Dissertations / Theses on the topic 'Orifice plate'

The orifice plate flow meter is the most common form of differential pressure flow meter used in industry. The standard discharge coefficient, which is defined by both British Standard and [SO 5167, is only valid if the flow approaching the meter is perfectly settled and fully developed. However, in practical applications the flow approaching the orifice meter is often disturbed by pipe-fittings and consequently the measurements become inaccurate. Basically, the design of the orifice plate meters that are independent of the upstream disturbances is a main goal for orifice plate metering. Either using a long straight pipe, or a flow conditioner upstream of an orifice plate, usually achieves this goal. In this project the effect of the fractal flow conditioner for both standard and non-standard flow conditions has been investigated in an experimental rig and simulation work. The results of using a combination of the fratal flow conditioner and orifice plate for non-standard flow conditions including swirling flow and asymmetric flow show that this package can preserve the accuracy of metering up to the level required in the Standards. The simulation results also show that the device can be used as a part of a flow metering package that will considerably reduce installation lengths. According to the main idea to introduce a predetermined turbulence flow caused by a flow conditioner for orifice plate flow metering, author was introduced another type of flow conditioner known as a metal foam flow conditioner. Open-cell metal foams with a porosity of 78.8% was formed and fashioned as a flow conditioner. Again the experimental results using the metal foam flow conditioner showed this metal foam flow conditioner demonstrated a good performance in terms of removing swirl and producing a repeatedly same flow profile within a short distance downstream of the flow conditioner. Furthermore, the low pressure drop across the metal foam is another advantage of this flow conditioner where the pressure loss coefficient for this flow conditioner is approximately 2.5.

The relationship between the Reynolds number (Re) and discharge coefficients (C) was investigated through differential pressure flow meters. The focus of the study was directed toward very small Reynolds numbers commonly associated with pipeline transportation of viscous fluids. There is currently a relatively small amount of research that has been performed in this area for the Venturi, standard orifice plate, V-cone, and wedge flow meters. The Computational Fluid Dynamics (CFD) program FLUENT© was used to perform the research, while GAMBIT© was used as the preprocessing tool for the flow meter models created. Heavy oil and water were used separately as the two flowing fluids to obtain a wide range of Reynolds numbers with high precision. Multiple models were used with varying characteristics, such as pipe size and meter geometry, to obtain a better understanding of the C vs. Re relationship. All of the simulated numerical models were compared to physical data to determine the accuracy of the models. The study indicates that the various discharge coefficients decrease rapidly as the Reynolds number approaches 1 for each of the flow meters; however, the Reynolds number range in which the discharge coefficients were constant varied with meter design. The standard orifice plate does not follow the general trend in the discharge coefficient curve that the other flow meters do; instead as the Re decreases, the C value increases to a maximum before sharply dropping off. Several graphs demonstrating the varying relationships and outcomes are presented. The primary focus of this research was to obtain further understanding of discharge coefficient performance versus Reynolds number for differential producing flow meters at very small Reynolds numbers.

The search for quieter internal combustion engines drives the quest for a better understanding of the acoustic properties of engine duct components. Simulations are an important tool for enhanced understanding; they give insight into the flow-acoustic interaction in components where it is difficult to perform measurements. In this work the acoustics is obtained directly from a compressible Large Eddy Simulation (LES). With this method complex flow phenomena can be captured, as well as sound generation and acoustic scattering. The aim of the research is enhanced understanding of the acoustics of engine gas exchange components, such as the turbocharger compressor.In order to investigate methods appropriate for such studies, a simple constriction, in the form of an orifice plate, is considered. The flow through this geometry is expected to have several of the important characteristics that generate and scatter sound in more complex components, such as an unsteady shear layer, vortex generation, strong recirculation zones, pressure fluctuations at the plate, and at higher flow speeds shock waves. The sensitivity of the scattering to numerical parameters, and flow noise suppression methods, is investigated. The most efficient method for reducing noise in the result is averaging, both in time and space. Additionally, non-linear effects were found to appear when the amplitude of the acoustic velocity fluctuations became larger than around 1~\% of the mean velocity, in the orifice. The main goal of the thesis has been to enhance the understanding of the flow and acoustics of a thick orifice plate, with a jet Mach number of 0.4 to 1.2. Additionally, we evaluate different methods for analysis of the data, whereby better insight into the problem is gained. The scattering of incoming waves is compared to measurements with in general good agreement. Dynamic Mode Decomposition (DMD) is used in order to find significant frequencies in the flow and their corresponding flow structures, showing strong axisymmetric flow structures at frequencies where a tonal sound is generated and incoming waves are amplified.The main mechanisms for generating plane wave sound are identified as a fluctuating mass flow at the orifice openings and a fluctuating force at the plate sides, for subsonic jets. This study is to the author's knowledge the first numerical investigation concerning both sound generation and scattering, as well as coupling sound to a detailed study of the flow.With decomposition techniques a deeper insight into the flow is reached. It is shown that a feedback mechanism inside the orifice leads to the generation of strong coherent axisymmetric fluctuations, which in turn generate a tonal sound.<br><p>QC 20121113</p>

This master’s thesis deals with the simulation of flow through the normalized orifice plate. There is described flow measurement with flowmeters, which reduces the cross-section of the pipe and causes the pressure difference before and after the flowmeter. Following is a description methods of modeling of turbulent flow and a description of software for the simulation of flow from the company Ansys. The theoretical part is followed a practical part, which is focused on determining the permanent pressure loss caused by the orifice plate and the verification of straight pipeline lengths between orifice and obstacle.

Turbulent and cavitation induced pipe vibration is a large problem in industry often resulting in pipe failures. This thesis provides an experimental investigation on turbulent flow and cavitation induced pipe vibration caused by sharp edged baffle plates. Due to large pressure losses across a baffle plate, cavitation can result. Cavitation can be destructive to pipe flow in the form of induced pipe wall vibration and cavitation inception. Incipient and critical cavitation numbers are design points that are often used in designing baffle plate type geometries. This investigation presents how these design limits vary with the influencing parameters by exploring a range of different baffle plate geometries. The baffle plates explored contained varying hole sizes that ranged from 0.159 cm to 2.54 cm, with the total through area, or openness, of each baffle plate ranging between 11% and 60%. Plate thickness varied from 0.32–0.635 cm. Reynolds numbers ranged from 5 x 10^4 -85 x 104. The results show that the cavitation design limits are function of size scale effects and the loss coefficient only. The results also show that the loss coefficient for a baffle plate varies not only with total through area ratio, but also due with the plate thickness to baffle hole diameter ratio. Pipe wall vibrations were shown to decrease with increased through area ratio and increased thickness to diameter ratios. An investigation was also performed to characterize the attenuation of vibration in the streamwise direction of a baffle plate. It was show that the attenuation was largely effected by the presence of cavitation. Attenuation was shown to be a function of the geometry of the baffle plate. This work resulted in empirical models that can be used for predicting pipe vibration levels, the point of cavitation inception, and the streamwise distance where the attenuation of vibration levels caused by a baffle plate occurs.

The thesis deals with analysis of measurement uncertainty. The theoretical knowledge presented in opening chapters is applied on indirect steam flow measurement by orifice plate. Calculation of steam flow is based on knowledge of pressure difference value, static pressure value and temperature. The data are acquired by experimental measurement in laboratory. The mass flow rate uncertainty is determined by normalized procedure (according to standard ČSN EN ISO 5167) and by detailed error analysis (according to standard ČSN ISO 5168) for comparison. Whole numerical computation employs python programming language in Spyder environment. Other computation result is steam consumption of washing cycle.

U mnogim granama tehnike javljaju se problemimerenja protoka fluida. Merne blende, zbog svojihmnogih prednosti predstavljaju najzastupljenijiinstrument za merenje protoka fluida kroz cevovode. Sadruge strane njihova upotreba povećava tro&scaron;kove radaindustrijskih postrojenja. Jedan od ciljeva ovedoktorske disertacije bio je ispitivanje novih oblikamernih blendi u cilju u&scaron;tede energije pri njihovom radu.U ovoj doktorskoj disertaciji predložen je algoritamispitivanja novih oblika mernih blendi. Takođe jekonstruisana i izrađena laboratorijska aparatura zanjihovo ispitivanje kao i diferncijalni &quot;U&quot; manometarza merenje malih razlika pritisaka. U okviru ovedoktorske disertacije dizajnirana su i ispitana tri novaoblika mernih blendi. U&scaron;teda energije je postignutadizajnom koji smanjuje otpor merne blende kaoelementa cevovoda. Novi oblici mernih blendi, kao ijedna standardnog oblika koja je poslužila kaoreferentna, ispitani su prema predloženom algoritmu. Uprvom koraku merne blende su dizajnirane uprogramskom paketu Solid Works. Zatim su, premapredloženom algoritmu, ispitane pomoću računarske simulacije u programskom paketu COMSOL Multiphysics. Po dobijanju zadovoljavajućih rezultata računarske simulacije, merne blende su izrađene na 3D &scaron;tampaču, FDM postupkom i ispitane na laboratorijskoj aparaturi. Rezultati laboratorijskih ispitivanja su upoređeni sa rezultatima računarske simulacije. Upoređeni rezultati računarske simulacije i laboratorijskih ispitivanja su pokazali da je računarska simulacija dobro opisivala situaciju. Rezultati laboratorijskog ispitivanja su pokazali znatan efekat u&scaron;tede energije. Takođe je utvrđeno da se pomoću računarske simulacije mogu dobiti podaci na osnovu kojih se može doneti odluka da li novi oblik merne blende treba korigovati ili ima smisla pristupiti laboratorijskom ispitivanju. Algoritam ispitivanja koji je predložen u ovoj doktorskoj disertaciji se pokazao efikasnim.&nbsp;<br>In many domains of technology, there are problemswith the measurement of fluid flow. Orifice plates,because of their many advantages, represent the mostcommon instrument for measuring fluid flow throughpipelines. On the other hand, their use increases theoperating cost of industrial plants. One of the goals ofthis doctoral dissertation was to test new forms oforifice plates for a reason to save energy during theirwork. An algorithm for testing new forms of orificeplates is proposed. Also, the laboratory equipment fortesting them was designed and made, as well as adifferential &quot;U&quot; manometer for measuring smallpressure differences. As part of this doctoraldissertation are designed and tested three new forms oforifice plates. Energy-saving was achieved by a designthat reduces the resistance of the orifice plate as anelement of the pipeline. New forms of orifice plates, as well as a standard shape, which served as a reference, were tested according to the present algorithm. In the first step, orifice plates are designed in the Solid Works software package. Then, according to the proposed algorithm, they were tested using computer simulation in COMSOL Multiphysics software package. After achieving satisfactory results of computer simulation, orifice plates are made on a 3D printer, using the FDM process and tested in the laboratory apparatus. The results of laboratory tests were compared with the results of computer simulations. Compared results of computer simulation and laboratory testing showed that computer simulation described the situation well. The results of the laboratory test showed a significant energy-saving effect. It was also found that computer simulation can obtain data that can decide whether a new form of orifice plate must be corrected or it makes sense to access laboratory testing. The algorithm proposed in this doctoral dissertation has proven effective.

The work deals with the design of a system of orifices for high pressure difference. The task of this work is to design a device for controlled discharge of steam-gas mixture from a volume compensator with an overpressure of 12,27 MPa to a tank with an overpressure of 0,02 MPa at a constant mass flow of 40 kg/h. The first part of the thesis contains the theory and also the basic principles of calculations. In the next part of the work, the theoretical properties of flow, such as the speed of sound in wet steam, are determined. This knowledge then serves the main goal of the work, namely to design a system of orifices to release steam-gas mixture from the volume compensator.

In this thesis computational models for cavitating flows around orifice plates has been studied and compared. The goal was to fit a model with experimental data and this was done with some success, although problems with numerical stability, long calculation times and geometry overfitting remain. Cavitation is a complex fluid phenomenon that can occur in pressurized liquid flows. It starts when the liquid pressure is lowered below the boiling pressure and water that undergoes cavitation forms vapor which later implodes violently. This process can cause problems such as noise, vibrations and corrosion in piping systems. Loud noise is a nuisance, however powerful vibrations and corrosion can have serious consequences for the structural integrity of pipes. The for example lessened performance, leakages or even failure. Therefore the minimization of cavitation is often a goal in orifice and piping design. Vattenfall AB, together with Forsmark and Ringhals nuclear plants have studied cavitating flows around orifice plates used for flow limitation. A set of data from laboratory tests made by Vattenfall was used as the basis of analysis. Existing computational models in OpenFOAM were tested and evaluated based on their ability to model the experimental data accurately, as well as their computational performance and stability. The cavitation phenomenon was difficult to simulate using established methods so a new method was created and verified. It is based on the Kunz cavitation model together with Large Eddy Simulations, but with turbulence as a predictor of cavitation. The new computational model will serve as a tool for knowing how to design orifices in the future, so that laboratory experiments will not have to be conducted for each new piping design.

A medição de vazão de escoamentos multifásicos é uma necessidade constante em diversas atividades industriais como exploração de óleo e gás, controle de linhas de transporte de vapor e monitoramento de sistemas de resfriamento de usinas nucleares. Dentre os meios disponíveis para a realização da medição de vazão mássica, os dispositivos de medição de pressão diferencial constituem um dos métodos mais simples, sendo sua construção, aplicação e operação em escoamentos monofásicos bem conhecidas e definidas por normas técnicas. No entanto, sua aplicação tem sido estendida a escoamentos multifásicos, geralmente estando aliada a uma técnica adicional de medição de fração de vazio ou fração volumétrica das fases. Este trabalho descreve o estudo numérico de escoamentos multifásicos através de medidores de vazão baseados em pressão diferencial como placas de orifício e bocais de vazão de raio longo. Para tal, primeiramente foram conduzidas simulações de escoamentos monofásicos através de placas de orifício e bocais de vazão de raio longo na faixa de número de Reynolds 15.000 500.000. Os resultados de coeficiente de descarga obtidos foram quantitativamente comparados com os valores preditos por norma ISO, apresentando desvio máximo de aproximadamente 4, 9% para as placas e de 1,0% para os bocais. Em uma segunda etapa, escoamentos do tipo gás úmido (wet gas) através de placas de orifício foram simulados através de três abordagens diferentes. Os resultados de vazão mássica total obtidos foram comparados com dados experimentais fornecidos pela PETROBRAS. As abordagens que consideram o escorregamento entre as fases apresentaram previsões mais próximas dos experimentos, com desvio relativo médio de 3,9%, enquanto a modelagem homogênea apresentou um desvio médio de 6, 6%. Nestes estudos, foram também avaliadas as estruturas desenvolvidas no escoamento através de visualizações da distribuição de fases. São também apresentadas duas sugestões para complementação da caracterização de um escoamento multifásico: (1) a introdução da informação de fração de vazio na formulação apresentada por Paz (2011) e (2) a análise estatística do sinal de pressão diferencial em placas de orifício. Com relação ao primeiro item, comparações quantitativas com dados experimentais sugeriram que a alternativa apresentada é viável para operações de monitoramento da produção. Já o último estudo mostrou qualitativamente a influência da quantidade de líquido na flutuação da pressão diferencial<br>The flowrate measurement of multiphase flows is a constant need at many industrial activities such as oil and gas exploration, steam transport lines control and monitoring of nuclear plants cooling systems. Within the available means for performing flowrate measurement, the differential pressure devices constitute one of the simplest methods, with their construction, application and operation in single phase flows being well known and defined by technical standards. However, their application has been extended to multiphase flows, usually being allied to a void fraction or phase volume fraction measurement technique. This work describes a numerical study of multiphase flows through differential pressure-based flowrate meters such as orifice plates and long radius nozzles. Firstly simulations of single phase flows through orifice plates and long radius nozzles were conducted in the Reynolds number range 15.000500.000. The obtained results of discharge coefficients were quantitatively compared to ISO Standard predicted values, showing a maximum deviation of approximately 4,9% for the orifice plates and of 1,0% for the nozzles. In a second stage, wet gas flows through orifice plates were simulated by means of three approaches. The calculated results of total mass flowrate were compared to experimental data provided by PETROBRAS. The approaches that considered the slip between phases provided the closest results to the experiments, with a mean relative error of 3, 9%, while the homogeneous modeling presented an error of 6, 6%. In these studies, the structures developed within the domain were also evaluated through the visualization of the phases distribution. Two suggestions for complementing the characterization of a multiphase flow are presented: (1) the introduction of void fraction information into the formulation presented by Paz (2011) and (2) the statistical analysis of the orifice plate pressure drop signal. Regarding the first item, quantitative comparison with experimental data suggested that the presented alternative is viable for production monitoring operations. The last study qualitatively revealed the influence of the liquid loading in the pressure drop fluctuation.

Purpose of this thesis is to check influence of turbulent model used for simulation of flow close to primary elementi inserted into piping. The goal is to check if results computed by these models are equal and how precise is their prediction.

Esta dissertação propõe o desenvolvimento de uma rede neural artificial (RNA) direcionada a ambientes foundation fieldbus para realização do cálculo de vazão em dutos fechados. Para tanto, a metodologia proposta utiliza-se de medidas de pressão, temperatura e pressão diferencial, as quais normalmente estão disponíveis em plantas industriais. A principal motivação do emprego das redes neurais reside no seu baixo custo e simplicidade de implementação, o que possibilita o emprego de apenas blocos fieldbus padrões tornando a metodologia independente do fabricante. Foi utilizada uma rede perceptron multicamadas com algoritmo de treinamento backpropagation de Levenberg-Marquardt. O treinamento foi realizado numa programação elaborada para o software Matlab TM. A arquitetura da rede neural foi determinada por métodos empíricos variando-se o número de neurônios e de camadas neurais até se atingir um erro aceitável na prática. Após esses treinamentos foi desenvolvida uma programação para realizar os cálculos de vazão em um ambiente foundation fieldbus utilizando-se para tanto o software DeltaV TM do fabricante Emerson Process Management. Foram obtidos resultados com erro relativo médio de valor de vazão em torno de 1.43% para um primeiro cenário utilizando uma placa de orifício e ar como fluido, e de 0,073% para um segundo cenário utilizando uma placa de orifício e gás natural como fluido, com relação aos valores obtidos através do instrumento multivariável 3095MV TM do fabricante Rosemount. Os valores de erro encontrados validam o método desenvolvido nessa dissertação.<br>This dissertation proposes the development of an artificial neural network (ANN) directed to foundation fieldbus environment for calculation of flow in closed ducts. The proposed methodology uses measurements of pressure, temperature and differential pressure, which are usually available in industrial plants. The main motivation of the use of neural networks lies in their low cost and simplicity of implementation, which allows the use of standard fieldbus blocks by just making the method independent of the manufacturer. It was used a multilayer perceptron network with backpropagation training and algorithm from Levenberg-Marquardt. The training was programmed in the software Matlab TM. The architecture of the ANN was determined by empirical methods by varying the number of neurons and neural layers until it reaches an acceptable error. After such trainings, it was developed a program to perform the flow calculations in an foundation fieldbus environment using Emerson Process Management\'s DeltaV TM software. The results were obtained with an average relative error of flow rate of 1.43% for the first scenario using an orifice plate and air as a process fluid, and 0.073% for a second scenario using an orifice plate and natural gas as the fluid related to the values obtained from Rosemount 3095MV TM multivariable instrument. The values of error found validate the method developed in this dissertation.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2011.<br>Despite the extensive research work carried out on flow through short square-edged orifice plates over the last century (e.g. Johansen, 1930; Benedict, 1977; Alvi et al., 1978; Swamee, 2005; ESDU, 2007), gaps in the engineering data still exist for certain ranges of flow conditions and geometries. The majority of data available in the literature are for Newtonian fluids in the turbulent flow regime (ESDU, 2007). Insufficient data have been observed for the orifice with pipe diameter ratio, β = 0.2, in the laminar flow regime. There are no experimental data for β = 0.3 and 0.57. The objective of this thesis was to conduct wide-ranging experimental studies of the flow in orifice plates, which included those geometrical configurations, by measuring pressure loss coefficients and discharge coefficients across the orifice plates using both Newtonian fluids and non-Newtonian fluids in both laminar and turbulent flow regimes. The test work was conducted on the valve test rig at the Cape Peninsula University of Technology. Four classical circular short square-edged orifice plates having, β = 0.2, 0.3, 0.57 and 0.7, were tested. In addition, two generation 0 Von Koch orifice plates (Von Koch, 1904), with equivalent cross sectional area were also tested for β = 0.57. Water was used as Newtonian fluid to obtain turbulent regime data and also for calibration purposes to ensure measurement accuracy and carboxymethyl cellulose, bentonite and kaolin slurries were used at different concentrations to obtain laminar and transitional loss coefficient data. The hydraulic grade line method was used to evaluate pressure loss coefficients (Edwards et al., 1985), while the flange tap arrangement method was used to determine the discharge coefficients (ESDU, 2007). A tube viscometer with three different pipe diameters was used to obtain the rheological properties of the fluids. The results for each test are presented in the form of pressure loss coefficient (kor) and discharge coefficient (Cd) against pipe Reynolds number (Re)

La croissance du développement des microsystèmes fluidiques de puissance dans la dernière décennie a augmenté considérablement le besoin de développer des instruments de mesure différents des instruments traditionnels. Le but du présent travail est l'étude et la fabrication des micro-débitmètres à pression différentielle. Dans ce cas, le principe de calcul du débit se fait par la mesure de la chute de pression à travers un micro-orifice dans un microcanal à section rectangulaire. Ces micro-débitmètres à micro-organe déprimogène sont destinés pour mesurer le débit dans les microsystèmes fluidiques opérant à gaz tels que les power MEMS. Pour ces derniers, actuellement, il n'existe aucun micro-débitmètre sur le marché adapté pour leurs conditions d'opération. Dans ce mémoire, une série de 16 micro-débitmètres de type orifice plat à section rectangulaire ont été fabriqués et testés expérimentalement. Leur géométrie est caractérisée par deux paramètres : un coefficient de contraction allant de 0,2 à 0,8 et un rapport de forme au niveau de l'orifice allant de 0,21 à 2,45. Le diamètre hydraulique des microcanaux varie entre 220 et 388 [micro]m.La variation de la chute de pression à travers le micro-orifice en fonction du débit a été mesurée pour chaque micro-débitmètre avec une pression d'entrée de 5, 6,5 et 8 bars.La plage de débit étudiée est entre 0,2 et 100 mg/s. Le coefficient de décharge de chaque micro-débitmètre a été déterminé. Par ailleurs, le comportement du coefficient de décharge a été étudié en fonction du nombre de Reynolds allant de 100 à 13000, et en fonction de la perte de pression adimensionnée, [[Delta]P/P[indice inférieur 1]], allant de 0,001 à 0,6. À même dimension géométrique, les résultats expérimentaux ont montré que le coefficient de décharge est fonction du nombre de Reynolds pour une valeur du facteur d'expansion, Y, supérieure à 0,9. Pour des valeurs de Y inférieures à 0.9, le coefficient de décharge est dépendant de [[Delta]P/P[indice inférieur 1]]. Les résultats expérimentaux ont été comparés aux résultats de la simulation numérique. De cette façon, le modèle numérique a été validé. Ce travail a permis de développer des micro-débitmètres capables de mesurer de faibles débits à l'ordre des milligrammes par seconde (mg/s) dans les microsystèmes fluidiques de puissance. Particulièrement, le travail a permis de répondre aux exigences de l'installation d'une micro-turbopompe en termes de mesure du débit de gaz. De plus, l'étude approfondie des micro-débitmètres a permis d'acquérir une connaissance plus élaborée de l'écoulement à travers ce type de restriction dans les microcanaux rectangulaires.La caractérisation expérimentale de ce type de micro-débitmètres a été faite pour la première fois. En effet, cette étude a permis de définir des corrélations empiriques du coefficient de décharge spécifiques à chaque dimension géométrique. Ces corrélations seront un bon outil de design de ce genre de mesure.

Cette thèse de doctorat explore la dynamique de propagation des ondes de détente dans les circuits de réacteurs nucléaires, en se concentrant sur une configuration représentative d'un scénario de type Accident par Perte de Réfrigérant Primaire (APRP) dans les Réacteurs à Eau Pressurisée (REP). L'étude examine les charges de pression transitoires sur les structures internes, en particulier le cloisonnement du cœur du réacteur, induites par les ondes de détente générées par la rupture brutale et totale (rupture guillotine) d'une des tuyauteries du circuit primaire de refroidissement du REP. Cette analyse est menée en combinant des mesures expérimentales sur un banc d'essai de géométrie simplifiée mais représentatif du scénario APRP et des simulations numériques. Ces simulations sont réalisées en faisant appel à une hiérarchie de modèles numériques: 1D, 2D axisymétriques et 3D, avec ou sans prise en compte des mécanismes d'interaction fluide-structure. Les modèles 1D incluent des représentations simplifiées ou modèles d'impédance des obstacles présents dans l'écoulement, indispensables pour réduire les coûts de simulation de la propagation des ondes au travers d'un circuit complet. Ces obstacles sont des diaphragmes de diamètre et d'épaisseur variables, représentatifs des singularités géométriques présentes dans les circuits parcourus par les ondes de détente. La comparaison calcul/expérience permet d'évaluer le potentiel prédictif des différentes stratégies mises en oeuvre. Le Chapitre 1 introductif du mémoire détaille le contexte et la motivation de l'étude menée en mettant en évidence l'importance d'une compréhension approfondie des phénomènes physiques associés au scénario APRP et la nécessité de modèles simplifiés pour simuler l'écoulement de fluides dans les géométries complexes d'un REP. Une revue de la littérature récapitule les principaux travaux dans l'analyse par voie numérique des réacteurs nucléaires et les simulations d'écoulement transitoire. Une anlyse des approches numériques développées pour la propagation d'ondes en présence d'obstacles avec description simplifiée est également menée pour des applications hors contexte nucléaire. Les Chapitres 2 et 3 présentent respectivement i) la plateforme expérimentale MADMAX utilisée pour produire les mesures de référence ainsi que l'évolution de ses configurations au cours de la thèse, ii) les modèles disponibles au sein du logiciel EUROPLEXUS et utilisés pour mener les simulations numériques des configurations étudiées expérimentalement. Le Chapitre 4 détaille les résultats des expériences et des simulations de la propagation des ondes de détente à travers un unique diaphragme de géométrie modulaire. L'impact de la géométrie des obstacles sur la propagation des ondes est analysé et les capacités prédictives de modèles numériques de complexité (et de coût) variable sont évaluées pour cette configuration de base. Le Chapitre 5 élargit l'analyse à la configuration complète de MADMAX, incorporant une conduite de dérivation avec plusieurs diaphragmes positionnés dans cette conduite. La comparaison détaillée des données expérimentales et des résultats des simulations révéle un bon accord dans la capture du comportement transitoire et des différentiels de pression entre les conduites du cœur et de la dérivation. Des configurations alternatives de MADMAX sont explorées dans le Chapitre 6, mettant en évidence les effets de variation du nombre des diaphragmes et de leur emplacement. Les expériences sur la plateforme MADMAX et les simulations EUROPLEXUS réalisées dans le présent travail contribuent à une meilleure compréhension des phénomènes d'écoulement transitoire dans les circuits de réacteurs nucléaires. [...]<br>This doctoral thesis explores the dynamics of rarefaction wave propagation in nuclear reactor circuits, focusing on a configuration representative of a Loss of Coolant Accident (LOCA) scenario in Pressurized Water Reactors (PWRs). The study examines transient pressure loads on internal structures, particularly the reactor core baffle, induced by rarefaction waves generated by the sudden and complete rupture (guillotine break) of one of the pipes in the primary cooling circuit of the PWR. This analysis is conducted by combining experimental measurements on a test bench with simplified geometry but representative of the LOCA scenario and numerical simulations. These simulations employ a hierarchy of numerical models: 1D, 2D axisymmetric, and 3D, with or without taking into account fluid-structure interaction mechanisms. The 1D models include simplified representations or impedance models of the obstacles in the flow, essential for reducing the simulation costs of wave propagation through an entire circuit. These obstacles are orifice plates of varying diameter and thickness, representative of the geometric singularities present in the circuits traversed by rarefaction waves. The comparison between calculations and experiments allows for evaluating the predictive potential of the various strategies implemented. Chapter 1 of the thesis introduces the context and motivation of the study, highlighting the importance of a thorough understanding of the physical phenomena associated with the LOCA scenario and the necessity of simplified models for simulating fluid flow in the complex geometries of a PWR. A literature review summarizes the main works in the numerical analysis of nuclear reactors and transient flow simulations. An analysis of the numerical approaches developed for wave propagation in the presence of obstacles with simplified descriptions is also conducted for applications outside the nuclear context. Chapters 2 and 3 respectively present i) the MADMAX experimental platform used to produce the reference measurements and the evolution of its configurations during the thesis, ii) the models available within the EUROPLEXUS software and used to perform the numerical simulations of the experimentally studied configurations. Chapter 4 details the results of the experiments and simulations of rarefaction wave propagation through a single modular orifice plate. The impact of obstacle geometry on wave propagation is analyzed, and the predictive capabilities of numerical models of varying complexity (and cost) are evaluated for this basic configuration. Chapter 5 expands the analysis to the complete MADMAX configuration, incorporating a by-pass pipe with several orifice plates positioned in this pipe. The detailed comparison of experimental data and simulation results reveals good agreement in capturing transient behavior and pressure differentials between the core and by-pass pipes. Alternative configurations of MADMAX are explored in Chapter 6, highlighting the effects of varying the number and placement of the orifice plates. The experiments on the MADMAX platform and the EUROPLEXUS simulations conducted in this work contribute to a better understanding of transient flow phenomena in nuclear reactor circuits. The proposed calculations/experiments comparisons provide quantitative indications on the predictive capacity of the simulation codes based on the choices of geometric singularity descriptions present in the flow. The thesis conclusion proposes some avenues for future analysis and improvements

碩士<br>國立中山大學<br>環境工程研究所<br>107<br>Diesel engine has better thermal efficiency and fuel economy than other engines, with the irreplaceable characteristics. Diesel engine is the first choice for the high torque output power machine. Although vehicles are equipped with catalytic converter to decrease the emission of pollutants, the environmental pollution may be caused by poor diffusion of the exhaust gas before entering the catalytic converter and short residence time with the catalyst. In this study, ANSYS FLUENT model is used as the research tool to explore the numerical simulation of the internal flow field of diesel engine exhaust pipe. According to inlet Temperature, orifice plate, velocity flow field, temperature flow field. And compared with the result of simulation and the result through the diesel engine experiment to find the best orifice plate model. According to the velocity flow field, when the inlet velocity is 3m/s, the flow field distribution before entering the catalyst, the orifice plate model type V is the best. According to the temperature flow field, the inlet velocity is 3m/s and the temperature is 200 °C, 300 °C and 400 °C. The results show that the different inlet temperature has no significant impact. In the engine experiment, the orifice plate model type V combined with metal catalyst, the best reduction rate is 84.4% at 300°C and 350°C. And the orifice plate model type V combined with ceramic fiber catalyst, the best reduction rate is 79.0% at 350°C. Non-orifice plate with metal catalyst, the best reduction rate is 69.5% at 300°C. And non-orifice plate with ceramic fiber catalyst, the best reduction rate is 69.4% at 400°C. The experimental results show that the flow field diffusion and the residence time in catalyst with the orifice plate model type V, have a better effect.

碩士<br>國立成功大學<br>航空太空工程學系碩博士班<br>96<br>The dynamics of coherent structures in jet column region of a sharp-edged orifice plane jet was extensively studied by means of hot-wire technique. The present study was conducted in a sharp-edged orifice plane jet (i.e. 450 beveled edge) and the height of orifice is set to 15mm, therefore, the aspect ratio is 20. The investigation of the flow structures and intrinsic dynamics of vortex interaction are defined in the fixed operating velocity at and the corresponding Reynolds number based on the orifice height is . However, the study of initial flow properties of sharp-edged and right angle orifice plane jet are undertaken within operating velocity of . It is found that jet flow is sensitive to initial conditions, particularly nozzle exit with irregular geometry. Due to the sudden contraction of the orifice jet, the vena contracta effect is formed and plays a crucial role at immediate exit of orifice of sharp-edged and right angle orifice plane jet as well. The vena contracta effect depends upon the jet exit velocity, i.e. the vena contracta effect will be more prominent at lower jet exit velocity. This effect leads the flow to accelerate. Due to the forming of vena contracta at the initial stage, the initially contract inward in momentum thickness, flow entrainment rate and shear layer width is discovered in sharp-edged orifice plane jet. It is found that the vena contracta effect will suppress the flow to spread and delays the development of the coherent structures. In addition, the orifice plane jets perform well in the mixing characteristic than that to the smooth contraction nozzle plane jet. The existence of the shedding frequency due to the separation on the sharp-edged walls is confirmed in study of Fourier and Wavelet power spectra. Meanwhile, the higher formation rate of sharp-edged orifice plane jet is found in flow visualization and spectral analysis. The frequency of the instability waves in the present case are varying as well as decreasing along the downstream direction. Moreover, two initial instability frequencies exist in tandem within the shear flow. It is expected that these two instability waves will compete to each other to extract energy from the mean flow or separation as well. On the other hand, the ‘forking of structures’ in wavelet coefficient indicates to the vortex pairing at former portion of merging process. The location of the vortex formation in present case is locate somewhere near X/H=0.8., and the occurrence of first and second vortex merging are believed at vicinity of X/H=1.2 and X/H=2.3, respectively. No apparent interchange between and at former and latter portion of vortex formation and merging. The presence of the negative Reynolds shear stress or energy production prompts the existence of the unstable boundary layer and oscillation of separation zone, which excites the shear flow under high amplitude. This behavior is presumed as self-oscillation in sharp-edged orifice plane jet. Experimental results show that kinetic energy contributes by mean energy advection term at initial flow development and the fluctuation kinetic energy increases drastically during the vortex formation and interaction.