Dissertations / Theses on the topic 'Coherent Jet'
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Bin, Baqui Yamin. "Sound generation from coherent structures in subsonic jets." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709362.
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Malla, Bhupatindra. "Study of High-speed Subsonic Jets using Proper Orthogonal Decomposition." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1352397174.
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Valsecchi, Pietro. "Temporal Numerical Simulations of Turbulent Coanda Wall Jets." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/195025.
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In a novel application of the temporal numerical simulation, an investigation ofturbulence modeling techniques is carried for the turbulent wall jet over aconvex surface (Coanda wall jet.) The simultaneous presence of multipleinstability mechanisms and the interaction with the turbulence dynamics at thesolid boundary produces a unique combination of different large turbulentcoherent structures that constitutes both a consistent challenge for numericalsimulations and an ideal test bed for turbulence models.The Temporal Direct Numerical Simulation (TDNS) of the Coanda wall jetrestricts the focus from the global turbulent Coanda wall jet to a smaller, localportion of the flow and offers a wide array of advantages to the present work. Inparticular, the size of the computational domain can be arbitrarily chosen inboth the spanwise and the streamwise directions. This allows to either suppressor enhance individual physical mechanisms and, consequently, to selectivelyreproduce different large coherent structures within the local flow. In the firstpart, temporal numerical simulations are employed to reproduce four differentflow scenarios of the local Coanda wall jet with a level of numerical resolutionthat, because of the reduced size of the computational domain, cannot be matchedby standard DNS of the entire physical flow (spatial DNS, or SDNS.)The TDNS of these four flow scenarios are then used in the second part for ana--posteriori analysis of different turbulence models in order to addresscommon shortcomings shown by Hybrid Turbulence Models (HTM). For each flowscenario, the turbulent flow field is deliberately decomposed in resolved andunresolved flows by the application of different filters in space correspondingto different grid resolution. The behavior of turbulence models can be reproducedfrom the resolved flow and compared to the turbulent stress tensor directlycalculated from the unresolved part of the flow field. Starting from the RANSlimit, turbulence models with different levels of complexity are studied.Successively, the performance of these models is analyzed at intermediatenumerical resolutions between RANS, LES, and DNS. Finally, an improvedformulation of the Flow Simulation Methodology (FSM) is proposed.
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SAKAI, Yasuhiko, Nobuhiko TANAKA, and Takehiro KUSHIDA. "On the Development of Coherent Structure in a Planet Jet (Part2, Investigation of Spatio-Temporal Velocity Structure by the KL Expansion)." The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9010.
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田中, 伸彦, Nobuhiko TANAKA, 康彦 酒井, Yasuhiko SAKAI, 睦. 山本, Mutsumi YAMAMOTO, 貴. 久保, and Takashi KUBO. "二次元噴流のコヒーレント構造発展に関する実験的研究 (第４報、速度二成分多点同時測定とKL展開による大スケール構造モデル)." 日本機械学会, 2005. http://hdl.handle.net/2237/9007.
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Decker, Rodrigo Koerich. "Analise de estruturas coerentes de larga escala em jatos de dispersão bifasicos." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266338.
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Orientadores: Milton Mori, Henry França Meier, Udo FritschingTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: Este trabalho propõe o estudo de estruturas coerentes de larga escala por meio da utilização da metodologia ¿Interparticle Arrival Time¿ (IAT) no escoamento de um jato bifásico. Experimentos foram desenvolvidos em relação a diferentes condições de velocidade inicial com diâmetro médio de partícula igual a 50 µm, e para duas diferentes misturas de partículas, 50 µm e 90 µm, em diferentes proporções, e comparados em relação a perfis de velocidade média, intensidade de turbulência e velocidade RMS. Medidas relacionadas à distribuição IAT foram também adquiridas para todas as condições analisadas. Os experimentos foram desenvolvidos para diferentes posições axiais e radiais a partir da saída do orifício de formação do jato. Perfis radiais de velocidade média, flutuação de velocidade (velocidade RMS), intensidade de turbulência e ¿interparticle arrival time¿ (em termos de distribuição Chi2 e número de desvios) foram obtidos pelo sistema de ¿Phase Doppler Anemometry¿, atravessando o sistema de medição ponto a ponto na direção desejada. Além disto, as variações das condições de velocidade inicial, distribuição de partículas e razão de carga permitem a obtenção de importantes informações em relação às estruturas locais do escoamento e seus efeitos sobre o transporte macroscópico e turbulento de partículas entre o centro do jato e as regiões de contorno do mesmo. Assim é possível identificar que no centro do jato não existe a formação de Estruturas Coerentes de Larga Escala (ECLE), ou seja, o escoamento é dominado por estruturas incoerentes. Existem também fortes indícios de formação de ECLE em uma região radial entre o centro e a região de contorno, sendo estas dependentes da condição inicial de velocidade da fase gás. Além disto, partículas com maior diâmetro suprimem a formação de ECLE. A distribuição IAT prova ser uma ferramenta importante na identificação dos locais onde ECLEs vêm a influenciar a distribuição de partículas, formando ¿clusters¿. A investigação extensiva de dados experimentais em relação ao comportamento da fase dispersa no escoamento gás sólido em um jato pode ser utilizada como uma importante fonte de dados para uma validação detalhada, por meio de simulação numérica, do escoamento disperso bifásico, incluindo as fortes interações entre as fases gás e particulada
Abstract: A study of large scale coherent structures by Interparticle Arrival Time (IAT) of a two phase jet flow is proposed. Measurements were carried out for different initial velocities with 50 µm particle mean diameter, and for two different particle mixtures with mean particle diameter of 50 µm and 90 µm, in different proportions, and analyzed in relation to different variables. Measurements related to IAT were also acquired for all analysis conditions. The experiments were developed for different axial and radial distances from the nozzle outlet. Radial profiles of mean velocity, RMS velocity, turbulence intensity and the IAT (in terms of Chi2 and number of deviation) were measured by a Phase Doppler Anemometry system, traversing the measuring device stepwise in the desired direction. Furthermore, the variation of the initial velocity conditions, particle diameter distributions, and particle loadings yield important information about the local flow structures and its effect on the macroscopic as well as the turbulent particle transport between the jet centre and the outer shear layer. Thus, it is possible to identify that in the centre line of the jet there is no formation of large scale coherent structures (ECLE), i. e., the flow is dominated by incoherent structures. There is also strong evidence of ECLE formation in a radial position between the centre and the outer shear layer of the jet, which are dependent on the gas initial velocity. Furthermore, particles with large diameter suppress ECLE formation. The IAT distribution proofs to be an important tool to identify regions where large scale coherent structures influence the particle distribution and tend to form particle clusters. The derived extensive experimental data set for the particle behaviour at the two-phase jet may serve as a basis for the detailed validation of numerical simulations of dispersed two phase flow behaviour including strong phase interactions between gaseous and particulate phases
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
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SAKAI, Yasuhiko, Nobuhiko TANAKA, and Takehiro KUSHIDA. "On the Development of Coherent Structure in a Plane Jet (Part1, Characteristics of Two-Point Velocity Correlation and Analysis of Eigenmodes by the KL Expansion)." The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9011.
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Kaffel, Ahmed. "Analyse des structures des écoulements et des instabilités développées par un rideau d'air cisaillé latéralement par un courant externe : application au cas des meubles frigorifiques de vente." Thesis, Valenciennes, 2017. http://www.theses.fr/2017VALE0011/document.
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Dans cette étude, le comportement aérodynamique du jet pariétal (Re = 8000) cisaillé latéralement par un courant de perturbation externe (ELS) de profil de vitesse uniforme (Ulf) a été étudié et analysé. Les expérimentations ont été réalisées par PIV et LDV sur une maquette aéraulique isotherme à échelle réduite d’un meuble frigorifique de vente. L’étude est centrée sur la région du jet située à proximité de la section de soufflage (x/e < 10) qui correspond à la zone dans laquelle se développent les instabilités et le processus de transition vers la turbulence. L’analyse des résultats obtenus avec et sans perturbation a mis en évidence que la perturbation entraîne une diminution significative du pouvoir d’entraînement du jet, une forte décroissance de la vitesse moyenne maximale, un faible épanouissement du jet et une augmentation globale des valeurs des moments d’ordre deux de toutes les composantes des contraintes de Reynolds. L’analyse par PIV résolue en temps (10 kHz) montre une topologie déformée et allongée des structures de Kelvin-Helmholtz (K-H) pour (Ulf = 0,5 ms-1) et détachée pour (Ulf = 1 ms-1). Les résultats de l’interaction mutuelle ente les couches interne et externe indiquent que le courant ELS brise partiellement le mécanisme de formation des dipôles de vortex qui deviennent irréguliers et moins prédictifs, ce qui conduit à l’allongement de la zone de transition et retarde donc l’apparition de la zone auto-similaire du jet. D’après la technique POD, l’ELS engendre une redistribution énergétique entre les modes. Le courant ELS affecte également les instabilités K-H en perturbant leur organisation bidimensionnelle, leur topologie, leur alignement et leur fréquence de passage mettant en évidence l’effet inhibiteur exercé sur le développement des structures primaires. Les corrélations spatiales Rvv reflètent la diminution des échelles de longueur dans le cas d’un jet perturbéIn this study, the aerodynamic behavior of the plane wall jet (Re = 8000) sheared laterally by an external lateral stream (ELS) of a uniform velocity profile (Ulf) was studied and analyzed. The experiments were carried out by PIV and LDV on a reduced-scale isothermal aeraulic model of a refrigerated display cabinet. The study focuses on the near-field region of the jet (x / e <10) which corresponds to the zone of transition to turbulence and onset and development of instabilities. The results obtained with and without perturbation showed a significant decrease in the entrainment rate, a strong decrease in the maximum velocity decay rate, a lower jet expansion and an overall increase in the values of second order moments of the Reynolds stress components. The time-resolved PIV analysis (10 kHz) shows a distorted and elongated topology of the Kelvin-Helmholtz (K-H) structures for (Ulf = 0,5 ms-1) and a detached topology for (Ulf = 1 ms-1). The results of the mutual interaction between the inner and outer layers indicate that the ELS partially breaks the vortex dipole formation mechanism which becomes irregular and less predictive, leading to the elongation of the transitional region and a lag effect in the beginning of the self-similarity region. POD technique reveals the role of the ELS in redistributing energy between the modes. The ELS also affects the K-H instabilities by disrupting their two-dimensional organization, topology, alignment and shedding frequency, highlighting the inhibitory effect exerted on the development of primary structures. The spatial correlations Rvv reflect the decrease of the length scales in the case of a perturbed jet
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Itasse, Maxime. "Effet sur le bruit de jet de l'excitation de modes instables : rôle des interactions non linéaires." Thesis, Toulouse, ISAE, 2015. http://www.theses.fr/2015ESAE0028/document.
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Cette étude s'inscrit dans l'effort de réduction des nuisances sonores des avions au décollage. Une des principales composantes est le bruit de jet, dont la partie à basse fréquence peut notamment être imputée au rayonnement acoustique directif des structures cohérentes de grande échelle engendrées par les instabilités dans la couche de mélange du jet. L'évolution de ces ondes d'instabilité peut être décrite au moyen des équations de Stabilité Parabolisées (PSE). Un premier objectif a été de déterminer si dans le cas d'un jet turbulent naturel, les interactions non linéaires entre les ondes d'instabilité ont un impact significatif sur sa dynamique et sur son rayonnement acoustique. À cet effet, une modélisation PSE non linéaire a été développée et appliquée à une configuration réaliste. La possibilité de manipuler ces ondes d'instabilité par non linéarité a ensuite été étudiée en vue d'une réduction du rayonnement acoustique. Pour cela, une analyse PSE a été menée pour déterminer l'effet sur le bruit de jet de l'excitation d'un ou plusieurs modes instables. Ces travaux de thèse ont permis de montrer, d'une part, que les non linéarités semblent avoir un impact mineur sur la dynamique des ondes d'instabilité dans le cas des jets turbulents naturels, et d'autre part, qu'il est possible de réduire le rayonnement acoustique des modes dominants par interactions non linéairesThis study is part of the effort to reduce aircraft noise during take-off. Jet noise is oneof the main contributors, of which lower frequency component can be attributed to thedirective acoustic field generated by the large-scale coherent structures arising from jetmixing-layer instabilities. The development of these instability waves can be describedusing Parabolized Stability Equations (PSE). A first objective was to determine if inthe case of a natural turbulent jet, nonlinear interactions between instability waveshave a significant impact on its dynamic and acoustic behaviour. For this purpose,a nonlinear PSE model has been developed and applied to a realistic configuration.Then, the possibility to manipulate these instability waves by means of nonlinearity wasinvestigated with a view to reduce noise. To this end, a PSE analysis has been carried outto assess the impact on jet noise of exciting one or more unstable modes. The findingsof this doctoral work demonstrate a minor impact of nonlinearities on the dynamics ofinstability waves for natural turbulent jets on the one hand, and the possibility to makethe initially dominant instability acoustically ineffective using nonlinear interactions onthe other hand
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SAKAI, Yasuhiko, Nobuhiko TANAKA, Mutsumi YAMAMOTO, and Takehiro KUSHIDA. "On the Development of Coherent Structure in a Planet Jet (Part 3, Multi-Point Simultaneous Measurement of Main Streamwise Velocity and the Reconstruction of Velocity Field by the KL Expansion)." The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9008.
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Hileman, James Isaac. "Large-scale structures and noise generation in high-speed jets." Connect to this title online, 2004. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1078776079.
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Thesis (Ph. D.)--Ohio State University, 2004.Title from first page of PDF file. Document formatted into pages; contains xxviii, 365 p.; also includes graphics. Includes bibliographical references (p. 269-279).
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Suigh, Rafael Oliveira. "Estruturas coerentes no transporte caótico induzido por ondas de deriva." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-08112016-102037/.
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Nesta tese foi estudado o transporte de partículas na borda do plasma confinado magneticamente em tokamaks a partir de um modelo para ondas de deriva proveniente de flutuaçõoes eletrostáticas geradas pela não uniformidade do plasma. Para investigar esse problema, consideramos o modelo com duas ondas de deriva, que possui uma complexa dinâmica não linear onde podemos encontrar tanto transporte anômalo quanto transporte difusivo. Para a encontras no plano de fases as Estruturas Lagrangianas Coerentes (ELCs) e os jatos, foram confeccionados mapas de Poincaré, diagramas de expoente de Lyapunov a tempo finito, diagramas de deslocamento quadrático, diagramas de autocorrelação da velocidade e o diagrama de retorno. Para avaliar o impacto dessas ELCs no transporte de partículas foram analisados a série temporal do desvio padrão médio, da dispersão relativa e dos saltos dentro do mapa de Poincar´e e também foram confeccionados histogramas com a distribuição desses saltos. Foi encontrado que, com duas ondas de deriva e para uma determinada combinação de parâmetros, surgem correntes de jato, que persistem por longos períodos, imersas na região caótica. Verificamos que, assim como nas ilhas, a região interna às correntes de jato são inacessíveis às ELCs. Também foi encontrado que, quando existe uma corrente de jato, o transporte observado na região caótica não é simétrico com uma pequena deriva na direção contraria ao jato. Esse fenômeno observado ocorre em contrapartida ao caso típico de sistemas com mistura em que as ELCs tem acesso a todo o plano de fase e o transporte é difusivo.In this thesis we studied the particle transport in the edge of magnetically confined plasma in tokamaks using a model of drift waves due to electrostatic fluctuations generated by the non-uniformity of the plasma. To investigate this issue, we consider the model with two drift waves, which has a complex nonlinear dynamics where we can find both anomalous and diffusive transport. To find the Lagrangian Coherent Structures (LCSs) and the jets, we used Poincaré maps, Finite time Lyapunov exponent diagrams, quadratic displacement diagrams, autocorrelation velocity diagrams and return displacement diagram. To evaluate the impact of LCSs in the transport of particles, we analyzed the time series of both average standard deviation and relative dispertion and also histograms of the distribution of these jumps. It was found that, with two drift waves and for a given combination of parameters, a jet streams appear in the phase space and persist for long periods of time immersed in the chaotic region. We found that, as well as on the islands, the inner region of the jet streams are inaccessible to LCSs. It was also found that when there is a jet stream, the transport observed in the chaotic region is not symmetrical and have a small drift in the opposite direction to the jet. This phenomenon is observed in contrast to the typical case of systems with mixing in wich the LCSs have access to all the phase space and the trasnport is diffusive.
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Léon, Olivier. "Étude du rayonnement acoustique d'instabilités hydrodynamiques de jets double-flux par les équations de stabilité parabolisées (PSE)." Phd thesis, Toulouse, INPT, 2012. http://oatao.univ-toulouse.fr/9138/1/leon_partie_1_sur_2.pdf.
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Dans le but de réduire le bruit de jet, source principale de nuisance sonore au décollage d'un avion, une compréhension fine des mécanismes aéroacoustiques mis en jeu est nécessaire. Les structures cohérentes de grande échelle se développant dans la couche de mélange d'un jet semblent responsables d'une part importante du bruit observé en champ lointain, surtout dans les basses fréquences. Une approche permettant d'étudier ces structures turbulentes est fournie par la théorie de stabilité, notamment au moyen des équations de stabilité parabolisées (PSE). L'étude de ces ondes d'instabilité est alors complémentaire d'autres approches (LES ou expériences), puisqu'elle permet de mettre en évidence la nature et la dynamique de ces structures, également présentes dans les résultats de simulations ou de mesures.
Au cours de ces travaux de thèse, nous nous sommes intéressés aux structures cohérentes se développant dans des jets à double flux étudiés au cours du projet européen CoJeN (Coaxial Jet Noise). En particulier, nous avons exploité une base de données issues de mesures de fluctuations de pression réalisées en champ proche et en champ lointain de ces jets. Nous avons alors pu comparer les résultats de notre modélisation PSE à ces mesures en périphérie immédiate du jet, confirmant ainsi la pertinence d’un tel modèle, même dans des configurations aussi complexes. De plus, le calcul du rayonnement acoustique en champ lointain engendré par les fluctuations de pression modélisées nous a permis de faire des comparaisons directes avec les niveaux et les directivités mesurés. Nous avons ainsi pu mettre en évidence quantitativement la contribution de ces structures turbulentes de grande échelle au bruit total rayonné par le jet.
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Pineau, Pierre. "Etude numérique de la production et de la propagation d'ondes non linéaires dans les jets supersoniques." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC034/document.
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Dans ce travail de thèse, les mécanismes à l'origine de la formation des chocs associés à la perception de crackle proche de jets supersoniques axisymétriques sont étudiés à l'aide de simulations numériques. Dans ces simulations, les équations de Navier-Stokes instationnaires et compressibles sont résolues en coordonnées cylindriques à l'aide de différences finies d'ordre élevé peu dissipatives et peu dispersives. Quatre jets temporels à des nombres de Mach de 2 et~3 et à des nombres de Reynolds compris entre 3125 et 50000 sont simulés dans un premier temps. Des ondes acoustiques de forte amplitude présentant d'importants gradients de pression sont mises en évidence à proximité des jets. Elles se forment par un mécanisme de raidissement à la source qui est étudié par le calcul de moyennes conditionnelles synchronisées autour des pics de pression en champ proche. Ces moyennes montrent un lien direct entre ces ondes non linéaires et la convection de structures cohérentes à desvitesses supersoniques dans les couches de~mélange. L'influence de la température sur la formation de ces ondes est examinée dans un second temps par le calcul de cinq jets temporels à des rapports de température de 1, 2 et 4, et à des nombres de Mach acoustique compris entre 2 et 4. À vitesse d'éjection constante, les niveaux de bruit produits par les jets chauds sont moins élevés que ceux du jet isotherme, mais les ondes non linéaires qu'ils rayonnent sont peu affectées par une hausse de température. À nombre de Mach constant, les niveaux augmentent avec la température, de même que l'asymétrie des fluctuations de pression, traduisant un renforcement du caractère non linéaire des ondes rayonnées. Ces variations pourraient être dues à celles de la vitesse de convection des structures cohérentes, qui augmente de façon significative avec la température lorsque le nombre de Mach est constant, mais diminue légèrement à vitesse~constante. Finalement, trois simulations de jets spatiaux isothermes et chauds à un nombre de Mach acoustique de 2 et à des nombres de Reynolds de 12500 et 50000 sont mises en \oe uvre. Des ondes de Mach présentant d'importants gradients de pression sont visibles au voisinage direct des jets. La formation de ces ondes est liée, comme dans le cas des jets temporels, à la convection supersonique de structures cohérentes dans les couches de mélange. Le champ lointain acoustique est enfin déterminé par des méthodes d'extrapolation linéaire et non linéaire. Lorsque la propagation est non linéaire, un raidissement additionnel des fronts d'onde est constaté en champ lointainNumerical simulations are carried out with the aim of investigating the formation of nonlinear steepened waves at the origin of crackle in the near acoustic field of supersonic jets. In these simulations, the compressible Navier-Stokes equations are solved in cylindrical coordinates using high-order low-dissipative and low-dispersive finite difference schemes.Four temporally-developing isothermal round jets are first simulated at Mach numbers of~2 and~3 and at Reynolds numbers ranging from 3,125 to 50,000. Strong acoustic waves containing sharp pressure variations are observed in the vicinity of the jets. Their formation process is described by the computation of conditional averages which are triggered by the detection of strong pressure peaks in the near field. Such steepened waves are then shown to be produced by the supersonic motion of coherent structures inside the jet shear layers.Temperature effects are then investigated by considering five temporal round jets at temperature ratios of 1, 2 and~4 and at acoustic Mach numbers of 2, 2.8 and 4. For a given jet speed, the sound levels produced by the hot jets are lower than those of the isothermal one. However, the properties of the steepened waves they generate are not significantly affected by a rise of temperature. On the contrary, when the Mach number is held constant, pressure levels are higher at high temperature. The skewness and kurtosis factors of pressure fluctuations are also increased, which indicates a strengthening of the asymmetry and the intermittency of the pressure fluctuations. It is likely that the influence of temperature on these waves results from the variations of the convection speed, which is found to significantly increase with temperature at constant Mach number, but to slightly decrease at constant jet speed.Finally, three simulations of spatially-developing axisymmetric, isothermal and hot jets at a Mach number of~2 and at Reynolds numbers of 12500 and 50000 are performed. Strong Mach waves possessing the distinctive features of crackle are visible in the near vicinity of the jets. As observed for temporal simulations, their formations are associated with the supersonic motion of large-scale coherent structures inside the jet shear layers. The far acoustic field is determined using linear as well as nonlinear extrapolation methods. When nonlinear propagation effects are taken into account, a further steepening of the wavefronts is observed with increasing propagation distance
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Lau, Kwok-keung. "Interactions of coherent structures in annular jets /." [Hong Kong] : University of Hong Kong, 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B13150364.
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Chow, Kin-keung. "Acceleration of coherent structures in free shear layer /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21710211.
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劉國強 and Kwok-keung Lau. "Interactions of coherent structures in annular jets." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31232632.
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周健強 and Kin-keung Chow. "Acceleration of coherent structures in free shear layer." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31240069.
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Laffay, Paul. "Etude aéroacoustique de la détente d'un écoulement haute pression à travers des plaques perforées." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC020/document.
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Le bruit généré par la détente d'un écoulement sous pression à travers des plaques multi-perforées ou des diaphragmes est étudié expérimentalement. Cette analyse est menée sur deux configurations géométriques distinctes dans lesquelles la plaque perforée est placée à la sortie d'un conduit cylindrique (configuration de jet libre) ou à l'intérieur de celui-ci (configuration de jet confiné).Dans un premier temps, une étude paramétrique acoustique est effectuée pour ces deux configurations en variant les caractéristiques géométriques des plaques perforées et les points de fonctionnement dans des régimes subsoniques et supersoniques. Les différentes sources de rayonnement pouvant apparaitre sur de tels systèmes de détente, sont alors identifiées. Par ailleurs, les effets acoustiques de chacun des paramètres géométriques sont mis en lumière, offrant ainsi une aide à la conception silencieuse de tels systèmes. Dans un second temps, l'intérêt est porté sur l'analyse de la composante à large bande dominante: le bruit de mélange. Cette étude est menée sur la configuration de jet libre et s'appuie sur des visualisations strioscopiques ainsi que sur des mesures de vélocimétrie par image de particules couplées à des acquisitions acoustiques en champ lointain. Dans le cas des diaphragmes, les différents résultats mettent en évidence des mécanismes sources du bruit de mélange similaires à ceux observés dans la littérature pour les jets isolés issus de tuyères. Le rayonnement à l'aval, dominant, est généré par l'interaction de grosses structures turbulentes cohérentes à la fin du cône potentiel du jet, tandis que dans les autres directions, le bruit est généré par la turbulence de petite échelle dans les couches de cisaillement du jet.Pour les plaques multi-perforées, des mécanismes comparables sont également identifiés. Néanmoins, selon la géométrie de ces plaques, deux zones sources distinctes du rayonnement aval sont identifiées favorisant l'apparition de deux bosses dans les spectres en champ lointain. Dans le cas de perforations éloignées, la bosse à plus haute fréquence domine le spectre aval et l'interaction des grosses structures turbulentes se produit au niveau de la fin du cône potentiel des jets. Lorsque les perforations sont en revanche proches, c'est la bosse à basse fréquence qui domine et l'interaction des grosses structures turbulentes cohérentes semble se produire près de la fin du cône potentiel du gros jet équivalent formé à l'aval à partir du mélange de l'ensemble des jets issus des perforations. Dans les autres directions, l'espacement des perforations joue également un rôle important sur le rayonnement acoustique, du fait d'une interaction plus ou moins rapide des jets entre eux. Cela a alors pour effet de modifier les zones de cisaillement et en conséquence le rayonnement acoustique de la même manière que dans la direction avalThe noise generated by the expansion of a pressurized flow through multi-perforated plates or diaphragms is experimentally investigated. The analysis is conducted on two distinct geometrical configurations in which the perforated plate is placed at the outlet of (free jet configuration) or inside (ducted jet configuration) a cylindrical duct.Firstly, an acoustic parametric study is carried out on these two configurations for various perforated plate geometries and for a number of operating points ranging from subsonic to supersonic. The different acoustic sources that can arise from such systems are thus identified. Furthermore, the effect of each geometrical parameter onto the radiated sound field is highlighted, thus providing guidelines for the silent design of such pressure release devices.In a second step, the focus is on the dominant broadband component, that is, the mixing noise. This part of the study is dedicated to the free jet configuration and is based on Schlieren imaging, as well as on Particle Image Velocimetry measurements, both coupled far-field sound measurements.In the diaphragm cases, the aerodynamic results show that the source mechanisms are similar to those reported in the literature about isolated jets from conventional nozzles. The downstream radiation is generated by the interaction of large coherent structures at the end of the jet potential core, while in the other directions it is generated by the small-scale turbulence from the shear layer.For multi-perforated plates, comparable mechanisms are also observed. However, depending on the plate geometry, two distinct source regions contributing to the downstream radiation are identified. They explain the presence of two broadband humps in the far-field spectra. In the case of widely spaced perforations, the higher frequency hump in the downstream spectrum increases and the interaction of the large turbulent structures occurs mainly at the end of the potential core of the small jets issuing the perforations. Conversely, when these perforations are close to each other, the small jets rapidly merge into a single larger one that has a longer potential core. As a result, larger coherent structures interact downstream of the small jet mixing region and therefore, a low-frequency hump dominates the downstream spectrum. In the other directions, the perforation spacing has also a significant impact on the acoustic radiation, due to a more or less rapid interaction of the jets. Consequently, the turbulence, as well as the shear zones of the various mixing layers, are modified. The geometric parameters thus have similar effects on the cross-stream as on the downstream radiation
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Wang, Tao. "Flow and cleaning behaviour of stationary coherent liquid jets impinging on vertical walls." Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648883.
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Spinosa, Emanuele. "Control of near-wall coherent structures in a turbulent boundary layer using synthetic jets." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/control-of-nearwall-coherent-structures-in-a-turbulent-boundary-layer-using-synthetic-jets(3a712f25-67b1-445d-8272-dc54a9f7aadc).html.
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The increase in CO2 emissions due to the significant growth of the level of air traffic expected in the next 40 years can be tackled with new technologies able to reduce the skin friction drag of the new generation aircraft. The ACARE (Advisory Council for Aeronautical Research in Europe), within the Flightpath 2015 Visions, has established stringent targets for drag reduction, which can be achieved only with innovative flow control methods. Synthetic jets are a promising method of flow control, especially for their ability to control the flow without the need of a bleed air supply. The application of synthetic jets for flow separation control has been already proven. Their application can also be extended to skin friction drag reduction in a turbulent flow. Indeed, most of turbulence production in a turbulent boundary layer is related to the dynamics of streamwise streaks and vortices in the near-wall region. Synthetic jets can be used to weaken these structures, to reduce turbulence production and consequently skin friction drag. The effectiveness of synthetic jets for skin friction drag reduction in a turbulent boundary layer has already been explored in a few works. However, there is a lack of understanding on the physical mechanism by which this effect is achieved. The aim of this work is to provide further insight on this. A series of experimental investigations are carried out, using three main measurement techniques: Particle Image Velocimetry, Liquid Crystal Thermography and Constant Temperature Anemometry. The effectiveness of a single round synthetic jet in controlling near-wall streamwise streaks and vortices in a laminar environment, in particular those that develop downstream of a circular cylinder, is verified. Turbulent boundary layer forcing is attempted using a synthetic jet array that produces coherent structures of the same scale as the streamwise vortices and streaks of a turbulent boundary layer. The synthetic jet array is able to create regions of lower velocity in the near-wall and of lower skin friction. A possible physical mechanism behind this has been proposed. With a few minor modification, it is believed that the performance of the synthetic jet array could be significantly improved. This can be achieved especially if the array is installed in a feed-forward control unit, which is only briefly explored in this work. In this case the information on the flow field gathered real-time with wall sensors can help to consistently improve the synthetic jet array performance in terms of skin friction drag reduction.
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Danaila, Ionut. "Etude des instabilites et des structures coherentes dans la zone de proche sortie d'un jet axisymetrique." Aix-Marseille 2, 1997. http://www.theses.fr/1997AIX22113.
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Le developpement spatial et temporel de l'ecoulement de jet axisymetrique, libre, dans la zone de proche sortie, est etudie numeriquement et theoriquement pour de faibles nombres de reynolds. Les simulations numeriques directes (dns) sont realisees avec le code nekton, qui resout les equations de navier-stokes 3d, incompressibles, par une methode d'elements spectraux. L'ecoulement se destabilise spontanement, sans aucun forcage instationnaire, et devient instable via une bifurcation de hopf. Pour des nombres de reynolds legerement super-critiques, les modes helicoidaux m = + 1 et m = 1 dominent l'ecoulement. Une double decomposition en serie de fourier du champ instationnaire permet d'identifier les modes instables et les structures coherentes associees. Pour de grands nombres de reynolds super-critiques, le mode variqueux m = 0 est amplifie et son evolution suit le scenario
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Speth, Rachelle Lea. "Controlling The Development of Coherent Structures in High Speed Jets and The Resultant Near Field." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1447419083.
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Nance, Donald Kirby. "Separating contributions of small-scale turbulence, large-scale turbulence, and core noise from far-field exhaust noise measurements." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19768.
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Thesis (Ph.D)--Aerospace Engineering, Georgia Institute of Technology, 2008.Committee Chair: Ahuja, Krishan K.; Committee Member: Cunefare, Kenneth; Committee Member: Lieuwen, Tim C.; Committee Member: Mendoza, Jeff; Committee Member: Sankar, Lakshmi.
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Favre-Marinet, Michel. "Structures cohérentes dans un jet rond excité." Grenoble 1, 1986. http://www.theses.fr/1986GRE10061.
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Un jet rond est faiblement excite par haut-parleur a la frequence preferentielle du jet permanent. Mesures par anemometrie a fil chaud et a fil froid des champs cinematique et thermique. Par la technique de moyenne de phase on separe les fluctuations periodiques et les fluctuations turbulentes des temperatures et des vitesses. Mise en evidence de la nature tourbillonnaire du mouvement periodique et de la concentration de vorticite dans les structures annulaires. Etude du role joue par les grosses structures dans la diffusion de la chaleur. Comparaison avec la theorie de la stabilite. Etude des interactios entre le mouvement periodique et la turbulence
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Silva, Carlos Frederico Neves Bettencourt da. "Le Rôle des structures cohérentes dans le contrôle et interactions entre échelles dans les jets ronds, plans et coaxiaux." Grenoble INPG, 2001. http://www.theses.fr/2001INPG0060.
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Dans cette etude, le role des structures coherentes pour trois differents problemes d'ecoulements turbulents et en transition est etudie par des simulations numeriques directes et des grandes echelles. La premiere etude concerne le controle des jets circulaires. La generation de jets en bifurcation avec trois forcages differents a ete etudiee par l'analyse de leur dynamique tourbillonnaire. Les taux d'elargissement les plus eleves sont obtenus par l'excitation simultanee du mode dominant et de son sous-harmonique. La possibilite de controler le jet a des nombres de reynolds eleves depend des chances de survie d'une structure tourbillonnaire primaire dans un milieu de forte activite turbulente a petite echelle. La deuxieme etude analyse l'effet des larges tourbillons sur les interactions locales entre echelles resolues et sous-maille dans des jets plans turbulents et en transition. Il est demontre comment la presence de ces structures augmente les echanges energetiques entre different echelles. Les mecanismes les plus importants pour la dynamique des echelles resolues sont l'advection et les interactions pression-vitesse, tandis que la diffusion sous-maille est localement plus importante que le transfert. L'hypothese d'equilibre local n'est pas verifiee a cause des valeurs locales tres elevees d'advection d'energie cinetique sous-maille. La dissipation visqueuse sous-maille se situe surtout au centre des tourbillons. La derniere etude est basee sur l'evolution des tourbillons dans le champ proche d'un jet coaxial. Cette etude analyse les tourbillons primaires resultant de l'instabilite de kelvin-helmholtz et du phenomene de fermeture entre les couches de cisaillement interieure et exterieure du jet. L'etude s'interesse aussi a la formation d'une grande region de recirculation, decrite par des travaux experimentaux anterieurs, et son role dans la generation de tourbillons longitudinaux, de nature differente des tourbillons resultant des instabilites secondaires dans des ecoulements cisailles libres.
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Gardner, Michael D. "Scan-Based Near-Field Acoustical Holography on Partially Correlated Sources." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3167.pdf.
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Leong-Hoï, Audrey. "Etude des techniques de super-résolution latérale en nanoscopie et développement d'un système interférométrique nano-3D." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAD048/document.
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Ce manuscrit de thèse présente l’étude des techniques de super-résolution latérale en nanoscopie optique, qui est une des nouvelles techniques d'imagerie haute résolution, aujourd'hui largement utilisée en biophysique et en imagerie médicale, pour imager et caractériser des nanostructures, tout en conservant les avantages de l'imagerie optique en champ lointain comme un vaste champ, la visualisation et l’analyse en temps réel…Un des défis futurs de la microscopie 3D super-résolue est d’éviter l’utilisation des marqueurs fluorescents. La microscopie interférométrique fait partie des techniques d’imagerie 3D sans marquage permettant la détection de nanostructures. Pour améliorer le pouvoir de détection de ce système optique, un premier protocole de traitement d’images a été développé et implémenté, permettant ainsi de révéler des structures initialement non mesurables. Puis, pour améliorer la résolution latérale du système, une nouvelle technique combinant l’interférométrie et le principe du nano-jet photonique a été développée permettant l’observation d’objets de taille inférieure à la limite de diffraction de l’instrument optiqueThis manuscript presents the study of the lateral super-resolution techniques in optical nanoscopy, which is a new high-resolution imaging method now widely used in biophysics and medical imaging, to observe and measure nanostructures, with the advantages of far field optical imaging, such as a large field of view, visualization and analysis in real time…One of the future challenges of 3D super resolution microscopy is to avoid the use of fluorescent markers. Interferometric microscopy is a 3D label-free imaging technique enabling the detection of nanostructures. To improve the detection capability of this optical system, a first version of a protocol composed of image processing methods was developed and implemented, revealing structures initially unmeasurable. Then, to improve the lateral resolution of the system, a new technique combining interferometry and the principle of the photonic nano-jet has been developed, thus allowing the observation of objects of a size smaller than the diffraction limit of the optical instrument
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Soulisse, Pierre. "Développement d'un dispositif expérimental pour la diffraction d'atomes rapides et étude de surfaces d'isolants ioniques." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00625450.
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Ce mémoire de thèse présente le développement d'un dispositif expérimental spécialement conçu pour l'étude de la diffraction d'atomes rapides et son utilisation pour suivre la croissance de couches minces sur un bâti d'épitaxie. Des études de surfaces de KBr(100) et de NaCl(100) avec ce nouveau dispositif sont présentées. Nous nous sommes intéressés notamment à la forme du potentiel que les atomes perçoivent lorsqu'ils diffusent sur une surface de KBr(100). Nous avons également mis en évidence lors de ces études un nouveau régime de diffraction qui semble correspondre à des mouvements longitudinaux et normaux cohérents. Grâce à des images mieux résolues, nous avons montré comment la diffraction d'atomes rapides permet d'observer et quantifier des défauts topologiques comme la mosaïcité. Une étude d'une surface d'Argent (110) est aussi présentée. Elle a permis d'observer la diffraction d'atomes rapides sur les métaux, montrant ainsi que GIFAD est applicable aux trois types de matériaux (isolants, semi-conducteurs et métaux) et que les processus d'excitations électroniques sur ces surfaces ne détruisent pas complètement la cohérence. Enfin des premiers résultats de GIFAD en tant que technique de suivi de croissance par épitaxie sont présentés dans ce travail.
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Iqbal, Muhammad Owais. "Coherent structure in a turbulent axisymmetric jet via a vector implementation of the proper orthogonal decomposition." 2006. http://etd.nd.edu/ETD-db/theses/available/etd-04172006-140501/.
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Thesis (Ph. D.)--University of Notre Dame, 2006.Thesis directed by Flint O. Thomas for the Department of Aerospace and Mechanical Engineering. "April 2006." Includes bibliographical references (leaves 117-121).
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Riese, Michael. "Study of large-scale coherent structures in the near field and transition regions of a mechanically oscillated planar jet." 2009. http://hdl.handle.net/2440/54150.
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Enhancing the performance of mixing and fluid entrainment by excitation of quasi-steady jets has been a subject of research for more than three decades. During the 1980s a special emphasis was placed on mechanically oscillating planar jets and the possibility to augment thrust of V/STOL aircraft. However, during this time, little attention was paid to the classification of flow regimes, the development of coherent structures or the existence of different regions in the flow within the jet near field. For the present study, a large aspect ratio nozzle was oscillated in the direction transverse to the width of the nozzle in simple harmonic motion. For a constant nozzle height, the stroke length, oscillation frequency and jet velocity were systematically varied. Over 240 flow cases were examined using a novel method of phase-locked flow visualisation. Following an initial analysis of the acquired data, a small subset of flow conditions was selected for further quantitative investigation using Particle Image Velocimetry (PIV). The phase-locked flow visualisation led to the identification and classification of three separate flow regimes, the Base Flow, the Resonant Flow and the Bifurcation Flow Regimes. Each regime is linked to the other regimes by the presence of a small number of repetitive coherent structures in the form of starting and stopping vortices. The analysis revealed a relationship between the stroke-to-nozzle height ratio and the ratio of the forcing frequency to the natural vortex shedding frequency in the planar jet. This directly contradicts the relationship between the Strouhal and Reynolds numbers of the jet that was proposed by previous investigators. Comparison of phase-locked PIV and flow visualisation data confirms both, the validity of the new regime classification and the identification of relevant large-scale structures. Time-averaged vorticity data are also used to further illustrate the differences between the three flow regimes. Investigation of the time-averaged qualitative data for the Base and Resonant Flow Regimes show that three distinct flow regions exist within both regimes. Adjacent to the nozzle is the initial formation region, where all large-scale structures form. This is followed by a coherent near-field region in which the jet exhibits very little spread for both the Base and Resonant Flow Regimes. Within this region no pairing of the large-scale vortices from the opposing sides of the flow can be found. This region is followed by a transition region that is marked by the sudden breakup and dissipation of all visible large-scale coherent structures. The vortex formation distance is then investigated using the available PIV data and compared with the results of previous investigations. The data show that the formation distance depends on the jet velocity, oscillation frequency and the stroke length. The agreement with previous data is poor due to differences in the method of measurement. Quantitative data are also used to investigate the centreline velocity decay in relation to changes of the jet Reynolds number and stroke-to-nozzle height ratio. The results show that the velocity decay rate increases with increasing stroke length as is expected from findings of earlier studies. In addition the centreline velocity decay rates in the mean jet transition region appear to be constant for each stroke length in the cases examined. Finally, conclusions are drawn and recommendations for future work are presented.http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1349701
Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2009
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Barannyk, Oleksandr. "Shear layer instabilities and flow-acoustic coupling in valves: application to power plant components and cardiovascular devices." Thesis, 2014. http://hdl.handle.net/1828/5372.
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In the first part of this dissertation, the phenomenon of self-sustained pressure os-cillations due to the flow past a circular, axisymmetric cavity, associated with inline gate valves, was investigated. In many engineering applications, such as flows through open gate valves, there exists potential for coupling between the vortex shedding from the up-stream edge of the cavity and a diametral mode of the acoustic pressure fluctuations. The effects of the internal pipe geometry immediately upstream and downstream of the shal-low cavity on the characteristics of partially trapped diametral acoustic modes were in-vestigated numerically and experimentally on a scaled model of a gate valve mounted in a pipeline that contained convergence-divergence sections in the vicinity of the valve. The resonant response of the system corresponded to the second acoustic diametral mode of the cavity. Excitation of the dominant acoustic mode was accompanied by pressure oscillations, and, in addition to that, as the angle of the converging-diverging section of the main pipeline in the vicinity of the cavity increased, the trapped behavior of the acoustic diametral modes diminished, and additional antinodes of the acoustic pressure wave were observed in the main pipeline.
In addition to that, the effect of shallow chamfers, introduced at the upstream and/or downstream cavity edges, was investigated in the experimental system that con-tained a deep, circular, axisymmetric cavity. Through the measurements of unsteady pressure and associated acoustic mode shapes, which were calculated numerically for several representative cases of the internal cavity geometry, it was possible to identify the configuration that corresponded to the most efficient noise suppression. This arrangement also allowed calculation of the azimuthal orientation of the acoustic modes, which were classified as stationary, partially spinning or spinning. Introduction of shallow chamfers at the upstream and the downstream edges of the cavity resulted in changes of azimuthal orientation and spinning behaviour of the acoustic modes. In addition, introduction of splitter plates in the cavity led to pronounced change in the spatial orientation and the spinning behaviour of the acoustic modes. The short splitter plates changed the behaviour of the dominant acoustic modes from partially spinning to stationary, while the long split-ter plates enforced the stationary behaviour across all resonant acoustic modes.
Finally, the evolution of fully turbulent, acoustically coupled shear layers that form across deep, axisymmetric cavities and the effects of geometric modifications of the cavity edges on the separated flow structure were investigated using digital particle image velocimetry (PIV). Instantaneous, time- and phase-averaged patterns of vorticity pro-vided insight into the flow physics during flow tone generation and noise suppression by the geometric modifications. In particular, the first mode of the shear layer oscillations was significantly affected by shallow chamfers located at the upstream and, to a lesser degree, the downstream edges of the cavity.
In the second part of the dissertation, the performance of aortic heart valve pros-thesis was assessed in geometries of the aortic root associated with certain types of valve diseases, such as aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. By varying the aortic root geometry, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.Graduate
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Amini, Noushin. "Turbulent Flow Analysis and Coherent Structure Identification in Experimental Models with Complex Geometries." Thesis, 2011. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10659.
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Turbulent flows and coherent structures emerging within turbulent flow fields have been extensively studied for the past few decades and a wide variety of experimental and numerical techniques have been developed for measurement and analysis of turbulent flows. The complex nature of turbulence requires methods that can accurately estimate its highly chaotic spatial and temporal behavior. Some of the classical cases of turbulent flows with simpler geometries have been well characterized by means of the existing experimental techniques and numerical models. Nevertheless, since most turbulent fields are of complex geometries; there is an increasing interest in the study of turbulent flows through models with more complicated geometries.
In this dissertation, characteristics of turbulent flows through two different facilities with complex geometries are studied applying two different experimental methods. The first study involves the investigation of turbulent impinging jets through a staggered array of rods with or without crossflow. Such flows are crucial in various engineering disciplines. This experiment aimed at modeling the coolant flow behavior and mixing phenomena within the lower plenum of a Very High Temperature Reactor (VHTR). Dynamic Particle Image Velocimetry (PIV) and Matched Index of Refraction (MIR) techniques were applied to acquire the turbulent velocity fields within the model. Some key flow features that may significantly enhance the flow mixing within the test section or actively affect some of the structural components were identified in the velocity fields. The evolution of coherent structures within the flow field is further investigated using a Snapshot Proper Orthogonal Decomposition (POD) technique. Furthermore, a comparative POD method is proposed and successfully implemented for identification of the smaller but highly influential coherent structures which may not be captured in the full-field POD analysis.
The second experimental study portrays the coolant flow through the core of an annular pebble bed VHTR. The complex geometry of the core and the highly turbulent nature of the coolant flow passing through the gaps of fuel pebbles make this case quite challenging. In this experiment, a high frequency Hot Wire Anemometry (HWA) system is applied for velocity measurements and investigation of the bypass flow phenomena within the near wall gaps of the core. The velocity profiles within the gaps verify the presence of an area of increased velocity close to the outer reflector wall; however, the characteristics of the coolant flow profile is highly dependent on the gap geometry and to a less extent on the Reynolds number of the flow. The time histories of the velocity are further analyzed using a Power Spectra Density (PSD) technique to acquire information about the energy content and energy transfer between eddies of different sizes at each point within the gaps.
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Müller, Christian. "Zeitaufgelöste Fluoreszenzspektroskopie unimolekularer Reaktionen im Überschalldüsenstrahl: trans-cis-Photoisomerisierung, Phenylringtorsion, intramolekularer Wasserstoffatomtransfer." Doctoral thesis, 2005. http://hdl.handle.net/11858/00-1735-0000-0006-B0C2-1.
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