This thesis constitutes detailed computational investigation on ow through the passages of a centrifugal compressor used for turbocharging applications. Given the dynamic nature of operation of the turbocharger, it becomes necessary to under- stand the ow that occurs within the blade passages and its e ect on performance. CFD is an established computational technique wherein the ow is dissected to fun- damental levels and a detailed picture is presented, application of this technique with limited and diverse sense towards understanding of ows through a turbocharger compressor has been successfully carried out by many before. This work presented attempts to address many of the lacuna reported and carries forward the work of several researchers to ll in the gaps. The complexity of the geometry of the blade shape poses many challenges in model- ing within the virtual space, an e ective way to overcome the obstacles is presented as a part of this work. Grid generation of the impeller and casing are discussed and adaptive approach is followed with generation of hexahedral grids for the impeller whereas tetrahedral for the casing. Since the grids of the impeller and its casing are di erent, ways of interfacing between the two domains in a CFD environment is discussed. An industry standard implicit 3D RANS solver was used to carry out the simula- tions. The importance of use of boundary conditions for the domain at unsteady operating points is presented in detail. On the choice made for turbulence model that governs the validity of the solution obtained, an extensive literature survey of the relevant topic as applicable for centrifugal compressors is presented and logic of the choice made for the present work is discussed. Menter's two equation SST-k! model emerges as the clear choice to be used even though the di erence in perfor- mance predictions by other turbulence models are insigni cant. Dynamics of ow at optimum design point, surge and choke of the compressor are presented in detail. With the geometry modeled with a tip clearance and the casing included within the simulation environment, it can be seen that the performance predicted is closer to actual at all operating points. A study of behavior of the compressor at extreme o design points is carried out and it can be seen that it depicts the trends that are seen in experimental works available in open literature. The distortion of pressure within the vaneless di user and the inviscid nature of the ow within the volute space are e ectively captured and an in depth analysis is carried out to uncover new patterns. A parametric study involving important geometric features such as the tip clearance and wrap angles are conducted leading to discovery of anomalies. The work summarizes to point out that the investigation carried out with the CFD simulations comprehensively leads to uncovering of ow dynamics within a complex system such as the centrifugal compressor within the limits of numerical analysis.

Cette thèse porte sur la compréhension et le contrôle des interactions dynamiques entre les mécanismes physiques et biologiques en considérant un procédé alternatif de séparation membranaire pour les bioprocédés industriels. L’objectif premier est un apport de connaissances scientifiques liées à la maîtrise de la bioréaction en considérant l'hydrodynamique complexe et les verrous rétention-perméation. Une technologie de filtration dynamique, appelée Rotating and Vibrating Filtration (RVF), a été spécifiquement étudiée. Elle se compose de cellules de filtration en série comprenant deux membranes circulaires planes fixées sur des supports poreux au voisinage d'un agitateur à trois pales planes attachées à un arbre central. Ce dispositif mécanique simple fonctionne en continu et génère une contrainte de cisaillement élevée ainsi qu'une perturbation hydrodynamique dans un entrefer étroit (pale-membrane). Les verrous scientifiques et techniques qui motivent ce travail, sont la caractérisation et la quantification (i) des champs de vitesse locaux et instantanés, (2) des contraintes pariétales de cisaillement à la surface de la membrane et (3) l'impact mécanique sur les cellules microbiennes.Dans ce but, des expériences et des simulations numériques ont été réalisées pour étudier l'hydrodynamique à des échelles globales et locales, en régimes laminaire et turbulent avec des fluides newtoniens dans des environnements biotique et abiotique. Pour l'approche globale, la distribution des temps de séjour (RTD) et le bilan thermique ont été réalisés et comparés aux précédentes études globales (courbes de consommation de puissance et de frottement). Une étude analytique des fonctions de distribution a été effectuée et les moments statistiques ont été calculés et discutés. Une analyse systémique a été utilisée pour décrire les comportements hydrodynamiques du module RVF. En combinant la simulation des écoulements (CFD) et les observations (RTD), les conditions et les zones de dysfonctionnement des cellules de filtration sont éclairées. Pour l'approche locale, la vélocimétrie laser (PIV) a été réalisée dans les plans horizontaux et verticaux et comparée à la simulation numérique (CFD). Une étude préliminaire basée sur une synchronisation entre la prise d’image et la position de l’agitateur (résolution angulaire) a permis d’accéder aux champs de vitesse moyens. Une campagne de mesure PIV a été réalisée sans synchronisation afin d’appliquer une décomposition orthogonale aux valeurs propres (POD) pour 'identifier les composantes moyennes, organisées et turbulentes des champs de vitesse (énergie cinétique). Pour l'application aux bioprocédés, un travail exploratoire a caractérisé l'effet de la filtration dynamique sur des cellules procaryotes (E. coli) en quantifiant l'intégrité cellulaire ou leur dégradation en fonction du temps et de la vitesse de rotation. / This thesis focuses on the understanding and the control of dynamic interactions between physical and biological mechanisms considering an alternative membrane separation into industrial bioprocess. It aims to carry scientific knowledge related to the control of bioreaction considering complex hydrodynamics and retention-permeation locks specific to membrane separation. A dynamic filtration technology, called Rotating and Vibrating Filtration (RVF), was investigated. It consists of filtration cells in series including two flat disc membranes fixed onto porous substrates in the vicinity of a three-blade impeller attached to a central shaft. This simple mechanical device runs continuously and generates a high shear stress as well as a hydrodynamic perturbation in the narrow membrane-blade gap. Several scientific and technical locks motivating this work are to characterize and to quantify (i) the velocity fields locally and instantaneously, (2) the shear stresses at membrane surface and (3) the mechanical impact on microbial cells.To this end, experiments and numerical simulations have been performed to investigate the hydrodynamics at global and local scales under laminar and turbulent regimes with Newtonian fluids under biotic and abiotic environment. For global approach, investigation of Residence Time Distribution (RTD) and thermal balance was carried out and compared to the previous global study (power consumption and friction curves). Analytical study of distribution functions was conducted and statistical moments were calculated and discussed. A systemic analysis was used to describe the hydrodynamic behaviors of the RVF module. Combining Computational Fluid Dynamics (CFD) and RTD observations, it leads to demonstrate dysfunctioning conditions and area. For the local approach, Particle Image Velocimetry (PIV) was be carried out in both horizontal and vertical planes and compared to CFD simulation. PIV preliminary study was conducted with a trigger strategy to access through angle-resolved measurements to an averaged velocity field. PIV further study were performed with a non-trigger strategy and applied to Proper Orthogonal Decomposition (POD) analysis in order to identify the coherent structure of the flow by decomposing the organized and turbulent fluctuations. For the bioprocess application, an exploratory work characterized the effect of Dynamic Filtration on prokaryote cell population (Escherichia coli) by quantifying cell integrity or damage as a function of time and rotation speed during filtration process in turbulent regime.

The present work is aimed at investigating the mechanisms of nanowire growth from aqueous solutions through a physical and chemical modeling. Based on this modeling, deriving an optimized process control is intended. The work considers two methods of nanowire growth. The first is the dielectrophoretic nanowire assembly from neutral molecules or metal clusters. Secondly, in the directed electrochemical nanowire assembly metal-containing ions are reduced in an AC electric field in the vicinity of the nanowire tip and afterwards deposited at the nanowire surface. To describe the transport and growth processes, continuum models are employed. Furthermore, it has been necessary to consider electro-kinetic fluid flows to match the experimental observations. The occurring partial differential equations are solved numerically by means of finite element method (FEM). The effect of the process parameters on the nanowire growth are analyzed by comparing experimental results to a parameter study. The evaluation has yielded that an AC electro-osmotic fluid flow has a major influence on the dielectrophoretic nanowire assembly regarding the growth velocity and morphology. In the case of directed electrochemical nanowire assembly, the nanowire morphology can be controlled by the applied AC signal shape. Based on the nanowire growth model, an optimized AC signal has been designed, whose parametrization allows to adjust to the chemical precursor and the desired nanowire diameter. / Ziel der vorliegenden Arbeit ist es, mittels physikalischer und chemischer Modelle die Mechanismen des Nanodrahtwachstums aus wässrigen Lösungen zu erforschen und daraus eine optimierte Prozesskontrolle abzuleiten. Dabei werden zwei Verfahren des Nanodrahtwachstums näher betrachtet: Dies sind die dielektrophoretische Assemblierung von neutralen Molekülen oder Metallclustern sowie die gerichtete elektrochemische Nanodrahtabscheidung (engl. directed electrochemical nanowire assembly), bei der metallhaltige Ionen im elektrischen Wechselfeld an der Nanodrahtspitze zunächst reduziert und anschließend als Metallatome abgeschieden werden. Zur Beschreibung der Transport- und Wachstumsprozesse werden Kontinuumsmodelle eingesetzt. Darüber hinaus hat es sich als notwendig erwiesen, elektrokinetische Fluidströmungen zu berücksichtigen, um die experimentellen Beobachtungen zu reproduzieren. Die auftretenden partiellen Differenzialgleichungen werden mittels der Finiten Elemente Methode (FEM) numerisch gelöst. Die Auswirkungen der Prozessparameter auf das Nanodrahtwachstum werden durch den Vergleich von experimentellen Ergebnissen mit Parameterstudien analysiert. Die Auswertung hat ergeben, dass für das dielektrophoretische Wachstum ein durch Wechselfeldelektroosmose (engl. AC electro-osmosis) angetriebener Fluidstrom die Drahtwachstumsgeschwindigkeit und -morphologie maßgeblich beeinflusst. Im Falle der gerichteten elektrochemischen Nanodrahtabscheidung lässt sich die Drahtmorphologie über das angelegte elektrische Wechselsignal steuern. Unter Verwendung des Wachstumsmodells ist ein optimiertes Signal generiert worden, dessen Parametrisierung eine gezielte Anpassung auf den chemischen Ausgangsstoff und den gewünschten Drahtdurchmesser erlaubt.

Indiana University-Purdue University Indianapolis (IUPUI) / We numerically investigate the underlying physics of two peculiar phenomena, which are axis-switching and saddle-back velocity profile, in both laminar and turbulent rectangular jets using lattice Boltzmann method (LBM). Previously developed computation protocols based on single-relaxation-time (SRT) and multiple-relaxation-time (MRT) lattice Boltzmann equations are utilized to perform direct numerical simulation (DNS) and large eddy simulation (LES) respectively. In the first study, we systematically study the axis-switching behavior in low aspect-ratio (AR), defined as the ratio of width over height, laminar rectangular jets with <italic>AR=1</italic> (square jet), 1.5, 2, 2.5, and 3. Focuses are on various flow properties on transverse planes downstream to investigate the correlation between the streamwise velocity and secondary flow. Three distinct regions of jet development are identified in all the five jets. The <italic>45&deg</italic> and <italic>90&deg</italic> axis-switching occur in characteristic decay (CD) region consecutively at the early and late stage. The half-width contour (HWC) reveals that <italic>45&deg</italic> axis-switching is mainly contributed by the corner effect, whereas the aspect-ratio (elliptic) feature affects the shape of the jet when <italic>45&deg</italic> axis-switching occurs. The close examinations of flow pattern and vorticity contour, as well as the correlation between streamwise velocity and vorticity, indicate that <italic>90&deg</italic> axis-switching results from boundary effect. Specific flow patterns for <italic>45&deg</italic> and <italic>90&deg</italic> axis-switching reveal the mechanism of the two types of axis-switching respectively. In the second study we develop an algorithm to generate a turbulent velocity field for the boundary condition at jet inlet. The turbulent velocity field satisfies incompressible continuity equation with prescribed energy spectrum in wave space. Application study of the turbulent velocity profile is on two turbulent jets with <italic>Re=25900</italic>. In the jets with <italic>AR=1.5</italic>, axis-switching phenomenon driven by the turbulent inlet velocity is more profound and in better agreement with experimental examination over the laminar counterpart. Characteristic jet development driven by both laminar and turbulent inlet velocity profile in square jet (<italic>AR=1</italic>) is also examined. Overall agreement of selected jet features is good, while quantitative match for the turbulence intensity profiles is yet to be obtained in future study. In the third study, we analyze the saddle-back velocity profile phenomenon in turbulent rectangular jets with AR ranging from 2 to 6 driven by the developed turbulent inlet velocity profiles with different turbulence intensity (<italic>I</italic>). Saddle-back velocity profile is observed in all jets. It has been noted that the saddle-back's peak velocities are resulted from the local minimum mixing intensity. Peak-center difference <italic>&Delta_pc</italic> and profound saddle-back (PSB) range are defined to quantify the saddle-back level and the effects of AR and <italic>I</italic> on saddle-back profile. It is found that saddle-back is more profound with larger AR or slimmer rectangular jets, while its relation with <italic>I</italic> is to be further determined.

Coronary artery disease (CAD) affects every fifth person in the world. The gold-standard treatment for CAD is stent implantation, however, the existing therapy is not sufficient due to many reasons. For instance, in-stent restenosis, biocompatibility, controlled degradation rate, protein adsorption, and adequate endothelialization are still the main concerns. In the last two decades, the field of stent technology has been grown rapidly and many new stent types and in vitro testing methods for stent characterization have been developed to minimize the aforementioned issues. In this vicinity, there are still many unaddressed issues: i) the quantitative analysis of corrosion is conducted with simpler samples made of stent material instead of stents, in most cases due to the absence of a mathematical model to calculate the entire stent surface area (ESSA); ii) in vitro stent testing in environments that are very far from actual physiological environments; iii) Evaluation of the influence of in-vitro test conditions on coated metallic stents; iv) absence of flow-induced shear stress (FISS) corrosion model, to mention a few. This thesis presents the novel ESSA model, the fluid dynamic experimental setup with the integration of various sensors and pH control, the influence of in vitro degradation behavior of the titanium oxynitride (TiOxNy) coated stainless steel stents and anodized AZ31 samples, and the FISS corrosion model. The results show some important contributions in this field, however, there is still a huge potential for the development of promising stent characterization solutions. / Die koronare Herzkrankheit (KHK) betrifft jeden fünften Menschen auf der Welt. Der Goldstandard bei der Behandlung von KHK ist die Stent-Implantation, doch die bestehende Therapie ist aus vielen Gründen nicht ausreichend. So sind beispielsweise die Restenose im Stent, die Biokompatibilität, die kontrollierte Abbaugeschwindigkeit, die Proteinadsorption und die angemessene Endothelialisierung nach wie vor die Hauptprobleme. In den letzten zwei Jahrzehnten hat sich die Stenttechnologie rasant weiterentwickelt, und es wurden viele neue Stenttypen und In-vitro-Testmethoden zur Stentcharakterisierung entwickelt, um die oben genannten Probleme zu minimieren. In dieser Umgebung gibt es noch viele ungelöste Probleme: i) die quantitative Analyse der Korrosion wird mit einfacheren Proben aus Stentmaterial anstelle von Stents durchgeführt, in den meisten Fällen aufgrund des Fehlens eines mathematischen Modells zur Berechnung der gesamten Stentoberfläche (ESSA); ii) In-vitro-Stent-Tests in Umgebungen, die sehr weit von der tatsächlichen physiologischen Umgebung entfernt sind; iii) Bewertung des Einflusses von In-vitro-Testbedingungen auf beschichtete metallische Stents; iv) Fehlen eines FISS-Korrosionsmodells (flow-induced shear stress), um nur einige zu nennen. In dieser Arbeit werden das neuartige ESSA-Modell, der strömungsdynamische Versuchsaufbau mit der Integration verschiedener Sensoren und pH-Kontrolle, der Einfluss des In-vitro-Degradationsverhaltens der mit Titanoxynitrid (TiOxNy) beschichteten Edelstahlstents und anodisierten AZ31-Proben sowie das FISS-Korrosionsmodell vorgestellt. Die Ergebnisse zeigen einige wichtige Beiträge in diesem Bereich, jedoch gibt es noch ein großes Potenzial für die Entwicklung von vielversprechenden Lösungen zur Charakterisierung von Stents.