As Diretrizes da Política Nacional de Transporte Hidroviário apresentam metas ambiciosas para os próximos anos quanto à construção de eclusas e ao aumento da participação do transporte aquaviário de carga na matriz brasileira. A bibliografia expõe que os custos são otimizados quando um desnível é transposto com a construção do menor número eclusas, o que resulta na busca pela transposição de desníveis significativos com a execução de eclusas com uma única câmara. No entanto, problemas hidráulicos encontrados junto às comportas de enchimento e esvaziamento estão entre as principais limitações para o aumento da altura de queda das eclusas. Os diferenciais de pressão entre as faces de montante e jusante das comportas e a variação do seu grau de abertura durante as operações de enchimento e esvaziamento de eclusas de navegação de média e alta queda geram escoamentos turbulentos, com velocidades e pressões capazes de produzir danos às estruturas. Com o objetivo de analisar os parâmetros hidráulicos do escoamento médio a jusante de comportas dos sistemas de enchimento e esgotamento de eclusas, do tipo segmento invertida, e as pressões instantâneas ao longo do teto e da base do conduto, de forma a identificar e caracterizar padrões de comportamento que auxiliem na elaboração de projetos e no aperfeiçoamento dessas estruturas, foram conduzidas duas investigações complementares, a experimental e a numérica. A investigação experimental, desenvolvida no Laboratório de Obras Hidráulicas do Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul, proporcionou a geração de dados discretos de pressão instantânea ao longo do teto e da base do conduto para 53 condições de abertura e vazão, para escoamento em regime permanente. A investigação numérica, realizada com o software Flow-3D®, de Dinâmica de Fluidos Computacional, viabilizou a geração de dados do escoamento médio no interior do conduto para 12 condições de abertura e vazão, que reproduziam as simulações experimentais. Os resultados das simulações realizadas no Flow-3D® com modelo de turbulência k- e demonstraram a sua aplicabilidade no estudo do escoamento médio a jusante de comportas de sistemas de enchimento e esvaziamento de eclusas. O modelo numérico reproduziu os dados experimentais de pressão a montante da comporta e os formatos das curvas de pressão ao longo da base e do teto do conduto a jusante da comporta, apresentando resultados mais aderentes para a base. Para as condições operacionais com a comporta parcialmente aberta, as menores pressões ocorreram no teto do conduto próximo à comporta, região de recirculação do escoamento, e junto ao terminal da comporta. A partir da análise dos dados foi possível a caracterização do comportamento das pressões médias, das flutuações de pressão e das pressões máximas e mínimas ao longo da base e do teto do conduto por meio da relação entre coeficientes adimensionais de posição e de pressão. / Brazilian Waterways Policy has ambitious goals for constructing navigation locks and increasing the participation of the cargo transport through waterways in the national transport matrix. Literature states that costs are optimized by the construction of fewer locks for the transposition of water levels by vessels, which results in the search for transposition of significant lifts by using navigation locks with single camera. However, the hydraulic problems in the filling and emptying systems, especially close to the valves, are among the major limitations to increase the lock lift. During filling and emptying operations of medium and high-lift locks, the pressure difference between upstream and downstream sides of lock valve and its opening generate turbulent flows with associated flow velocities and pressures capable of damaging the structures. In the current research, experimental and numerical investigations were conducted in order to analyze the mean flow through lock culvert valves and the instantaneous pressures behavior along the culvert roof and base, and to identify and to characterize hydraulic parameters which could be useful for project development and improvement of these structures. The experimental research was conducted at the “Laboratório de Obras Hidráulicas” of the “Instituto de Pesquisas Hidráulicas” of the “Universidade Federal do Rio Grande do Sul” and provided the generation of discrete data of instantaneous pressure along the culvert roof and base for 53 conditions of flow and valve opening. Experimental simulations were performed with steady state flow. Numerical investigation applied the Computational Fluid Dynamics software Flow-3D® and produced information for the mean flow inside the culvert for 12 valve opening and flow conditions, which reproduced the experimental simulations. valve opening and flow conditions, which reproduced the experimental simulations. The numerical results, obtained by using the k-e turbulence model, demonstrated the applicability of Flow-3D® in the study of the mean flow downstream of lock culvert valves. The numerical model was able to reproduce the experimental data of pressure along the culvert base and roof presenting more accuracy to base data. For partially open gate conditions, the lowest pressures were verified next to the valve lip and at the downstream culvert roof close to the valve, which correspond to the recirculating flow region. From data analysis it was possible to characterize the behavior of the mean pressure, pressure fluctuations and extreme pressures along the culvert base and roof by the relationship between dimensionless coefficients of position and pressure.

A crescente preocupação ambiental e a necessidade de se criar produtos mais eficientes têm impulsionado os pesquisadores a realizarem estudos acerca da aerodinâmica veicular. Estes dois fatores constituem os principais motivos, pelos quais existe uma grande procura por conhecimento nesta área. Esta ciência pode ser considerada relativamente nova e ainda carece de uma base de dados. Entender como a aerodinâmica se relaciona com o consumo de combustível nos automóveis, à medida que o arrasto impõe resistência ao deslocamento dos mesmos, é algo que tem estimulado as indústrias automotivas a investirem grandes esforços na obtenção de ferramentas, que possam representar as condições de tráfego normais e, assim conseguir prever o desempenho do produto em desenvolvimento. Os túneis de vento e a simulação computacional surgem neste ambiente como as principais ferramentas de análise e predição do escoamento ao redor do veículo. Por isso seu entendimento faz-se de extrema necessidade. Ter conhecimento sobre a concepção do seu projeto, como funcionam, seus pontos fortes e suas fraquezas, são requisitos necessários para a pessoa que deseja estudar esta ciência. O presente trabalho traz uma contextualização histórica da aerodinâmica veicular nas indústrias automotiva e automobilística, além de apresentar aspectos técnicos relacionados aos túneis de vento e simulação computacional. Abordando as vantagens e desvantagens de cada ferramenta, expõe-se o fato de que estas ferramentas são complementares no estudo aerodinâmico. Para exemplificar a utilização dessas ferramentas, foi realizado um estudo aerodinâmico sobre uma geometria básica, que representa com similaridade os veículos tipo hatchback, denominada Modelo SAE em ambiente computacional. Os conceitos acerca do arrasto veicular e estabilidade veicular foram expostos para embasar este estudo. Este modelo foi submetido a diferentes geometrias traseiras e condições de escoamento simétricas e assimétricas. Este estudo demonstrou que o arrasto e a estabilidade veicular compreendem conceitos distintos e, dessa forma, é possível diminuir o arrasto de um veículo sem haver perda de estabilidade. / The growing environmental concern and the necessity to create more efficient products have motivated researchers to conduct studies about the aerodynamic vehicle. These two aspects are the main reasons which are promoting a great demand for knowledge in this theme. This science may be considered relatively new and still lacks more databases. Understand how aerodynamics is related to automobiles fuel consumption such as drag resistance imposed to their displacement, is something that has made the automotive industries invest considerable effort in obtaining tools which may represent the normal traffic conditions and thus, able to predict the performance of the product in development stage. The wind tunnels and computer simulations appear in this environment as the main tools for analysis and prediction of the flow around vehicle. The understanding about them is so of utmost necessity. Knowing how it was designed, how they work, their strengths and weaknesses are essential requirements for the person who wants to study this science. This material presents a historical development of vehicle aerodynamics in automotive and motor-racing industries, indeed technical aspects related to wind tunnels and computational fluid dynamics. Exposing the advantages and disadvantages of both tools, it is evidenced these tools complement each other during an aerodynamic study. To exemplify these tools utility an aerodynamic research was conducted using a basic form geometry known as SAE Model that represents with similarity the hatchback vehicles in the market. Drag and vehicle stability concepts were exposed to build a solid basis for this study. This model was submitted to different rear geometries, symmetric and asymmetric flow conditions. It could be demonstrated that drag and vehicle stability have distinct concepts and therefore it is possible diminish the first without damaging the later.

A inserção de ar em escoamentos de altas velocidades ao longo de estruturas hidráulicas é uma técnica bastante eficiente para prevenir a cavitação. A sua importância é majorada quando se considera os custos econômicos e as questões de segurança que estão associadas à estabilidade de uma barragem. No presente trabalho são apresentados equacionamentos para quantificar a entrada de ar em vertedores através de aeradores de fundo. Essas equações foram obtidas utilizando princípios físicos de conservação de massa, energia e quantidade de movimento nos escoamentos de ar e água que ocorrem no aerador, permitindo organizar informações advindas de cada fase. Ressalta-se que buscou-se tornar o equacionamento independente da subpressão do jato, uma vez que esta subpressão é um parâmetro de difícil determinação a priori pelo projetista. Entretanto, toda formulação é direcionada justamente para melhor representar este parâmetro utilizando os princípios físicos clássicos e as variáveis decorrentes da sua utilização. Buscou-se a validação de modelos teóricos obtidos por meio de formulações baseadas nas leis de conservação de massa, quantidade de movimento e energia para aeradores de fundo. Neste contexto, comparam-se os resultados dos equacionamentos propostos e os dados experimentais encontrados na literatura, tendo se verificado boas correlações. Este tipo de quantificação essencialmente teórica de incorporação do ar em aeradores de fundo ainda é raro e o presente trabalho visa contribuir na validação de modelos com estas características. Adicionalmente, efetua-se a comparação com as equações empíricas e semi-empíricas encontradas na literatura. A experiência adquirida na área mostra que esta é a forma mais adequada de abordar o problema. / The introduction of air in flows around bottom aerators in spillways of dams is an efficient technique to prevent cavitation. Its importance is increased when one considers the costs involved and the safety issues that are associated with the stability of a large dam. Equations are presented in this study to quantify the air inlet through bed aerators in flows along spillways. The equations were obtained using the physical principles of conservation of mass, energy and momentum in both the flows of air and water in the aerator, allowing to organize the information obtained from each phase. It was possible to show the parameters that are relevant for quantifying the induced air flow in bed aerators. In addition, a comparison was conducted between the equations resulting from this analysis and empirical and semi-empirical expressions found in the literature. It is noteworthy to mention that one of the objectives of this study was to obtain a final equation independent of the relative pressure under the jet, since this low pressure is a parameter difficult to determine a priori by the designer. However, the entire formulation was directed precisely to better represent this parameter using the principles of classical physics and the variables arising from their use. The experience acquired in this area shows that this is the most appropriate way to address this problem.

As Diretrizes da Política Nacional de Transporte Hidroviário apresentam metas ambiciosas para os próximos anos quanto à construção de eclusas e ao aumento da participação do transporte aquaviário de carga na matriz brasileira. A bibliografia expõe que os custos são otimizados quando um desnível é transposto com a construção do menor número eclusas, o que resulta na busca pela transposição de desníveis significativos com a execução de eclusas com uma única câmara. No entanto, problemas hidráulicos encontrados junto às comportas de enchimento e esvaziamento estão entre as principais limitações para o aumento da altura de queda das eclusas. Os diferenciais de pressão entre as faces de montante e jusante das comportas e a variação do seu grau de abertura durante as operações de enchimento e esvaziamento de eclusas de navegação de média e alta queda geram escoamentos turbulentos, com velocidades e pressões capazes de produzir danos às estruturas. Com o objetivo de analisar os parâmetros hidráulicos do escoamento médio a jusante de comportas dos sistemas de enchimento e esgotamento de eclusas, do tipo segmento invertida, e as pressões instantâneas ao longo do teto e da base do conduto, de forma a identificar e caracterizar padrões de comportamento que auxiliem na elaboração de projetos e no aperfeiçoamento dessas estruturas, foram conduzidas duas investigações complementares, a experimental e a numérica. A investigação experimental, desenvolvida no Laboratório de Obras Hidráulicas do Instituto de Pesquisas Hidráulicas da Universidade Federal do Rio Grande do Sul, proporcionou a geração de dados discretos de pressão instantânea ao longo do teto e da base do conduto para 53 condições de abertura e vazão, para escoamento em regime permanente. A investigação numérica, realizada com o software Flow-3D®, de Dinâmica de Fluidos Computacional, viabilizou a geração de dados do escoamento médio no interior do conduto para 12 condições de abertura e vazão, que reproduziam as simulações experimentais. Os resultados das simulações realizadas no Flow-3D® com modelo de turbulência k- e demonstraram a sua aplicabilidade no estudo do escoamento médio a jusante de comportas de sistemas de enchimento e esvaziamento de eclusas. O modelo numérico reproduziu os dados experimentais de pressão a montante da comporta e os formatos das curvas de pressão ao longo da base e do teto do conduto a jusante da comporta, apresentando resultados mais aderentes para a base. Para as condições operacionais com a comporta parcialmente aberta, as menores pressões ocorreram no teto do conduto próximo à comporta, região de recirculação do escoamento, e junto ao terminal da comporta. A partir da análise dos dados foi possível a caracterização do comportamento das pressões médias, das flutuações de pressão e das pressões máximas e mínimas ao longo da base e do teto do conduto por meio da relação entre coeficientes adimensionais de posição e de pressão. / Brazilian Waterways Policy has ambitious goals for constructing navigation locks and increasing the participation of the cargo transport through waterways in the national transport matrix. Literature states that costs are optimized by the construction of fewer locks for the transposition of water levels by vessels, which results in the search for transposition of significant lifts by using navigation locks with single camera. However, the hydraulic problems in the filling and emptying systems, especially close to the valves, are among the major limitations to increase the lock lift. During filling and emptying operations of medium and high-lift locks, the pressure difference between upstream and downstream sides of lock valve and its opening generate turbulent flows with associated flow velocities and pressures capable of damaging the structures. In the current research, experimental and numerical investigations were conducted in order to analyze the mean flow through lock culvert valves and the instantaneous pressures behavior along the culvert roof and base, and to identify and to characterize hydraulic parameters which could be useful for project development and improvement of these structures. The experimental research was conducted at the “Laboratório de Obras Hidráulicas” of the “Instituto de Pesquisas Hidráulicas” of the “Universidade Federal do Rio Grande do Sul” and provided the generation of discrete data of instantaneous pressure along the culvert roof and base for 53 conditions of flow and valve opening. Experimental simulations were performed with steady state flow. Numerical investigation applied the Computational Fluid Dynamics software Flow-3D® and produced information for the mean flow inside the culvert for 12 valve opening and flow conditions, which reproduced the experimental simulations. valve opening and flow conditions, which reproduced the experimental simulations. The numerical results, obtained by using the k-e turbulence model, demonstrated the applicability of Flow-3D® in the study of the mean flow downstream of lock culvert valves. The numerical model was able to reproduce the experimental data of pressure along the culvert base and roof presenting more accuracy to base data. For partially open gate conditions, the lowest pressures were verified next to the valve lip and at the downstream culvert roof close to the valve, which correspond to the recirculating flow region. From data analysis it was possible to characterize the behavior of the mean pressure, pressure fluctuations and extreme pressures along the culvert base and roof by the relationship between dimensionless coefficients of position and pressure.

[pt] Modelos RANS (Reynolds Average Navier-Stokes) estão entre os modelos mais empregados para resolver escoamentos turbulentos, devido a seu baixo custo computacional. A maioria dos modelos RANS usa a aproximação de Boussinesq, baseada em uma relação linear entre a parte deviatórica do tensor de Reynolds e o tensor taxa de deformação, com a viscosidade turbulenta sendo o parâmetro positivo de proporcionalidade. Contudo, esses modelos falham em várias situações, e um grande esforço tem sido feito pela comunidade científica com intuito de melhorar a previsibilidade do modelo desenvolvendo modelos não lineares. Análises de modelos de ordem superior empregando tensores ortogonais objetivos têm mostrado que estes são muito promissores para melhorar a previsão dos componentes normais do tensor de Reynolds. No presente trabalho, modelos não lineares baseados no quadrado do tensor taxa de deformação e no tensor não persistência de deformação foram avaliados para uma faixa de número de Reynolds baseados na velocidade de atrito, variando de 395 até 5200. Novas funções de parede foram desenvolvidas, utilizando energia cinética turbulenta e o módulo do tensor taxa de deformação para determinar a velocidade e comprimento característicos. Além disso, um novo modelo turbulento de uma-equação baseado somente na equação de transporte da energia cinética turbulenta foi proposto juntamente com uma equação de fechamento algébrica para modelar a dissipação da energia cinética turbulenta. Os resultados dos modelos para escoamento em canal foram comparados com os dados DNS, apresentando uma melhor aderência aos dados DNS em comparação com os resultados de outros modelos RANS encontrados na literatura. / [en] Reynolds Average Navier Stokes (RANS) models are among the most employed models to solve turbulent flows, due to their low computational cost. The majority of RANS models use the Boussinesq approximation, based on a linear relation between the deviatoric part of Reynolds stress tensor and the rate of strain tensor, with the turbulent viscosity as the positive proportionality parameter. However, these models fail in several situations, and a great deal of effort has been made by the scientific community aiming to improve model prediction through the development of non-linear models. Analysis of higher-order models employing objective orthogonal tensors has shown that these are very promising to improve the prediction of the normal components of the Reynolds stress. In this work, non-linear models based on the square of the rate-strain tensor and non-persistence tensor were examined for a range of friction Reynolds number from 395 to 5200. New wall damping functions were developed, employing the turbulent kinetic energy and intensity of the rate of strain tensor to determine the turbulent characteristic velocity and length. Further, a new one-equation turbulent model based only on the turbulent kinetic energy transport equation was proposed coupled with an algebraic closure equation to model the turbulent kinetic energy dissipation. The models prediction for a channel flow were compared with DNS data and presented a better adherence to the DNS data, than the results of other RANS models available in the literature.

Three-dimensional (3D) turbulent boundary layers (TBLs) play a crucial role in determining the aerodynamic properties of most aero-mechanical devices. However, accurately predicting these flows remains a challenge due to the complex nonlinear and nonlocal physics involved, which makes it difficult to develop universally applicable models. This limitation is particularly significant as the industry increasingly relies on simulations to make decisions in high-consequence environments, such as the certification or aircraft, and high-fidelity simulation methods that don't rely on modeling are prohibitively expensive. To address this challenge, it is essential to gain a better understanding of the physics underlying 3D TBLs. This research aims to improve the predictive accuracy of turbulence models in 3D TBLs by examining the impact of model assumptions underpinning turbulent constitutive relations, which are fundamental building blocks of every turbulence model. Specifically, the study focuses on the relevance and necessity of nonlinear and nonlocal model assumptions for accurately predicting 3D TBLs. The study considers the attached 3D boundary layer flow over the textbf{Be}nchmark textbf{V}alidation textbf{E}xperiment for textbf{R}ANS/textbf{L}ES textbf{I}nvestiagtions (BeVERLI) Hill as a test case and corresponding particle image velocimetry data for the investigation. In a first step, the BeVERLI Hill experiment is comprehensively described, and the important characteristics of the flow over the BeVERLI Hill are elucidated, including complex symmetry breaking characteristics of this flow. Reynolds-averaged Navier-Stokes simulations of the case using standard eddy viscosity models are then presented to establish the baseline behavior of local and linear constitutive relations, i.e., the standard Boussinesq approximation. The tested eddy viscosity models fail in the highly accelerated hill top region of the BeVERLI hill and near separation. In a further step, several nonlinear and nonlocal turbulent constitutive relations, including the QCR model, the model by Gatski and Speziale, and the difference-quotient model by Egolf are used as metrics to gauge the impact of nonlinearities and nonlocalities for the modeling of 3D TBLs. It is shown that nonlinear and nonlocal approaches are essential for effective 3D TBL modeling. However, simplified reduced-order models could accurately predict 3D TBLs without high computational costs. A constitutive relation with local second-order nonlinear mean strain relations and simplified nonlocal terms may provide such a minimal model. In a final step, the structure and response of non-equilibrium turbulence to continuous straining are studied to reveal new scaling laws and structural models. / Doctor of Philosophy / Airplanes and other flying objects rely on the way air flows around them to generate lift and stay in the sky. This airflow can be very complex, especially close to the surface of the object, where it is affected by friction with the object. This friction generates a layer of air called a boundary layer, which can become turbulent and lead to complex patterns of airflow. The boundary layer is generated by the friction between the air and the surface of the object, which causes the air molecules to "stick" to the surface. This sticking creates a layer of slow-moving air that slows down the flow of air around the object. This loss of momentum creates drag, which is one of the main factors that resist the motion of objects in the air. The slowing of the air flow in the boundary layer is due to the viscosity of the air, which is a measure of how resistant the air is to deformation. The molecules in the air have a tendency to stick together, making it difficult for them to move past each other. This resistance causes the momentum of the air to be lost as it flows over the surface of the object because air molecules close to the surface "pull" on the ones farther away. Understanding how turbulent boundary layers (TBLs) work is essential to accurately predict the airflow around these objects using computer simulations. However, it's challenging because TBLs involve complex physics that are difficult to model accurately. This research focuses on a specific type of TBL called a three-dimensional (3D) TBL. This study looks at how different assumptions affect the accuracy of computer simulations that predict this type of airflow. It is found that using more complex models that take into account nonlinear and nonlocal physics can help predict 3D TBLs more accurately. However, these models are computationally expensive, and it is also found that simpler models can work well enough and are cheaper. This research further establishes important physical relations of the mechanisms pertaining 3D TBLs that could support the advancement of current models.

No description available.

Convergent-Divergent (C-D) nozzles are used in rocket engines to produce thrust as a reaction to the acceleration of hot combustion chamber gases in the opposite direction. To maximize the engine performance at high altitudes, large area ratio, bell-shaped or contoured nozzles are used. At lower altitudes, the exit pressure of these nozzles is lower than the ambient pressure. During this over-expanded condition, the nozzle-internal flow adapts to the ambient pressure through an oblique shock. But the boundary layer inside the divergent portion of the nozzle is unable to withstand the pressure rise associated with the shock, and consequently flow separation is induced. Numerical simulation of separated flows in rocket nozzles is challenging because the existing turbulence models are unable to correctly predict shock-induced flow separation. The present thesis addresses this problem. Axisymmetric, steady-state, Reynolds-Averaged Navier-Stokes (RANS) simulations of a conical nozzle and three sub-scale contoured nozzles were carried out to numerically predict flow separation in over-expanded rocket nozzles at different nozzle pressure ratios (NPR). The conical nozzle is the JPL 45◦-15◦ and the contoured nozzles are the VAC-S1, the DLR-PAR and the VAC-S6-short. The commercial CFD code ANSYS FLUENT 13 was first validated for simulation of separated cold gas flows in the VAC-S1 nozzle. Some modeling issues in the numerical simulations of flow separation in rocket nozzles were determined. It is recognized that compressibility correction, nozzle-lip thickness and upstream-extension of the external domain are the sources of uncertainty, besides turbulence modeling. In high-speed turbulent flows, compressibility is known to affect dissipation rate of turbulence kinetic energy. As a consequence, a reduction in the spreading rate of supersonic mixing layers occurs. Whereas, the standard turbulence models are developed and calibrated for incompressible flows and hence, do not account for this effect. ANSYS FLUENT uses the compressibility correction proposed by Wilcox [1] which modifies the turbulence dissipation terms based on turbulent Mach number. This, as shown in this thesis, may not be appropriate to the prediction of flow separation in rocket nozzles. Simulation results of the standard SST model, with and without the compressibility correction, are compared with the experimental data at NPR=22 for the DLR-PAR nozzle. Compressibility correction is found to cause under-prediction of separation location and hence its use in the prediction of flow separation is not recommended. In the literature, computational domains for the simulation of DLR subscale nozzles have thick nozzle-lips whereas for the VAC subscale nozzles they have no nozzle-lip. Effect of nozzle-lip thickness on flow separation is studied in the DLR-PAR nozzle by varying its nozzle-lip thickness. It is found that nozzle-lip thickness significantly influences both separation location and post-separation pressure recovery by means of the recirculation bubbles formed at the nozzle-lip. Usually, experimental values of free stream turbulence are unknown. So conventionally, to minimize solution dependence on the boundary conditions specified for the ambient flow, the computational domain external to the nozzle is extended in the upstream direction. Its effect on flow separation is studied in the DLR-PAR nozzle through simulations conducted with and without this domain extension. No considerable effect on separation location and pressure recovery is found. The two eddy-viscosity based turbulence models, Spalart-Allmaras (SA) model and Shear Stress Transport (SST) model, are well known to predict separation location better than other eddy-viscosity models, but with moderate success. Their performances, in terms of predicting separation location and post-separation wall pressure distribution, were compared with each other and evaluated against experimental data for the conical and two contoured nozzles. It is found that they fail to predict the separation location correctly, exhibiting sensitivity to the range of NPRs and to the type of nozzle. Depending on NPR, the SST model either under-predicts or over-predicts Free Shock Separation (FSS). Moreover, it also fails to capture Restricted Shock Separation (RSS). With compressibility correction, it under-predicts separation at all NPRs to a greater extent. Even though RSS is captured by using compressibility correction, the transition from FSS to RSS is over-predicted [2]. Early efforts by few researchers to improve predictions of nozzle flow separation by realizability corrections to turbulence models have not been successful, especially in terms of capturing both the separation types. Therefore, causes of turbulence modeling failure in predicting nozzle flow separation correctly were further investigated. It is learnt that limiting of the shear stress inside boundary layer, due to Bradshaw’s assumption, and over-prediction of jet spreading rate are the causes of SST model’s failure in predicting nozzle flow separation correctly. Based on this physical reasoning, values of the a 1 parameter and the two diffusion coefficients σk,2 and σω,2 were empirically modified to match the predicted wall pressure distributions with experimental data of the DLR-PAR and the VAC-S6-short nozzles. The results confirm that accurate prediction of flow separation in rocket nozzles indeed depends on the correct prediction of spreading rate of the supersonic separation-jet. It is demonstrated that accurate RANS simulation of flow separation in rocket nozzles over a wide range of NPRs is feasible by modified values of the diffusion coefficients in turbulence model.

Cette thèse propose une modélisation numérique 2D des écoulements en zone de jet de rive avec un code Volume-Of-Fluid. Dans un premier temps, le détail de la structure interne de l’écoulement de jet de rive généré par l’effondrement d’un front d’onde turbulent sur une plage imperméable lisse est étudié. Le modèle numérique est ensuite étendu à la simulation des écoulements en milieu poreux internes à la plage. L’utilisation d’une unique équation de quantité de mouvement (VARANS) et de la méthode 1-fluide, permet de résoudre simultanément les écoulements de l’eau et de l’air à la surface et dans une plage perméable. Ce modèle a été confronté à une série de cas tests analytiques et à de récentes mesures expérimentales. Les résultats numériques montrent l’aptitude du modèle VOF-VARANS à reproduire les écoulements en zone de jet de rive sur une plage imperméable fixe. / A 2D numerical modeling of flows in the swash zone is proposed using a Volume-Of- Fluid code. The detailed flow structure of a bore-driven swash event over an impermeable beach is first studied. The numerical model is then developed to account for porous media flow within the beach. The unique VARANS momentum equation and 1-fluid method used allow to solve simultaneously both surface and subsurface flows of air and water phases in the swash zone. This model is validated against a series of analytical tests cases and confronted to recent experimental measurements. The numerical results highlight the ability of the VOF-VARANS model to reproduce swash flows over and within a permeable beach.

The primary requirements for a modern industrial gas turbine consist of a continuous trend of an increasing efficiency combined with very low emissions in a robust, cost-effective manner. To fulfil these tasks a high turbine inlet temperature together with advanced dry low NOX combustion chambers are employed. These dry low NOX combustion chambers generate a rather flat temperature profile compared to previous generation gas turbines, which have a rather parabolic temperature profile before the nozzle guide vane. This means that the nozzle guide vane endwall heat load for modern gas turbines is much higher compared to previous generation gas turbines. Therefore the prediction of the nozzle guide vane flow field and endwall heat transfer is crucial for the engineering task of the design layout of the vane endwall cooling system. The present study is directed towards establishing new in-depth aerodynamic and endwall heat transfer knowledge for an advanced nozzle guide vane of a modern industrial gas turbine. To reach this objective the physical processes and effects which cause the different flow fields and the endwall heat transfer pattern in a baseline configuration, a combustion chamber variant, a heat shield variant without and with additional cooling air and a cavity variant without and with additional cooling air have been investigated. The variants, which differ from the simplified baseline configuration, apply design elements which are commonly used in real modern gas turbines. This research area is crucial for the nozzle guide vane endwall heat transfer, especially for the advanced design of the nozzle guide vane of a modern industrial gas turbine and has so far hardly been investigated in the open literature. For the experimental aerodynamic and endwall heat transfer research of the baseline configuration of the advanced nozzle guide vane geometry a new low pressure, low temperature test facility has been developed, designed and constructed, since no experimental heat transfer data exist in the open literature for this type of vane configuration. The new test rig consists of a linear cascade with the baseline configuration of the advanced nozzle guide vane geometry with four upscaled airfoils and three flow passages. For the aerodynamic tests the two middle airfoils and the hub and the tip endwall are instrumented with pressure taps to monitor the Mach number distribution. For the heat transfer tests the temperature distribution on the hub endwall is measured via thermography. The analysis of these measurements, including comparisons to research in the open literature shows that the new test rig generates accurate and reproducible results which give confidence that it is a reliable tool for the experimental aerodynamic and heat transfer research on the advanced nozzle guide vane of a modern industrial gas turbine. Previous own research work together with the numerical analysis performed in another part of the project as well as conclusions from a detailed literature study lead to the conclusion that advanced Navier-Stokes CFD tools with the v2-f turbulence model are most suitable for the calculation of the flow field and the endwall heat transfer of turbine vanes and blades. Therefore this numerical tool, validated against different vane and blade geometries and for different flow conditions, has been chosen for the numerical aerodynamic and endwall heat transfer research of the advanced nozzle guide vane of a modern industrial gas turbine. The evaluation of the numerical and experimental investigations of the baseline configuration of the advanced design of a nozzle guide vane shows the flow field of an advanced mid-loaded airfoil design with the features to reduce total airfoil losses. For the hub endwall of the baseline configuration of the advanced design of a nozzle guide vane the flow characteristics and heat transfer features of the classical vane endwall secondary flow model can be detected with a very weak intensity and geometric extension compared to the studies of less advanced vane geometries in the open literature. A detailed analysis of the numerical simulations and the experimental data showed very good qualitative and quantitative agreement for the three-dimensional flow field and the endwall heat transfer. These findings, together with the evaluations obtained from the open literature, lead to the conclusions that selected CFD software Fluent together with the applied v2-f turbulence model exhibits a high level of general applicability and is not tuned to a special vane or blade geometry. Therefore the CFD code Fluent with the v2-f turbulence model has been selected for the research of the influence of the several geometric variants of the baseline configuration on the flow field and the hub endwall heat transfer of the advanced nozzle guide vane of a modern industrial gas turbine. Most of the vane endwall heat transfer research in the open literature has been carried out only for baseline configurations of the flow path between combustion chamber and nozzle guide vane. Such a simplified geometry consists of a long, planar undisturbed approach length upstream of the nozzle guide vane. The design of real modern industrial gas turbines however requires often significant variations from this baseline configuration consisting of air-cooled heat shields and purged cavities between the combustion chamber and the nozzle guide vane. A detailed evaluation of the flow field and the endwall heat transfer shows major differences between the baseline and the heat shield configuration. The heat shield in front of the airfoil of the nozzle guide vane influences the secondary flow field and the endwall heat transfer pattern strongly. Additional cooling air, released under the heat shield has a distinctive influence as well. Also the cavity between the combustion chamber and the nozzle guide vane affects the secondary flow field and the endwall heat transfer pattern. Here the influence of additional cavity cooling air is more decisive. The results of the detailed studies of the geometric variants are applied to formulate guidelines for an optimized design of the flow path between the combustion chamber and the nozzle guide vane and the nozzle guide vane endwall cooling configuration of next-generation industrial gas turbines. / QC 20100917