<p>  </p> <p>In this thesis, two optimizations of squealer tip geometries are completed for first stage turbine blades for use in a supercritical carbon dioxide turbine. First, an optimization is performed on a baseline trapezoidal turbine blade and a set of solution geometries is chosen from along the Pareto front. Next, a second optimization is completed on an advanced blade design and the geometries are grouped by performance characteristics and geometric features. The success of similar geometries across these two optimizations is also analyzed and demonstrates consistency of performance increases from tip geometries over the baseline geometry. An analysis of a flat tip geometry in a stationary condition is also performed to begin validation of annular cascades as a method for testing squealer tip geometries. </p>

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: An accurate description of the atmospheric boundary layer (ABL) is a prerequisite for computational fluid dynamic (CFD) wind studies. This includes taking into account the thermal stability of the atmosphere, which can be stable, neutral or unstable, depending on the nature of the surface fluxes of momentum and heat. The diurnal variation between stable and unstable conditions in the Namib Desert interdune was measured and quantified using the wind velocity and temperature profiles that describe the thermally stratified atmosphere, as derived by Monin- Obukhov similarity theory. The implementation of this thermally stratified atmosphere into CFD has been examined in this study by using Reynoldsaveraged Navier-Stokes (RANS) turbulence models. The maintenance of the temperature, velocity and turbulence profiles along an extensive computational domain length was required, while simultaneously allowing for full variation in pressure and density through the ideal gas law. This included the implementation of zero heat transfer from the surface, through the boundary layer, under neutral conditions so that the adiabatic lapse rate could be sustained. Buoyancy effects were included by adding weight to the fluid, leading to the emergence of the hydrostatic pressure field and the resultant density changes expected in the real atmosphere. The CFD model was validated against measured data, from literature, for the flow over a cosine hill in a wind tunnel. The standard k-ε and SST k-ω turbulence models, modified for gravity effects, represented the data most accurately. The flow over an idealised transverse dune immersed in the thermally stratified ABL was also investigated. It was found that the flow recovery was enhanced and re-attachment occurred earlier in unstable conditions, while flow recovery and re-attachment took longer in stable conditions. It was also found that flow acceleration over the crest of the dune was greater under unstable conditions. The effect of the dune on the flow higher up in the atmosphere was also felt at much higher distances for unstable conditions, through enhanced vertical velocities. Under stable conditions, vertical velocities were reduced, and the influence on the flow higher up in the atmosphere was much less than for unstable or neutral conditions. This showed that the assumption of neutral conditions could lead to an incomplete picture of the flow conditions that influence any particular case of interest. / AFRIKAANSE OPSOMMING: 'n Akkurate beskrywing van die atmosferiese grenslaag (ABL) is 'n voorvereiste vir wind studies met berekenings-vloeimeganika (CFD). Dit sluit in die inagneming van die termiese stabiliteit van die atmosfeer, wat stabiel, neutraal of onstabiel kan wees, afhangende van die aard van die oppervlak vloed van momentum en warmte. Die daaglikse variasie tussen stabiele en onstabiele toestande in die Namib Woestyn interduin is gemeet en gekwantifiseer deur gebruik te maak van die wind snelheid en temperatuur profiele wat die termies gestratifiseerde atmosfeer, soos afgelei deur Monin-Obukhov teorie, beskryf. Die implementering van hierdie termies gestratifiseerde atmosfeer in CFD is in hierdie studie aangespreek deur gebruik te maak van RANS turbulensie modelle. Die handhawing van die temperatuur, snelheid en turbulensie profiele in die lengte van 'n uitgebreide berekenings domein is nodig, en terselfdertyd moet toegelaat word vir volledige variasie in die druk en digtheid, deur die ideale gaswet. Dit sluit in die implementering van zero hitte-oordrag vanaf die grond onder neutrale toestande sodat die adiabatiese vervaltempo volgehou kan word. Drykrag effekte is ingesluit deur die toevoeging van gewig na die vloeistof, wat lei tot die ontwikkeling van die hidrostatiese druk veld, en die gevolglike digtheid veranderinge, wat in die werklike atmosfeer verwag word. Die CFD-model is gevalideer teen gemete data, vanaf die literatuur, vir die vloei oor 'n kosinus heuwel in 'n windtonnel. Die standaard k-ε en SST k-ω turbulensie modelle, met veranderinge vir swaartekrag effekte, het die data mees akkuraat voorgestel. Die vloei oor 'n geïdealiseerde transversale duin gedompel in die termies gestratifiseerde ABL is ook ondersoek. Daar is bevind dat die vloei herstel is versterk en terug-aanhegging het vroeër plaasgevind in onstabiele toestande, terwyl vloei herstel en terug-aanhegging langer gevat het in stabiele toestande. Daar is ook bevind dat vloei versnelling oor die kruin van die duin groter was onder onstabiele toestande. Die effek van die duin op die vloei hoër op in die atmosfeer is ook op hoër afstande onder onstabiele toestande gevoel, deur middel van verhoogte vertikale snelhede. Onder stabiele toestande, is vertikale snelhede verminder, en die invloed op die vloei hoër op in die atmosfeer was veel minder as vir onstabiel of neutrale toestande. Dit het getoon dat die aanname van neutrale toestande kan lei tot 'n onvolledige beeld van die vloei toestande wat 'n invloed op 'n bepaalde geval kan hê.

O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais. / The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais. / The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais. / The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

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.