We present theory and experiments for thin film particle-laden flow on an incline. At higher particle concentration and inclination angle, a new phenomenon is observed in which a large particle-rich ridge forms at the contact line. We derive a lubrication theory for this system which is qualitatively compared to preliminary experimental data. The ridge formation arises from the creation of two shocks due to the differential transport rates of fluid and particles. This parallels recent findings of double shocks in thermal-gravity driven flow [A. L. Bertozzi et. al., PRL, 81, 5169 (1998), J. Sur et. al., PRL 90, 126105 (2003), A. M¨unch, PRL 91, 016105 (2003)]. However, here the emergence of the shocks arises from a new mechanism involving the settling rates of the species. / PRL 94(11) March 25, 2005 117803 / NSF

Particle ingestion in gas turbine applications can be detrimental to performance and pose significant safety concerns. Areas of high sand concentration are hazardous to aircraft, requiring precautions like routine inspections and maintenance. The engine failure modes are dependent on particle composition, concentration, and size. Particles containing certain minerals tend to melt and stick to turbine blades, which is known as glazing. Alternatively, particles may erode blades from repeated collisions, or they may fill cooling passage holes. Therefore, it is necessary to develop systems that identify these parameters as particles are ingested. This thesis introduces three separate systems responsible for collecting sand concentration, size distribution, and material composition of sand. A particle visualization technique (ParVis), developed at Virginia Tech, was used to validate two sensors developed by commercial partners. One sensor measures particle size and velocity with a method similar to Laser Doppler Velocimetry (LDV). The second sensor measures particle composition with X-Ray Fluorescence (XRF) by physically sampling particles in a flow. There has been little research on applying XRF to moving particles, so experimental data were collected to demonstrate the effectiveness of the sensor. Detection comparisons between two particle types showed promising outcomes for the XRF. Meanwhile, the ParVis technique was iterated to overcome previous limitations and implemented into the testing process to provide particle concentration measurements. Particularly, improvements led to increased accuracy and reliability of the method such as reducing variance in concentration approximations. / Master of Science / Aircraft are constantly ingesting particles into their engines. Those operating in dusty environments are at higher risks of engine failure because more particles are ingested, which cause damage in several ways. As engine manufacturers push the turbine operating temperatures higher for efficiency and emissions, sand particles reach melting temperatures and stick to turbine blades, which results in overheating. Because of the potential risks to life, sand ingestion research continues to provide solutions for improving aircraft safety. This study explores the capabilities of new sensors to quantify characteristics of ingested particles, including the concentration, size distribution, and material composition of sand. An illumination technique for measuring sand concentration from particle imaging was developed at Virginia Tech. The technique was iterated to overcome previous limitations and improve its reliability during this study. It provides a more accurate depiction of the testing conditions that can be used to diagnose and calibrate sensors. In this case, two sensors issued by Creare were tested, one of which measures size and particle velocity, while the other measures sand composition. The first sensor relies on non-intrusive optical measurements and can be mounted directly to an engine inlet. The second sensor collects particles from the inlet flow and applies X-Ray Fluorescence (XRF) to the moving particles. There has been little research on applying XRF to a flow of particles, so experimental data were critical to demonstrate the effectiveness of the sensor. technique was iterated to overcome previous limitations and implemented into the testing process to provide particle concentration measurements.

Un grand nombre d'écoulements naturels et industriels mettent en jeu des particules (sédimentation,lit fluidisé, sprays...). Les écoulements chargés en particules sont bien décrits numériquement sous l'hypothèse des particules plus petites que toutes les échelles de l'écoulement. Cette thèse consiste à simuler numériquement une turbulence homogène et isotrope soutenue chargée en particules dont la taille est supérieure à l'échelle de Kolmogorov. Pour se faire une méthode de simulation a été développée au sein du code Thétis puis validée. L'originalité de cette méthode consiste en l'utilisation d'une approche de pénalisation associée à la viscosité dans la zone solide. Les particules sont transportées de façon lagrangienne. Les principaux résultats concernent trois simulations faisant varier le rapport de densité entre le fluide et le solide. Chaque simulation simule le mouvement de 512particules avec un diamètre 22 fois plus grand que l'échelle spatiale de Kolmogorov remplissant ainsi3% du volume total. La dispersion des particules est étudiée et montre des comportements comparables à ceux observés pour des particules ponctuelles. Un intérêt particulier est porté sur le régime collisionnel. On observe que la corrélation des vitesses avec le fluide environnant réduit le nombre de chocs frontaux par rapport au cas théorique de particules d'un gaz dense. L'effet de la prise en compte du fluide visqueux entre les particules (couche de lubrification) lors de la collision a été étudiée. L'écoulement moyen à l'échelle des particules est aussi analysé, mettant en évidence l'existence d'une couche de dissipation autour des particules. / Many applications and natural environment flows make use of particles (sedimentation, fluidized bed,sprays...). Particle laden flows are described correctly by numerical methods when the particles are smaller than all other spatial scales of the flow. This thesis involves the numerical simulation of a particle laden sustained homogeneous isotropic turbulence whose particle's size is larger than the Kolmogovov spatial scale. A numerical method has been developed and validated in the numerical code Thetis. The novelty of this method is the viscosity penalization approach. The particles are tracked by a Lagrangian way. The main results obtained are related to three simulations where the density ratio between the solid and the fluid varies. Each simulation reproduces the movement of 512particles whose diameter is 22 times the Kolmogorov spatial scale (3% volumetric solid fraction).The dispersion of particles is studied and has similar behavior than those observed with point particles simulations. The collision regime is also investigated. It is shown that he number of frontal collision is lower than its estimate for kinetic theory of gazes because there is a correlation between the particles velocity and the surrounding fluid. The modification of the collision regime when the lubrication film between particles at collision is taken into account is studied. Finally, the averaged flow around particles is analyzed and shows that there is a dissipation layer around particles.

Particle-laden flows involve in many energy and industrial processes within a wide scale range. Solid fuel combustion and gasication, drying and catalytic cracking are some of the examples. It is vital to have a better understanding of the phenomena inside the reactors involving in particle-laden flows for process improvements and design. Computational fluid dynamics (CFD) can be a robust tool for these studies with its advantage over experimental methods. The large variation of length scales (101- 10-9 m) and time scales (days-microseconds) is a barrier to execute detailed simulations for large scale reactors. Current state-of-the-art is to use models to bridge the gap between small scales and large scales. Therefore, the accuracy of the models is key to better predictions in large scale simulations.    Particle-laden flows have complexities due to many reasons. One of the main challenge is to describe how the particle-fluid interaction varies when the particles are reacting. Particle and the fluid interact through mass, momentum and heat exchange. Mass, momentum and heat exchange is presented by the Sherwood number (Sh), drag coefficient (CD) and Nusselt number (Nu) in fluid dynamics. Currently available models do not take into account for the effects of net gas flow generated by heterogeneous chemical reactions. Therefore, the aim of this research is to propose new models for CD and Nu based on the flow and temperature fields estimated by particle-resolved direct numerical simulations (PR-DNS). Models have been developed based on physical interpretation with only one fitting parameter, which is related to the relationship between Reynolds number and the boundary layer thickness. The developed models were compared with the simulation results solving intra-particle flow under char gasification. The drawbacks of models were identied and improvements were proposed.    The models developed in this work can be used for the better prediction of flow dynamics in large scale simulations in contrast to the classical models which do not consider the effect of heterogeneous reactions. Better predictions will assist the design of industrial processes involving reactive particle-laden flows and make them highly effcient and low energy-intensive.

Aircraft propulsion systems can be exposed to a variety of solid particulates while operating in either arid or other hazardous environments. For conventional takeoff and landing aircraft, debris can be ingested directly into the gas turbine powerplant which is exposed to the ambient environment. For helicopters and other vertical takeoff and landing (VTOL) aircraft, rotor down wash presents a particular threat during takeoff and landing operations as significant amounts of groundlevel particles can be entrained in the surrounding air and subsequently ingested into the engine. Prolonged exposure to particle ingestion events leads to premature engine wear and, in extreme cases, rapid engine failure. Expanding our current understanding of these events is the first step to enabling engine manufacturers to mitigate these damage mechanisms through novel engine designs. The work described in this dissertation is aimed at increasing the scientific understanding of these ingestion events through the development of two distinct diagnostic instruments. First, an anisokinetic particle sampling probe is designed to be used for in-situ particle sampling inside of a gas turbine engine compressor. Offtake of particles during engine operation in dusty conditions will provide researchers with an improved understanding of particle breakage tendency and component erosion susceptibility. Both experimental and numerical investigations of the probe present a comprehensive realization of probe performance characteristics. Secondly, a novel particle visualization technique is developed to provide users with particle distribution and particle mass flow estimates at the inlet of a gas turbine engine. This technique yields both time-resolved and time-averaged quantities, allowing users to have a comprehensive account of particles entering the engine. / Doctor of Philosophy / Foreign debris ingested into aircraft engines can cause serious damage and degrade their performance. The source of these ingested particles may be from atmospherically suspended ash due to volcanic eruption, high altitude ice crystals, or ground-level sand and dust. Both conventional takeoff and landing aircraft and vertical takeoff and landing (VTOL) aircraft are at risk. In extreme cases, exposure to a particle-laden atmosphere has resulted in catastrophic engine failure and loss of life. For this reason, researchers are intensely focused on mitigating the effects of these harmful particulates. The work described in this dissertation establishes two novel diagnostic capabilities. These are aimed at providing the research community with an increased understanding of how particles enter an aircraft powerplant as well as describe the behavior of these particles as they traverse the initial stages of an engine. The first instrument described is a particle sampling probe which is meant to be inserted into the compressor section of a gas turbine engine. This probe will offtake particles as they enter the engine after they have had an opportunity to interact with the rotating components of the compressor. In doing so, researchers gain an improved understanding of particle breakage tendency and component erosion susceptibility. The second instrument provides a snapshot of particle distribution at the inlet of the engine as well as estimates of total particle mass flow. This capability allows researchers to have a precise understanding of the quantity of ingested material as well as a qualitative understanding of how the inflow distribution of particles looks. Each of the developed tools represent a first step to enabling engine manufacturers to mitigate these damage mechanisms through novel engine designs.

A novel higher-order moment-closure method is applied for the Eulerian treatment of gas-particle multiphase flows characterized by a dilute polydisperse and polythermal particle phase. Based upon the polydisperse Gaussian-moment model (PGM) framework, the proposed model is derived by applying an entropy-maximization moment-closure formulation to the transport equation of the particle-number density function, which is equivalent to the Williams-Boltzmann equation for droplet sprays. The resulting set of first-order robustly-hyperbolic balance laws include a direct treatment for local higher-order statistics such as co-variances between particle distinguishable properties (i.e., diameter and temperature) and particle velocity. Leveraging the additional distinguishing variables, classical hydrodynamic droplet evaporation theory is considered to describe unsteady droplet vaporization. Further, studying turbulent multiphase flow theory, a first-order hyperbolicity maintaining approximation to turbulent flow diffusion-inertia effects is proposed. Investigations into the predictive capabilities of the model are evaluated relative to Lagrangian-based solutions for a range of flows, including aerosol dispersion and fuel-sprays. Further, the model is implemented in a massively parallel discontinuous-Galerkin framework. Validation of the proposed turbulence coupling model is subsequently performed against experimental data, and a qualitative analysis of the model is given for a qualitative liquid fuel-spray problem.

Le système immunitaire adaptatif joue un rôle de premier plan dans la défense contre les infections. La réponse humorale, impliquant la production d'anticorps, est un élément important de la réponse immunitaire adaptative. Au cours d'une infection, des cellules B spécifiques du système immunitaire prolifèrent et libèrent de grandes quantités d'anticorps qui se lient sélectivement à la protéine cible (antigène) trouvée sur le pathogène invasif, induisant la destruction du pathogène.Cependant, le système immunitaire ne répond pas toujours suffisamment efficacement pour détruire les agents pathogènes, et les mécanismes de tolérance empêchent la génération d'anticorps contre les protéines humaines - comme les marqueurs de surface cellulaire sur les cellules cancéreuses ou les cytokines impliquées dans des maladies inflammatoires et auto-immunes - qui pourraient être des cibles thérapeutiques importantes. Par conséquent, il existe un grand intérêt pour la recherche et le développement d'anticorps spécifiques qui peuvent être utilisés pour le traitement des patients par immunothérapie. En raison de leur grande affinité et de leur liaison sélective aux antigènes, les anticorps monoclonaux (mAbs) sont apparus comme des agents thérapeutiques puissants. Les anticorps monoclonaux dérivés de cellules B individuelles ont une séquence unique et présentent une affinité de liaison pour un antigène spécifique. Cependant, jusqu'à maintenant, la découverte des mAbs a été limitée par l'absence de méthodes à haut débit pour le criblage direct et à grande échelle de cellules B primaires non immortalisées pour découvrir les rares cellules B qui produisent des anticorps spécifiques d'intérêt clinique. Ceci est maintenant possible avec l'émergence et l'amélioration des méthodes de compartimentation in vitro pour l'encapsulation et le criblage de cellules uniques dans des gouttelettes picolitriques. Dans mon projet de doctorat, je décris le développement d'immunodosages et de dispositifs microfluidiques pour le criblage phénotypique direct de cellules individuelles à partir de populations de cellules B enrichies. Ce développement a permis une analyse détaillée de la réponse immunitaire humorale, avec une résolution à l’échelle de la cellule unique. C’est aussi un élément essentiel d'un pipeline de détection d'anticorps couplant le criblage phénotypique de cellules individuelles au séquençage d'anticorps sur cellules uniques. Il est maintenant possible, pour la première fois, de cribler des millions de cellules B individuelles en fonction de l'activité de liaison des anticorps sécrétés et de récupérer les séquences d'anticorps / The adaptive immune system plays a leading role in defense against infection. The humoral response, involving the production of antibodies, is an important component of the adaptive immune response. During an infection, specific B cells of the immune system proliferate and release large amounts of antibodies which bind selectively to the target protein (antigen) found on the invading pathogen, inducing destruction of the pathogen. However, the immune system does not always respond efficiently enough to destroy pathogens, and tolerance mechanisms prevent the generation of antibodies against human protein - such as cell surface markers on cancer cells or cytokines involved in inflammatory and autoimmune disease - that could be important therapeutic targets. Hence, there is great interest in research and development of specific antibodies that can be used for immunotherapy of patients. Due to their high affinity and selective binding to antigens, monoclonal antibodies (mAbs) have emerged as powerful therapeutic agents. Monoclonal antibodies derived from single B cells have a unique sequence and display binding affinity for a specific antigen. However, until now, the discovery of mAbs has been limited by the lack of high-throughput methods for the direct and large-scale screening of non-immortalized primary B cells to uncover rare B cells which produce the specific antibodies of clinical interest. This is now becoming possible with the emergence and improvement of in vitro compartmentalization methods for single-cell encapsulation and screening in picoliter droplets. In my PhD project, I describe the development of binding immunoassays and microfluidic devices for the direct phenotypic screening of single-cells from enriched B cell populations. This development has enabled detailed analysis of the humoral immune response, with single-cell resolution and is an essential component of an antibody-discovery pipeline coupling single-cell phenotypic screening to single-cell antibody sequencing. It is now possible, for the first time, to screen millions of single B cells based on the binding activity of the secreted antibodies and to recover the antibody sequences