In der vorliegenden Arbeit wurde das Verhalten dünner Flüssigkeitsfilme an gekrümmten Substratoberflächen durch experimentelle Beschichtungsversuche basierend auf der non-invasiven laserinduzierten Fluoreszenzmesstechnik und durch numerische Filmsimulationen mit Hilfe des Volume-of-Fluid Mehrphasenmodells untersucht. Besonderes Interesse galt dabei dem Finden optimaler Einflussgrößenkombinationen zur Reduzierung des Fettkanten-Effekts. In der hierfür durchgeführten Parameterstudie wurden sowohl Applikationsparameter wie der Kantenrundungsradius und die Applikationsschichtdicke als auch Stoffparameter der untersuchten Flüssigkeit wie die Viskosität und die Oberflächenspannung variiert. Neben qualitativen Beschreibungen der entstandenen Fettkantengestalten sind als Resultate auch Größen zur Quantifizierung der Fettkanten festgelegt worden und systematisch dargestellt. Es konnte nachgewiesen werden, dass ungünstige und geeignete Parameterkonfigurationen existieren, welche prägnante bzw. kaum auffällige Fettkanten erzeugen, insbesondere im Experiment. Über die dabei eingreifenden Mechanismen der zugrundeliegenden Strömungen wurden konkrete Hypothesen aufgestellt, auch um die resultierenden Proportionalitäten der Fettkantengrößen bezüglich der Einflussgrößen zu plausibilisieren. Weiterhin konnte eine Aussage über die Signifikanz der untersuchten Einflussgrößen getroffen werden. Abschließend wurde eine geeignete dimensionslose Kenngröße generiert, um den Fettkanten-Effekt parameterübergreifend beschreiben zu können, wodurch mittels der Ähnlichkeitstheorie auch eine gewisse Abschätzung des Fettkanten-Effekts ermöglicht wird. / In this study the behaviour of a thin liquid layer at a curved solid edge was examined by experimental coating investigations based on the laser-induced fluorescence technique and by numerical film simulations based on the Volume-of-Fluid multiphase flow model, respectively. The main motivation was to find optimal combinations of influencing quantities to reduce the fat-edge effect. Therefore a study of these quantities was performed, in which application parameters like edge radii of curvature and application layer thicknesses as well as determining liquid properties like viscosity and surface tension have been varied. Results are described qualitatively at corresponding fat-edge shapes and quantified by suitable fat-edge parameters, which had to be identified and selected. It could be shown that adverse and appropriate influencing parameter combinations exist, which generate conspicuous and less distinctive fat-edges, respectively - especially in laboratory experiments. The experimental findings and proportionalities regarding fat-edge shapes and dimensions are found to be physically plausible. Furthermore an order of significance of the influencing quantities established. Eventually, a dimensionless quantity was derived by dimensional analysis, which describes the fat-edge effect. Thus, the fat-edge effect has also been described by the application of similarity theory and the corresponding dimenionless number, respectively.

In der vorliegenden Arbeit wurde das Verhalten dünner Flüssigkeitsfilme an gekrümmten Substratoberflächen durch experimentelle Beschichtungsversuche basierend auf der non-invasiven laserinduzierten Fluoreszenzmesstechnik und durch numerische Filmsimulationen mit Hilfe des Volume-of-Fluid Mehrphasenmodells untersucht. Besonderes Interesse galt dabei dem Finden optimaler Einflussgrößenkombinationen zur Reduzierung des Fettkanten-Effekts. In der hierfür durchgeführten Parameterstudie wurden sowohl Applikationsparameter wie der Kantenrundungsradius und die Applikationsschichtdicke als auch Stoffparameter der untersuchten Flüssigkeit wie die Viskosität und die Oberflächenspannung variiert. Neben qualitativen Beschreibungen der entstandenen Fettkantengestalten sind als Resultate auch Größen zur Quantifizierung der Fettkanten festgelegt worden und systematisch dargestellt. Es konnte nachgewiesen werden, dass ungünstige und geeignete Parameterkonfigurationen existieren, welche prägnante bzw. kaum auffällige Fettkanten erzeugen, insbesondere im Experiment. Über die dabei eingreifenden Mechanismen der zugrundeliegenden Strömungen wurden konkrete Hypothesen aufgestellt, auch um die resultierenden Proportionalitäten der Fettkantengrößen bezüglich der Einflussgrößen zu plausibilisieren. Weiterhin konnte eine Aussage über die Signifikanz der untersuchten Einflussgrößen getroffen werden. Abschließend wurde eine geeignete dimensionslose Kenngröße generiert, um den Fettkanten-Effekt parameterübergreifend beschreiben zu können, wodurch mittels der Ähnlichkeitstheorie auch eine gewisse Abschätzung des Fettkanten-Effekts ermöglicht wird. / In this study the behaviour of a thin liquid layer at a curved solid edge was examined by experimental coating investigations based on the laser-induced fluorescence technique and by numerical film simulations based on the Volume-of-Fluid multiphase flow model, respectively. The main motivation was to find optimal combinations of influencing quantities to reduce the fat-edge effect. Therefore a study of these quantities was performed, in which application parameters like edge radii of curvature and application layer thicknesses as well as determining liquid properties like viscosity and surface tension have been varied. Results are described qualitatively at corresponding fat-edge shapes and quantified by suitable fat-edge parameters, which had to be identified and selected. It could be shown that adverse and appropriate influencing parameter combinations exist, which generate conspicuous and less distinctive fat-edges, respectively - especially in laboratory experiments. The experimental findings and proportionalities regarding fat-edge shapes and dimensions are found to be physically plausible. Furthermore an order of significance of the influencing quantities established. Eventually, a dimensionless quantity was derived by dimensional analysis, which describes the fat-edge effect. Thus, the fat-edge effect has also been described by the application of similarity theory and the corresponding dimenionless number, respectively.

The present thesis deals with two-phase electrohydrodynamic simulations of bubble and droplet dynamics under externally applied electric fields. We used the Coupled Level-Set and Volume-of-fluid method (CLSVOF) and two different electrohydrody-namic formulations to study the process of bubble and drop formation from orifices and needles, the interactions of two conducting drops immersed in a dielectric medium, and the oscillations of sessile drops under two different ways of applying external elec-tric field. For the process of bubble formation in dielectric liquids due to the injection of air from submerged orifices and needles, we show that a non-uniform electric field pro-duces smaller bubbles while a uniform electric field changes only the bubble shape. We further explain the reason behind the bubble volume reduction under a non-uniform electric field. We show that the distribution of the electric stresses on the bubble inter-face is such that very high electric stresses act on the bubble base due to a non-uniform electric field. This causes a premature neck formation and bubble detachment lead-ing to the formation of smaller bubbles. We also observe that the non-uniform elec-tric stresses pull the bubble interface contact line inside the needle. With oscillatory electric fields, we show that a further reduction in bubble sizes is possible, but only at certain electric field oscillation frequencies. At other frequencies, bubbles bigger than those under a constant electric field of strength equal to the amplitude of the AC electric field, are produced. We further study the bubble oscillation modes under an oscillatory electric field. We implemented a Volume-of-fluid method based charge advection scheme which is charge conservative and non-diffusive. With the help of this scheme, we were able to simulate the electrohydrodynamic interactions of conducting-dielectric fluid pairs. For two conducting drops inside a dielectric fluid, we observe that they fail to coalesce when the strength of the applied electric field is beyond a critical value. We observe that the non-coalescence between the two drops occur due to the charge transfer upon drop-drop contact. The electric forces which initially bring the two drops closer, switch direction upon charge transfer and pull the drops away from each other. The factors governing the non-coalescence are the electric conductivity of the drop’s liquid which governs the time scale of charge transfer relative to the capillary time scale and the magnitude of the electric forces relative to the capillary and the viscous forces. Similar observations are recorded for the interactions of a charged conducting drop with an interface between a dielectric fluid and a conducting fluid which is the same as the drop’s liquid. For the case of a pendant conducting drop attached to a capillary and without any influx of liquid from the capillary, we observed that the drop undergoes oscillations at lower values of electric potential when subjected to a step change in the applied electric potential. At higher values of electric potential, we observed the phenomenon of cone-jet formation which results due to the accumulation of the electric charges and thus the electric forces at the drop tip. For the formation of a pendant conducting drops from a charged capillary due to liquid injection, we observed that the drops are elongated in presence of an electric field. This happens because the free charge which appears at the drop tip is attracted towards the grounded electrode. This also leads to the formation of elongated liquid threads which connect the drop to the capillary during drop detachment. We plotted the variation of total electric charge inside the drops with respect to time and found the charge increases steeply as the drop becomes elongated and moves towards the grounded electrode. For sessile drop oscillations under an alternating electric field, two different modes of operations are studied. In the so called ‘Contact mode’ case, the droplet is placed on a dielectric coated grounded electrode and the charged needle electrode remains in direct contact with the drop as it oscillates. In the ‘Non-contact mode’ case, the drop is placed directly on the grounded electrode and electric potential is applied to a needle electrode which now remains far from the drop. We show that the drop oscillations in the contact mode are caused by concentration of electric forces near the three phase contact line where the electric charge accumulates because of the repulsion from the needle. For the non-contact mode, we observe that the electric charge is attracted by the needle towards the drop apex resulting in a concentration of the electric forces in that region. So the drop oscillates due to the electric forces acting on a region near the drop tip. We also present the variation of the total electric charge inside the drop with respect to time for the two cases studied.

L’émergence de bruits auparavant inaudibles dans les réservoirs à carburants automobiles requiert des constructeurs une meilleure compréhension des phénomènes physiques intervenants au sein de leurs produits. Dans cette thèse, différents travaux ont été conduits autour de l’étude du ballottement de fluide dans une cuve rigide rectangulaire partiellement remplie de fluide et soumise à une excitation extérieure. La première partie présente un état de l’art sur le sloshing suivant trois approches complémentaires - approche analytique, approche numérique et approche expérimentale - permettant d’orienter les travaux. Dans une deuxième partie, une étude préliminaire sur le sloshing dans une cuve rectangulaire soumise à une excitation harmonique forcée est réalisée. La confrontation des résultats numériques entre une approche linéaire - basée sur la théorie d’écoulement potentiel tenant compte de la viscosité du fluide [Schotté et Ohayon, 2013] - et une approche non linéaire commerciale – basée sur la résolution des équations de Navier-Stokes - permet de définir un paramètre de linéarité. Ce dernier permet de déterminer les cas de sloshing qui nécessitent une résolution non linéaire et ceux pour lesquels la théorie linéaire suffit pour prédire le phénomène. La troisième partie de ce document présente une étude expérimentale du ballottement de fluide dans une cuve rectangulaire rigide soumise à un freinage automobile. Deux niveaux de remplissage créant deux types d’impacts contre les parois (avec et sans enfermement de poche d’air) ont été analysés. Les essais menés ont permis de mesurer les forces engendrées par le mouvement du fluide, les pressions d’impact en paroi ainsi que le champ de vitesse par méthode Particle Image Velocimetry (PIV). Ce chapitre constitue une importante base de données expérimentales ayant permis d’étudier précisément le phénomène physique. L’étude est complétée par une confrontation des résultats expérimentaux avec des résultats Computational Fluid Dynamics (CFD). Enfin, pour conclure ce mémoire, une étude du sloshing dans un réservoir en tenant compte de la Fluid-Structure Interaction (FSI) est présentée. Le choix du couplage a été porté sur un schéma partitionné itératif faible avec, dans un premier temps, une approche potentielle instationnaire, puis avec une approche Volume Of Fluid (VOF) pour la physique fluide. Les limites d’un tel couplage dans le cas d’étude d’un réservoir partiellement rempli de fluide et attaché de manière flexible en fonction du rapport de masse fluide-réservoir ont été mises en évidence. La correction du schéma de couplage par l’effet de masse ajoutée présentée dans [Song et al., 2013] permet la résolution d’un système couplé quel que soit le rapport de masse en jeu et améliore de manière significative la convergence en réduisant également fortement le temps de calcul. / The present thesis focuses on an investigation of the sloshing phenomenon in a partially filled fuel tank submitted to a harmonic excitation motion. In the first part, the confrontation of numerical results between a linear approach - taking into account viscosity - and a nonlinear approach based on a commercial code leads to define a parameter of linearity. This parameter allows determining cases of sloshing who require non-linear resolution and those who need a linear theory to predict the phenomenon. An experimental study of fluid sloshing in a rectangular tank submitted to an automotive braking is conducted. Tests leaded allow measuring global forces engendered by the motion of the fluid, pressure of fluid impact and velocity field by PIV. This chapter provides an important data base and helps to investigate on the physical phenomenon. This study is completed by CFD results. To conclude, a numerical model for fluid-structure interactions is presented. Limits of this segregated partitioned coupling in case of sloshing in tank flexibly attached are highlighted, depending mostly on the mass ratio between fluid and tank structure. An added-mass term is integrated to the corrected staggered scheme ensuring systematically the convergence of the coupled solution and reducing significantly the iterations required.

The aluminothermic (AT) process utilises a self-propagating high-temperature synthesis (SHS) type reaction for producing primarily thermite steel and alumina slag at high temperatures during the welding of rails. In this work, an investigation on the early stages of the aluminothermic process, the separation of AT reaction products and mould filling has been carried out, using both experimental and computational methods to predict the time duration of a complete separation and to obtain a better understanding of the internal multiphase flow within the crucible and mould. The decomposition of AT reaction products after the combustion and the subsequent mould filling by thermite steel and alumina slag have been simulated numerically, using a diffusive phase field and volume-of-fluid model. However, to minimize numerical errors on the input parameters of the high- temperature multiphase flow, a careful review on transport properties has been made. Missing data, e.g. the contact angle of thermite steel on waterglass-bonded mould and crucible wall material has been investigated experimentally. Being further necessary for the prediction of the separation time of AT reaction products in compacted thermite, results on the propagation front velocity show a decreasing trend with increasing initial compact temperature. Further, the combustion front velocity is used for a subsequent analysis of the separation time, which is obtained from the phase distribution of thermite steel, alumina slag and intermetallic compounds, using a combustion front quenching (CFQ) methodology. Moreover, geometric modifications on the crucible and mould have been developed for a reduction in changeover time, as well as an optimized multiphase flow field. Their performance during crucible discharge and mould filling has been verified numerically. Furthermore, alumina slag inclusions have been tracked within the mould using a volume-of-fluid approach with their final positions being verified through an authentic welding. / Während des aluminothermischen (AT) Prozesses findet eine SHS-Reaktion Anwendung, um primär Thermitstahl und Aluminiumoxidschlacke bei hohen Temperaturen für das Verschweißen von Bahnschienen herzustellen. In dieser Arbeit wurden Anfangsstadien, welche die Separation der AT-Reaktionsprodukte sowie das Füllen der Gießform einbeziehen, unter Anwendung von sowohl experimentellen als auch numerischen Verfahren untersucht. Damit konnte die Zeitdauer einer kompletten Separation ermittelt und ein genaueres Verständnis der Mehrphasenströmung in Tiegel und Gießform erlangt werden. Die Separation der AT-Reaktionsprodukte nach der aluminothermischen Reaktion und die anschließende Formfüllung wurden mit einem diffusen Phasenfeld und einem Volume-of-Fluid-Modell numerisch berechnet. Für die Minimierung numerischer Fehler in den Eingangsgrößen dieser Hochtemperatur-Mehrphasenströmungen wurde eine intensive Literaturrecherche durchgeführt und fehlende Parameter, wie zum Beispiel die Kontaktwinkel von Thermitstahl auf Wasserglas gebundenem Form- und Tiegelmaterial, wurden experimentell ermittelt. Messungen der Reaktionsfrontgeschwindigkeit in gepresstem Thermit sind notwendig für eine Vorhersage der Separationszeit der AT-Reaktionsprodukte, und die Ergebnisse zeigen einen linear abfallenden Trend mit zunehmender Anfangstemperatur des verdichteten Materials. In dieser Arbeit wurde die Geschwindigkeit der Reaktionsfront verwendet, um aus der Phasenverteilung von Thermitstahl, Aluminiumoxidschlacke und intermetallischen Verbindungen als Ergebnis des CFQ-Experimentes die Separationszeit in verdichtetem Thermit zu approximieren. Es wurden Modifikationen an Tiegel und Gießform erprobt, die für eine Verbesserung der internen Strömungsführung sowie für die Reduzierung der Umrüstzeit sorgen sollen. Die Effizienz dieser Veränderungen wurde anschließend mit numerischen Methoden überprüft. Des Weiteren konnten durch eine Realschweißung die numerisch vorhergesagten finalen Positionen von Schlackeeinschlüssen innerhalb der Gießform verifiziert werden.

High speed planing hulls are currently widely used for example in recreational and emergency vessel applications. However, very little CFD research has been done for planing vessels, especially for those with stepped hulls. A validated CFD method for planing stepped hulls could be a valuable improvement for the design phase of such hulls. In this thesis, a CFD method for stepped hulls, with a primary focus on two-step hulls, is developed using STAR-CCM+. As a secondary objective, porpoising instability of two-step hulls is investigated. The simulations are divided into two parts: In the first part a method is developed and validated with existing experimental and numerical data for a simple model scale planing hull with one step. In the second part the method is applied for two two-step hulls provided with Hydrolift AS. A maximum two degrees of freedom, trim and heave, are used, as well as RANS based k-w SST turbulence model and Volume of Fluid (VOF) as a free surface model. The results for the one-step hull mostly corresponded well with the validation data. For the two-step hulls, validation data did not exists and they were first simulated with a fixed trim and sinkage and compered between each other. In the simulations with free trim and heave both hulls experienced unstable porpoising behavior.

A significant level of research is currently being carried out in the development of driver support systems as they are expected to play a key role in minimizing road vehicle accidents and creating a safe driving environment under harsh weather conditions. However, the performance of some components used by existing driver support systems like LIDAR and visual cameras are affected by extreme weather conditions such as heavy rain fall and snow. Therefore, it is paramount to identify key locations in an automotive vehicle where such systems are least affect by external weather conditions, thereby, improving their overall performance. The field of research that deals with such questions from a simulation perspective is called contamination modeling. At the moment, one of the biggest knowledge gaps in this field is how to consider the effect of different materials on the movement of liquids such as water on different automotive surfaces like glass, plastic, rubber and painted metal. The work presented in this research study has been carried out to investigate and establish the most suitable simulation strategies to match numerical predictions with experimental data for flow of water over different automotive surfaces. Following a comprehensive parametric study of simulation parameters, it was found that the most suitable model that can be tweaked to achieve different flow properties with different surfaces is a dynamic contact angle model. The Blended Kistler model available in STAR-CCM+ required specific values for static, advancing and receding contact angles to optimize a surface for a given material. Therefore, droplet experiments of two droplet sizes were initially carried out for all tested materials at different inclinations and necessary flow parameters were recorded. All experiments were carried out using an approach known as light induced fluorescence imaging where the captured images provided a very convenient method for post processing in computational software. Results from droplet experiments showed that water moved quickest on plastic and slowest on glass. Static contact angle measurements were carried out first on horizontal surfaces. Afterwards, the surface was inclined at 15, 30, 45, 60, and 75 degrees to measure changes in contact angle and velocities. The surfaces for glass and painted metal were directly taken from the door of a Volvo S60 while a separate surface was used for plastic and rubber. These results were then used to create simulation setups for rivulets in STAR-CCM+ with the multiphase modeling approach known as volume of fluid. Rivulet simulations were carried out for all four materials at five different inclinations and the results were compared and validated with experimental data. The results show good correlation between numerical predictions for rivulet movement and experimental data emphasising on the possibility of fine-tuning the surfaces of a simulation setup to represent different material properties.

Early in the ship design process, naval architects must often evaluate and compare multiple hull forms for a specific set of requirements. Analytical tools are useful for quick comparisons, but they usually specialize in a specific hull type and are therefore not adequate for comparing dissimilar hull types. Scale model hydrodynamic testing is the traditional evaluation method, and is applicable to most hull forms. Scale model tests are usually performed on the largest model possible in order to achieve the most accurate performance predictions. However, such testing is very resource intensive, and is therefore not a cost effective method of evaluating multiple hull forms. This thesis explores the testing of small scale models. It is hypothesized that although the data acquired by these tests will not be accurate enough for performance predictions, they will be accurate enough to rank the performance of the multiple hull forms being evaluated.

This paper covers information research of basic design rules of industrial wet sumps. It describes mathematical models of vortices and method for their identification and visualization. Then the author focuses on CFD modeling of surface vortices with single phase and multiphase approach with Volume of Fluid method. Basic principles of multiphase CFD modelling in OpenFOAM and ANSYS Fluent are given. Description and benchmarking of suitable turbulence models is also present. The single phase and multiphase approach were successfully validated for a simple test case of bathtub surface vortex. Satisfactory agreement with experimental data was achieved. The accuracy and behavior of both solvers were compared between each other. This gives us useful tool for evaluation of inflow condition and danger of surface vortex occurrence in wet sumps. The acquired knowledges were used to design an experimental test case with geometry similar to industrial wet sump. A map of surface vortex occurrence has been created for different operating points. One of the operating point has been used for numerical simulation (both single phase and multiphase). Partial agreement with experimental observation has been achieved.

Práce komplexně popisuje vodní a vodovzdušné chlazení pomocí metod CFD (Computational Fluid Dynamics) konkrétně s využitím software ANSYS FLUENT. Skládá se ze dvou hlavních částí, z nichž první se zabývá numerickým popisem jediné vodní kapky a druhá popisem směsí kapek představující paprsek válcové a ploché trysky. Je založena převážně na vícefázových modelech proudění a vlastních uživatelsky definovaných funkcí (User Defined Functions, UDF) představujících stěžejní část práce. Uvedené výpočtové modely jsou ve většině případů verifikovány pomocí experimentálních dat nebo jiných numerických modelů. V první části práce jsou teoreticky postupně rozebrány všechny tři použité vícefázové modely proudění. První z nich, Volume Of Fluid model (VOF), byl použit pro modelování jediné kapky (mikromodel). Zatímco zbývající dva, Euler-Euler model a Euler-Lagrange model, byly aplikovány v modelu celého paprsku trysky (makromodel). Mikromodel popisuje dynamiku volného pádu vodní kapky. Pro malé průměry kapek (~100µm) standardní model povrchového napětí (Continuum Surface Force, CSF) způsoboval tzv. parazitní proudy. Z toho důvodu je v práci rozebrána problematika výpočtu normál, křivostí volných povrchů a povrchového napětí jako zdroje objemových sil v pohybových rovnicích. Makromodel se zabývá studiem dynamiky celého paprsku tj. oblastí od ústí trysky po dopad na horký povrch, bere v úvahu kompletní geometrii, tzn. např. podpůrné válečky, bramu, spodní část krystalizátoru apod. V práci je rozebrána 2D simulace dopadu paprsku válcové trysky pomocí VOF modelu Euler-Lagrange modelu na horký povrch. Pro případ s VOF modelem byl navržen model blánového varu. Euler-Euler model a Euler-Lagrange model byly využity pro simulaci paprsku ploché trysky horizontálně ostřikující horkou bramu přímo pod krystalizátorem nad první řadou válečků. Pro Euler-Euler model byl navržen model sekundárního rozpadu paprsku založený na teorii nejstabilnější vlnové délky (Blob jet model). Jelikož diskrétní Lagrangeovy částice tvořily v určitých místech spíše kontinuální fázi, byl navržen a otestován model pro konverzi těchto částic do VOF.