous de l’ordre de 20 % de la saturation. Un système d’éclairage avec une LED de puissance et un jeu de lentilles optiques a été conçu pour visualiser correctement la bulle. / This study of the stability of an acoustic cavitation bubble is part of an ANR project started in September 2009 (SONONUCLICE ANR-09-BLAN-0040-02). It takes place in the continuity of the works on the optimization process of lyophilisation of pharmaceutical products conducted by the “Transferts couplés de matière et de chaleur” team of LAGEP (ESCPE/UCB, Lyon) laboratory, which is the project’s team leader, and the studies of ultrasound-assisted crystallization in the RAPSODEE Centre. The application of power ultrasound into liquids produces thousands of bubbles. This phenomenon is called acoustic cavitation. The bubbles formed don’t have the same size, their oscillations are not in phase, and their spatial density in the fluid is not homogeneous: this phenomenon is very complex and involves multiple variables very difficult to isolate. Even if this phenomenon is chaotic, it allows to observe macroscopic effects on the nucleation and crystal growth of ice in undercooled solutions. These effects have a capital importance for industrial applications such as freezing and lyophilisation (also called freeze drying). Although ultrasound has a noticeable influence on crystallization, the origin of these effects remains unclear. The multi-bubble approach doesn’t give any hint on the microscopic mechanisms involved. In order to isolate the main actor of these effects, this study aims at isolating a single cavitation bubble. To do that, a cubic levitation cell made of optical glass was build. In this cell, an acoustic pressure is applied by a piezoelectric glued to the bottom’s external face of the cell. With this cell is possible to rebuild all the oscillations states of the bubble, and in combination with our optical system we can see the bubble’s dynamics and its stages like: expansion, collapse and rebounds. For the crystallization part of this study, a crystal’s detection system was developed. It is based on the variations of the bubble’s periodicity (measured by a microphone pill) introduced by the sudden appearance of a foreign body in its vicinity. This method requires the correlation of the signals from a filtered microphone and the harmonics signals from a microphone, in order to known the oscillation state of the bubble and detect variations on the bubble’s dynamics. Experiments of bubble perturbations by a thin wire were made. The detection system was used to trigger the image recording of a fast camera, in order to capture the final moments of the bubble. This method should be allowing the early detection of new crystals in the proximity of the bubble. Around the levitation cell, various systems have been developed. A degassing and filling system for the cavitation cell allow us to work with degased water around the 20 % of its saturated concentration of air. An illumination system based in a power LED and a set of optical lenses was used to view the bubble correctly.

The importance of hydraulic structures has become an essential mitigating mean for floodsthat occur more often due to climate change. Thus, the importance and safety of flooddischarge tunnels has promoted further studies and experiments on the topic to mitigatedamages, such as cavitation that arise because of high speed flows.After an experimental study on a physical model was carried out on the flood discharge tunnelin Zipingpu Water Conservancy project, a CFD model was designed and simulated in thecommercial software ANSYS Fluent. The simulations aimed to evaluate and examine the riskfor cavitation in the tunnel, examine the design problems of the structure and analyse theinstalled aerators for the mitigation of cavitation. Moreover, using CFD models as acomplementary form to physical models was analyzed.A three dimensional geometry of the discharge tunnel was built in ANSYS Spaceclaim and themesh conducted with ANSYS mesh generator. The known boundary condition such as thedesign flow conditions, velocity inlet, pressure inlets and pressure outlet were set. For themodel a multiphase VOF scheme with RANS approach, k-ϵ turbulence model and a standardwall function was set.The results from the initial simulations showed that the discharge tunnel was under cavitationrisk, since the recorded cavitation index in the tunnel was below 1.8. After having revised thelayout of the aerators in order to mitigate cavitation risk, the results from the simulations withadded aerators were sufficient to mitigate the risk as the cavitation index was still below 1.8.The results for the cavitation index remained unchanged even in the simulated models with adifferent solver setup that were used in the comparison with the experimental data in order tovalidate them.As a conclusion, it was recommended that the tunnel design has to be revised and improvedby adding more aerators and air vents to mitigate the cavitation risk. Furthermore, more studieson the discharge tunnel or similar tunnels with similar conditions should be carried out in orderto validate the results of this study and determine if numerical models are preferable to physicalmodels

Cylinder liners in heavy-duty truck engines are subjected to intense vibrations and may sustain damage from the cavitation of bubbles in the coolant liquid, with some risks of leakage and engine breakdown. An ultrasonic oscillating probe was used to simulate the pitting rates and behavior of samples extracted from cylinder liners, which are made of grey cast iron, with differences in surface roughness, glycol and inhibitor content in coolant, coolant temperature and graphite flake class; bainitic microstructures were also tested. Measurements consisted of mass losses under set intervals during experiments lasting 2.5 or 4 hours. Affected surfaces were later evaluated with scanning electron microscopy and confocal microscopy. Results indicate higher cavitation damage with: lower concentrations of glycol and absence of corrosion/cavitation inhibitors in the coolant liquid, lower liquid temperatures between 76⁰C and 90⁰C, and presence of B-type graphite class in the microstructure. Results regarding surface roughness were inconclusive. A sequence of surface damage mechanisms has been proposed, with corresponding microscope observations, to explain the mass loss trends and the associated microstructural changes over time.

No description available.