Des crises vibratoires ont été constatées dans plusieurs centrales thermiques d’EDF opérant avec du fioul lourd, certaines ayant entraîné l’arrêt du foyer. Ce travail traite des instabilités de combustion pouvant se déclencher dans ce type de système où le combustible liquide est injecté avec de la vapeur d’eau et où l’écoulement d’air est mis en rotation. Ces phénomènes vibratoires résultent d’un couplage résonant entre la dynamique de la combustion et l’acoustique du foyer. La réponse acoustique des flammes diphasiques non-prémélangées swirlées reste largement méconnue et est difficilement analysable sur le foyer réel. L’objectif de ce travail est donc d’étudier la stabilité des chaudières EDF à partir de l’analyse de la réponse d’une flamme diphasique non-prémélangée swirlée issue d’un injecteur générique et soumise à des perturbations de la vitesse acoustique. Cette réponse est déterminée sur un dispositif original (DIFAV) équipé d’un swirler et d’un injecteur bi-fluides fonctionnant à la vapeur d’eau et au dodécane. Ce système est constitué des principaux éléments des brûleurs utilisés sur les centrales thermiques EDF à une échelle 1/7000. Le dispositif est conçu pour facilement modifier la géométrie de la tête d’injection, les conditions d’injection de combustible et de vapeur et ainsi contrôler le spray généré. Des visualisations à la sortie d’une buse d’injection montrent l’influence de la topologie de l’écoulement diphasique dans l’injecteur sur la taille des gouttes mesurées dans le spray. Des mesures de taille et de vitesse des gouttes lorsque le rapport des débits de vapeur et de combustible (GLR) est modifié sont réalisées. Ces données comparées à des modèles ont permis d’estimer l’évolution de la taille des gouttes générées par l’injecteur qui équipe les centrales thermiques lorsque le GLR varie. Une analyse modale du foyer DIFAV et d’un modèle simplifié de la chaudière réelle est ensuite menée. Les fréquences propres et les taux d’amortissement du foyer DIFAV sont déterminés expérimentalement en soumettant le système à une modulation acoustique externe. Un modèle acoustique simplifié composé de trois cavités couplées représentatif du brûleur DIFAV est également développé. Des simulations acoustiques réalisées avec COMSOL Multiphysics sur une coupe transverse d’une chaudière générique représentative de la chaudière industrielle permettent d’identifier trois modes à basses fréquences établis entre les plenums et la chambre de combustion qui sont susceptibles d’être instables. La sensibilité de ces modes à la géométrie du foyer et aux conditions limites est étudiée. La réponse de la flamme générique lorsqu’elle est soumise à des modulations acoustiques de l’écoulement d’air en amont du brûleur est ensuite mesurée sur le banc DIFAV pour différents niveaux d’excitation et deux topologies de flamme lorsque les conditions d’injection sont modifiées. Les mécanismes qui pilotent l’évolution du gain de l’une des fonctions de transfert généralisées (FDF) de la flamme sont étudiés à l’aide de visualisations en moyenne de phase de l’écoulement et de mesures des vitesses axiale et azimutale de l’écoulement d’air au cours d’un cycle de modulation. Une forte sensibilité de la phase de la FDF à l’amplitude des perturbations acoustiques est observée. Un adimensionnement par le nombre de Strouhal basé sur la vitesse débitante et la longueur efficace de la flamme est proposé pour transposer ces FDFs sur le brûleur réel. Une analyse de stabilité du foyer DIFAV est réalisée en intégrant les FDF au modèle acoustique afin de déterminer les cycles limites des oscillations lorsque la longueur de la chambre de combustion varie. Ces calculs sont comparés aux fréquences des instabilités auto-entretenues mesurées aux cycles limites dans le foyer DIFAV. [...] / Vibratory crises have been observed in EDF thermal power plants operating with heavy fuel oil. Such instabilities may lead to shutdown and damage the boiler. This work deals with combustion instabilities that can take place in boilers equipped with steam-assisted atomizers and where the airflow is swirled. These vibratory phenomena result from a resonant coupling between the combustion dynamics and the boiler acoustics. Analyses of combustion dynamics of non-premixed swirling spray flames remain rare and are difficult to realize on the real system. The objective of this work is to analyze the stability of EDF boilers using the response of generic non-premixed swirling spray flames submitted to acoustic velocity disturbances. This response is determined on an original device (DIFAV) equipped with a swirling vane and a twin-fluid atomizer operated with steam and dodecane. This burner is equipped with the main elements of those used in the thermal power plant, but has a reduced scale of 1/7000. The influence of the injector geometry and of the operating conditions on the spray generated by the injector can be studied. Spray visualizations at the outlet of the injector reveal the relationship between the topology of the two-phase flow in the injector and the measured droplet size. Measurements of the droplet diameter and velocity as a function of the gas-to-liquid ratio (GLR) have been performed at the outlet of the injector. These data have been compared to models and were used to estimate the evolution of the droplets diameter as a function of the GLR generated by the industrial injector. A modal analysis of the DIFAV combustor is then carried out and a simplified acoustic model made of three coupled cavities is developed. The natural frequencies and damping rates of the DIFAV combustor are determined experimentally when it is submitted to acoustic modulation. Acoustic simulations are performed with COMSOL Multiphysics on a simplified geometrical model of the industrial boiler. Three low frequency modes established between the plenums and the combustion chamber have been identified and may be unstable. Their sensitivity to modifications of the boiler geometry and boundary conditions are studied. Flame responses subjected to acoustic modulations of the airflow rate are then measured on the DIFAV combustor for several amplitudes and two flames topologies obtained at globally lean condition. Phase-conditioned flame visualizations and measurements of swirl number fluctuations during an acoustic forcing cycle are conducted to explain the mechanisms that control the evolution of gain of the Flame Describing Function (FDF). A high sensitivity of the phase of the FDF to the amplitude of the acoustic disturbance is observed. The Strouhal number based on the airflow velocity and the effective length of the flame is used to transpose these FDF on the industrial burner. FDF are integrated in the acoustic model of the DIFAV setup to carry out a stability analysis and predict the limit cycle oscillations as a function of the combustion chamber length. These calculations are compared to frequencies of self-sustained instability measured at the limit cycles in the DIFAV combustor. A reasonable agreement is obtained showing the validity of the stability analysis for the non-premixed two-phase flames investigated based on the knowledge of their FDF. Finally, a stability analysis of the EDF boiler is conducted with the COMSOL Multiphysics model by including the acoustic flame response of the industrial burner in the simulation. This FDF is deducted from the dimensionless FDF measured on the generic burner. The Rayleigh criterion is used to analyze the stability of the combustor as a function of the flame length for different boundary conditions. Indications are given to improve the stability of the EDF boiler.

O presente trabalho propõe a execução de ensaios de medição do número de swirl em bancada de fluxo em regime permanente, com a utilização de um dispositivo modular e dutos de admissão do cabeçote de um motor diesel produzidos via prototipagem rápida (PR). A medição do número de swirl com dutos produzidos via PR, traz como principais vantagens: reprodutibilidade dos ensaios, facilidade de simular e mensurar o número de swirl dos potenciais desvios no processo de fundição ou usinagem, além da redução no tempo para o desenvolvimento de novas geometrias dos dutos de admissão. O trabalho é experimental e uma unidade do cabeçote estudado foi encaminhado para o laboratório da EPUSP e o número de swirl medido para posterior comparação dos dados. Após a fase inicial de aquisição de dados e ajustes no projeto do dispositivo, essa unidade do cabeçote foi seccionada e digitalizada para que a geometria interna fosse reproduzida via prototipagem rápida. Os dutos de admissão foram montados no dispositivo modular para a realização dos testes em bancada. Todos os testes foram realizados no mesmo equipamento e com o mesmo sistema de controle, com o intuito de reduzir o número de variáveis externas na aquisição de dados. Quando realizou-se a comparação das médias dos resultados do número de swirl do cabeçote e do dispositivo modular com o uso de prototipagem rápida não foram encontradas diferenças estatisticamente significantes. O método proposto representou o escoamento de ar da admissão do modelo de cabeçote analisado. / The present work proposes to execute steady state bench test, swirl number measurements, using a modular device and cylinder head intake ports from a diesel engine manufactured via rapid prototype (RP) techniques. Swirl number measurements with intake ports produced by RP, bring as main advantages: Tests reproducibility, easy to measure the swirl number variances in consequence of potential casting or machining process deviations besides of time reduction to the development of new intake ports geometry. The research is experimental and one sample of the investigated cylinder head was sent to the laboratory and the swirl number was measured for later results comparison. After the early development phase of data acquisition and design improvements, this cylinder head sample was then sectioned and digitalized as to know to have the same internal geometry in the intake ports produced via rapid prototype. The intake ports were assembled in the modular device to perform bench tests. All tests were performed in the same rig and with the same control system with aiming to reduce the external variables during data acquisition. When the mean results analysis was performed in order to compare the results between cylinder head and modular device using rapid prototype, no statistically significant changes were found. The proposed method represented the investigated cylinder head´s intake air flow.

Dans le contexte actuel de raréfaction de l'eau, une meilleure efficacité de l'utilisation de l'eau est essentielle pour maintenir une croissance économique durable. En France, en période ordinaire, 48% d'eau est utilisé pour l'irrigation. Ce pourcentage augmente jusqu'à 79% en période d'été. Cela souligne la nécessité d'utiliser des méthodes d'irrigation performantes. La micro-irrigation offre la meilleure efficience, cependant, son utilisation n'est pas très répandue. Dans le monde, ce système ne couvre que 3% des terres irriguées et 5% en France, du fait de la sensibilité de ce système au colmatage, ce qui augmente le coût de son installation et de sa maintenance. Ce colmatage est fortement lié aux faibles sections de passage du distributeur de micro-irrigation. En effet, un labyrinthe constitué de chicanes est généralement inséré dans les distributeurs. Les chicanes existantes, qui jouent un rôle important pour générer des pertes de pression et assurent la régulation du débit sur le réseau d'irrigation, produisent des zones de recirculation où la vitesse est faible voire nulle. Ces zones de recirculation favorisent le dépôt de particules ou autre développement biochimique provoquant le colmatage du goutteur. La caractérisation de la topologie de l'écoulement dans le labyrinthe du goutteur doit être décrite pour analyser la sensibilité du goutteur au colmatage qui réduit considérablement ses performances.Des expériences utilisant la micro-PIV et un ensemencement avec des particules de 1 µm sont menées sur dix motifs répétitifs pour analyser les régions qui peuvent être sensibles au colmatage. Un goutteur fonctionne avec un débit faible, et la section transversale du labyrinthe est d'environ 1mm2. Le nombre de Reynolds varie de 400 à 800. Ainsi, cette étude expérimentale permet d'analyser le régime d'écoulement et son influence. Un algorithme de traitement est développé pour obtenir la moyenne et les fluctuations des vitesses. Une attention particulière est apportée à la validation de la technique micro-PIV et aux courbes débit-pression qui quantifient la performance globale du goutteur. Plusieurs modèles de turbulence, implémentés dans ANSYS/Fluent, sont utilisés pour modéliser l'écoulement au sein du labyrinthe. Les résultats des expériences de micro-PIV et des modélisations sont comparés afin de valider le modèle numérique. Puis, des méthodes avancées d’analyses tourbillonnaires ont été utilisées pour détecter précisément la vorticité et les zones de recirculations. L'objectif global de ce manuscrit est d'identifier le meilleur modèle qui permettra ensuite de prédire et analyser les zones sensibles au colmatage afin de les réduire grâce à l'optimisation de géométrie. / In the present context of increasing water scarcity, a better water use efficiency is essential to maintain a sustainable economical growth. Moreover, water use efficiency covers also important environmental and social issues. Micro-irrigation system has the best water efficiency, nevertheless, its use is not much widespread. In the world, this system covers only 3 % of land irrigated against 4% in France, as this system is sensitive to clogging, which increases the installation cost.The baffle-fitted labyrinth-channel is largely used in micro-irrigation systems. The existing baffles, which play an important role for generating pressure losses and ensure the flow regulation on the irrigation network, produce vorticities where the velocity is low or zero. These vorticities favor the deposition of particles or other biochemical development causing emitter clogging. Flow topology characterization in the labyrinth-channel of emitter must be described to analyze emitter clogging sensibility which drastically reduces its performance.Micro-PIV experiments, using 1µm particles, are conducted on ten-pattern repeating baffles to characterize the labyrinth-channel flow and to analyze regions which can be sensitive to clogging. An emitter works with a weak flow rate, and the labyrinth-channel cross-section is about 1 mm2 Reynolds number varies from 400 to 800. So, this experimental investigation allows analyzing the flow regime and its influence. A treatment algorithm is developed to get the mean and fluctuating velocities. Advanced swirl analysis method is adapted to precisely detect the vorticity. Particular attention is focused on the technique acquisition and on pressure losses curves accuracy in the labyrinth-channel flow since this curve represents the emitter global performance.Several turbulent models, implemented in ANSYS/Fluent, are used to perform modelling of the labyrinth-channel geometry. The micro-PIV and modeling results comparisons are presented in order to validate numerical model. The global objective of this manuscript is to identify the best model which allows to predict and analyze the sensitive areas in order to reduce them thanks to geometry optimization.

Orientador: Eugenio Spano Rosa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-07T21:12:52Z (GMT). No. of bitstreams: 1 Martins_JasonAlves_M.pdf: 1693632 bytes, checksum: 9c8933692155bfbbb91d774a1f849391 (MD5) Previous issue date: 2006 / Resumo: O presente trabalho investiga os mecanismos de separação sólido-líquido em separadores tubo-ciclônicos. O trabalho é desenvolvido a partir de testes experimentais e simulação numérica. A etapa experimental investiga a influência do aumento de viscosidade sobre a eficiência do separador. Através de uma análise dimensional, os dados experimentais são reduzidos em grupos adimensionais. Obtem-se uma correlação entre a eficiência de separação e os grupos adimensionais. Ela revela como a eficiência depende dos parâmetros geométricos e operacionais do separador. A correlação obtida possibilita dimensionar estes separadores para cenários com elevada viscosidade. As simulações numéricas são realizadas utilizando um método de volumes finitos. O processo de separação é estudado através do adimensional Stokes. São introduzidos os conceitos de superfície de captura e tempo de residência de partículas. Define -se um importante parâmetro do escoamento, o comprimento de decaimento. Propõe-se um modelo unidimensional para o separador. Realiza-se com base neste modelo uma análise comparativa entre dois separadores. Os resultados são coerentes com dados experimentais e indicam quais características geométricas melhoram a eficiência do separador / Abstract: This work investigates the solid-liquid separation mechanisms in swirl tubes through experimental and numerical analysis. In the experimental phase, it is analyzed the impact of the viscosity increase on the separation efficiency of swirl tubes. The experimental data are reduced using dimensional analysis. A functional relationship between the separation efficiency and the dimensionless groups is obtained, allowing to calculate the separation efficiency dependency on the liquid viscosity, flow rate, particle size, and other geometrical parameters of the separator. This relationship helps to design these desander devices to scenarios with high viscosity. Numerical simulations are carried out in a structured grid using a finite volume method. Separation process is studied through the Stokes number. The concepts of capture surface and residence time of particles are introduced and an important flow field parameter, the length of decay is defined. A one-dimensional model is proposed for the swirl tube. A comparative analysis between two separators is done based on the one-dimensional model. The results are in agreement with experimental data and indicate which geometrical features help to improve the separator efficiency / Mestrado / Termica e Fluidos / Mestre em Engenharia Mecânica

Low swirl burners (LSBs) have gained popularity in heating and gas power generation industries, in part due to their proven capacity for reducing the production of NOx, which in addition to reacting to form smog and acid rain, plays a central role in the formation of the tropospheric ozone layer. With lean operating conditions, LSBs are susceptible to combustion instability, which can result in flame extinction or equipment failure. Extensive work has been performed to understand the nature of LSB combustion, but scaling trends between laboratory- and industrial-sized burners have not been established. Using hydrogen addition as the primary method of flame stabilization, the current work presents results for a 2.54 cm LSB to investigate potential effects of burner outlet diameter on the nature of flame stability, with focus on flashback and lean blowout conditions. In the lean regime, the onset of instability and flame extinction have been shown to occur at similar equivalence ratios for both the 2.54 cm and a 3.81 cm LSB and depend on the resolution of equivalence ratios incremented. Investigations into flame structures are also performed. Discussion begins with a derivation for properties in a multicomponent gas mixture used to determine the Reynolds number (Re) to develop a condition for turbulent intensity similarity in differently-sized LSBs. Based on this requirement, operating conditions are chosen such that the global Reynolds number for the 2.54 cm LSB is within 2% of the Re for the 3.81 cm burner. With similarity obtained, flame structure investigations focus on flame front curvature and flame surface density (FSD). As flame structure results of the current 2.54 cm LSB work are compared to results for the 3.81 cm LSB, no apparent relationship is shown to exist between burner diameter and the distribution of flame surface density. However, burner diameter is shown to have a definite effect on the flame front curvature. In corresponding flow conditions, a decrease in burner diameter results a broader distribution of curvature and an increased average curvature, signifying that compared to the larger 3.81 cm LSB, the flame front of the smaller burner contains tighter, smaller scale wrinkling.

<p>Two-stroke, opposed piston engines have gained recent attention for their improved thermal efficiency relative to the conventional inline or V-configuration. One advantage of two-stroke, opposed piston engines is a reduction in heat losses since there is no cylinder head. Another advantage is improved gas exchange via uniflow scavenging since the exhaust and intake ports may be located near bottom dead center of the exhaust and intake pistons, respectively. One challenge with the design of two-stroke engines is promoting turbulence within the cylinder. Turbulence is important for mixing air and fuel in the cylinder and for increasing flame speed during combustion. </p> <p>This work investigates the flow and turbulence through two-stroke, opposed piston engines using computational fluid dynamics (CFD). Specifically, the role of intake manifold and intake port geometry on turbulence within the cylinder was investigated by systematically modifying the engine geometry. Turbulence was then quantified using three metrics: circulation around the cylinder axis (swirl), circulation normal to the cylinder axis (tumble), and volume average turbulent kinetic energy (TKE) within the cylinder.</p> Increasing the swirl angle from 0 degrees to 10 degrees increased the in-cylinder swirl by a factor of 3. Increasing the swirl angle also increased the volume average TKE by a range of 7.6% to 36.5% across the three cylinders of the engine. A reverse tilt angle of 15 degrees increased tumble circulation near the piston face but decreased tumble circulation by a factor of 3 near the center of the cylinder. The next step for research on this would be to apply more geometric manipulations to the manifold of the swirl engine design to balance the mass flow rate for each port. Following the redesign of the manifold the next step is to perform a dynamic CFD test to verify the mass flow has been balanced under a dynamic scenario.

No description available.

The purpose of the diploma thesis is to establish on survey of swirl pump from previous years and his optimization via which is suggested the second degree of synchronous pump whereas they should work together like a total artificial heart. Hydraulic and constructional proposal is solved. Conception is realized experimentally also with help of CFD calculation, results are compared with each other.

This diploma thesis describes hydraulic design of Swirl turbine, dedicated to be used for tidal powerplant and study possibilities of the turbine to work in turbine, reverse turbine, pump and reverse pump regime. From individual regimes, graphical characteristics of created hydraulic design were created and compared, using CFD simulations.

The aim of this work was to develop a proposal regarding hydro-energy potential of small flows of water through the city „Hovězí near Vsetín“. The available water energy was used for running a Swirl Turbine featuring a siphon arrangement. This new concept makes use of a modified Kaplan Turbine, operating at small water heads. It operates also at higher revolutions and has higher discharge.