Nesta tese é apresentado um esquema novo de alta resolução upwind (denominado TDPUS-C3) para reconstrução de fluxos numéricos para leis de conservação não lineares e problemas relacionados em DFC. O esquema é baseado nos critérios de estabilidade CBC e TVD e desenvolvido utilizando condições de diferenciabilidade \'C POT. 3\'. Além disso, é realiozada a implementação da associação do esquema TDPLUS-C3 com a modelagem de turbulência RNG \'\\kappa - \\epsilon\'. O propósito é obter soluções numéricas de sistemas hiperbólicos de leis de conservação para dinâmica dos gases e equações de Navier-Stokes para escoamento incompreensível de fluidos newtonianos e não newtonianos (viscoelásticos). Fazendo o uso do esquema TDPUS-C3, a precisão global dos métodos numéricos é verificada acessando o erro em problemas teste (benchmark) 1D e 2D. Um estudo comparativo entre os resultados do esquema TDPUS-C3 e os esquemas upwind convencionais para leis de conservação hiperbólicas complexas é também realizado. A Associação das modelagens numéricas (upwinding mais RNG \'\\kappa - \\epsilon\') é , então, examinada na simulação de escoamentos turbulentos de fluidos newtonianos envolvendo superfícies livres móveis, usando a metodologia URANS. No geral, em termos do comportamento global, concordância satisfatória é observada / In this thesis, a new high-resolution upwind scheme (named TDPUS-C3) for reconstruction of numerical fluxes for nonlinear conservation laws and related CFD problems in presented. The scheme is based on CBC and TVD stability criteria and developed by employing differentiability condictions (\'C POT. 3\'). In additon, the implementation of an association of the TDPUS-C3 scheme with the RNG \'\\kappa - \\epsilon\' turbulence modelling is also performed. The purpose is to obtain numerical solutions of systems of hyperbolic conservation laws for gas dynamics and Navier-Stokes equations for incompressible flow of Newtonian and non-Newtonian (viscoelstic) fluids. By using the TDPUS-C3 scheme, the global accuracy of the numerical methods is verified by assessing the error on 1D and 2D benchmark test cases. A comparative study between the TDPUS-C3 scheme and convectional upwind schemes to solve standard and complex hyperbolic conservation laws is also accomplished. The association of the numerical modelling (upwinding plus RNG \'\\kappa - epsilon\') is then examined in the simulation of turbulent Newtonian fluid flows involving moving free surfaces, by using URANS methodology. Overall, satisfactory agreement is found in terms of the overall behaviour

Três esquemas de captura de descontinuidade são apresentados para simular hiperbólicos de leis de conservação e equações de Navier-Stokes incompressíveis, a saber: FDHERPUS (Five Degree Hermite Upwind Scheme); RUS (Rational Upwind Scheme); e CSPUS (Cubic Spline Polynomial Upwind Scheme). Esses esquemas são baseados nos critérios de estabilidade CBC e TVD e implementados nos contextos das metodologias diferenças finitas e volumes finitos. A precisão local dos esquemas é verificada acessando o erro e a taxa de convergência em problemas testes de referência. Um estudo comparativo entre os esquemas estudados (incluido o WENO5) e o esquema bem estabelecido de van Albada, para resolver leis de conservação lineares e não lineares, é também realizado. O esquema de convecção que fornece melhores resultados em leis de conservação hiperbólicas é então examinado na simulação de escoamentos de fluidos newtonianos com superfícies livres móveis de complexidade crescente; resultados satisfatórios têm sido observados em termos do comportamento global / Three shock capturing schemes for numerical solution of hyperbolic conservation laws and incompressible Navier-Stokes equations are presented, namely: FDHERPUS (Five Degree Hermite Polynomial Upwind Scheme); RUS (Rational Upwind Scheme); and CSPUS ( Cubic Spline Polynomial Upwind Scheme). These schemes are based on CBC and TVD stability criteria and implemented in the context of finite volume methodologies. The local observed accuracy of the schemes is verified by assessing the error and convergence rate on benchmark test cases. A comparative study between the schemes (including WENO5) and the well established van. Albada scheme to solve standard linear and nonlinear hyperbolic conservation laws is also accomplished. The scheme that has provided better results in hyperbolic conservation laws is then examined in the simulation of Newtonian moving free surface flows of increasing complexity, satisfactory agreement has been observed in terms of the overall behavior

Este trabalho de pesquisa é dedicado ao desenvolvimento, análise e implementação de um novo esquema upwind de alta resolução (denominada PFDPUS) para a aproximação de termos convectivos em leis de conservação e problemas relacionados em mecânica dos fluídos. Usando variáveis normalizadas de Leonard, o equema PFDPUS é baseado em uma função polinomial por partes que satisfaz os critérios de estabilidade CBC e TVD. O desempenho do esquema PEDPUS é investigado na solução das equações de advecção de escalares, Burgers, Euler e MHD. O novo esquema é então aplicado para simular escoamentos incompressíveis envolvendo superfícies livres móveis. Para tanto, o esquema PFDPUS é implementado dentro do software CLAWPACK para problemas compressíveis, e no código Freeflow para poblemas incompressíveis. Os resultados numéricos são comparados com dados experimentais, numéricos e analíticos / This work is dedicated to the development, analysis and implementation of a new high-resolution upwind scheme (called PFDPUS) for approximation of convective terms in conservation laws and related fluid mechanics problems. By using the normalized variables of Leonard, the PFDPUS scheme is based on a piecewise polynomical function that satisfies the CBC and TVD stability criteria. The performance of the PFDPUS scheme is assessed by solving advection of scalars, Burgers, Euler and MHD equations. Then the new scheme is applied to simulate incompressible flows involving moving free surfaces. The PFDPUS scheme is implemented into the CLAWPACK software for compressible problems, and in the Freeflow code for incompressible problems. The numerical results are compared with experimental, numerical and analytical data

Neste trabalho apresenta-se um novo esquema prático tipo upwind de alta resolução, denominado EPUS (Eight-degree Polynomial Upwind Scheme), para resolver numericamente equações de conservação TVD e é implementado no contexto do método das diferenças finitas. O desempenho do esquema é investigado na resolução de sistemas hiperbólicos de leis de conservação e escoamentos incompressíveis complexos com superfícies livres. Os resultados numéricos mostraram boa concordãncia com outros resultados numéricos e dados experimentais existentes / Is this work a new practical high resolution upwinding scheme, called EPUS (Eight-degree Polynomial Upwind Scheme), for the numerical solution of transient convection-dominated conservation equations is present. The scheme is based on TVD stability criterion and is implemented in the context of the finite difference methodology. The performance of the scheme is investigated by solving hyperbolic systems of conservation laws and complex incompressible flows with free surfaces. The numerical results displayed good agreement with other existing numerical and experimental data

A presente tese trata da análise experimental do efeito da geometria da seção transversal do canal e do desempenho de refrigerantes de reduzido GWP (Global Warming Potential) durante a ebulição convectiva em canais de reduzidas dimensões. A tese inclui ainda um estudo extenso e crítico da literatura sobre métodos de previsão da perda de pressão e do coeficiente de transferência de calor, e sobre estudos experimentais em canais não-circulares e de refrigerantes com reduzido GWP na ebulição convectiva em canais de dimensões reduzidas. Resultados para o coeficiente de transferência de calor e perda de pressão durante a ebulição convectiva foram obtidos para canais com geometrias de seção circular, quadrada e triangular para o refrigerante R134a. Nos testes utilizou-se canais com perímetros internos similares obtidos a partir da conformação de um tubo com diâmetro interno igual a 1,1 mm. No caso do canal circular, dados foram também levantados para os HFOs R1234ze(E) e R1234yf e o hidrocarboneto R600a, fluidos com reduzido GWP. Ensaios foram executados para amplas faixas de fluxos de calor e velocidades mássicas, temperaturas de saturação de 31 e 41°C e títulos de vapor entre 0 e 0,95. Aspectos relacionados aos efeitos da geometria e do fluido refrigerante foram minuciosamente investigados através da análise paramétrica dos resultados. Com base na comparação do banco de dados coletado com os métodos de previsão disponíveis na literatura, constatou-se que estes proporcionam previsões satisfatórias apenas para condições experimentais especificas. Portanto, novos métodos de previsão da perda de pressão e do coeficiente de transferência de calor foram desenvolvidos com base nos dados levantados no presente estudo. Os métodos propostos preveem satisfatoriamente o banco de dados do presente estudo e resultados independentes disponíveis na literatura. Adicionalmente, com base nos resultados levantados, verificou-se que dissipadores de calor baseados em multi-microcanais com canais de seção triangular apresentam desempenho superior comparados a dissipadores com canais quadrados e circulares. / The present thesis concerns an experimental study on the effects of cross-sectional geometry and low GWP refrigerants on the thermal-hydraulic performance for convective boiling inside micro-scale channels. Experimental results for heat transfer coefficient and pressure drop gradient during convective boiling were obtained for circular, square and triangular channels for the fluid R134a. The evaluated channels present the same external perimeter and equivalent diameters of 1.1, 0.977 and 0.835 mm, respectively. In the case of the circular geometry, experimental results were also acquired for the HFOs R1234ze(E) and R1234yf and the hydrocarbon R600a (isobutane), which are fluids with low GWP and null ODP. Experiments were performed for a wide range of heat fluxes and mass velocities, saturation temperatures of 31 and 41°C and vapor qualities up to 0.95. The experimental data were carefully analyzed and discussed based on a parametrical analysis focusing on the effect of the cross-sectional geometry and the working fluid. Subsequently, the experimental data were compared against the most quoted predictive methods from literature. In general, it was verified that none of the predictive methods were able to accurately capture the experimental trends of the overall database. So, new predictive methods for the pressure drop and heat transfer coefficient were developed based on the broad database obtained in the present study. The proposed methods provided satisfactory results not only for the experimental database used for its development, but also for independent databases collected in the literature. Additionally, based on the data obtained in the present study and a performance analysis taken into account pressure drop, heat transfer coefficient and the channel packing factor, triangular cross sectional geometry is recommended for heat sinks.

Une étude expérimentale est menée afin de comprendre le phénomène de nucléation lors de l'ébullition. Cette étude est menée sur des surfaces polies miroir ou ultra-polies en aluminium, l’acétone étant le fluide de travail. L'analyse est réalisée en fonction de la topographie de la surface liée au degré de polissage et en fonction du revêtement de la surface dans le but de modifier sa mouillabilité. L’étude a mis en avant trois catégories de comportement, fonctions de l’état de surface : les surfaces nano lisses, les surfaces nano lisses avec défauts et les surfaces rugueuses. Les bonnes caractéristiques obtenues avec des échantillons nano lisses comportant des défauts aléatoirement répartis ont conduit à la réalisation d’échantillons nano lisses avec des défauts de position et de taille contrôlés. Les résultats obtenus avec ces derniers échantillons présentent les meilleures performances. Une amélioration supérieure à un facteur deux par rapport aux surfaces rugueuses est observée, ce qui représente un gain substantiel. Bien qu’il soit le fondement de la plupart des modèles théoriques, le nucléus à l’origine de la formation d’une bulle n’a jamais été observé expérimentalement car sa taille dépasse la capacité des moyens de mesure traditionnels. Dans ce mémoire, une méthode optique - basée sur la résonnance de plasmons sur des surfaces comportant un réseau de diffraction - est utilisée dans le but d’étudier ce phénomène. Les expériences mettent en évidence la capacité de cette méthode à mesurer la variation de la température pariétale de l’échantillon avant le déclenchement de l’ébullition. Les mesures de résonance plasmon montrent qu’il n’y a pas de modification de la densité du fluide au voisinage de la paroi pour des surchauffes proches du déclenchement de l’ébullition. La nucléation est trop rapide pour être mesurée. Cependant, des premiers nuclei de condensation ont été détectés par cette méthode, ce qui constitue un résultat très prometteur. / An experimental study was conducted in order to understand the phenomenon of nucleation in boiling. This study was done on smooth surface or ultra-smooth surface made of aluminum, the working fluid is acetone. The analysis was realized as a function of the topography of the sample, roughness level, and as a function of nanocoating of the surface in order to modify the wettability. The study classed the sample in three categories, depending on the surface condition: the ultra-smooth surface, the ultra-smooth surface with defect and the rough surface. The good characteristics were obtained for the ultra-smooth sample with randomly distributed defects led to the fabrication of ultra-smooth sample with controlled artificial cavity. The results obtained with these latter samples present the best performances. A two-fold improvement over rough surfaces is observed, representing a substantial gain. Although it is the foundation of most theoretical models, the nucleus at the origin of the formation of a bubble has never been observed experimentally because its size exceeds the capacity of the traditional means of measurement. In this memory, an optical method - based on the resonance of plasmons on surfaces with a diffraction grating - is used to study this phenomenon. The experiments demonstrate the ability of this method to measure the temperature variation in the wall of the sample before boiling. Plasmon resonance measurements show that there is no change in the density of the fluid near the wall for overheating close to the boiling point. The nucleation is too fast to be measured. However, first nuclei of condensation were detected by this method, which is a very promising result.

Cette thèse est une contribution à l'étude de la dynamique et du contrôle des oscillations grande-échelle qui se développent en régime subsonique dans le sillage d'un corps de révolution modélisant le corps central d'un lanceur. Pour plusieurs configurations (disque, sphère, culot franc), la transition stationnaire/instationnaire est caractérisée par une étude de stabilité de l'écoulement axisymétrique à faible nombre de Reynolds. On montre tout d'abord que les oscillations sont liées à une instabilité absolue du sillage proche. On utilise ensuite une approche globale de la stabilité, mieux adaptée aux écoulements non parallèles. Une unique séquence de bifurcation est mise en évidence pour cette classe d'écoulements, impliquant un mode stationnaire et un mode oscillant à basse fréquence. Une analyse basée sur la théorie des formes normales montre qu'au seuil d'apparition des instationnarités, la fréquence et l'organisation spatiale de l'écoulement sont fixées par l'interaction non linéaire de ces modes. On montre également qu'augmenter la compressibilité affaiblit la production des perturbations et augmente leur transport, ce qui induit une stabilisation de l'écoulement. Une analyse de sensibilité des valeurs propres à un forçage stationnaire permet ensuite de développer une approche systématique du contrôle en boucle ouverte en régime compressible. Cette approche est appliquée au culot franc, ce qui constitue un premier pas dans la perspective d'un contrôle de l'écoulement en configuration industrielle. Diverses méthodes ont été analysées, notamment l'introduction d'un! corps secondaire, un dépôt d'énergie ou un! souffla ge au culot («base bleed»).

<p>Relationships between stresses during the drying process, particle structural and functional properties, and particle engineering by the drying process were addressed in this thesis. In the first part, the importance of the drying phase and the effect of the drying rate on the intragranular porosity of microcrystalline cellulose pellets were investigated. Differences in porosities of dried pellets could be explained by liquid-related differences in densification during convective drying rather than by differences in densification during wet agglomeration. An increased drying rate gave more porous pellets with a lower compression shear strength, and thereby stronger tablets. The next part dealt with modulation of solid-state stability and tabletting behaviour of amorphous lactose by incorporation of different polymers by spray drying. Increased content and molecular weight of poly(vinylpyrrolidone) (PVP) resulted in an increased resistance to crystallisation provoked by heat and moisture. The stabilising effect was even more evident after long-term storage. However, the glass transition temperature was almost unaffected and may, therefore, be questioned as a stability indicator for these types of materials. The presence of the polymers resulted in somewhat less deformable particles. Incorporation of PVP increased the compactability, whilst a surfactant decreased it, which could be shown to be related to differences in particle-particle adhesivity between the different particles. This thesis contributes to increased mechanistic understanding in the area of particle engineering that may lead to better prediction and optimisation of the functionality of pharmaceutical particles, which is of the utmost importance in the development and production of solid dosage forms.</p>

Relationships between stresses during the drying process, particle structural and functional properties, and particle engineering by the drying process were addressed in this thesis. In the first part, the importance of the drying phase and the effect of the drying rate on the intragranular porosity of microcrystalline cellulose pellets were investigated. Differences in porosities of dried pellets could be explained by liquid-related differences in densification during convective drying rather than by differences in densification during wet agglomeration. An increased drying rate gave more porous pellets with a lower compression shear strength, and thereby stronger tablets. The next part dealt with modulation of solid-state stability and tabletting behaviour of amorphous lactose by incorporation of different polymers by spray drying. Increased content and molecular weight of poly(vinylpyrrolidone) (PVP) resulted in an increased resistance to crystallisation provoked by heat and moisture. The stabilising effect was even more evident after long-term storage. However, the glass transition temperature was almost unaffected and may, therefore, be questioned as a stability indicator for these types of materials. The presence of the polymers resulted in somewhat less deformable particles. Incorporation of PVP increased the compactability, whilst a surfactant decreased it, which could be shown to be related to differences in particle-particle adhesivity between the different particles. This thesis contributes to increased mechanistic understanding in the area of particle engineering that may lead to better prediction and optimisation of the functionality of pharmaceutical particles, which is of the utmost importance in the development and production of solid dosage forms.

Despite years of research in high speed boundary layer flow, there is still a need for insightful experiments to realize key features of the flow like boundary layer response to different conditions and related transition mechanisms. Volumes of data on the these problems point to the fact that there is still much to be understood about the nature of boundary layer instability causing transition and growth of boundary layer in different conditions. Boundary layer stability experiments have been found to be more useful, in which the boundary layer is perturbed and its behavior observed to infer useful conclusions. Also, apart from the stability part, the effect of various changes in boundary layer due to the perturbation makes interesting observation to gain more insight into the understood and the not so understood facets of the same. In view of the above, the effect of a steady axisymmetric thermal bump is investigated on a hypersonic boundary layer over a 60º sharp cone cylinder model. The thermal bump, placed near tip of the cone, perturbs the boundary layer, the behavior of which is observed by recording the wall heat flux on the cone and cylinder surface using platinum thin film sensors. The state of the boundary layer is qualitatively assessed by the wall heat flux comparisons between laminar and turbulent values. The same thermal bump also acts as a heat addition source to boundary layer in which case this recorded data provides a look into the effect of the heat addition to the wall heat flux. To gain a larger view of heat addition causing changes to the flow, effects of change in enthalpy are also considered. Experiments are performed in the IISc HST2 shock tunnel facility at 2MJkg−1 stag-nation enthalpy and Mach number of 8,with and without the thermal bump to form comparisons. Some experiments are also performed in the IISc HST3 free piston driven shock tunnel facility at 6MJkg−1, to investigate the effect of change in stagnation enthalpy on the wall heat flux. To support the experimental results theoretical comparisons and computational studies have also been carried out. The results of experiments show that the laminar boundary layer over the whole model remains laminar even when perturbed by the thermal bump. The wall heat flux measurements show change on the cone part where there seems to be fluctuation in the temperature gradients caused by the thermal bump, which decrease at first and then show an increase towards the base of the cone. The cylinder part remains the same with and without the thermal bump, indicating heavy damping effects by the expansion fan at cone cylinder junction. A local peak in wall heat flux is observed at the junction which is reduced by 64% by the action of the thermal bump. The possible reason for this is attributed to the increased temperature gradients at the wall due to delayed dissipation of heat that is accumulated in the boundary layer as a result of the thermal bump action. The comparison of data for enthalpies of 2MJkg−1 and 6MJkg−1 show that there are negligible real gas effects in the higher enthalpy case and they do not affect the wall heat flux much. Also it is found that the thermal bump fails to dump heat into the flow directly though it creates heat addition virtually by mere discontinuity in the surface temperature and causes temperature gradients fluctuation in the boundary layer. Considering the thermal bump action and the change in stagnation enthalpy of the flow, there seems to be no change in both cases that can be attributed to a common observation resulting from the factor of change in heat inside the boundary layer.