L’optimisation des chambres de combustion est généralement réalisée à l'aide d’outils desimulation numérique. Lorsque le carburant est injecté sous forme liquide, la qualité des simulationsdépend en partie de la définition des conditions aux limites imposées pour cette phase à proximité del'injecteur (diamètre, vitesse et flux volumique des gouttes, vitesse de glissement entre phases). Cesconditions aux limites sont généralement définies à partir d'une analyse expérimentale dans desconditions réalistes d’injection, qui fait appel, dans le meilleur des cas, à l’utilisation del’Anémogranulomètre Phase Doppler (PDA). Cependant, cette technique ponctuelle est coûteuse entemps pour une caractérisation globale de l’injecteur et fournit une mesure des flux volumiques avecdes limitations. Il est également difficile d’accéder à des grandeurs telles que la vitesse de la phasegazeuse en présence des gouttes. Pour répondre à cette problématique, il paraît judicieux de mettre enœuvre des techniques de diagnostic optique spatialement résolues. Cette étude consiste à développer des techniques optiques de champ couplant des approches basées sur la diffusion de Mie, sur l'émission fluorescente des gouttes ou de traceurs et utilisant des algorithmes de type PIV, pour caractériser de manière simultanée et quantitative la granulométrie, la vitesse et le flux volumique de la phase dispersée, ainsi que la vitesse de la phase continue dans les brouillards de gouttes au sein d’une configuration réaliste de foyer aéronautique. Une attentionparticulière est portée à l'étude de la précision de la mesure. Ainsi, des comparaisons sont effectuéesavec des bases de données complètes obtenues à l’aide du PDA. L'analyse de ces résultats estconfrontée aux modèles de l'optique physique régissant les phénomènes de fluorescence et dediffusion de la lumière par des particules à l’aide de simulations. Cette démarche nous permetd'interpréter efficacement les résultats obtenus par imagerie directe et de définir les paramètresd'acquisition et de traitement assurant une précision optimale des mesures. / The optimization of combustion chambers is generally carried out using numerical simulation tools.When fuel is injected in liquid form, the simulation quality depends on the boundary conditionsimposed to this phase close to the injector (diameter, velocity and volume flux of the droplets, slipvelocity between phases). These boundary conditions are usually set from an experimental analysisunder realistic conditions of injection, which in the best case uses Phase Doppler Anemo-granulometry(PDA). However, this point measurement technique is time consuming for an overall injectorcharacterization and provides a measurement of the volume flux with some limitations. It is alsodifficult to access variables such as the velocity of the gas phase in the presence of droplets. Toaddress this problem, it seems appropriate to implement spatially resolved optical diagnostictechniques. This study consists in the development of optical field techniques which combine approaches based onMie scattering, fluorescent emission from droplets or tracers and use PIV algorithms to characterizesimultaneously and quantitatively size, velocity and volume flux of the dispersed phase, and velocityof the continuous phase in droplet sprays in a realistic configuration of aeronautical injector. Aparticular attention is given to the study of the measurement accuracy. Thus, comparisons are carriedout with complete databases obtained with the PDA. The analysis of these results is faced withphysical optics models governing phenomena of fluorescence and light scattering by particles usingsimulations. This approach allows us to effectively interpret the results obtained by direct imaging anddefine acquisition and processing parameters ensuring optimum accuracy.

Particle Image Velocimetry (PIV) is a powerful technique to measure the velocity at many points in a flow simultaneously by performing correlation analysis on images of particles being transported by the flow. These images are acquired by illuminating the flow with two light pulses so that each particle appears once on each image. <p> The spatial resolution is an important parameter of this measuring system since it determines its ability to resolve features of interest in the flow. The super-resolution technique maximises the spatial resolution by augmenting the PIV analysis with a second pass that identifies specific particles and measures the distance between them. <p> The accuracy of the procedure depends on both the success with which the proper pairings are identified and the accuracy with which their centre-to-centre distance can be measured. This study presents an analysis of both the systematic uncertainty and random uncertainty associated with this process. The uncertainty is analysed as a function of several key parameters that define the quality of the image. The uncertainty analysis is performed by preparing 4000 member ensembles of simulated images with specific setpoints of each parameter. <p> It is shown that the systematic uncertainty is negligible compared to the random uncertainty for all conditions tested. Also, the image contrast and the selection of a threshold for the particle search are the most critical parameters influencing both success rate and uncertainty. It is also shown that high image intensities still yield accurate results. The search radius used by the super-resolution algorithm is shown to be a critical parameter also. By increasing the search radius, the success rate can be increased although this is accompanied by an increase in random uncertainty.

Particle Image Velocimetry (PIV) is a powerful technique to measure the velocity at many points in a flow simultaneously by performing correlation analysis on images of particles being transported by the flow. These images are acquired by illuminating the flow with two light pulses so that each particle appears once on each image. <p> The spatial resolution is an important parameter of this measuring system since it determines its ability to resolve features of interest in the flow. The super-resolution technique maximises the spatial resolution by augmenting the PIV analysis with a second pass that identifies specific particles and measures the distance between them. <p> The accuracy of the procedure depends on both the success with which the proper pairings are identified and the accuracy with which their centre-to-centre distance can be measured. This study presents an analysis of both the systematic uncertainty and random uncertainty associated with this process. The uncertainty is analysed as a function of several key parameters that define the quality of the image. The uncertainty analysis is performed by preparing 4000 member ensembles of simulated images with specific setpoints of each parameter. <p> It is shown that the systematic uncertainty is negligible compared to the random uncertainty for all conditions tested. Also, the image contrast and the selection of a threshold for the particle search are the most critical parameters influencing both success rate and uncertainty. It is also shown that high image intensities still yield accurate results. The search radius used by the super-resolution algorithm is shown to be a critical parameter also. By increasing the search radius, the success rate can be increased although this is accompanied by an increase in random uncertainty.

Ce travail présente les résultats de recherches sur le contrôle d'écoulement dans les liquides diélectriques. L'objectif est d'étudier les potentialités du contrôle d'écoulement au moyen d'actionneurs ElectroHydroDynamiques. La 1re partie de cette thèse est notamment consacrée à l'étude bibliographique générale du contrôle d'écoulement et des techniques disponibles pour la mesure de vitesse de fluide. La méthode PIV est choisie pour caractériser l'écoulement de panache chargé. Cependant la présence d'un champ électrique intense dans un liquide diélectrique remet potentiellement en question l'hypothèse selon laquelle les traceurs suivent fidèlement les mouvements du liquide. Des études théorique et expérimentale permettent de préciser les conditions d'un traceur idéal et de choisir le meilleur type d'ensemencement pour l'huile de silicone. La 2nde partie de ce travail est consacrée à l'étude du contrôle d'écoulement sur un profil d'aile NACA0015 à ultra-bas Reynolds (Re < 5000). Une étude bibliographique présente les stratégies de contrôle d'écoulement autour de profil d'aile ainsi que les types d'actionneurs EHD appliqués aux liquides diélectriques. L'écoulement naturel en champ de vitesse moyen puis instationnaire est caractérisé et comparé à l'écoulement contrôlé. Le calcul de la force à partir d'un bilan de quantité de mouvement (Navier-Stokes), permet d'estimer les efforts hydrodynamiques appliqués par le fluide sur le profil immergé. Des polaires de portance et de traînée sont obtenues et permettent de quantifier l'efficacité de l'actionneur EHD. Enfin, les mécanismes de contrôle sont précisés et mettent en lumière les potentiels et les limites de l'actionneur. / This work presents results of research on flow control in a dielectric liquid. The aim is to demonstrate our ability to control flow by means of ElectroHydroDynamic actuation. The first part of this PhD thesis is dedicated to a general overview of flow control and the methods available for measuring fluid velocity. The PIV method is selected to charaterize the flow of a charged plume. However, the presence of a high electric field in the dielectric liquid might bring into question the validity of using PIV, which is based on the fact that tracers accurately follow fluid movement. Theoretical and experimental studies were performed to find the proper conditions for using an ideal tracer that guarantees the accuracy of velocity measurements. This part enables us to choose the best seeding particle in silicone oil. The second part of this work is devoted to the study of flow control on a NACA0015 wing profile at ultra-low Reynolds numbers (Re < 5000). A bibliographic study presents strategies of flow control around wing profiles and in addition deals with different EHD actuators for dielectric liquids. Mean velocity fields and unsteady velocity fields of baseline flow are characterized and compared to controlled flow. The calculation of force based on the conservation of momentum (Navier-Stokes equations) enables us to estimate the hydrodynamic stresses applied by the fluid to the immersed profile. Lift and drag polarities are obtained to quantify the efficiency of the EHD actuator. Finally, the mechanisms of control are clarified and highlight the potential and limits of the EHD actuator for flow control applications.

<p>Nanosecond spark plasma actuators provide an opportunity to reduce pollutants by promoting efficient combustion in engines or provide targeted, tunable, flow control over vehicles, due to their ability to influence flow and combustion through multiple mechanisms. The plasma actuators can be physically unobtrusive, can be turned on and off and their low duty cycle, large bandwidth, and light weight make them more appealing than other control approaches. One method by which these plasma actuators interact with the environment is by inducing a complex local flow field and in order, to design scalable, high frequency actuators effectively, it is necessary to first understand the flow induced by a single spark discharge. Most experimental analysis on the flow induced by spark discharges has been restricted to qualitative descriptions of the flow field, primarily due to the difficulties associated with measuring such a transient and highly complex flow with sufficient spatiotemporal resolution. Quantitative, experimental characterization of the flow induced by a spark discharge remains lacking. </p><p> </p><p>A spark discharge produces a shock wave and a hot gas kernel with a complex flow field following the shock. In this work, combined experimental and theoretical characterization of the spark induced flow is performed through a series of high spatiotemporal resolution measurements of the density and velocity fields and reduced-order modeling. The work investigates the mechanisms driving the cooling and vorticity generation in spark induced flow and the 3D nature of the flow field. Planar (2D-3C) and volumetric (3D-3C) velocity measurements are taken using stereoscopic particle image velocimetry (SPIV) and tomographic PIV, respectively. Density measurements are taken using background oriented schlieren (BOS) and high speed schlieren imaging is used to capture the shock wave induced by the spark.</p><p> </p><p>The work shows that spark plasma discharges induce vortex rings whose vorticity is likely generated due to baroclinic torque arising from the non-uniform strength of the induced shock wave. The hot gas kernel cools in two stages: an initially fast cooling regime, followed by a slower cooling process. Reduced order analytical models are developed to describe the cooling observed in the fast regime and the role of the vortex rings in the entrainment of cold ambient gas and the cooling of the hot gas kernel. The results show that the vortex rings entrain ambient gas and drive cooling in the fast, convective regime, cooling approximately 50% of the hot gas within the first millisecond of the induced flow. An increase in the electrical energy deposited in the spark gap increases the shock strength and curvature and increases the vortex ring strength, thereby increasing the cooling rate and expansion of the hot gas kernel. The volumetric velocity measurements capture one of the two induced vortex rings and provide a framework for the improvements needed in future tomographic PIV experiments of the spark induced flow field, necessary in assessing the 3D nature of the induced vortex rings.</p><p> </p><p> The results of this work provide the first set of quantitative, experimental data on flow induced by nanosecond spark discharges that can be used for validation of computational fluid dynamics (CFD) simulations. The results demonstrate that spark plasmas induce vortex ring-driven mixing flows and the results on mixing and cooling of the hot gas kernel can be extended to any passive scalars present in the flow field as well as inform pulsation frequencies and actuator designs for flow and combustion control. The results from the reduced order modeling can inform future studies and applications of nanosecond spark discharges and can be extended to a variety of other types of plasma discharges like laser sparks, long duration sparks and surface discharges with similar induced flow fields.<br></p>

Konvektions- und Erstarrungsvorgänge sind sowohl in natürlichen als auch in technischen Prozessen von grundlegender Bedeutung und stehen dabei miteinander in komplexer Wechselwirkung. Die vorliegende Arbeit beschreibt die Entwicklung eines experimentellen Aufbaus, mit dem sich vielfältige Formen dendritischer Erstarrung und thermosolutaler Konvektion in optisch transparenten Materialsystemen initiieren lassen. Besonderes Augenmerk liegt dabei auf der Implementierung optischer Messtechnik und automatisierter Bildauswertung. Die hier entwickelte komplexe Bildverarbeitung erlaubt die simultane Anwendung verschiedener Verfahren der Strömungs- und Temperaturmessung: Eine automatisierte Bildsegmentierung quantifiziert unterschiedliche Feststofffraktionen; mittels Lagrangian Particle Tracking (LPT) werden die Trajektorien frei beweglicher Kristalle bestimmt und Particle Image Velocimetry/Thermometry (PIV/T) misst Strömungs- und Temperaturfeld im Fluid. Für die simultane Verwendung dieser Verfahren unter Minimierung von Quereffekten stellt die vorliegende Arbeit eine Reihe von Erweiterungen und Neuentwicklungen oben genannter Standardverfahren vor: Mit dem neuartigen Ansatz des Spectral Random Masking kann das Geschwindigkeitsfeld einer (unmaskierten) Teilchenfraktion (PIV-Tracer) ohne den Einfluss einer zweiten (maskierten) Teilchenfraktion (Blasen oder Feststoffpartikel) bestimmt werden. Dieser neuartige Algorithmus maskiert entsprechende Bildbereiche mittels zufälliger Intensitätsmuster und vermeidet so Probleme herkömmlicher Verfahren. Die Verwendung von Thermochromic Liquid Crystal (TLC)-Partikeln als Strömungstracer ermöglicht zusätzlich zur Particle Image Velocimetry (PIV) die Visualisierung des Temperaturfeldes mittels Liquid Crystal Thermometry (LCT). Um dabei genaue quantitative Messungen bei Anwesenheit mehrerer Feststofffraktionen zu erreichen, wurde eine neue Methode der Farbinterpolation entwickelt. Diese generiert RGB-Bilder, welche nur die Färbung der TLC-Partikel repräsentieren. Die anschließende Verarbeitung von RGB-Tripeln und räumlichen Farbabhängigkeiten durch ein künstliches neuronales Netz (KNN) ermöglicht es, verlässliche globale Temperaturfelder zu bestimmen. Die Kombination dieses KNN-Systems mit einem entsprechenden Kalibrierverfahren verbessert dabei die Genauigkeit und den messbaren Temperaturbereich der Liquid Crystal Thermometry (LCT) im Vergleich zu herkömmlichen Verfahren. Mit dem hier etablierten experimentellen Aufbau und Messschema können quantitative globale Studien zur gegenseitigen Beeinflussung von Erstarrung und Strömung unter simultaner Betrachtung verschiedener Feldgrößen durchgeführt werden. Damit ist ein tieferes Verständnis der komplexen physikalischen Vorgänge möglich. Die vorliegende Arbeit demonstriert dies anhand einer experimentellen Studie über die doppelt-diffusive Konvektion während der Kristallisation einer wässrigen Ammoniumchloridlösung NH4Cl(aq).:Zusammenfassung Danksagung 1. Einleitung 2. Physikalische Grundlagen 2.1. Konvektion 2.1.1. Freie thermische Konvektion 2.1.2. Doppelt-diffusive Konvektion 2.2. Erstarrung 2.3. Wechselwirkung zwischen Erstarrung und Strömung 3. Methoden der bildgebenden optischen Messtechnik 3.1. Digitale Bildverarbeitung 3.2. Optische Strömungsmessung 3.2.1. Particle Image Velocimetry 3.2.2. Lagrangian Particle Tracking 3.3. Liquid Crystal Thermometry 3.3.1. Farbkalibrierung 3.3.2. Simultane Temperatur- und Strömungsmessung 3.4. Bisheriger Einsatz optischer Messtechniken für Erstarrungsexperimente 4. Experimenteller Aufbau 4.1. Ammoniumchlorid als transparentes Modellsystem 4.2. Messzelle 4.3. Labortechnik 4.3.1. Temperaturmesstechnik 4.3.2. Temperaturregelung 4.3.3. Temperaturregime und experimenteller Ablauf 4.4. Bildgebung 4.4.1. Laser-Lichtschnittverfahren 4.4.2. Durchlichtverfahren 4.4.3. LED-Lichtschnittverfahren 4.4.4. Kombinationsmöglichkeiten und Einsatz der Bildgebungsverfahren 5. Implementierung und Weiterentwicklung der digitalen Bildverarbeitung 5.1. Detektion und Quantifizierung verschiedener Feststofffraktionen 5.1.1. Bildsegmentierung 5.1.1.1. Statische Hintergrundmaskierung 5.1.1.2. Dynamische Segmentierung 5.1.2. Bestimmung der Feststoffanteile 5.1.3. Quantifizierung der Bewegung der äquiaxialen Kristalle 5.2. Bestimmung des Geschwindigkeitsfeldes der kontinuierlichen Phase 5.2.1. Spectral Random Masking 5.2.2. PIV-Analyse der kontinuierlichen Phase 5.3. Messung des Temperaturfeldes der kontinuierlichen Phase 5.3.1. Farbinterpolation mittels maskierter Faltung 5.3.2. Kalibrierung der Liquid Crystal Thermometry 5.3.2.1. Bestimmung des Farbspiels der TLC-Partikel 5.3.2.2. Temperaturmessung mittels künstlicher neuronaler Netze 5.3.3. Anwendung und Genauigkeit der Temperaturmessung 5.4. Simultane Quantifizierung von Erstarrung, Strömung und Temperatur 6. Demonstration der Messtechnik anhand ausgewählter Experimente 6.1. Analyse globaler Merkmale der Erstarrungsexperimente 6.1.1. Entwicklung verschiedener Konvektionsregime 6.1.2. Wachstum verschiedener Kristallfraktionen 6.2. Bedingungen lokaler äquiaxialer Erstarrung 6.2.1. Äquiaxiales Kristallwachstum infolge lokaler Unterkühlung 6.2.2. Nukleation äquiaxialer Kristalle durch kolumnares Kristallwachstum 6.3. Erkenntnisgewinn und Möglichkeiten der Experimente 7. Zusammenfassung und Ausblick 7.1. Bewertung des experimentellen Aufbaus und der entwickelten Messtechnik 7.2. Optimierungsmöglichkeiten der Messtechnik 7.3. Möglichkeiten und Bedeutung zukünftiger experimenteller Untersuchungen A. Technische Zeichnungen B. Materialeigenschaften der verwendeten NH4 Cl-Lösungen C. Weiterführende Details der Temperaturmessung und -regelung C.1. Kalibrierung der Thermoelemente C.2. Kalibrierung der Thermistoren C.3. Entwicklung und Einrichtung eines Peltier-Luftkühlers D. Weiterführende Details und Illustrationen der entwickelten Bildverarbeitung D.1. Verwendete Python Bibliotheken D.2. Signalflussplan des Spectral Random Masking D.3. Particle Image Velocimetry/Thermometry D.4. Empfindlichkeitsanalyse des künstlichen neuronalen Netzes D.5. Abschätzung der Genauigkeit der LCT während der Experimente E. Erstarrungsexperimente E.1. Lichtschnittbeleuchtung E.1.1. Thermisch stabile Schichtung E.1.2. Thermisch instabile Schichtung E.1.3. Thermisch neutrale Schichtung E.2. Hintergrundbeleuchtung und doppelwandiger Behälter E.2.1. Thermisch stabile Schichtung E.2.2. Thermisch instabile Schichtung Symbolverzeichnis Indexverzeichnis Abkürzungsverzeichnis Literatur Selbstständigkeitserklärung / Convection and solidification processes are of fundamental importance in both natural and technical processes and are subject to complex interaction. The present work presents the development of an experimental setup to initiate various forms of dendritic solidification and thermosolutal convection in optically transparent material systems. Special attention is given to the implementation of optical measurement techniques and automated image processing. The complex image processing developed here allows the simultaneous application of different methods for flow and temperature measurement: An automated image segmentation quantifies different solid fractions; with Lagrangian Particle Tracking (LPT) the trajectories of free moving crystals are determined and Particle Image Velocimetry/Thermometry (PIV/T) measures flow and temperature field in the fluid. For the simultaneous use of these methods while minimizing cross-effects, this thesis illustrates a number of extensions and new developments of the above mentioned standard methods: With the novel approach of Spectral Random Masking the velocity field of an unmasked particle fraction (PIV tracer) can be determined without the influence of a second (masked) particle fraction (bubbles or solid particles). This novel algorithm masks corresponding image areas by random intensity patterns and thus avoids typical problems of conventional methods. The use of Thermochromic Liquid Crystal (TLC) particles as flow tracers enables the visualization of the temperature field by Liquid Crystal Thermometry (LCT) in addition to flow measurements by Particle Image Velocimetry (PIV). To achieve accurate quantitative measurements in the presence of several solid fractions, a new method of color interpolation was developed. This method generates RGB-images, which only represent the coloration of the TLC particles. The subsequent processing of RGB triples and spatial color dependencies using an artificial neural network (ANN) allows to determine reliable global temperature fields. The combination of this ANN system with a corresponding calibration procedure improves the accuracy and measurable temperature range of the LCT compared to conventional methods. With the experimental setup and measurement scheme established here, quantitative global studies on the mutual influence of solidification and flow can be performed under simultaneous consideration of different physical quantities. Compared to previous studies, this allows a deeper understanding of the complex physical processes. The present work demonstrates this with an experimental study of double diffusive convection during crystallization of an aqueous ammonium chloride solution NH4Cl(aq).:Zusammenfassung Danksagung 1. Einleitung 2. Physikalische Grundlagen 2.1. Konvektion 2.1.1. Freie thermische Konvektion 2.1.2. Doppelt-diffusive Konvektion 2.2. Erstarrung 2.3. Wechselwirkung zwischen Erstarrung und Strömung 3. Methoden der bildgebenden optischen Messtechnik 3.1. Digitale Bildverarbeitung 3.2. Optische Strömungsmessung 3.2.1. Particle Image Velocimetry 3.2.2. Lagrangian Particle Tracking 3.3. Liquid Crystal Thermometry 3.3.1. Farbkalibrierung 3.3.2. Simultane Temperatur- und Strömungsmessung 3.4. Bisheriger Einsatz optischer Messtechniken für Erstarrungsexperimente 4. Experimenteller Aufbau 4.1. Ammoniumchlorid als transparentes Modellsystem 4.2. Messzelle 4.3. Labortechnik 4.3.1. Temperaturmesstechnik 4.3.2. Temperaturregelung 4.3.3. Temperaturregime und experimenteller Ablauf 4.4. Bildgebung 4.4.1. Laser-Lichtschnittverfahren 4.4.2. Durchlichtverfahren 4.4.3. LED-Lichtschnittverfahren 4.4.4. Kombinationsmöglichkeiten und Einsatz der Bildgebungsverfahren 5. Implementierung und Weiterentwicklung der digitalen Bildverarbeitung 5.1. Detektion und Quantifizierung verschiedener Feststofffraktionen 5.1.1. Bildsegmentierung 5.1.1.1. Statische Hintergrundmaskierung 5.1.1.2. Dynamische Segmentierung 5.1.2. Bestimmung der Feststoffanteile 5.1.3. Quantifizierung der Bewegung der äquiaxialen Kristalle 5.2. Bestimmung des Geschwindigkeitsfeldes der kontinuierlichen Phase 5.2.1. Spectral Random Masking 5.2.2. PIV-Analyse der kontinuierlichen Phase 5.3. Messung des Temperaturfeldes der kontinuierlichen Phase 5.3.1. Farbinterpolation mittels maskierter Faltung 5.3.2. Kalibrierung der Liquid Crystal Thermometry 5.3.2.1. Bestimmung des Farbspiels der TLC-Partikel 5.3.2.2. Temperaturmessung mittels künstlicher neuronaler Netze 5.3.3. Anwendung und Genauigkeit der Temperaturmessung 5.4. Simultane Quantifizierung von Erstarrung, Strömung und Temperatur 6. Demonstration der Messtechnik anhand ausgewählter Experimente 6.1. Analyse globaler Merkmale der Erstarrungsexperimente 6.1.1. Entwicklung verschiedener Konvektionsregime 6.1.2. Wachstum verschiedener Kristallfraktionen 6.2. Bedingungen lokaler äquiaxialer Erstarrung 6.2.1. Äquiaxiales Kristallwachstum infolge lokaler Unterkühlung 6.2.2. Nukleation äquiaxialer Kristalle durch kolumnares Kristallwachstum 6.3. Erkenntnisgewinn und Möglichkeiten der Experimente 7. Zusammenfassung und Ausblick 7.1. Bewertung des experimentellen Aufbaus und der entwickelten Messtechnik 7.2. Optimierungsmöglichkeiten der Messtechnik 7.3. Möglichkeiten und Bedeutung zukünftiger experimenteller Untersuchungen A. Technische Zeichnungen B. Materialeigenschaften der verwendeten NH4 Cl-Lösungen C. Weiterführende Details der Temperaturmessung und -regelung C.1. Kalibrierung der Thermoelemente C.2. Kalibrierung der Thermistoren C.3. Entwicklung und Einrichtung eines Peltier-Luftkühlers D. Weiterführende Details und Illustrationen der entwickelten Bildverarbeitung D.1. Verwendete Python Bibliotheken D.2. Signalflussplan des Spectral Random Masking D.3. Particle Image Velocimetry/Thermometry D.4. Empfindlichkeitsanalyse des künstlichen neuronalen Netzes D.5. Abschätzung der Genauigkeit der LCT während der Experimente E. Erstarrungsexperimente E.1. Lichtschnittbeleuchtung E.1.1. Thermisch stabile Schichtung E.1.2. Thermisch instabile Schichtung E.1.3. Thermisch neutrale Schichtung E.2. Hintergrundbeleuchtung und doppelwandiger Behälter E.2.1. Thermisch stabile Schichtung E.2.2. Thermisch instabile Schichtung Symbolverzeichnis Indexverzeichnis Abkürzungsverzeichnis Literatur Selbstständigkeitserklärung

The knowledge of the behavior of non-spherical particles suspended in turbulent flows covers a wide range of applications in engineering and science. Dispersed two-phase flows and turbulence are the most challenging subjects in engineering, and when combined it gives rise to more complexities as the result of the inherent stochastic nature of the turbulence of the carrier-phase together with the random distribution of the dispersed phase. Moreover, for anisotropic particles the coupling between the translation and rotation of particle increases the complication. Because of the practical importance of prolate particleladen turbulent flows, the plenty of numerical and experimental works have been conducted to study such suspensions. Numerical approaches have given valuable insight of turbulent suspension flows, although the computation has been only carried out at the macro scale and models, not including flow distortion around the particle, comprise the detail of the flow in the order of a particle size. In addition, the model of the forces imposed on the particle by the fluid and mass point treatment are strictly valid for infinitely small particle having size less than all scales of the fluid turbulence. Fully resolved solution at the scale of the dispersed phase in turbulent flows for high Reynolds number has been recently performed but is still a challenge. On the other hand, the presence of particle as the dispersed phase makes experimental measurements much more complicated than those with single phase as a result of particles interference. The area of considerable difficulty with this type of experiments is the measurement of the fluid-phase velocity remarkably close to the particle surface. Generally, experimental researches have been concentrated on measuring the mean velocity and Reynolds stresses of the carrier-phase, and the mean velocity, fluctuations, orientation and accumulation of the non-spherical particles. Higher-order quantities, including Lagrangian particle velocity correlations, the carrier-phase turbulence modulation, and two-particle and particlefluid velocity correlations are also of interest. It has been found that the rotational and translational movements of the fibershaped particle depend on the nature of carrier-phase field and fiber characteristics such as aspect ratio, fiber Stokes number, fiber Reynolds number, and the ratio of fiber to flow length scale. With the development of PIV (Particle Image Velocimetry) and PTV (Particle Tracking Velocimetry) techniques, it has been appeared that combined PIV/PTV will be the best available choice for the experimental study of dispersed two-phase flows. The purpose of combined PIV/PTV measurement of two-phase systems is simultaneous measurements of fluid and suspended objects, where the PIV measurement of the fluid phase are combined with PTV measurement of the dispersed phase. The objective of this doctoral thesis is to study the behavior of rod-like particles suspended in wall-bounded turbulent flow through simultaneous PIV/PTV measurements of the velocity of the flow field and particle motion. As a representative of rod-like particles, I have employed cellulose acetate fibers with the length to diameter ratio (aspect ratio) larger than one. Here, It has been considered only dilute suspensions with no flocculation; thus fiber-fiber interaction is negligible. The measurements have been conducted within the parallel planes (2D view) illuminated by laser in the streamwise direction in thin film suspension flowing on the water table setup at Linné FLOW Centre, KTH Mechanics Lab. It is shown that this setup is a well-behaved experimental model of half channel flows often used in Direct Numerical Simulation (DNS) investigations. Therefore, the experimental results are comparable to their DNS counterpart where it is convenient. A single camera PIV technique has been used to measure flowing suspension. Therefore, it has been needed to preprocess images using a spatial median filter to separate images of two phases, tracer particles as representative of fluid and fibers suspended. The well-known PIV processing algorithms have been applied to the phase of fluid. I have also introduced a novel algorithm to recognize and match fibers in consecutive images to track fibers and estimate their velocity. It is not feasible to study all relevant aspects of particle-laden turbulent flows in a single study. In this study, I present the statistics of the rotational and translational motion of fiber-like particles and the surrounding fluid velocity. To the author’s knowledge, remarkably little experimental work has been published to date on simultaneous measurement of fiber motion and turbulence field in a turbulent fiber suspension flow to reveal dynamics of fibers in this regime. Therefore, the results of this work will be profitable in better understanding of such multiphase flows. The statistical analysis of the translational motion of fibers shows that the size of fiber is a significant factor for the dynamical behavior of the fiber near the wall. It has been observed that, in the region near the wall, the probability of presence of the long fibers is high in both the high-speed and low-speed streaks of flow, and the mean velocity of fibers almost conforms to the mean velocity of flow; whereas the short fibers are mostly present in the low-speed areas, and the fiber mean velocity obey the dominant flow velocity in these areas. In the far-wall regions, the translation of fibers is practically unaffected by the aspect ratio, whereas it depends crucially on the wall-normal distance. Moreover, it was found that in the case of long fibers near the wall, the low speed fibers mostly are orientated in streamwise direction. On the other hand, there is no preferential orientation for fast long fibers. Although wall-normal velocities were not measured in this study, it is hypothesized that this behavior is a result of fibers being affected by the sweep and ejection events known to occur in wall-bounded turbulent flow. The fast fibers are in sweep environment and comes from the upper layer. The low speed fibers are into ejection areas in the vicinity of the wall, and the wall has a stabilizing effect on them. The short fibers are still oriented mostly in streamwise direction for a certain range of low velocity. Furthermore, since a considerable change of the fiber behavior is observed in a certain ratio of the fiber length to the fiber distance from the solid wall, it is supposed that this ratio is also a prominent parameter for the behavior of fiber near the wall. The results presented are in terms of viscous wall units wherever are denoted by superscript “+”.

Shallow foundations rested on Leda clay that are widely distributed in Eastern Canada exhibit shrinkage characteristics and are prone to differential settlements. Due to this reason, significant repairs are necessary to the foundations and basements of residential structures constructed in Leda clay deposits. Differential settlements are commonly attributed to the changes in the natural water content of soils associated with water infiltration, evaporation or plant transpiration (i.e., tree-roots-suction). Various research studies have been undertaken to estimate the possible settlements of shallow foundations associated with the water infiltration or evaporation. Several thumb rules have been proposed through research studies, providing recommendations with respect to the distance at which trees must be planted as a function of their heights at maturity such that differential settlements can be avoided. However, limited studies have been carried out to estimate or model the settlements of shallow foundations taking into account the influence of tree-roots-suction. In the present research program, a comprehensive experimental study regarding the deformation characteristics of a sandy loam soil from Ottawa due to tree-root-suction is undertaken, using specially designed equipment. The study has been undertaken using a sandy loam soil so that the testing program can be conducted in a shorter period of time. An artificial rooting system (ARS) was designed and placed in a specially designed tank at the University of Ottawa to simulate tree-roots-suction and measure soil surface settlements associated with a decrease in natural water content (or increase in soil suction) using particle image velocimetry (PIV) technique. The ARS consists of an artificial root, suction generator, matric suction and volumetric water content monitoring devices. The variation of matric suction and volumetric water content are monitored at various depths using the instrumentation of the ARS. Based on the results of the experimental studies, a methodology is proposed to model the settlement behaviour of sandy loam soils due to suction from ARS, using commercial finite element software, SEEP/W and SIGMA/W (i.e. software package of GeoStudio 2007). The study offers a reasonably good comparison between the measured surface settlements and those estimated using the finite element modelling analysis. The modelling methodology presented in this thesis is promising and may be extended for estimating the settlement behaviour associated with the tree roots suction of Leda clay deposits and to other soils.

In many areas of aerodynamics the technique of Large Eddy Simulation (LES) has proved a practical way of modelling the unsteady phenomena in numerical simulations. Few applications are as dependent on such an approach as the prediction of flow within a gas turbine combustor. Like any form of Computational Fluid Dynamics (CFD), LES requires specification of the velocity field at the inflow boundary, with much evidence suggesting the specification of inlet turbulence can be critical to the resultant accuracy of the prediction. While a database of time-resolved velocity data may be obtained from a precursor LES calculation, this technique is prohibitively expensive for complex geometries. An alternative is to use synthetic inlet conditions obtained from experimental data High-speed Particle Image Velocimetry (PIV) is used here to provide planar velocity data at up to 1kHz temporal resolution in two test cases representative of gas turbine combustor flows (a vortex generator in a duct and an idealised combustor). As the data sampling rate is approaching a typical LES time-step it introduces the possibility of applying instantaneous experimental data directly as an inlet condition. However, as typical solution domain inlet regions for gas turbine combustor geometries cannot be adequately captured in a single field of PIV data, it is necessary to consider a method by which a synchronous velocity field may be obtained from multiple PIV fields that were not captured concurrently. A method is proposed that attempts to achieve this by a combined process of Linear Stochastic Estimation and high-pass filtering. The method developed can be generally applied without a priori assumptions of the flow and is demonstrated to produce a velocity field that matches very closely that of the original PIV, with no discontinuities in the velocity correlations. The fidelity and computational cost of the method compares favourably to several existing inlet condition generation methods. Finally, the proposed and existing methods for synthetic inlet condition generation are applied to LES predictions of the two test cases. There is shown to be significant differences in the resulting flow, with the proposed method showing a marked ii reduction in the adjustment period that is required to establish turbulent equilibrium downstream of the inlet. However, it is noted the presence of downstream turbulence generating features can mask any differences in the inlet condition, to the extent that the flow in the core of the combustor test case is found to be insensitive to the inlet condition applied at the entry to the feed annulus for the test conditions applied here.

<p>Accurately assessing the risk and growth of rupture among intracranial aneurysms (IA) remains a challenging task for clinicians. Hemodynamic factors are known to play a critical role in the development of IAs, but the specific mechanisms are not well understood. Many studies have sought to correlate specific flow metrics to risk of growth and rupture but have reported conflicting findings. Computational fluid dynamics (CFD) has predominantly been the methodology used to study IA hemodynamics. Yet, CFD assumptions and limitations coupled with the lack of CFD validation has precluded clinical acceptance of IA hemodynamic assessments and likely contributed to the contradictory results among previous studies. Experimental particle image velocimetry (PIV) studies have been noticeably limited in both scope and number among IA studies, in part due to the complexity associated with such experiments. Moreover, the limited understanding of the robustness of hemodynamic metrics across varying flow and measurement environments and the effect of transitional flow in IAs also remain open issues. In this work, techniques to enhance IA PIV capabilities were developed and the first volumetric pulsatile IA PIV study was performed. A novel blood analog solution—a mixture of water, glycerol and urea— was developed and an autonomous methodology for reducing experimental noise in velocity fields was introduced and demonstrated. Both of these experimental techniques can also be used in PIV studies extending beyond IA applications. Further, the onset and development of transitional flow in physiological, pulsatile waveforms was explored. The robustness of hemodynamic metrics such as wall shear stress, oscillatory shear index, and relative residence time across varying modalities, spatiotemporal resolutions, and flow assumptions was explored. Additional hemodynamic metrics which have been demonstrated to be influential in other cardiovascular flows but yet to be tested in IA studies were also identified and considered. Ultimately this work provides a framework for future IA PIV studies as well as insight on using hemodynamic evaluations to assess the risk of growth and rupture of an IA, thereby taking steps towards enhancing the clinical utility of such analysis.</p>