Tesi sul tema "Shadowgraph"

The effects of swirling flow and spark locations on the specific rate of growth of flame area, the flame speed and the convection velocity are investigated experimentally in a constant volume vessel near the lean misfire limit for an equivalence ratio of 0.645 using the shadowgraph technique. The circular and the elliptical models are used as flame contours to calculate the flame speed and the convection velocity. The circular model indicates that the flame speed decreases as the swirl flow decays and as the spark location is moved towards the center of the combustion chamber. The modified elliptical model shows the same result for the average flame speed $S\sb{ws}$. Both models show an overlap in convection velocity when comparison is made at a given spark location for different swirl levels because of cyclic variation; even though the average is higher for higher swirl level. The specific rate of growth of flame area (${1\over A}{dA\over dt}$) is obtained using three models for flame area A: (i) 2-D flame area $A\sb{f}$ measured from the photographs, (ii) spherical flame geometry model, and (iii) ellipsoidal geometry model. The stretch factor $K=({\delta\sb{l}\over u\sb{l}}) ({1\over A}{dA\over dt})$ at 0.5 ms from ignition time for the 2-D and the spherical models at ${r\over R}=0.68$ was within the range 0.63-0.97 and at ${r\over R}=0.55$ was within the range 0.5-0.59. The stretch factor for the ellipsoidal model at ${r\over R}=0.68$ was within the range 0.53-1.05 and at ${r\over R}=0.55$ was within the range 0.46-0.53. All three models for flame area indicate that the specific rate of growth of flame area and stretch factor at 0.5 ms from ignition time decrease as the swirl flow decays and as the spark location approaches the center of the combustion chamber.

In this thesis, the stability, transition and turbulence of thermal plumes were investigated by numerical simulation. Experiments were also conducted, but only for the validation of the simulation code being used. The effect of variable transport properties on a large eddy simulation of a turbulent axisymmetric plume was examined, and it was shown that an in-house incompressible Navier-Stokes solver, which is based on a standard Smagorinsky LES model, with the effects of variable properties incorporated using a modified Sutherlands law, predicts the correct statistical behaviours of the turbulent plume. The near-field puffing instability in thermal planar plumes, which had received little attention in the literature, was investigated by direct numerical simulation. The associated lapping flow instability, forming bulge structures over a heated floor section, was studied using a channel flow model, which allows the lapping flow velocity to be varied. The parametric dependencies were found for the bulge formation and the oscillation frequencies in the lapping flow. Further, the Prandtl number dependent transitional behaviours in the near-field were investigated, and direct stability analysis was conducted to study the lapping flow and stem instabilities. Experiments using a shadowgraph technique and an in-house, two-dimensional, two-component particle image velocimetry, with water as the working fluid, provided validations for the near-field unsteady behaviours of thermal plumes. A ventilated filling box flow with a transitional planar plume was also investigated by direct numerical simulation. A mapping of transitional flow behaviours was obtained, and the parametric dependencies of turbulence statistics and mean flow characteristics were investigated. The three-dimensionality was shown to have only minor effects on the transitional ventilated filling box flows being considered.

A comprehensive understanding of high-speed liquid jets is required for their introduction into engine and combustion applications. Their transient nature, short lifetime, unique characteristics and the inability to take many experimental readings, has inhibited this need. This study investigates the outflow of a high-speed liquid jet into quiescent atmospheric air. The key characteristics present are, a bow shock wave preceding the jet head, an enhanced mixing layer and the transient deformation of the liquid jet core. The outflow regime is studied in an experimental and numerical manner. In the experimental investigation, a high-speed liquid water jet is generated using the momentum exchange by impact method. The jet velocity is supersonic with respect to the impinged gaseous medium. The resulting jet speed is Mach 1.8. The jet is visualised with the use of shadowgraph apparatus. Visualisation takes place over a variety of time steps in the liquid jet???s life span and illustrates the four major development stages. The stages progress from initial rapid core jet expansion to jet stabilisation and characteristic uniform gradient formation. The visualisation shows that at all stages of the jet???s life it is axi-symmetric. One dimensional nozzle analysis and a clean bow shock wave indicate that the pulsing jet phenomenon can be ignored. In the numerical investigation, a time marching finite volume scheme is employed. The bow shock wave characteristics are studied with the use of a blunt body analogy. The jet at a specific time frame is considered a solid body. The jet shape is found to have an important influence on the shock position and shape. Analysis of the results indicates a shock stand-off similar to that seen in experimental observations and the prediction of shock data. The jet life span is modelled using a species dependent density model. The transient calculations reproduce the key jet shape characteristics shown in experimental visualisation. The mushrooming effect and large mixing layer are shown to develop. These effects are strongest when the shock wave transience has yet to stabilise. Quantitative analysis of the mixing layer at varying time steps is presented.

Circulation control involves tangentially blowing air around a rounded trailing edge in order to augment the lift of a wing. The advantages of this technique over conventional mechanical controls are reduced maintenance and lower observability. Despite the technology first being proposed in the 1960s and well-studied since, circulation control is not in widespread use today. This is largely due to the high mass flow requirements. Increasing the jet velocity increases both the efficiency (in terms of mass flow) and effectiveness. However, as the jet velocity exceeds the speed of sound, shock structures form which cause the jet to separate. Recent developments in the field of fluidic thrust vectoring (FTV) have shown that an asymmetrical convergent-divergent nozzle capable of producing an irrotational vortex (IV) has the potential to prevent separation through eliminating stream-wise pressure gradients. In this study, the feasibility of preventing separation at arbitrarily high jet velocities through the use of asymmetrical nozzle geometries designed to maintain irrotational (and stream-wise pressure gradient free) flow is explored. Furthermore, the usefulness of an adaptive nozzle geometry for the purpose of extending circulation control device efficiency and effectiveness is defined. Through a series of experiments, the flow physics of supersonic curved wall jets is characterised across a range of nozzle geometries. IV and equivalent area ratio symmetrical convergent-divergent nozzles are compared across three slot height to radius ratios (H/R): H/R = 0.1, H/R = 0.15, H/R = 0.2. The conclusion of this study is that at low H/R (0.1 and 0.15), there is no significant difference in behaviour between IV and symmetrical nozzles, whilst at high H/R (0.2), the IV nozzles begin separating whilst correctly expanded due to the propagation of pressure upstream from the edge of the reaction surface via the boundary layer. Consequently, it is shown that symmetrical nozzles of equivalent mass flow at high H/R have a higher separation NPR compared to IV nozzles. Specifically, the elimination of favourable, in addition to adverse stream-wise pressure gradients contradicts the expected behaviour of IV nozzles. The separation NPR for nozzles tested in this study, in addition to past studies is subsequently plotted against the throat height to radius ratios (A*/R). This shows that in fact, no previous experiments have shown a higher separation NPR for IV nozzles compared to symmetrical nozzles of equivalent mass flow. The overall outcome is that neither fixed geometry IV, nor adaptive nozzles are justified to maintain attachment, or to improve efficiency. This is because fixed nozzle geometries designed for higher separation NPR do not show any performance deficit when operating at lower NPRs. However, the throat height could be varied to maximise effectiveness (at the expense of mass flow). The contributions to new knowledge made by this study are as follows: the development of a new method of combining shadowgraph and schlieren images to simplify and enhance visualisation of supersonic flows; the use of pressure sensitive paint (PSP) to study the structure of the supersonic curved wall jet before and after separation; the identification of a clear mechanism for the separation of supersonic curved wall jets, valid over a broad range of nozzle geometries (including a clarification of previously unexplained behaviour witnessed in prior studies); the explanation that reattachment hysteresis occurs due to the upstream movement of the point of local separation at full separation (specifically, this explains why certain geometries such as backward-facing steps prevent reattachment hysteresis).

NUMERICAL AND EXPERIMENTAL STUDY OF TRANSIENT LAMINAR NATURAL CONVECTION OF HIGH PRANDTL NUMBER FLUIDS IN A CUBICAL CAVITY
Obai Younis Taha Elamin

La convección natural en espacios cerrados, se encuentra ampliamente en sistemas naturales e industriales. El objetivo general de este trabajo es desarrollar y validar una herramienta de simulación capaz de predecir las tasas de enfriamiento de aceite en un tanque. Esta herramienta ha de tener en cuenta la variación de la viscosidad del aceite para dar información detallada de las tasas de enfriamiento del aceite bajo diferentes condiciones de contorno térmicas realisticas.
En primer lugar, la influencia de diferentes condiciones de contorno térmicas en las paredes, la variación de la viscosidad y la conductividad de la pared en la convección natural del flujo laminar transitorio en una cavidad cúbica con seis paredes térmicamente activo están analizadas.
Para analizar el efecto individual de las paredes laterales de la cavidad en el proceso de enfriamiento, la segunda parte de este estudio considera que, tanto numéricamente como experimentalmente, la transición de la convección natural laminar en una cavidad cúbica con dos paredes opuestas frías y verticales.
Nuevas relaciones de escala que tengan en cuenta la variación de la viscosidad con la temperatura, no publicadas anteriormente en la literatura, se derivan de las velocidades de la capa límite, por el tiempo necesario para la capa límite para alcanzar el estado estacionario y para la velocidad y el espesor de las intrusiones horizontales.
NUMERICAL AND EXPERIMENTAL STUDY OF TRANSIENT LAMINAR NATURAL CONVECTION OF HIGH PRANDTL NUMBER FLUIDS IN A CUBICAL CAVITY
Obai Younis Taha Elamin

Free convection in enclosed spaces is found widely in natural and industrial systems. The general objective of this work is to develop and validate a simulation tool able to predict the cooling rates of oil in a tank. This tool has to take into account the variation of the oil viscosity to give detailed information of the cooling rates of the oil under different realistic thermal boundary conditions.
First, the influence of different thermal wall boundary conditions, the variation of the viscosity and the wall conductivity on the transient laminar natural convection flow in a cubical cavity with the six walls thermally active is studied numerically.
To analyze the individual effect of the side walls of the cavity on the cooling process, the second part of this study considers, numerically and experimentally, the transient laminar natural convection in a cubical cavity with two cold opposite vertical walls. The shadowgraph technique is employed to visualize the development of the transient convective flow. New scaling relations that take into account the viscosity variation with temperature, not reported previously in the literature, are derived for the boundary layer velocities, for the time needed for the boundary layer to reach the steady state and for the velocity and thickness of the horizontal intrusions.

In this study, thermocapillary-driven convection around a gas bubble under a horizontal heated wall is experimentally investigated under gravitational conditions. The thermocapillary convective flow under conditions beyond the laminar steady state towards turbulent flow is explored in detail. Generally, Marangoni convection is more critical and important under microgravity conditions rather than on earth. Under low gravity, this surface tension induced flow can dictate both heat and mass transfer processes. Thus, thermocapillary convection should be considered by manufacturers during material production processes in space. Moreover, temperature gradients can be purposefully used to eliminate or move bubbles or drops suspended in liquid materials. In addition to that, thermocapillary convective flow appears in many other applications like manufacturing of single-walled carbon nanotubes and mono crystal production, to mention only few examples. Researchers have always seen Marangoni convection as an interesting topic for both numerical and experimental studies. Regarding the configuration of the injected gas bubble under a horizontal heated wall, this physical problem is mainly characterized by a dimensionless number that represents the ratio of convective heat flow induced by capillary convection to the heat transfer due to conduction which is termed Marangoni number (Mg). The past decade has seen different approaches to describe the flow behaviour at high Marangoni numbers. The thermocapillary flow has been mainly investigated and categorized regarding a stable laminar behaviour and a non-laminar one, which is characterized by periodic or non-periodic oscillations. Through previous studies, the point of the transition of the thermocapillary flow from the periodic oscillatory zone to the non-periodic one has been well investigated. However, there is a lack of information about this non-periodic behaviour at very high temperature gradients. Therefore, in the current study, our experimental investigations focus mainly on exploring different factors affecting the non-periodicity of the Marangoni convection and on explaining how this flow behaves under conditions above the transitional Marangoni number (Mg tran ). The experimental work was launched using a PIV technique and shadowgraphy. In addition to that, temperature measurements at different locations in the matrix fluid around the air bubble were conducted to determine the undisturbed temperature gradients at different boundary conditions. The transient observation of both velocity and temperature measurements at locations near the bubble allowed deeper insight in the behaviour of the thermocapillary bubbleconvection. Moreover, through shadowgraphy, a qualitative evaluation of the fluid flow periodicity around the gas bubble was achieved. The implementation of experiments inside a pressure chamber under gauge pressure conditions formed a novel methodology to enable us conducting experiments under higher temperature gradients in order to reach high Marangoni numbers. The thermocapillary bubble convection was categorized into laminar, periodic oscillatory, and non-periodic oscillatory flow. The periodic fluid flow oscillations were categorized in symmetric and asymmetric ones depending on the different applied boundary conditions. The non-periodic fluid flow oscillations around the gas bubble were also achieved at high temperature gradients for different bubble aspect ratios. We proved that for every bubble size, the non-periodic oscillatory state of the fluid flow around the gas bubble undergoes four different modes (A-D). The last one (phase D) is a developed turbulent state starting at Mg- numbers of 75000 for the smallest bubble aspect ratio of 1.2 up to the maximal measured Mg- number of 140000 for a bubble aspect ratio of 2.3. Hence, turbulent thermocapillary bubble convection was realized and studied in our experimental configuration. Moreover, the thermocapillary flow driving velocities at the bubble periphery were measured at different boundary conditions. This study clearly demonstrates that it is the high magnitude of the driving velocity that initiates the interactions between thermocapillary flow vortices leading finally to a highly developed oscillation mode (turbulent state) and that buoyancy plays a secondary role in the described flow configuration.:1 INTRODUCTION 2 LITERATURE REVIEW 3 EXPERIMENTAL SETUP AND METHODOLOGY 4 RESULTS AND DISCUSSION 5 CONCLUSIONS AND RECOMMENDATIONS
In dieser Arbeit wird die thermokapillare Konvektion um eine Gasblase unter einer horizontal beheizten Wand unter Gravitationsbedingungen experimentell untersucht. Diese thermokapillare konvektive Strömung jenseits des laminaren stationären Zustands in Richtung turbulenter Strömung steht in dieser Arbeit im Fokus. Im Allgemeinen ist die Marangoni-Konvektion unter Schwerelosigkeitsbedingungen kritischer und wichtiger als auf der Erde. Unter geringen Schwerkraftkräften kann diese durch Oberflächenspannung induzierte Strömung sowohl Wärme- als auch Stoffübergangsprozesse maßgeblich bestimmen. Daher sollte die thermokapillare Konvektion bei Materialproduktionsprozessen im Weltraum berücksichtigt werden. Darüber hinaus können Temperaturgradienten gezielt angewendet werden, um in flüssigen Materialien suspendierte Blasen oder Tropfen zu entfernen oder zu bewegen. Außerdem tritt thermokapillare Strömung in vielen anderen Anwendungen auf, beispielsweise bei der Herstellung von einwandigen Kohlenstoffnanoröhren oder der Herstellung von Einkristallen, um nur einige Beispiele zu nennen. Forscher haben die Marangoni-Konvektion immer als ein wichtiges und interessantes Thema für numerische und experimentelle Studien betrachtet. In Bezug auf die Konfiguration der injizierten Blase unter einer horizontal beheizten Wand wird dieses physikalische Problem hauptsächlich durch eine dimensionslose Kennzahl, die das Verhältnis des durch Kapillarkonvektion induzierten konvektiven Wärmeübertragungs zur Wärmeübertragung durch Leitung darstellt und als Marangoni-Zahl (Mg) bezeichnet wird, definiert. In den letzten Jahrzehnten wurden verschiedene Ansätze zur Beschreibung des Strömungs-Verhaltens bei höheren Marangoni-Zahlen verfolgt. Dabei wurde die Thermokapillarströmung grundsätzlich in ein stabiles laminares und ein nicht laminares (oszillierendes) Verhalten, das durch periodische oder nicht periodische Geschwindigkeit- und Temperatur-Fluktuationen gekennzeichnet ist, eingeteilt. Durch frühere Studien wurde das Regime des Übergangs des thermokapillaren Verhaltens von der periodischen Schwingungszone zur nichtperiodischen gut untersucht. Es fehlen jedoch immer noch detaillierte Informationen über das nichtperiodische Verhalten bei sehr hohen Temperaturgradienten. Daher konzentrieren sich unsere experimentellen Untersuchungen in der vorliegenden Studie hauptsächlich auf die Untersuchung verschiedener Faktoren, die die Nichtperiodizität der konvektiven Thermokapillarströmung beeinflussen, und auf eine Klärung, wie sich diese Strömung unter verschiedenen Randbedingungen über der kritischen Marangoni-Zahl (Mg c ) verhält.Die experimentelle Arbeit wurde sowohl mit einer PIV-Technik als auch mit der Shadowgraph- Technik durchgeführt. Darüber hinaus waren Temperaturmessungen auf Sensorbasis an verschiedenen Stellen in der verwendeten Flüssigkeit um die Luftblase geeignet, um die ungestörten Temperaturgradienten bei verschiedenen Randbedingungen zu bestimmen. Die zeitabhängige Messung sowohl von Geschwindigkeiten als auch von Temperaturen an Orten in der Nähe der Blase lieferte Informationen über das Verhalten der Konvektion der thermokapillaren Strömung. Darüber hinaus wurde durch die Shadowgraph-Technik eine qualitative Bewertung der Fluidströmungsperiodizität um die Blase ermöglicht. Die Durchführung von Experimenten in einer Druckkammer unter Überdruck-Bedingungen bildet eine neuartige Methode, um solche Experimente unter höheren Temperaturgradienten durchzuführen und höhere Marangoni-Zahlen zu erreichen. Die thermokapillare Blasenkonvektion wurde in dieser Arbeit in laminaren stetigen Flüssigkeitsströmungen, periodischen und nichtperiodischen oszillierenden Flüssigkeitsströmungen eingeteilt. Die periodischen Fluidströmungsschwingungen wurden in Abhängigkeit von unterschiedlichen Randbedingungen in symmetrische und asymmetrische eingeteilt. Die nichtperiodischen Strömungsoszillationen um die Gasblase wurden auch bei hohen Temperaturgradienten für verschiedene Blasenaspektverhältnisse erreicht. Wir konnten zeigen, dass für jede Blasengröße der nichtperiodische Schwingungszustand der Strömung um die Gasblase vier verschiedene Modi (A-D) besitzen kann. Die letzte (Phase D) ist ein hoch entwickelter turbulenter Zustand, der bei Mg-Zahlen von 75000 für das kleinste Blasenaspektverhältnis von 1,2 bis zur maximal gemessenen Mg-Zahl von 140000 für das Blasenaspektverhältnis von 2,3 beginnt. Der ausgebildete turbulente Zustand der thermokapillaren Strömung konnte mit unserer experimentellen Konfiguration erstmalig erreicht werden. Darüber hinaus konnten die Antriebsgeschwindigkeiten der thermokapillaren Strömung an der Peripherie der Blase bei verschiedenen Randbedingungen gemessen werden. Diese Studie zeigt deutlich, dass es die Höhe der Antriebsgeschwindigkeit ist, welche die Wechselwirkungen zwischen thermokapillaren Strömungswirbeln unterschiedlicher Größe antreibt, die schließlich zu chaotischen Schwingungen der im Folgenden beschriebenen Grenzlinie führen. Diese Studie zeigt auch, dass die Auftriebskonvektion in der beschriebenen Strömungskonfiguration eine untergeordnete Rolle spielt.:1 INTRODUCTION 2 LITERATURE REVIEW 3 EXPERIMENTAL SETUP AND METHODOLOGY 4 RESULTS AND DISCUSSION 5 CONCLUSIONS AND RECOMMENDATIONS

Thesis (M.S. in Aeronauticl Engineering)--Naval Postgraduate School, June 2003.
Thesis advisor(s): Garth V. Hobson, Raymond P. Shreeve. Includes bibliographical references (p. 67). Also available online.

L’oxydation par plasma électrolytique (ou oxydation micro-arc) est un procédé de traitement des alliages légers (Al, Mg, V, Ti, etc.) apte à pallier les limites de l’anodisation, en particulier au regard des contraintes environnementales. Bien que connu depuis de nombreuses années, les mécanismes sous-jacents à ce procédé assisté par des micro-décharges restent peu ou mal compris. L’objectif de ce travail est de cerner les mécanismes de formation et de développement des micro-décharges et d’associer leurs caractéristiques aux propriétés des couches d’oxyde élaborées sur l’alliage d’aluminium Al2214.La démarche adoptée consiste à associer étroitement l'étude des micro-décharges, la caractérisation des couches élaborées, et les mécanismes de claquage de la couche d'oxyde en cours de croissance. A l’aide de moyens originaux de vidéo rapide (> 125 000 images/s) et d'ombroscopie, la dépendance de l’évolution des micro-décharges aux paramètres macroscopiques du procédé a clairement été établie. L’importance de la présence et de la position de contre-électrodes a été mise en évidence et étudiée. Il est également montré que le choix judicieux de la fréquence et de la densité de courant anodique améliore la qualité des couches obtenues. Une fréquence de l’ordre du kHz semble la mieux appropriée.Enfin, à partir de mesures synchrones, un retard à l’apparition des micro-décharges par rapport au front montant des impulsions de courant a été mis en exergue. Très sensible aux paramètres du procédé, ce retard est probablement lié aux mécanismes de claquage de la couche d'oxyde isolante. Des scénarios concernant ces mécanismes ont ainsi été proposés
Plasma electrolytic oxidation is a surface treatment process applied to light weight alloys (Al, Mg, V, Ti, etc.) which may advantageously replace conventional anodizing, especially regarding environmental issues. Though this process has been known for many years, the underlying mechanisms that govern this micro-discharge assisted process remain poorly understood. This work aims at better identifying the breakdown and development mechanisms of the micro-discharges and at correlating the micro-discharge characteristics to the properties of the layers grown onto Al2214 aluminium alloy samples. The approach consists in coupling the study of the micro-discharges, the characterization of the grown layers and the breakdown mechanisms. By means of high rate video recording (> 125 000 frames/s) and shadowgraph techniques, the dependence of the evolution of the micro-discharges with the macroscopic process parameters has been clearly established. The important role of counter-electrodes and their respective position with respect to the sample have been identified and studied. It is also shown that the suitable choice of current frequency and anodic current density may greatly improve the quality of the resulting oxide layers. Current frequency in the kHz range seems most appropriate to grow thick and defect-free homogeneous layers.Finally, from synchronous measurements, it has been pointed out a delay in the onset of micro-discharges with respect to the rising edge of the current pulses. Besides this delay is strongly sensitive to the process parameters, it is probably related to the breakdown mechanisms of the insulating layer. Scenarios for these mechanisms have been proposed

Process industries are in general depending, in one way or the other, on fluid mechanics.Specifically, paper manufacturing, which probably is the dominant processindustry in Sweden, is depending on the flow of cellulose fibres suspended in water.As a part of the process the suspension, consisting of fibres in water, is spread out onor between two moving permeable weaves, i.e. wires. The speed of this is usually 10–30 m/s and the suspension is spread out by a plane jet issuing from a headbox nozzle.It has been show that the conditions in the headbox and jet have a large influence onthe quality of the final paper sheet. Primarily, streaks in the paper sheet are believedto be the result of streamwise streaks in the headbox jet.The thesis is aimed at the flow phenomena which occur in the headbox jet. Theinvestigations have been made with numerical calculations, stability theory and modelexperiments using water, as well as experiments with a real paper machine headboxand fibre suspension. In the thesis an introduction to the hydrodynamics of planeliquid jets is presented together with a description of the paper forming process andthe fluid mechanics of headbox flow.The basic flow and stability of a two-dimensional plane liquid jet has been investigatedby numerical calculations, stability theory and experiments. The calculationsof the laminar basic flow is successfully compared to pitot-tube measurements of thestreamwise velocity profile. By visualisations of the flow it is found that wave disturbanceson the jet has a severe effect on the flow. These waves can be predicted bylinear stability theory, which shows the presence of five convectively unstable modes.These can be divided into three types and by comparison with the experiments thetype of the visible waves is determined. These waves seem to initiate a break-up ofthe jet, which leads to strong streamwise streaks inside the jet.By flow visualisation of headbox flow of an experimental paper machine, togetherwith analysis of the resulting paper structure using the wavelet method the correspondencebetween flow disturbances and paper quality was investigated. It was shownthat the wave instability, which is present on the low Reynolds number water jet, alsocan be found in the real the headbox jet. It is shown that these waves play an importantrole in the dynamics of the headbox jet and also have an influence on the final papersheet.
QC 20100825

The motion of shock waves is important in many fields of engineering and increasingly so with medical applications and applications to inertial confinement fusion technologies. The flow structures that moving shock waves create when they encounter a change in area is complex and can be difficult to understand. Previousresearchers have carried out experimental studies and many numerical studies looking at this problem in more detail. There has been a discrepancy between numerical and experimental work which had remained unanswered. One of the aims of this project is to try and resolve the discrepancy between numerical and experimental work and try to investigate what experimental techniques are suitable for work of this type and the exact way in which they should be applied. Most previous work has focused on sharp changes in geometry which induce immediate flow separation. In this project rounded corners will also be investigated and the complex flow features will be analyzed.Two geometries, namely a sharp 172 degree knife-edge and a 2.8 mm radius rounded corner will be investigated at three experimental pressure ratios of 4, 8 and 12 using air as the driver gas. This yields experimental shock Mach numbers of 1.28, 1.46 and 1.55. High-speed schlieren and shadowgraph photography with varying levels of sensitivity were used to qualitatively investigate the wave structures. Particle image velocimetry (PIV), pressure-sensitive paint (PSP) and traditional pressure transducers were used to quantify the flow field. Numerical simulations were performed using the commercial package Fluent to investigate the effect of numerical schemes on the flow field produced and for comparison with the experimental results. The sharp geometry was simulated successfully using an inviscid simulation while the rounded geometry required the addition of laminar viscosity. Reynolds number effects will be only sparsely referred to in this project as the flows under investigation show largely inviscid characteristics. As the flow is developing in time rather than in space, quotation of a distance-based Reynolds number is not entirely appropriate; however, Reynolds number based on the same spatial location but varying in time will be mentioned. The density-based diagnostics in this project were designed to have a depth of field appropriate to the test under consideration. This approach has been used relatively few times despite its easy setup and significant impact on the results. This project contains the first quantative use of PIV and PSP to shock wave diffraction. Previous studies have almost exclusively used density-based diagnostics which, although give the best impression of the flow field, do not allow for complete analysis and explanation of all of the flow features present. PIV measurements showed a maximum uncertainty of 5% while the PSP measurements showed an uncertainty of approximately 10%.The shock wave diffraction process, vortex formation, shear layer structure, secondary and even tertiary expansions and the shock vortex interaction were investigate. The experimental results have shown that using one experimental technique in isolation can give misleading results. Only by using a combination of experimental techniques can we achieve a complete understanding of the flow field and draw conclusions on the validity of the numerical results. Expanding the range of the experimental techniques currently in use is vital for experimental aerodynamic testing to remain relevant in an industry increasingly dominated by numerical research. To this end, significant research work has been carried out on extending the range of the PSP technique to allow for the capture of shock wave diffraction, one of the fastest transient fluid processes, and for applications to low-speed flow (< 20 ms−1).

Afin de se rapprocher des conditions du mélange homogène du moteur essence, plusieurs fluides sont injectés dans l'atmosphère à une pression amont et une température variées. Cinq prototypes d'injecteurs réels trois-trous de Continental ont été utilisés. En augmentant la pression d'injection, l'écoulement passe par quatre régimes où le niveau de développement de cavitation varie. Le coefficient de décharge Cd dépend essentiellement du nombre de cavitation. Au point critique de cavitation, deux corrélations ont été obtenues reliant respectivement Cd et le nombre de cavitation critique au nombre de Reynolds correspondant. Le jet en champ proche est gouverné par trois nombres sans dimensions : celui de Weber, de Reynolds et de cavitation. L'effet de chacun d'eux sur l'angle du jet à la sortie a été obtenu. La comparaison des résultats entre deux injecteurs a montré que le rapport entre la longueur et le diamètre de l'orifice est d'une influence d'ordre 1 sur l'angle du jet
In order to get closer to the homogeneous mixture conditions of a gasoline engine, different fluids are injected into the atmosphere at varying upstream pressure and temperature. Five three-hole real injector prototypes from Continental were used. When injection pressure is increased, the internal flow goes through four regimes where the cavitation development level varies from one to another. The discharge coefficient Cd was found mainly dependent on the cavitation number. At the cavitation critical point, two correlations between Cd and the critical cavitation number on one side respectively, and the correspondent Reynolds number on the other side were found. The near field jet is ruled by three dimensionless numbers : Weber, Reynolds and cavitation. The effect of each one of them on the jet angle at the orifice outlet was obtained. By comparing the results of two injectors, it was found that the length over diameter ratio has a first order influence on the jet angle

La thermodiffusion, également appelé effet Soret, décrit le couplage entre les gradients de température et les flux massiques qui en résultent. Ce phénomène intervient dans de nombreux processus naturels et applications industrielles. En particulier, les réservoirs pétroliers sont sujets à ce phénomène impliquant des fluides multi constituants confinés dans une matrice poreuse et soumis à un gradient de température. Néanmoins, malgré beaucoup des progrès, il existe relativement peu de mesures fiables de ce phénomène et sa modélisation reste largement un problème ouvert. L’objectif principal de cette thèse s’inscrit dans ce cadre, à savoir développer une approche expérimental permettant de fournir des données de références sur la thermodiffusion notamment dans l’optique de quantifier l’effet de la pression sur cette dernière. Ainsi, durant cette thèse, nous avons développé une cellule de thermodiffusion en milieu libre qui permet d’étudier par shadowgraphie les fluctuations de non équilibre induites par effet Soret. L’appareil de mesure a ensuite été utilisé pour étudier deux mélanges binaires représentatifs de fluides pétroliers, à savoir le mélange équimassique tétraline/dodécane (en phase liquide) et le mélange dioxyde de carbone/méthane (en phases gaz et supercritique). En complément, des simulations de dynamique moléculaire ont été réalisées sur le mélange dioxyde de carbone/méthane. Par analyse dynamique des images de shadowgraphie nous avons pu déterminer les coefficients de diffusion et Soret en fonction de la pression pour le mélange tétraline/dodécane. Aux incertitudes près, nous observons une décroissance linéaire avec la pression pour ces coefficients. De plus nous avons observé l’effet du confinement de la cellule sur les fluctuations en très bon accord avec la théorie et les simulations. Pour le mélange dioxyde de carbone/méthane l’analyse dynamique a montré une cinétique difficilement accessible de par les limites physiques et informatiques du dispositif expérimental utilisé. L’analyse statique montre, quant à lui, une croissance rapide de l’amplitude des fluctuations avec la pression jusqu’à un seuil au-delà duquel elle décroît. Sur ce mélange les simulations de dynamique moléculaire ont montré un bon accord avec les prédictions théoriques
Thermodiffusion, also called the Soret effect, describes the coupling between temperature gradient and resulting fluxes. This phenomenon is involved in a number of natural and industrial processes. In particular, multi components fluids in petroleum reservoirs are subjected to this phenomenon because of the geo-thermal gradient. Nevertheless, in spite of a lot of advances, there are few available data of this phenomenon and the establishment of a theoretical model, able to give a quantitative estimation of these transport coefficients whatever molecules in presence, is still an open question. The principal aim of this thesis is to develop an experimental approach allowing providing reference data on thermodiffusion as a function of the pressure. During this thesis, we developed a high pressure thermodiffusion cell in free medium, enabling us to study concentration non-equilibrium fluctuations induced by the Soret effect by means of shadowgraph optical technique. With this setup we investigated two binary mixtures representatives of petroleum fluids; namely the equimassic tetralin/dodecane mixture in liquid phase and the carbon dioxide/methane mixture in gaseous and super critical state. Furthermore, molecular dynamic simulations on the second mixture were performed. Using a dynamic image analysis, we have measured molecular diffusion and Soret coefficient for the tetralin/dodecane mixture. Within experimental uncertainties, we observed a linear decrease of these coefficients with the pressure. Furthermore, we were able to observe the effect of confinement (finite size effect induced by cell vertical boundary conditions) on fluctuation dynamics, in good agreement with calculations and simulations based on hydrodynamic fluctuation theory on similar solutal Rayleigh number. Concerning the carbon dioxide/methane mixture, the dynamic analysis revealed a kinetic too fast for our experimental apparatus. Conversely, static analysis revealed a rapid increase of the non-equilibrium fluctuation magnitude as a function of the pressure up to a threshold beyond which it decreases. On this mixture, performed molecular dynamic simulations provided results in good agreement with expected theoretical behaviour

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
O presente trabalho apresenta uma análise experimental da combustão turbulenta de sprays de etanol, mediante o uso de técnicas de diagnóstico laser, em queimadores tipo obstáculo. São empregadas a fluorescência induzida por plano laser (PLIF) do radical hidroxila (OH), para mapear a frente de chama, a velocimetria por imagens de partículas (PIV), para determinar o campo de velocidades das gotas do spray e Shadowgraphy, para obter o diâmetro e velocidade de gota. Uma caracterização da estrutura do escoamento de ar a jusante do corpo rombudo é realizada com PIV estéreo para diferentes números de Reynolds. Os resultados mostram uma similitude do escoamento na zona de recirculação. As maiores flutuações turbulentas de velocidades são encontradas na região de vórtice e indicam anisotropia no tensor de Reynolds. Os resultados de Shadowgraphy revelam que as gotas do spray não são perfeitamente esféricas em regiões perto do atomizador. O diâmetro médio Sauter (SMD) foi medido em varias posições na região de recirculação. As gotas de maior diâmetro apresentaram as maiores velocidades e as pequenas são ligeiramente desviadas pela zona de recirculação nas regiões mais afastadas da linha central. Os experimentos reativos realizados com diversos valores de vazão de etanol e ar indicam que a frente de chama é descolada do queimador, sua forma é determinada principalmente pela vazão de etanol e a intensidade de luminescência é aumentada com a velocidade do ar. Em alguns casos o escoamento de ar muda a forma do spray. Uma quantidade de gotas apreciável sempre consegue atravessar a frente de chama. O campo de velocidade das gotas é influenciado pelo incremento da velocidade do escoamento anular de ar.
This work presents an experimental analysis of turbulent combustion of ethanol sprays through the use of laser diagnostic techniques in a bluff-body burner. Are employed the planar laser-induced fluorescence (PLIF) of the hydroxyl (OH), to map the flame front, the particle image velocimetry (PIV) to determine the velocity field of the spray droplets and Shadowgraphy to obtain the droplet diameter and velocity. A characterization of the structure of the air flow downstream of the bluff-body is performed with stereo PIV at different Reynolds numbers. The results evidence flow similarity in the recirculation zone. The largest turbulent velocity fluctuations are found in the vortex region, which implies the anisotropy of the Reynolds stresses. The results of Shadowgraphy indicate that the spray droplets are not perfectly spherical near the atomizer. The evolution of Sauter mean diameter (SMD) is measured at various positions at the recirculation region. The largest diameter droplets have the highest velocity and the smaller are slightly deviated by recirculation zone in the far furthest from the centerline. The reactive experiments are performed with different ethanol and air flow rates and indicate that the flame front is detached from the burner, the shape is determined by the ethanol flow rate and the luminescence intensity increases with the air velocity. In some case the air flow changes the shape of the spray. An appreciable number of droplets always passe through the flame front. The velocity of the droplets is influenced by the increase of speed air velocity.

Au cours de cette thèse, un modèle LBM MPMC avec échanges thermiques est développé. Des tests d'assimilation de données et des mesures par flot optique sont réalisés en vue d'une validation. Le cadre d'application de cette thèse est celui du mélange d'un fluide cryogénique avec l'eau. Dans une première partie, un travail bibliographique rappelant l'équation de Boltzmann, ses diverses hypothèses et simplifications, ainsi que l'aspect algorithmique de la LBM sont exposés. Une comparaison entre opérateur de collision SRT et MRT est réalisée, et une simulation de phénomènes turbulents à différents nombres de Reynolds est étudiée, notamment avec le benchmark de l'instabilité de Von Karman. Dans une seconde partie, le modèle MPMC de Shan & Cehn est rappelé puis étendu au cas où les échanges thermiques entre composants sont présents. Des validations quantitatives sont faites, notamment avec le benchmark du fluide de Couette à deux phases ou à deux composants, du test de cohérence vis-à-vis de la loi de Laplace, ou encore par rapport à un benchmark faisant intervenir la conduction thermique. Des tests qualitatifs de condensation en milieu multicomposants sont proposés pour valider l'aspect des échanges thermiques entre composants en présence d'une transition de phase. Dans la troisième partie de cette thèse, une méthode de validation par assimilation de données est introduite, avec le filtrage de Kalman d'ensemble. Un test d'estimation d'état d'un fluide di-phasique est réalisé, et la compatibilité du filtrage de Kalman d'ensemble par rapport au modèle LBMMPMC est évaluée. Pour la validation du comportement du modèle d'un point de vue de la présence de deux composants, un fluide de substitution (non-cryogénique) au GNL, le butane, a été choisi pour permettre des observations dans des conditions expérimentales accessibles. Puis, une plateforme expérimentale d'injection de butane liquide dans une colonne d'eau sous pression est présentée. Des images d'ombroscopie issues d'expériences de remontée de butane liquide dans de l'eau sont exposées et un algorithme de calcul de flot optique est appliqué à ces images. Une évaluation qualitative des champs de vitesses obtenus par application de cet algorithme est réalisée
In this thesis, a LBM MPMC model with heat exchange is developed. Data assimilation tests and optical flow measurements are made in order to validate the model. The application context of this thesis is the mixture of a cryogenic fluid with water. In the first part, a bibliographical work reminding the Boltzmann equation and its various assumptions and simplifications, as well as the algorithmic aspect of the LBM are exposed. A comparison between SRT and MRT collision operator is performed, and a simulation of turbulent phenomena at different Reynolds numbers is studied, especially with the benchmark of the instability from Von Karman. In the second part, the MPMC model from Shan & Chen is reminded and extended to the case of the inter-component heat exchanges. Quantitative validations are made, especially with the benchmark of a two-phase or two-component Couette fluid. Consistency is tested against Laplace's law rule, or against a benchmark involving heat conduction. Qualitative testing of condensations in a multi-component medium are proposed to validate the heat exchange between components in the presence of a phase transition. In the third part of this thesis, a validation method for data assimilation is introduced, with the ensemble Kalman filter. A state estimation test of a bi-phase fluid is realized, and compatibility of the ensemble Kalman filtering to the LBM MPMC model is assessed. For validation of the behavior of the model for a two-component case, a substitution fluid (non-cryogenic) for LNG, butane, was selected to permit observations in experimental conditions which are accessible. Then, an experimental platform of injection of liquid butane in a pressurised water column is presented. Shadowgraph images from liquid butane experiments in water are exposed and an optical flow calculation algorithm is applied to these images. A qualitative assessment of the velocity field obtaines by application of this algorithm is performed

Ce travail de thèse repose sur l'élaboration et l'exploitation d'un banc expérimental dédié à l'étude d'un écoulement cavitant dans un micro-canal, pour des conditions proches de celles de l'injection diesel. Ce banc a été développé dans le but de faire varier différents paramètres, notamment l'état de surface des parois du canal. Plusieurs méthodes optiques (imagerie en transmission, strioscopie et interférométrie) ont été mises en place afin de visualiser l'écoulementet d'en extraire des informations quantitatives. Les images en transmission permettent de visualiser la formation de vapeur dans le canal. Elles sont sensibles au gradient de masse volumique et font ainsi apparaître des couches de cisaillement, des structures turbulentes et des ondes de pression. Leur interprétation est rendue délicate par cette richesse en information et nécessite de recourir aux autres techniques optiques. Il ressort de ce travail que la cavitation se forme dans la couche de cisaillement, sous l'effet combiné de la dépression engendrée par le décollement à l'entrée du canal et de tourbillons générés par des instabilités dans la couche de cisaillement. La confrontation des résultats obtenus à l'aide des différentes techniques optiques, notamment les champs de pression reconstruits à partir des interférogrammes, montre que la zone de formation de la cavitation ne correspond pas à la zone de minimum de pression moyenne de l'écoulement. Il apparaît aussi que certaines bulles de vapeur ont une durée de vie bien supérieure à ce que prévoient les modèles de dynamique de bulles. On suspecte que des fluctuations de pression de l'ordre de 20 bar, associées à la turbulence, contribuent à la prolongation de ces temps de vie. Un algorithme de PIV, appliqué à des couples d'images en transmission, permet de montrer une augmentation importante des fluctuations de vitesse en sortie de canal lorsque les poches de vapeur se développent. Cette augmentation devient plus significative quand les poches atteignent60% de la longueur du canal. L'écoulement cavitant est essentiellement piloté par le nombre de cavitation K. Les conditions d'apparition et de développement de la cavitation ont été quantifiées dans différents canaux, en faisant varier des paramètres géométriques, la pression amont ou la température. L'influence de la hauteur du canal et du rayon de courbure à l'entrée de l'orifice est conforme aux données de la littérature. Une dépendance du nombre de cavitation critique Kcrit à l'apparition de la cavitation au nombre de Reynolds Re est montrée. Enfin, l'influence de l'état de surface des parois a fait l'objet d'une étude spécifique. Cette partie du travail demande probablement à être complétée mais l'état de surface semble avoir une influence sur la cavitation. D'après les cas étudiés au cours de cette thèse, une surface rugueuse ou texturée avec des motifs suffisamment espacés peut retarder l'apparition de la cavitation et une rugosité limitée (jusqu'à Ra = 0,7 μmici) peut favoriser le développement des poches de vapeur.

This dissertation presents an experimentally supported multi-physics model of a dielectric barrier discharge boundary layer flow control actuator. The model is independent of empirical data about the specific behavior of the system. This model contributes to the understanding of the specific mechanisms that enable the actuator to induce flow control. The multi-physics numerical model couples a fluid model, a chemistry model, and an electrostatics model. The chemistry model has been experimentally validated against known spectroscopic techniques, and the fluid model has been experimentally validated against the time-resolved shadowgraphy. The model demonstrates the capability to replicate emergent flow structures near a wall. These structures contribute to momentum transport that enhance the boundary layer’s wall attachment and provide for better flow control. An experiment was designed to validate the model predictions. The spectroscopic results confirmed the model predictions of an electron temperature of 0.282eV and an electron number density of 65.5 × 10⁻¹²kmol/m³ matching to within a relative error of 12.4% and 14.8%, respectively. The shadowgraphic results also confirmed the model predicted velocities of flow structures of 3.75m/s with a relative error of 10.9%. The distribution of results from both experimental and model velocity calculations strongly overlap each other. This validated model provides new and useful information on the effect of Dielectric Barrier Discharge actuators on flow control and performance. This work was supported in part by NSF grant CNS-0960081 and the HokieSpeed supercomputer at Virginia Tech.
Ph. D.

Au cours des dernières années, la culture de microalgues est largement étudiée pour produire des biocarburants et d’autres produits de valeur en fixant le dioxyde de carbone de l’atmosphère, afin d’atténuer simultanément les effets du changement climatique et de réduire la dépendance à l’égard des carburants fossiles. En comparaison avec les systèmes ouverts, les photobioréacteurs fermés sont davantage utilisés en laboratoire, car ils permettent de contrôler avec précision les facteurs environnementaux tels que le pH, la concentration en éléments nutritifs, etc. Le principe de fonctionnement d’un photobioréacteur repose sur l’injection de bulles dans le milieu de culture pour (i) apporter du dioxyde de carbone aux cellules (ii)agiter le liquide. Par l’apport d’énergie lumineuse les cellules transforment le carbone inorganique en carbone organique par photosynthèse. Ainsi, les phénomènes physiques - l’écoulement, transfert de matière, transfert radiatif - et les phénomènes biologiques - photosynthèse, croissance cellulaire et mort - coexistent dans un photobioréacteur. Plus important encore, tous les phénomènes de base ne sont pas complètement indépendants les uns des autres. Des recherches récentes ont révélé que le comportement des bulles avait également une incidence directe sur le processus biologique. En raison du comportement significatif des bulles sur la productivité d'un photobioréacteur, la génération de bulles a été étudiée dans cette thèse au moyen de méthodes expérimentales et numériques.Dans l'étude expérimentale, nous avons conçu puis fabriqué un nouveau photobioréacteur afin d'étudier le bullage in situ. L’emploi d’une technique d’ombroscopie couplée à une caméra vidéo a permis l’enregistrement de séries de bulles. Les images traitées ont permis de mesurer des caractéristiques de bulles (fréquence, volume, facteur de forme). Le volume moyen de bulle et la fréquence de formation de bulles augmentent avec le débit de gaz. De plus, la distribution volumique monodisperse à faible débit devient de plus en plus polydisperse par l’accroissement de celui-ci. L’évolution de la forme des bulles lors de leur remontée dans le liquide a été évaluée par l’emploi de facteurs de forme. Ces facteurs diminuent avec la remontée des bulles et traduisent une déformation horizontalement. A débit élevé, les formes des bulles oscillent et coalescent plus fréquemment.La simulation du bullage a été réalisé par l’emploi d’une méthode Volume of Fluid (VOF) et d’une bibliothèque open source de mécanique numérique des fluides OpenFOAM. Ces choix de méthodes sont motivés en raison de la robustesse d'OpenFOAM en matière de simulation d'écoulements diphasiques rapportée dans la littérature. Une première étude numérique de simulation 2D a permis de déterminer les valeurs appropriées des paramètres numériques (nombre de Courant et la taille du maillage) tout en minimisant le temps de calcul par rapport à une pré-étude 3D. Sans surprise, nous avons déterminé que la taille des mailles devait être inférieure au diamètre de la buse pour obtenir des résultats significatifs. De façon plus surprenante, nous avons observé que le nombre maximum de Courant n’a pas d’importance particulière pour ces simulations (dans une limite raisonnable : 0 à 1). Les simulations 3D ont été menées sur un supercalculateur. Elles ont montré que le volume des bulles et l’évolution de leur forme calculées numériquement étaient en accord avec les résultats expérimentaux. Cependant, les simulations 3D n’ont pas permis de représenter la polydispersité de la distribution volumique des bulles en raison d’un temps de calcul nécessaire trop important pour générer une population de bulles suffisamment nombreuse. Au final, l'outil numérique a aussi été utilisé avec succès pour explorer plusieurs caractéristiques hydrodynamiques de mélange dans le liquide
The working principle of a typical photobioreactor is to inject gas bubbles into the culture medium, providing CO2 to the cells and also stirring the liquid. Subsequently, the cells convert inorganic carbon into organic carbon through photosynthesis under illumination. Therefore, physical phenomena, e.g. bubbly flow, mass transfer, radiative transfer, and biological phenomena, e.g. photosynthesis, cell growth and death, coexist in a photobioreactor. More importantly, all the basic phenomena are not completely independent to each other. For example, bubble volume and bubble shape can influence gas-liquid mass transfer according to Young-Laplace equation and Henry's law. Moreover, some recent research revealed that bubble behaviors also directly affect the biological process. In view of the important impact of bubble behaviors on productivity of a phototbioreactor, the bubbly flow was investigated in this thesis by both experimental and numerical methods.In the experimental study, we first manufactured a new photobioreactor in order to study the bubbles and other phenomena. Subsequently, the bubbles were captured by high speed camera by virtue of a shadowgraphy technique and bubble behaviors were obtained by processing and analyzing the images. From the experimental results, we found that both averaged bubble volume and bubbling frequency increased with gas flow rate. Furthermore, we also discovered that the distribution of bubble volume was almost monodisperse at low flow rate, and it became more and more polydisperse with increasing flow rate. Regarding bubble shape evolution, we used two shape factors, viz. aspect ration and circularity, to quantitatively study it. We found that both shape factors dropped rapidly during bubble rising (within the limit of the field of view of our video camera), which implied that bubbles were flattened in the course of rising. Nonetheless, bubbles became more vertically elongated at higher flow rate, partially due to the more frequent bubble coalescence at higher flow rate.In the numerical study, we adopted VOF method and OpenFOAM, an open source CFD library, as our numerical tool to represent bubbly flow. First of all, the robustness of OpenFOAM in simulating two-phase flow was validated by literature survey. Subsequently, 2D simulations were carried out for seeking the appropriate and not very time-consuming numerical parameters, i.e. maximum Courant number and mesh size. We found that mesh size should somehow be smaller than the nozzle diameter to have meaningful results. On the other hand, maximum Courant number had no particular importance in the simulations (as long as between 0 and 1). Furthermore, 3D simulations were in good agreement with the experiments in terms of bubble volume and bubble shape evolution. However, 3D simulations were not able to represent the polydispersity of bubble volume due to the limited computing power. In addition, several hydrodynamic characteristics were also explored by the proposed numerical tool, which gave reasonable results.To conclude, bubble behaviors were successfully captured by experimental methods and represented by numerical methods in this thesis, which will help us go further in understanding the complicated physical-biological phenomena of a photobioreactor

Three methods were developed to better understand and characterize the near-field dynamic processes of rotary bell atomization. The methods were developed with the goal of possible integration into industry to identify equipment changes through changes in the primary atomization of the bell. The first technique utilized high-speed imaging to capture qualitative ligament breakup and, in combination with a developed image processing technique and PIV software, was able to gain statistical size and velocity information about both ligaments and droplets in the image data. A second technique, using an Nd:YAG laser with an optical filter, was used to capture size statistics at even higher rotational speeds than the first technique, and was utilized to find differences between serrated and unserrated bell ligament and droplet data. The final technique was incorporating proper orthogonal decomposition (POD) into image data of a side-profile view of a damaged and undamaged bell during operation. This was done to capture differences between the data sets to come up with a characterization for identifying if a bell is damaged or not for future industrial integration.

Jusqu’à récemment, la plupart des applications des arcs électriques mettaient en oeuvre les propriétés du coeur de la colonne, un effort particulier a donc été effectué pour développer des méthodes de caractérisation de ces zones dont la température moyenne est de l’ordre de 10000 K. Avec le développement de la plasma-chimie, le diagnostic des zones périphériques d’arcs et des décharges hors équilibre est devenu un enjeu primordial. Les méthodes de mesure classiques sont mal adaptées pour cette tâche ; le but du travail présenté dans cette thèse se résume donc au développement et à la validation de techniques de diagnostic adaptées à ces zones, dont la température cinétique n’excède pas 8000 K. Deux méthodes innovantes basées sur l’indice de réfraction, l’ombroscopie quantitative et la déflectométrie moirée, ont été étudiées en détails. Les résultats théoriques ainsi que le traitement des données obtenues ont été validés sur un jet de plasma laminaire d’argon, un modèle parfait de zone périphérique. Pour sonder les décharges hors équilibre, l’utilisation du spectre UV de OH a été aussi envisagée. À cette occasion, un programme de simulation de spectre moléculaire a été développé. L’étude des spectres synthétiques obtenus a permis de mettre au point des méthodes de mesure simples de la température rotationnelle et vibrationnelle pour une large gamme de résolution. Une des méthodes développées a été mise en œuvre sur une décharge à faible intensité de courant. On montre que les résultats obtenus par spectroscopie moléculaire sur le radical OH sont très proches de ceux obtenus à l’aide d’une simulation
Until recently, most of electrical arcs applications were dealing with the properties of the centre of the plasma column, a large number of works was then done to develop diagnostic techniques dedicated to those area where the mean temperature is about 10000 K. With the emergence of plasma chemistery, the diagnostic of arc’s peripheral areas and un-equilibrium discharges become a goal of prime importance. Classical diagnostic techniques are not adapted to those objects where the maximum temperature is around 8000 K; the principal aim of this work was to develop and check diagnostic techniques. Two inovating techniques based on refractive index, the quantitative shadowgraphy and the moiré deflectometry were studied extensively and checked on a laminar plasma jet, a perfect model of arc’s peripheral area. To probe unequilibrium discharge, the use of UV OH spectrum was considered. At this occasion, a spectrum simulation software was written. The study of synthetic spectra lead to the creation of simple measurement methods of rotationnal and vibrationnal OH temperature for a large range of resolution. Those methods was checked on a low power electric discharge. It can be shown that result from molecular spectroscopy are close to those obtained by simulation

Concerns about the use of certain chemical species within the aerospace field are growing in recent years. A European regulation, REACh, now makes the use of hydrazine uncertain in – among others- attitude control thrusters. Green monopropellants, which are alternatives for this species already exist, but they all require a catalyst to react. Catalysts constitute the limiting factor for the lifespan of satellites because of the number of thermal cycles they endure. A joint project between ONERA, the French aerospace research center and CNES, the French space agency, was born to develop a high-performance green monopropellant thruster operating without any catalyst. Sizing the thruster and particularly its combustion chamber is not an easy task because of the explosive properties and the lack of knowledge regarding the monopropellant reaction process. The thesis aims at simulating the flow in a combustion chamber using CNES05, a new promising green monopropellant. This monopropellant has a very low vapor pressure and is an energetic liquid. As such, its reaction above a certain temperature -which is called decompositionis not well understood and must be observed closely. For this matter, a test bench was created, and it paved the way for the development of a specific model of decomposition. Indeed, even if the CNES05 decomposition cannot be modeled with the classical theory of isolated droplets, the setup showed us the order of magnitude of the reaction kinetics and the presence of a break up phenomenon. Using this model, the simulations of the flow inside the combustion chamber give us the heat flux profile through its walls, a sizing parameter for the thruster. Large recirculation zones are observed and the influence of the angle of injection seems to be the major injection parameter of influence. The sensitivity of the parameters used in the model is also studied.

L’aérosolthérapie a pour objectif de délivrer un médicament dans les voies respiratoires. Le nébuliseur pneumatique est un dispositif permettant de générer des gouttelettes de liquide de diamètre micrométrique. Son processus d’atomisation a cependant été peu analysé. Ainsi, les performances du nébuliseur, caractérisées par le diamètre des gouttes et la masse de médicament inhalable par le patient, et atteignent un palier. Notre travail consiste à utiliser un modèle numérique diphasique en 3D basé sur une géométrie donnée et paramétré sous ANSYS Fluent. Plusieurs méthodes sont utilisées pour caractériser expérimentalement la génération de l’aérosol : l’ombroscopie, la diffractométrie laser et l’anémométrie phase Doppler. Notre modèle est validé par rapport aux données expérimentales et peut donc être exploité pour analyser les processus de génération. L’influence de plusieurs paramètres physiques sur les caractéristiques de l’aérosol produit est étudiée. Ainsi, l’étape de génération de gouttelettes est optimisée pour le développement d’un nouveau nébuliseur. Le transport des gouttes aux poumons du patient est optimisé empiriquement
The purpose of aerosol therapy is to deliver drugs into respiratory airways. The jet nebulizer is a device used to generate liquid droplets with a diameter lower than 5 μm. However its atomization process was not much analyzed. Nebulizer performances, which are characterized with droplet size and drug mass inhaled by the patient, are empirically optimized and have reached a plateau. Our work consists in setting a 3D diphasic numerical model on ANSYS Fluent, based on a given geometry. Several methods are used to experimentally characterize aerosol generation: shadowgraphy, laser diffractometry and phase Doppler anemometry. Our model is validated by experimental data and helps predicting generation processes. The influence of several geometric and physical parameters on the output is studied. From these data, droplet generation is optimized for the development of a new nebulizer. Droplet transport to the patient lungs is empirically optimized

For performance optimisation of modern liquid cryogenic bipropellant rocket combustion chambers, one component which plays an important role in reducing the wall side heat flux, is the behaviour of the cooling film. At the Institute of Space Propulsion of the German Aerospace Center (DLR) in Lampoldshausen, hot test runs have been performed using the experimental combustion chamber BKM, to investigate the wall side heat flux which is -- among other factors -- dependent on cooling film properties. To gain more insight into the film behaviour under real rocket-like conditions, optical diagnostics have been applied. The chosen methods were shadowgraphy and OH* imaging producing optical data sets which are analysed in this study. In this context, a description of the necessary background information is given, concerning rocket combustion chambers, film cooling and optical diagnostics of O2/H2 combustion. The applied methodology for optical analysis is described, followed by a presentation of the results. During the test campaign, it became clear that the optical setup was not optimised for creating meaningful shadowgraphy recordings which is why the shadowgraphy data has to be treated as flame emission imaging. The behaviour of the gas layer adjacent to the chamber wall could be characterised based on qualitative (luminosity, LOx shadow, reflection, recirculation zone and flame shape) and quantitative (layer thickness, layer length, pressure conditions) analysis. The thickness could be identified for each load step and an average length of the layer was found as well. OH* imaging has been used supplementary to support the observations from the flame emission images. An in depth frame by frame analysis was not possible due to time constraints. However, the time averaged images yielded results in accordance to the flame emission and could give a relative figure for the temperature distribution in the combustion volume. An artefact in the data was found, stemming presumably from the image intensifier. This artefact needs to be researched for a future error reduction in the data of this and other campaigns. Additionally, the thickness of the layer suggested a correlation to the models for film cooling efficiency. Such a correlation could not be established. Nevertheless, the film cooling models show the same behaviour as the data obtained from the flame emission imaging. Finally, suggestions are given how the data analysis and the optical setup could be improved for future, similar campaigns.

The thesis summarizes general and up-to-date knowledge of descaling during the continuous production of the hot-rolled steel and proposes further streamlining of this process in industrial production. The first chapter of the thesis deals with the origin, structure and physical properties of the scales. The second chapter describes the principles of descaling by using a high pressure flat water jet. The third chapter introduces the principles of the experimental methods and describes the used laboratory equipment. The fourth chapter summarizes the description of the particular experiments and their evaluation, and thus represents the focus of the dissertation. It is divided into six sections which independently solve predefined objectives of the dissertation. The first section focuses on the height and structure development of the scales on 54SiCr6 and HDT580X steels. It has been proven that the height of the formed scales increases with the time and temperature of the oxidation. The layered nature of the scales was verified at the same time. The second section examines the effect of the nozzle stabilizer on the focussing and distribution of the impact pressure of the nozzle. Experiments have shown that increase of 11 % of an average maximum nozzle pressure can be achieved, depending on the type of nozzle and the length of the stabilizer. The third section deals with the analysis of shadowgraphy images of water jet structures of the nozzles. A script was developed for analysis of these shadowgraphy photos by an adaptive thresholding. The findings are correlated using a regression analysis with an average heat transfer coefficient. It has been reported that most of the standard nozzle configurations produced disintegrated stream of little droplets at the height of the rolled surface. The fourth section focuses on the area of water jet overlap, especially the area of the so-called washout, where the impact pressure of one nozzle is reduced by the nozzle stream of the other. The influence of the pressure change and the mutual displacement of the nozzles is investigated. The analysis showed that the change of pressure did not have any effect on the percentage of reduction of the impact pressure in the area of the washout. It has been shown that if the area of the washout is wide the descaling efficiency in this area may be reduced. The fifth section builds on the previous section and focuses directly on the areas of waterjet overlaps. The influence of the change of rotation and pitch of the nozzles is studied. Experiments have shown that small changes in nozzle pitch do not have a significant impact on impact pressure and heat transfer coefficient. The effect of nozzle rotation, on the other hand, was a significant factor for the efficiency and homogeneity of the descaling of the surface. The last section deals with the effect of the rolling speed on the heat transfer coefficient in the descaling process. The regression model has shown that with a higher rolling speed there is a reduction in the average heat transfer coefficient. Conclusion summarizes the results of the dissertation and proposes which findings can be used in the industry to make the descaling process more effective.

Ce travail de thèse propose une description originale de la fragmentation aérodynamique d’une goutte d’eau, induite par une onde de choc plane, pour des régimes à la frontière entre les modes gouvernés par l’instabilité de Rayleigh-Taylor et ceux dominés par l’instabilité de Kelvin-Helmholtz. Un banc expérimental composé d’un tube à choc couplé à des diagnostics d’imagerie rapide est exploité pour caractériser les processus de fragmentation. Les résultats expérimentaux sont complétés par des simulations numériques réalisées à partir du code multiphasique compressible open-source ECOGEN. L’effet de l’onde de choc sur la goutte est évalué grâce à une modélisation théorique basée sur l’acoustique géométrique permettant de décrire la dynamique spatio-temporelle des réflexions d’onde à l’intérieur de la goutte et de prédire le lieu des points de plus haute densité d’énergie. Le champ de pression est résolu à partir de simulations numériques qui indiquent que la tension de rupture de l’eau est atteinte pour une onde de choc évoluant à un nombre de Mach de 1.7. Dès lors, un processus de cavitation dont les conséquences sur la dynamique de la fragmentation pourraient être significatives, est possible. Concernant la dynamique interfaciale, les expériences comme les simulations révèlent le développement d’une perturbation azimutale transverse à l’origine d’une structure ligamentaire périodique. Une analyse de Fourier des résultats numériques 3-D suggère que l’initiation de cette déstabilisation est indépendante des effets capillaires, à l’inverse de sa croissance. La dynamique ligamentaire apparaît être un processus cyclique dont la fréquence est celle du lâché de vortex dans le sillage del a goutte. Ce schéma récurrent cesse après quatre cycles. Il s’en suit alors la perte de l’intégrité structurelle du corps résiduel de la goutte des suites du développement d’une cavité gazeuse, dans le liquide, qui agit comme une région de fragilité et donc, facilite la fragmentation
This thesis proposed a groundbreaking description of the shock-induced aerodynamic fragmentation of a water droplet at the transition of the Rayleigh-Taylor Piercing and the Shear-Induced Entrainment regimes. An experimental facility consisting of a shock tube and high-speed imaging diagnostics is used to investigate the fragmentation processes. Experimental results are supported with numerical simulations performed with the open-source code ECOGEN dedicated to multiphase compressible flows. The shock wave effect on the droplet is assessed by a theoretical modelling based on geometrical acoustics which allows for the description of the wave spatio-temporal dynamics and enables to predict the time-dependent location of the highest energy density. Pressure fields are determined using numerical simulations. It appears that the water tensile rupture is reached for a shock wave Mach number of 1.7 from which bubble cloud cavitation may occur by causing signification changes in the fragmentation dynamics. As regards to the interfacial dynamics, both experiments and numerical simulations show the development of a transverse azimutal modulation resulting in the periodic ligament structure at the droplet surface. Contrary to the modulation growth, its initiation seems to be independent of the capillary effects as revealed by a Fourier analysis of the 3-D numerical results. The ligament dynamics is a cyclic process driven by the vortex shedding process in the wake of the droplet. Four cycles have been observed before the residual droplet core breaks up owing to the growth of an air cavity inside the droplet that acts as weak spot, and thus facilitating the droplet split-off

L'étude de l'injection d'un fluide dans des conditions de hautes pressions reste encore aujourd'hui un challenge. Lorsque la pression critique des fluides est dépassée, l'état supercritique est atteint, faisant disparaître la distinction entre liquide et gaz. Pour ces conditions extrêmes, les données expérimentales sont peu nombreuses et nécessitent d'être consolidées. Dans cette étude, un nouveau banc d'essai a été réalisé au laboratoire CORIA dans le but d'étudier des injections non-réactives d'éthane et de propane dans une atmosphère sub- et supercritique d'azote ou d'hélium. Les données ont été collectées à partir de quatre diagnostics optiques : l'ombroscopie, la DBI, la radiographie et la CBOS. Des informations qualitatives sur la topologie des jets et de leur couche de mélange sont apportées. Des mesures quantitatives de longueur de cœur dense, d'angle d'ouverture et de densité sont complétées par une étude phénoménologique à l'aide de la théorie des mélanges binaires
Studying a fluid flow under high-pressure conditions through reliable experiments is still nowadays a challenge. When the chamber pressure exceeds the critical pressure of working fluids the supercritical state of matter is reached and the distinction between gas and liquid becomes blurred. For such special conditions, experimental data are scarce and need to be consolidated. In the present study, a new test bench has been designed at CORIA Lab to study the non-reactive injection of ethane and propane into nitrogen or helium under sub- and supercritical conditions. Experimental data are collected from four image-based techniques : shadowgraphy, diffused backlight illumination (DBI), radiography and color background oriented schlieren (CBOS). Qualitative information on topology of the jets and their mixing layer are provided. Quantitative measurements of dense core length, jet spreading angle and density field are supported by a phenomenological study based on binary mixing theory

Growing interest in biomedical applications of nonthermal plasmas inspires the development of new plasmas sources. Dielectric barrier (DBD) and corona discharges produced in ambient air or in noble gas flow are typically applied. Direct production of plasma in liquids has a great potential for sterilization of liquid substances and extracorporeal blood treatment. The physical mechanisms of discharge formation in liquid medium are not fully understood.The first part of this thesis deals with the initiation and development of the nanosecond discharge in liquid dielectrics (deionized water, ethanol and n-pentane). Time-resolved shadowgraph visualization, optical emission spectroscopy and electrical diagnostics are applied to investigate the discharge formation on point anode.We have shown that depending on the applied voltage amplitude three different scenario can occur in the polar dielectric, namely, cavitation of a bubble, discharge development in the gaseous cavity (bush-like mode) and initiation of the filamentary discharge (tree-like mode) propagating in bulk liquid. Formation of the bush-like and the tree-like discharges is governed by distinct physical mechanisms, resulting in strongly different plasma parameters.In the second part of this work we address the question of how cold atmospheric plasma interacts with living cells in-vitro and in-vivo, and what is the mechanism of plasma induced cell death. Flowcytometry based cell viability assay with two markers AnnexinV (AV) and Propidium iodide (PI), demonstrates a dose dependent induction of the apoptosis for human T lymphocyte (Jurkat) and epithelial (HMEC) cells treated with DBD plasma. In nude mice model, induction of apoptosis and necrosis in dose dependant manner is observed by electron microscopy in thin epidermis sections. Histological analysis shows significant lesions appeared in epidermis, dermis, hypodermis and muscle as a function of treatment duration. Production of hydrogen peroxide in culture medium (PBS) exposed to DBD plasma is measured using selective fluorescent probe (Amplex® Red). Cell viability of human thyroid epithelial (HTori-3) and melanoma (1205Lu) cells demonstrates nonmonotonous dependence on H2O2 concentration. The major role of plasma produced hydrogen peroxide and DBD electric field is suggested.

Le phénomène de Rayleigh-Bénard correspond à l'état instable dans lequel se trouve une couche horizontale d'un fluide dilatable, soumise à un gradient de température DT. Si ce dernier dépasse une valeur critique DTc, des mouvements convectifs naissent à l'intérieur du fluide. Concernant les fluides à seuil, le phénomène devient plus complexe. Le seuil s'ajoute aux forces stabilisatrices au sein du fluide et modifie de manière fondamentale le transfert de matière et le transfert thermique. Au départ, le fluide est au repos ; le gradient de vitesse est alors nul et la viscosité efficace infinie partout. L'approche de stabilité linéaire est incapable de fournir une solution aux équations d'écoulement car on doit perturber, par les forces d'Archimède, un fluide d'une viscosité infinie. Dans ce travail de thèse, des expériences de Rayleigh-Bénard ont été effectuées sur des solutions à base de Carbopol 940 présentant un seuil de contrainte. Le dispositif expérimental nous a permis d'avoir des résultats quantitatifs et qualitatifs intéressants. Les mouvements thermoconvectifs ont ensuite été filmés par la technique d'ombroscopie. L'effet non-linéaire au début de la convection a été observé.

Dans ce document, nous présentons nos travaux sur les décharges dans l'heptane. L'une des conditions retenue pour ces études est le choix d'un gap micrométrique. Nous avons travaillé avec des gaps compris entre 10 et 150 µm qui correspondent à des tensions de claquage comprises entre 1 et 15 kV. Du claquage jusqu'à 1 µs, la décharge a été caractérisée par ombroscopie et par spectroscopie d'émission optique (SEO). L'ombroscopie a montré que la vitesse de propagation de l'onde de choc et de la bulle est de l'ordre de 1200 m s-1 et 100 m s-1, respectivement. Au-delà de 1 µs, la dynamique de la bulle a été étudiée. Une nouvelle méthode est proposée pour estimer la pression à l'initiation de la décharge. La technique est basée sur la réponse d'une "bulle test" qui se trouve dans le champ acoustique d'une nouvelle décharge dont on veut connaître la pression. Elle est aux environs 80 bar. La SEO a montré une dominance des rayonnements continus pendant les premières 200 ns qui ont été attribués à la recombinaison électron-ion. Au-delà de 200 ns, les rayonnements continus s'effondrent et les raies d'émission deviennent dominantes. L'étude de l'élargissement de la raie H[alpha] de l'hydrogène a montré que la densité électronique peut atteindre 1019 cm-3. En ce qui concerne l'interaction plasma-surface, nous avons pu démontrer que l'impact créé est gouverné par la quantité de charges déposée. Sa morphologie est une résultante d'un équilibre entre la force due à la pression et la force de Marangoni. Nous avons étudié dans une dernière partie la synthèse des nanoparticules de platine (diamètre 5 nm) insérées dans une matrice de carbone hydrogéné présentant un ordre à courte distance
In this document, we report our work on discharges in heptane. One of the specific conditions selected is the choice of a micrometric gap distance. Typically, gaps were between 10 and 150 µm, corresponding to breakdown voltages between 1 and 15 kV. From breakdown up to 1 µs, the plasma discharge was characterized by shadowgraphy and optical emission spectroscopy (OES). Shadowgraphy results showed that the velocities of shock wave and bubble interface are about 1200 m s-1 and 100 m s-1, respectively. Beyond 1 µs, experimental and theoretical studies of the oscillatory dynamics of the bubble are made. Then, we proposed a new method to estimate the pressure at discharge breakdown. The technique is based on the response of a 'test bubble' present in the acoustic field of a new discharge whose pressure is to be known. It is estimated to be about 80 bar. OES, between 300 and 800 nm, showed a dominance of continuous radiations during the first 200 ns which were attributed to electron-ion recombination processes. Beyond 200 nm, continuous radiations collapse and then, the emission lines dominate the spectrum. The study of the H? line broadening showed that the electron density can reach 1019 cm-3. Regarding the interaction of the discharge with the electrode surfaces, we demonstrated that the diameter of the impact is governed by the quantity of charges deposited by the discharge. However, the impact morphology is determined by a balance between the force exerted by the plasma pressure and the Marangoni's force. Finally, we studied the possibility to synthesize platinum nanoparticles (5 nm in diameter) embedded in a matrix of hydrogenated carbon exhibiting a short range order

Les particules d'aérosol sont une composante essentielle de l'atmosphère, et cette importance s'amplifie lors d'une éventuelle libération dans l'atmosphère de matières radioactives sous forme particulaire. En effet, pour améliorer la connaissance autour de la contamination des sols consécutive à une émission de particules, il est important d'étudier le rabattement des particules par la pluie sous le nuage. Dans ce but, des expériences sont menées à l'échelle microphysique (expérience BERGAME) pour quantifier l'efficacité des gouttes de pluie à collecter les particules. Ceci permet au final d'améliorer la modélisation du lessivage des aérosols atmosphériques par la pluie à méso-échelle. Le modèle utilisé est DESCAM qui décrit de manière détaillée les distributions granulométriques en masse et en nombre des particules pour chaque type d'aérosol et des hydrométéores et calcule leur évolution due aux processus microphysiques nuageux. L'expérience BERGAME a été dimensionnée et construite pour mesurer l'efficacité de collecte car les mesures de ce paramètre se sont avérées en désaccord avec les modèles classiques de la littérature pour les gouttes de pluie d'un diamètre supérieur au millimètre. Un montage optique a été imaginé pour tenter de comprendre quels mécanismes de collecte sont négligés dans les modèles standards. Un nouveau modèle d'efficacité de collecte pour les gouttes d'un diamètre de 2 mm est alors proposé prenant en compte pour les grosses gouttes une recirculation turbulente dans le sillage de la goutte capable d'augmenter de façon importante la capture des petites particules. Les nouvelles efficacités de collecte ainsi mesurées et paramétrées sont ajoutées au modèle de nuage DESCAM. Des modifications significatives sur la modélisation du lessivage par DESCAM sont observées, ouvrant ainsi la voie à une amélioration de la modélisation de la contamination des sols par les modèles de dispersion atmosphérique.

Nous nous intéressons au transport turbulent de particules de taille grande devant l'échelle de Kolmogorov. Cette situation se retrouve à la fois dans les écoulements naturels (comme le transport de sédiments) et dans les écoulements industriels (solutés solides dans un mélangeur par exemple). Pour aborder ce problème, nous étudions la dynamique de particules de taille proche de l'échelle intégrale, de densité égale ou légèrement différente de celle du fluide, dans un écoulement turbulent de von Kármán contra-rotatif, à l'aide d'un montage de suivi lagrangien rapide. L'étude de la dynamique rapide des particules montre une diminution forte des fluctuations selon la taille, mais aussi l'apparition d'un phénomène nouveau : à partir d'une certaine taille, les particules n'explorent plus l'écoulement de façon homogène. Cette exploration préférentielle est liée à la structure moyenne de l'écoulement de von Kármán, qui crée une force de piégeage. Cette force devient alors supérieure aux fluctuations des particules quand leur taille dépasse une taille critique. Une étude dans le régime laminaire, où l'écoulement moyen domine largement les fluctuations, a en effet mis en évidence un piégeage fortement accru. Les particules orbitent alors pendant des temps très longs autour des attracteurs stables des particules fluides de l'écoulement laminaire. Même en régime pleinement turbulent, le déplacement des particules entre ces zones s'effectue sur des durées longues, décorrélées des temps de la dynamique turbulente. Nous avons adapté les outils d'analyse pour caractériser cette dynamique et l'avons comparée à celle de particules isodenses dans un écoulement de von Kármán qui possède deux états asymétriques. Nous avons également élaboré un modèle qui reproduit ces caractéristiques dans les cas symétrique et asymétrique. Ces questions sont intimement liées au transfert de masse ou de chaleur entre une particule et l'écoulement. Nous avons donc aussi étudié la fusion de grosses billes de glace en turbulence développée, analysant l'influence de la taille des billes et de la vitesse de glissement sur le transfert thermique, à l'aide d'un montage d'ombroscopie afocale. Nous avons notamment montré que les grosses billes de glace fondent dans un régime ultime de convection forcée lorsqu'elles sont librement advectées par l'écoulement.

Les particules atmosphériques sont un sujet d’importance dans plusieurs couches de la société. Leur présence dans l’atmosphère est aussi bien une problématique météorologique et climatique qu’un enjeu de santé publique, notamment de par l’accroissement des maladies cardiovasculaires. En particulier, les particules radioactives émises dans l’atmosphère à la suite d’un accident nucléaire peuvent polluer les écosystèmes durant plusieurs années. Le récent accident du Centre Nucléaire de Production d’Électricité de Fukushima Daiichi en 2011 nous rappelle que, même aujourd’hui, le risque zéro n’existe pas. À la suite d’une émission dans l’atmosphère, les particules nanométriques diffusent et s’agglomèrent alors que les particules de plusieurs micromètres sédimentent. Les tailles intermédiaires vont, quant à elles, pouvoir être transportées à l’échelle globale dont le mécanisme principal de rabattement au sol provient des interactions avec les nuages et les précipitations. Afin d’améliorer la connaissance de la contamination des sols consécutive à de tels accidents, la compréhension de la capture des aérosols par les nuages est alors essentielle. Dans ce but, un modèle microphysique est implémenté dans ce travail, considérant les mécanismes microphysiques qui interviennent dans la capture des aérosols par des gouttes de nuage, notamment les forces électrostatiques dès lors que les radionucléides ont pour propriété de fortement se charger. Des mesures en laboratoire sont alors réalisées à l’aide de In-CASE (In-Cloud Aerosols Scavenging Experiment), expérience conçue dans ce travail, afin de comparer le modèle développé aux observations, et ce, toujours à une échelle microphysique où les paramètres d’influence régissant la capture au sein du nuage sont contrôlés. Par ailleurs, des systèmes de charge des particules et des gouttes sont conçus pour soigneusement maîtriser les charges électriques, tandis que l’humidité relative est précisément pilotée. Les nouvelles connaissances de la capture des particules par des gouttes de nuage qui en découlent, concernant entre autres les effets électrostatiques, sont ensuite incorporées au modèle de nuage convectif DESCAM (Detailed SCAvenging Model). Ce modèle à microphysique détaillée décrit un nuage de sa formation jusqu’aux précipitations, permettant d’étudier l’impact des nouvelles données sur le rabattement des particules à méso-échelle. De plus, des modifications sont apportées à DESCAM pour élargir l’étude aux nuages stratiformes qui constituent en France, la majorité des précipitations. À terme, cette étude ouvre la voie à l’amélioration de la modélisation du rabattement atmosphérique des particules, et notamment à la contamination des sols dans les modèles de crise de l’Institut de Radioprotection et de Sûreté Nucléaire
Atmospheric particles are a key topic in many social issues. Their presence in this atmosphere is a meteorological and climatic subject, as well as a public health concern since these particles are correlated with the increase of cardiovascular diseases. Specially, radioactive particles emitted as a result of a nuclear accident can jeopardise ecosystems for decades. The recent accident at the Fukushima Daiichi’s nuclear power plant in 2011 reminds us that the risk, even extremely unlikely, exists.After a release of nuclear material in the atmosphere, nanometric particles diffuse and coagulate, while micrometric particles settle due to gravity. Nevertheless, the intermediate size particles can be transported at a global scale when the main mechanism involved in their scavenging comes from the interaction with clouds and their precipitations. To enhance the ground contamination knowledge after such accidental releases, the understanding of the particle in-cloud collection is thus essential. For this purpose, a microphysical model is implemented in this work, including the whole microphysical mechanisms acting on the particle collection by cloud droplets like the electrostatic forces since radionuclides are well-known to become significantly charged. Laboratory measurements are then conducted through In-CASE (In-Cloud Aerosols Scavenging Experiment), a novel experiment built in this work, to get comparisons between modelling and observations, once again at a microphysical scale where every parameter influencing the particle in-cloud collection is controlled. Furthermore, two systems to electrically charge particles and droplets are constructed to set the electric charges carefully while the relative humidity level is also regulated. These new research results related to the particle collection by cloud droplets following the electrostatic forces, among others effects, are thus incorporated into the convective cloud model DESCAM (Detailed SCAvenging Model). This detailed microphysical model describes a cloud from its formation to the precipitations, allowing the study at a meso-scale of the impact of the new data on the particle scavenging. Moreover, some changes are made in DESCAM to expand the study to stratiform clouds since the major part of the French precipitations come from the stratiform ones. Finally, this work paves the way for the enhancement of the atmospheric particle scavenging modelling, including the ground contamination in the crisis model used by the French Institute in Radiological Protection and Nuclear Safety

碩士
國立臺南大學
戲劇創作與應用學系碩士班
95
This thesis will focuses on learn, create, and play process of students at school shadow play club, Mitou Elementary. After they learn the traditional shadow play Li Nor-cha disturb East China Sea，they make group creative job as Li Nor-cha disturb the Internet Ca’fe. They even design and made the shadow puppies by themselves, then teamwork to perform this campus shadow play. The main purpose of this research is to design a proper course syllabus for elementary shadow play club. This syllabus could be the reference of future campus club operation. Then the research will based on the operation result to provide workable suggestions and problem-resolving strategies. Through this research, researcher promotes the knowledge and understanding of traditional shadow play and campus shadow play. It would help research objects (i.e. elementary students) understand the differences between traditional and campus shadow play on puppet making and performance style. After the teaching of shadow play club, researcher wish students will love shadow play more, and increase the appreciation of shadow play, then achieve purpose of preserve shadow play. Following is the brief research results of this research: 1. The syllabus research of elementary school shadow play club. This research will develop a concrete course. 2. The teaching progress of elementary shadow play include 4 different stages as: preparation, development, operation, and arrangement. 3. Through the teaching of elementary school shadow play club, it would increase students’ favoring and understanding toward traditional shadow play. 4. Through the teaching of elementary school shadow play club, it would increase students’ abilities on script writing, puppet making and playing. It would also trigger student creativeness to innovate the performance skill and content. This will attract more audiences to enjoy the beauty of shadow play. 5. The research probe to resolve the difficulties of elementary shadow play club. This research also suggests school to find more resources to ease problems. It would help the shadow play more prosperous than ever.

Effervescent atomization has been a topic of considerable investigation in the literature due to its important advantages over other atomization mechanisms. This work contributes to the development of both effervescent atomizers and also laser-based techniques for spray investigation In order to develop non-intrusive measurement techniques for spray applications, a procedure is suggested to characterize the shape of droplets using image-based droplet analyzers. Image discretization which is a major source of error in droplet shape measurement is evaluated using a simulation. The accuracy of StereoPIV system in conducting droplet velocity measurement in a spray field is also investigated. To assist in the design of effervescent atomizers, bubble formation during gas injection from a micro-tube into liquid cross-flow is investigated using a Shadow-PIV/PTV system. The generated spray fields of two effervescent atomizers which operate using a porous and a typical multi-hole air injector are compared using qualitative images and Shadow-PTV measurement.

This present study seeks to contribute detailed visualization data on a pool boiling experiments using HFE-7000. Particle Image Velocimetry (PIV) was used to measure the time resolved whole field liquid velocity. Bubble dynamic parameters such as nucleation site density, bubble departure diameter, contact angles and frequency were obtained in shadowgraphy measurements. Infrared thermometry with an IR camera was used for observation of temperature fluctuations of nucleation sites. The experiments were taken for the heat flux from 0.042 kW/m^2 to 0.266 kW/m^2, six experimental conditions in total. To provide a supplementary description of heat transfer mechanism, a novel bubble characterization technique, reflection interference contrast microscopy (RICM), was used to obtain detailed information on bubble dynamic parameters on the microscopic scale. Bubble diameter was obtained from RICM pictures. Comparison between the experiments results and previous empirical correlation were made. Agreements and discrepancies were discussed.

In this study, the phenomenon of two-phase flow was investigated in a square channel. The experiment was performed with stagnant liquid conditions. The gas and liquid dynamics of the bubbly flow were observed in two regions far from the inlet. Air was inserted through a porous media at three superficial gas velocities: 4.6 mm/s, 2.5 mm/s, and 1.4 mm/s. Two techniques were applied in the experiment to measure the bubbly flow: an optical probe and an in-house developed tracking algorithm. Measurements of the bubble interface velocity, void fraction, bubble frequency, time of flight, and Sauter mean diameter were obtained by using the optical probe. The duration of the probe measurements for all three flow rates and both regions lasted approximately 33 hours. The tracking algorithm was used to analyze the experimental data for two visual methods: shadowgraphy and Particle Tracking Velocimetry (PTV). Shadowgraphy provided gas-phase measurements of the bubble centroid velocity and its fluctuations, void fraction, bubble size, and Reynolds stresses. Five data sets were acquired for each flow rate, resulting in a total of 327,540 shadowgraphy images. Liquid parameters such as the velocity, fluctuations in the velocity, and the Reynolds stresses were provided by PTV. Only one data set containing 10,918 images was obtained from liquid measurements for each flow rate. One data set was sufficient to provide reliable statistics since tracking two consecutive images lead to approximately 15,000 velocity vectors. The data obtained from this study was an effort to assist in the verification, validation, and improvement of two-phase flow simulations.

The present work is concerned with fundamental studies on the liquid fuel transport in the intake manifold of small carburetted engines. This work is motivated by the need for development of technologies to meet the stringent cold-start emission norms that are to be prescribed for two-wheelers in particular. More specifically, visualization studies conducted in a transparent manifold made of quartz in a small four-stroke 110-cc two-wheeler engine have shown the presence of gasoline films on the walls of the inlet manifold under cold start conditions. Advanced Laser diagnostic techniques such as Planar Laser Induced Fluorescence (PLIF) have been utilized to measure the thickness of the fuel films. The Sauter Mean Diameter for the fuel droplets at the carburettor exit is measured using Laser Shadowgraphy technique. It is observed that the films are present both at idling conditions and under load. This large amount of liquid fuel entering the engine leads to incomplete combustion and higher emissions of unburned hydrocarbons. A detailed analysis of the effects of heating the inlet manifold has been performed. The potential of this manifold heating strategy in reducing hydrocarbon emissions has been assessed and found to be promising. In addition, a need of proper control of the fuel exiting the carburettor is shown to reduce emissions and increase fuel efficiency.