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1
Riaud, Antoine Jean-Pierre René. "Etude des potentialités offertes par la synthèse de champs d'ondes acoustiques de surface pour l'actionnement de liquides et la manipulation sans contact." Thesis, Ecole centrale de Lille, 2016. http://www.theses.fr/2016ECLI0010/document.
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Lorsque des ondes acoustiques de surface rayonnent dans des fluides, elles provoquent deux effets non linéaires : la pression de radiation et le streaming acoustique. Ces deux effets ont trouvé un grand nombre d’applications pour la microfluidique digitale, la manipulation sans contact et le tri cellulaire. Néanmoins, ces systèmes se heurtent à deux limites. D’une part, chaque application requiert une onde acoustique spécifique : il n’existe pas de dispositif multifonction à ce jour. D’autre part, l’exploration des fonctionnalités offertes par les ondes de surface les plus simples (ondes planes, ondes focalisées) n’a pas permis de réaliser des pinces sélectives permettant de manipuler individuellement des particules ou cellules indépendamment de leurs voisines.Dans une première partie de la thèse, nous développons deux méthodologies pour synthétiser des champs complexes d’ondes de surface. La première méthode utilise un réseau de 32 peignes interdigités contrôlé par la technique du filtre inverse pour générer des champs sur demande. La seconde résout un problème inverse afin de concevoir un transducteur holographique générant spécifiquement le champ demandé. Dans la seconde partie de la thèse, nous utilisons le filtre inverse pour (i) réaliser un laboratoire sur puce multifonction et (ii) étudier le potentiel d’ondes de surface particulières appelées ondes de surface tourbillonnaires. Ces ondes permettent une manipulation sélective et sans contact d’objets microscopiques. Nous terminons la thèse en équipant un microscope d’un transducteur holographique de vortex acoustiques afin de réaliser une manipulation sélective et sans contact de cellules<br>When surface acoustic waves radiate in nearby fluids, they trigger two nonlinear effects: acoustic radiation pressure and acoustic streaming. These two effects find numerous applications for digital microfluidics, contactless manipulation and biological cell sorting. Nonetheless, these systems face two limitations. On the one hand, each application requires a specific acoustic wave: there is no multifunction device so far. On the other hand, search for functionalities offered by simple surface acoustic waves (plane and focused waves) has failed to provide a selective tweezers able to manipulate individual particles or cells independently of their neighbors. In the first part of this thesis, we develop two methods to synthesize complex surface acoustic wave fields. The first one employs an array of 32 interdigitated transducers controlled by the inverse filter to generate arbitrary fields on demand. The second method solves an inverse problem to design a holographic transducer to generate a predefined field. In the second part of the thesis, we use the inverse filter to (i) implement a multifunction lab on a chip and (ii) investigate the potentialities of a special type of surface acoustic waves called swirling surface waves. These waves enable a selective and contactless manipulation of microscopic objects. We conclude the thesis by integrating a holographic acoustical vortex transducer on a microscope in order to selectively manipulate biological cells without contact
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Williams, Julian Scott. "Nonlinear problems in vortex sound." Thesis, University of Leeds, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305854.
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Hammoud, A. H. "Vortex induced acoustic resonances in a rectangular duct." Thesis, Swansea University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637212.
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This thesis reports the results of an experimental investigation of vortex induced acoustic resonances in a rectangular duct containing two plates located in tandem. The effects of varying the plate spacing and the leading edge shape were investigated. Tests were conducted in both an open channel and in a rectangular wind tunnel. Measurements were made of acoustic amplitude, frequency and phase relationship between the acoustic field and cortex shedding. Short tests were also conducted with an absorber unit mounted in the wind tunnel wall. Results of tandem plate configuration showed in most cases the presence of two discrete resonances during which the phase of shedding of the first resonance is similar to that of the upstream plate alone while during the second resonance, there was a much smaller variation in phase. In between the two resonances, there was a sudden jump in phase and amplitude as the flow velocity was further increased due to the re-excitation of the resonance. The effect of varying the plate spacing has a marked effect on both the velocity range at which the resonances were excited and the natural Strouhal number. At some plate spacings, these two resonances were excited alternately while at other spacings, there was a wide break between them. The application of tandem plates as a general means to suppress resonance was unsuccessful. It was also found that resonance can be totally suppressed by using an absorber unit.
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Tutar, Mustafa. "Computational modelling of vortex shedding from offshore risers." Thesis, University of Hertfordshire, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.268046.
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Li, Wenhua. "Flow/acoustics mechanisms in two- and three-dimensional wake vortices." Diss., Manhattan, Kan. : Kansas State University, 2007. http://hdl.handle.net/2097/400.
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Harris, Ashley M. "Accoustic properties of toroidal bubbles and contruction of a large apparatus /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FHarris.pdf.
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Gopalan, Gaurav. "Quasi-static acoustic mapping of helicopter blade-vortex interaction noise." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/1757.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.<br>Thesis research directed by: Aerospace Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Nair, Ashwati. "Capturing Vortex Dynamics to Predict Acoustic Response using Machine Learning." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546427424013197.
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Harris, Ashley M. "Acoustic properties of toroidal bubbles and construction of a large apparatus." Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1675.
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Approved for public release, distribution is unlimited<br>When a burst of air is produced in water, the result can be a toroidal bubble. This thesis is concerned with experimental investigations of three acoustical properties of toroidal bubbles: (i) propagation through high-intensity noise, (ii) emission, and (iii) scattering. In (i), an attempt to observe a recent prediction of the acoustic drag on a bubble is described, which is analogous to the Einstein-Hopf effect for an oscillating electric dipole in a fluctuating electromagnetic field. No effect was observed, which may be due to insufficient amplitude of the noise. In (ii), observations of acoustic emissions of volume oscillations of toroidal bubbles are reported. Surprisingly, the emission occurs primarily during the formation of a bubble, and is weak in the case of very smooth toroidal bubbles. In (iii), we describe an experiment to observe the effect of a toroidal bubble on an incident sound field. In addition to the acoustical investigations, we describe the construction of a large hallway apparatus for further investigations and for hands-on use by the public. The tank has cross section 2 feet by 2 feet and height 6 feet, and the parameters of reservoir pressure and time between air bursts are adjustable by the observer.<br>Lieutenant, United States Navy
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Sanchez, Padilla Benjamin. "Rotational mechanical effects driven by the transfer of the acoustic orbital angular momentum." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0452.
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Ce travail de thèse traite des effets mécaniques rotationnels résultant de l'interaction son-matière en présence de transfert de moment angulaire de nature orbitale. Deux approches expérimentales sont mis en œuvre, toutes deux utilisant des ondes ultrasonores se propageant dans l'air et des objets de taille centimètrique obtenus par impression 3D imprimés et se comportant comme des miroirs structurés imprimant un profil de phase hélicoïdal au champ réfléchi. Le résultat principal consiste en la mesure directe quantitative du moment angulaire orbital porté par un faisceau vortex via deux approches indépendantes. La première est basée sur l’utilisation d’un miroir hélicoïdal placé à l’interface air-eau, et la seconde repose sur le développement d'un oscillateur mécanique de torsion forcé par le transfert de moment angulaire<br>We study the rotational mechanical effects resulting from sound-matter interaction in the presence of orbital angular momentum transfer. A set of experimental realizations are implemented by using ultrasonic waves propagating in the air and 3D printed centimeter-sized objects acting as structured mirrors imparting a helical phase profile to the reflected wave. The main result consists of the quantitative direct measurement of the orbital angular momentum carried by acoustic vortex beams via two independent approaches. The first one is based on the use of a freely rotating helical mirror placed at air-water interface, and the second one relies on the development of a torsional mechanical oscillator driven by acoustic orbital angular momentum
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Rodenhiser, Rebecca J. "An Ultrasonic Method for Aircraft Wake Vortex Detection." Digital WPI, 2005. https://digitalcommons.wpi.edu/etd-theses/1004.
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"This thesis documents the experimental proof of concept study for an ultrasonic method of wake vortex detection. A new acoustic technique is utilized to measure the circulation produced in the wake of lift-generating aircraft. Ultrasonic signals are transmitted in a path around the wake vortex, and are used to determine the average in-line velocity component along the acoustic path. It is shown herein that this velocity component is directly proportional to the net circulation value within the acoustic path. This is the first study to take this methodology and implement it in a realistic airport setting. This project included constructing a prototype and conducting field tests to prove the validity of this technology in a realistic environment setting. During field tests an acoustic path enclosed the vorticity shed behind one wing of a Piper PA-28 aircraft. Fourteen initial test flights were conducted in calm atmospheric conditions, and results show circulation values measured are comparable in magnitude and direction to expected circulations generated by the Piper PA-28 aircraft. Additional testing in various atmospheric conditions revealed the scope of practice for such a measurement technology. This study demonstrates the validity of the acoustic method in detecting aircraft wake vortices. Future investigations and applications utilizing this technique are discussed within."
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Chuang, Fu-sheng. "The interacting boundary layer and acoustic field generated by vortex motion /." The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487266691096485.
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Kelly, Mary E. "Predicting the high-frequency airloads and acoustics associated with blade-vortex interaction." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1513/.
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As a rotorcraft descends or manoeuvres, the interactions which occur between the rotor blades and vortical structures within the rotor wake produce highly impulsive loads on the blades and with these a highly intrusive external noise. Brown’s Vorticity Transport Model has been used to investigate the influence of the fidelity of the local blade aerodynamic model on the quality of the prediction of the high-frequency airloads associated with blade-vortex interactions and thus on the accuracy with which the acoustic signature of the aircraft can be predicted. Aerodynamic, wake structure and acoustic predictions using the Vorticity Transport Model are compared against the HART II wind tunnel data for an experimental rotor based on the characteristics of the Bo105 rotor. The model can resolve very accurately the structure of the wake, and allows significant flexibility in the way that the blade loading can be represented. The predictions of two models for the local blade aerodynamics are compared for all three of the HART II flight cases. The first model is a simple lifting-line model and the second is a somewhat more sophisticated lifting-chord model based on unsteady thin aerofoil theory. The predicted positions of the vortex cores agree with measured data to within a fraction of the blade chord, and the strength of the vortices is preserved to well downstream of the rotor, essentially independently of the resolution of the calculation or the blade model used. A marked improvement in accuracy of the predicted high-frequency airloads and acoustic signature of the HART II rotor is obtained when the lifting-chord model for the blade aerodynamics is used instead of the lifting-line type approach. Errors in the amplitude and phase of the loading peaks are reduced and the quality of the prediction is affected to a lesser extent by the computational resolution of the wake. Predictions of the acoustic signature of the rotor are similarly affected, with the lifting-chord model at the highest resolution producing the best representation of the distribution of sound pressure on the ground plane below the rotor.
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Bernard, Ianis. "Manipulation de particules et génération de vortex par ondes acoustiques de surface en géométrie microfluidique." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY015/document.
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Dans cette thèse, nous nous sommes intéressés à la manipulation par forces acoustiques de particules et de fluide à petite échelle. Nous avons construit pour cela un système où des ondes acoustiques de surface sont générées sur un substrat piézo-électrique de LiNbO3 à partir d’électrodes interdigitées, puis émises dans une cavité microfluidique, à une fréquence de l’ordre de 37 MHz soient des longueurs d’onde d'environ 100 µm.Dans le cas où deux ondes stationnaires sont émises perpendiculairement et à la même fréquence, nous montrons théoriquement et expérimentalement la présence d’un terme d’interférence qui, selon le déphasage temporel entre les deux ondes, va modifier la localisation des ventres et nœuds de pression dans la cavité, mais aussi donner lieu à des tourbillons dont l’axe de rotation est perpendiculaire au substrat.Nous montrons théoriquement que ces tourbillons proviennent de la forme particulière des écoulements redressés en paroi et, en injectant des microparticules, nous avons déterminé des vitesses angulaire de plusieurs rad/s. Leur disposition spatiale suit une périodicité d'une demi-longueur d'onde, et leur sens de rotation est alternée entre tourbillons voisins horaires et anti-horaires. Que cela soit avec des globules rouges ou des particules de latex, nous avons identifié une dynamique complexe, avec la formation d’agrégats au centre des vortex sous l’effet des forces de radiations et une répartition en différents niveaux par effet de lévitation acoustique dans l’épaisseur de la cavité, en accord avec l'analyse.Dans le cas où des particules d’une dizaine de micromètres sont utilisées, nous observons, outre l’arrangement des objets dans les nœuds de pression, une rotation individuelle de chaque objet, à des vitesses angulaires plus élevées. Nous interprétons ces observations comme la première mise en évidence d’un couple d’origine acoustique sur des microparticules et cellules biologiques à partir d’ondes acoustiques de surface, constituant l’analogue à petite échelle des effets de couples acoustiques décrits par Busse et Wang en 1981.La thèse propose une description détaillée des différentes montages électriques et microfluidiques, avec les différentes étapes conduisant à un laboratoire sur puce permettant la génération tant de forces que de couples acoustiques, mais aussi la manière de qualifier électriquement et optiquement ses performances<br>The focus of this PhD thesis was on particles and fluid handling through acoustic forces, at a very small scale. For this purpose, we built a micro-system based on surface acoustic waves emitted from interdigitated electrodes on a lithium niobate piezoelectric substrate. Those waves then leak into a fluid contained in a microfluidic cavity, at a frequency of 37 MHz, leading to 100 µm wavelengths.If two stationnary waves are emitted perpendicularly and at the same frequency, we theoretically and experimentally show evidence of interferences that can, depending on the time phase shift between them, nto only alter the positions of pressure nodes and antinodes in the acoustic cavity, but also give birth to acoustic vortices which axis is normal to the substrate surface.We theoretically show that those vortices come from the special behaviour of acoustic streaming due to a moving surface. Then, while injecting microparticles in the cavity, we measure angular velocities of a few rad/s. Those vortices spatial disposition follows a half-wavelength period, and their rotation alternates between neighbours: clockwise or anticlockwise. We identify a complex dynamic concerning their 3D structure, since small particles tend to aggregate in vertical columns in the center of the vortex because of radiation forces, with a vertical modulation in the height of the cavity, in good agreement with theoretical predictions.When 10 µm large particles are used instead, we observe individual rotations, even for spherical objects, with higher rotation velocities. We believe those observations to be the first evidence of an acoustic net torque exerted on micro-objects such as biological cells or beads stemming from surface acoustic waves, thus a small scale equivalent of acoustic torques described by Busse and Wang in 1981.This manuscript develops a detailed description of both electric and microfuidic devices, giving the successive steps leading to a lab on chip designed to generate acoustic forces and torques at once, and also the method for qualifying and quantifying electrically and optically its performances
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MEN'SHOV, Igor, and Yoshiaki NAKAMURA. "On Instability of Acoustic Waves Propagating in Stratified Vortical Flows." The Japan Society of Mechanical Engineers, 2002. http://hdl.handle.net/2237/9091.
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Roth, Brian D. "Acoustic source and data acquisition system for a helicopter rotor blade-vortex interaction (BVI) noise reduction experiment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA326229.
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Thesis (M.S. in Engineering Acoustics) Naval Postgraduate School, December 1996.<br>"December 1996." Thesis advisor(s): Robert M. Keolian, Steven R. Baker. Includes bibliographical references (p. 59). Also available online.
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O'Connor, Jacqueline. "Response of a swirl-stabilized flame to transverse acoustic excitation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/43756.
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This work addresses the issue of transverse combustion instabilities in annular gas turbine combustor geometries. While modern low-emissions combustion strategies have made great strides in reducing the production of toxic emissions in aircraft engines and power generation gas turbines, combustion instability remains one of the foremost technical challenges in the development of next generation combustor technology. To that end, this work investigates the response of a swirling flow and swirl-stabilized flame to a transverse acoustic field is using a variety of high-speed laser techniques, especially high-speed particle image velocimetry (PIV) for detailed velocity measurements of this highly unsteady flow phenomenon. A description of the velocity-coupled transverse instability mechanism is explained with companion measurements describing each of the velocity disturbance pathways. Dependence on acoustic frequency, amplitude, and field symmetry is discussed. Significant emphasis is placed on the response of a swirling flow field to a transverse acoustic field. Details of the dynamics of the vortex breakdown bubble and the shear layers are explained using a wide variety of measurements for both non-reacting and reacting flow cases. This thesis concludes with an overview of the impact of this work and suggestions for future research in this area.
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Carr, M. I. "The excitation of acoustic resonances in an axial flow compressor stage by vortex shedding from aerofoil section blading." Thesis, Swansea University, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636209.
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In recent years continuing development of the axial flow compressor for use in the aero-engine has increased its susceptibility to unsteady flow phenomena which can cause severe blade vibration. A source which has emerged and become of considerable importance is excitation by acoustic resonances. An experimental investigation in a single stage axial flow compressor rig has been performed to ascertain whether acoustic resonances can be excited by vortex shedding from loaded aerofoil section blades. A further experimental programme, to study further the effect of inter-row spacing, was peformed in both an open jet facility and a wind tunnel facility with a tandem plate arrangement. Results showed that acoustic resonances could be excited in a compressor stage in which there was severe blade loading. The speed range over which the resonances were excited was demonstrated to be not only a function of the degree of loading but also the inter-row spacing. Vortex shedding will drive a resonance when the shedding is correlated by the resonant acoustic field and interaction between the vortices and the acoustic field in the vicinity of the blades may result in a net positive input of acoustic energy. As a result the phase of the acoustic field as vortices pass over the trailing edge of the shedding blades and the leading and trailing edges of the downstream blades, control the energy generation. The inter-row spacing controls the phase of the downstream blade interaction and therefore is a major factor influencing the resonant acoustic amplitude. As well as the fundamental acoustic mode, a resonance can also drive significant blade vibration in two other consequential frequency bands which are: a) Sum and Difference frequency bands due to acoustic non-linearity and b) Sidebands of the fundamental modes due to spatial modulation effects caused by flow distortions.
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Harris, Christopher A. "Acoustics and Fluid Dynamics Studies of High Speed Jet Noise Reduction Devices." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1218687698.
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Murray, Henry Hall IV. "Turbulence and Sound Generated by a Rotor Operating Near a Wall." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/71332.
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Acoustic and aerodynamic measurements have been carried out on a rotor operating in a planar turbulent boundary layer near a wall for a variety of thrust conditions and yaw angles with respect to the inflow. At the highest thrust condition a strong flow reversal in the wall-rotor tip gap was observed. Average velocity fields filtered by the angular position of the rotor show that the flow reversal is fed by jets of fluid that tend to form below the blade as it passes by the wall. Instantaneous velocity measurements show the presence of strong vortices in the tip gap. These vortices were characterized and found to be both stronger and more numerous on the downstroke side of the tip gap. Additionally, vortices with the same handedness as the bound circulation in the blade were more numerous and only located on the downstroke side of the tip gap. Those with the opposite handedness were found to be only located on the upstroke side. Unexpectedly strong far-field acoustic response at the blade passage frequency at this highest thrust condition and is believed to be due to an interaction of the blade tip with these vortices. At moderate thrust, when the rotor was yawed toward the downstroke side the far field acoustic response at the blade passage frequency was found to increase. The opposite was true as it was yawed toward the upstroke side. At the highest thrust, however the unyawed rotor had the strongest blade passage frequency response which is believed to be due to stronger vortex-tip interaction in this case.<br>Master of Science
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Besnard, Stephane. "Performance and application of the Modular Acoustic Velocity Sensor (M.A.V.S.) current meter for laboratory measurements." Texas A&M University, 2004. http://hdl.handle.net/1969.1/1538.
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Every type of current meter is different and has its proper characteristics. Knowing the performance of a current meter is essential in order to use it properly either for field or laboratory measurements (such as in the Offshore Technology Research Center wave basin). A study of the MAVS (Modular Acoustic Velocity Sensor) in a wave basin is a first step essential for later deployment in real studies.
This thesis is based on data obtained from different series of laboratory measurements conducted in the OTRC wave basin. The objective of the first part of the study was to characterize the MAVS frequency response using benchmarks such as tow tests or wave tests. These benchmarks allowed us not only to characterize the sensor but also to eventually correct some of the measurement distortions due to flow blockage, vortex shedding, or vibrations of the mounting structure, for example.
After the preliminary study was done, we focused on the potential use of the MAVS in the OTRC wave basin. Indeed, in the case of a study of a scale model in the wave basin, the stresses applied to the model have to be accurately known. In the case of current-induced loads, this includes contributions from both the mean flow and the turbulence. Thus, after correcting the values measured by the MAVS, a mapping of the current jet was executed to determine its three-dimensional structure in the wave basin.
Knowing the structure of the current in the OTRC wave basin, it was then possible to define a domain in which the current can be considered uniform with a certain tolerable error. This domain of uniformity will allow us to validate the use of the OTRC wave basin to study large models such as FPSOs (Floating Production, Storage and Offloading Units).
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Li, Bo. "Aerodynamic and acoustic analysis of the tip-leakage flow past a single ailfoil." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC042/document.
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L'écoulement de jeu est un phénomène très important dans les turbomachines. Il provient du mouvement relatif entre la pale et la paroi d'extrémité, et la différence de pression à travers la pale. L'écoulement de jeu est extrêmement complexe pour sa nature tridimensionnelle et instable, et son existence conduit à de nombreux effets défavorables, par exemple, les pertes de performance aérodynamique et les émissions de bruit. C'est pourquoi l'écoulement de jeu a motivé de nombreuses recherches expérimentales et numériques. Afin d'améliorer la compréhension du écoulement de jeu et le bruit de large bande associé, une campagne de recherche a été menée au LMFA. En ce qui concerne l'écoulement de jeu, cette campagne de recherche comprend une expérience avec des technologies de mesure avancées, un calcul zonal LES et une série de calculs RANS / URANS. L'expérience et les simulations considèrent une configuration simple de l'écoulement de jeu à un faible nombre de Mach. Les résultats expérimentaux et numériques sont analysés de façon systématique et approfondie dans la présente étude. Enfin, des efforts sont déployés pour la modélisation et la prédiction du bruit à large bande avec des résultats expérimentaux et numériques. On observe dans l'expérience un système à multiple-tourbillon, avec une tourbillon de jeu intense. Les différentes analyses sur les caractéristiques d'écoulement montrent un bon accord entre l'expérience et le ZLES dans la région du écoulement de jeu. L'approche zonale (RANS-LES) s'avère être un outil puissant pour fournir une description détaillée du écoulement de jeu, avec un coût de calcul limité. Cependant, les calculs RANS et URANS surestiment globalement la diffusion de la tourbillon. En outre, l'oscillation du tourbillon de jeu est étudiée en utilisant des champs instantanés de PIV et l'amplitude d'oscillation est évaluée. La réponse dynamique de la tourbillon de jeu est également étudiée avec URANS aux fréquences choisies. Deux modèles de prédiction du bruit en champ lointain, correspondant à deux sources acoustiques différentes, sont reformulés et mis en oeuvre avec les données de champ proche des simulations numériques. Ces prédictions sont comparées aux mesures à champ lointain. En utilisant les données ZLES, le modèle de l’écoulement de jeu sur-estime le bruit généré dans la région de jeu. Le modèle de bruit de bord de fuite est implémenté avec les données ZLES et les données RANS et fournit une très bonne prédiction dans une large bande de fréquence<br>The tip-leakage flow is a common flow feature in turbomachines. It originates from the relative motion between the blade tip and the end-wall, and the pressure difference across the blade. The tip-leakage flow is extremely complex for its three-dimensional unsteady nature, and its existence leads to many unfavourable effects, such as aerodynamic performance losses and noise emissions. These issues have motivated extensive experimental and numerical researches from both aerodynamic and aeroacoustic points of view. In order to improve the understanding of the tip-leakage flow and its associated broadband noise, a research campaign has been carried out at LMFA. Regarding the tip-leakage flow, this research campaign includes an experiment with advanced measurement technologies, a zonal LES computation and a series of RANS/URANS computations. Both the experiment and the simulations consider a single-airfoil configuration at low Mach number. Experimental and numerical results are analysed systematically and thoroughly in the current study. Finally, efforts are put on the broadband noise modelling and prediction based on the experimental and numerical results. A multi-vortex system with an intense tip-leakage vortex is observed in the experiment. The various analyses of the flow characteristics show a good agreement between the experiment and the ZLES in the blade tip region. The zonal (RANS-LES) approach proves itself to be a powerful tool to provide a detailed description of the tip-leakage flow, with a limited computational cost. However, the RANS and URANS computations globally over-estimate the diffusion of the tip-leakage vortex. Furthermore, the random oscillation of the tip-leakage vortex is investigated using PIV instantaneous flow fields and the wandering amplitude is evaluated. The dynamic response of the tip-leakage vortex is also studied with URANS at selected frequencies. Two far-field noise prediction models, corresponding to two different acoustic sources, are reformulated and implemented with the near-field data from the numerical simulations. These predictions are compared to the far-field measurements. Using the ZLES data as input, the blade-tip self-noise model is found to over-estimate the noise generated in the blade-tip region. The trailing-edge noise model is implemented with the time-averaged ZLES and the RANS near-field data, and yields a very good prediction within a broad range of frequency
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Rask, Olaf Haller. "The Reduction of Mixing Noise and Shock Associated Noise using Chevrons and other Mixing Enhancement Devices." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1223056142.
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Assoum, Hassan. "Étude expérimentale des couplages entre la dynamique d’un jet qui heurte une plaque fendue et l’émission sonore générée." Thesis, La Rochelle, 2013. http://www.theses.fr/2013LAROS420/document.
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Un jet heurtant une plaque fendue peut générer, dans certaines configurations, des nuisances sonores. En effet, l’interaction de l’écoulement et de l’obstacle au niveau de la fente, sous certaines conditions, donne naissance à une perturbation remontant l’écoulement et pouvant contrôler son détachement à sa naissance. La perturbation produite par cette boucle de rétroaction optimise le transfert d’énergie du champ aérodynamique du jet vers le champ acoustique rayonné. Afin d’appréhender la dynamique tourbillonnaire, d’analyser les couplages entre cette dernière et les émissions sonores générées et de mieux comprendre les phénomènes responsables de ces nuisances, un dispositif expérimental basé sur de la métrologie laser a été réalisé. Ce système permet, d’une part, la génération de l’écoulement et la maitrise de ses paramètres (confinement, vitesse, forme,…) et d’autre part, la réalisation de plans lasers et de mesures par imagerie de particules (PIV). Ainsi le travail présenté dans ce manuscrit concerne les couplages qui existent entre la dynamique de l’écoulement heurtant une plaque fendue et les champs acoustiques générés. Les mesures de champs cinématiques d’un jet plan heurtant une plaque fendue par Vélocimétrie par Images de Particules (PIV) sont réalisées simultanément avec des mesures de champs acoustiques. Après avoir caractérisé les écoulements étudiés, on présente par des graphes spatio-temporels, les corrélations entre les signaux acoustiques et les vitesses de l’écoulement depuis la sortie du jet jusqu’à son arrivée à la plaque fendue. Ces corrélations sont calculées de deux manières : à partir de signaux bruts dans un premier temps, puis, dans un second temps, avec une méthode de pré-blanchiment (terme anglo-saxon : ‘’pre-whitening’’). Cette méthode vise à mettre en exergue l’existence d’une instabilité globale du jet qui existe dans les signaux analysés. Cette instabilité est importante pour la boucle de rétroaction des sons auto-entretenus, mais quasiment masquée devant les phénomènes principaux dominants (tourbillons primaires) dans le calcul des inter-corrélations<br>Self-sustaining sounds related to aero-acoustic coupling occurs in impinging jets when a feedback loop is present between the jet exit and a slotted plate: the downstream-convected coherent structures and upstream-propagating pressure waves generated by the impingement of the coherent structures on the plate are phase locked at the nozzle exit. The upstream-propagating waves excite the thin shear layer near the nozzle lip and result in periodic coherent structures. The period is determined by the convection speed of the coherent structures and the distance between the nozzle and the plate. Simultaneous measurements of the velocity fields and the acoustic waves in a plane jet impinging a slotted plate were performed using time-resolved particle image velocimetry (PIV) and a microphone. A better understanding of the flow physics and the aero-acoustic coupling are obtained thanks to spatio-temporal cross-correlations between the transverse velocity and the acoustic signals. Cross-correlations are calculated using two different methods: classical analysis of the original signals and by developing a pre-whitening technique. The latter method is useful for analyzing small random signals superimposed on a high amplitude pure tone
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Petchenko, Arkady. "Numerical study of flame dynamics." Doctoral thesis, Umeå : Institute of Physics, Umeå Univ, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1313.
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Goyal, Rahul. "FLOW FIELD IN A HIGH HEAD FRANCIS TURBINE DRAFT TUBE DURING TRANSIENT OPERATIONS." Doctoral thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-66297.
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Hydroelectricity plays an important role to balance the stability of grid network. In order to improve the stability of presently high loaded grids, hydropower plants are being operated over a wide range of operations and experiencing frequent start-stop, load rejection, and load acceptance. The turbines need to sustain sudden change in their operating condition to balance the grid frequency. Francis turbines have been widely used because of their wider operating range and higher stability in operation during rapid load variation. This has resulted in severe damage to the turbines as they are not normally designed to operate under such transient conditions. Several low and high frequency pressure fluctuations prevail during transients operating conditions. Generally, wall pressure measurements are performed which may not provide sufficient information to investigate the flow instabilities related to these fluctuations. Thus, the main objective of the present work is to simplify and perform optical measurements in a turbine during transient operating conditions to investigate the flow field. The measurements have been performed at the Water Power Laboratory using a high head model Francis turbine. The turbine is a 1:5.1 scale down model of a prototype operating at the Tokke Power Plant, Norway. The model runner diameter, net head, and discharge at the best efficiency point (BEP) were 0.349 m, 12 m, and 0.2 m3 s-1, respectively. A total ten pressure sensors were mounted at different locations namely, turbine inlet, vaneless space, and draft tube. The data were acquired at a sampling rate of 5 kHz. The instruments and sensors have been calibrated according to guidelines available in IEC standards. The determined total uncertainty in the measurement of hydraulic efficiency was ±0.15% at BEP condition. The velocity measurements in the draft tube cone were performed using a 2D PIV system and the images were sampled at a rate of 40 Hz. Steady state measurements were carried out considering the realistic design and off-design operating conditions of the prototype turbine. Therefore, the angular speed of the runner was maintained constant for all steady state conditions during the measurements. The maximum hydraulic efficiency (92.4%) was observed at nED = 0.18, QED = 0.15, and a = 9.8º, which is named BEP. It is observed that the turbine experiences significant pressure fluctuations at the vaneless space, runner, and the draft tube. The fluctuations due to rotor-stator interaction (RSI) were observed to be most dominating at high load condition, however, fluctuations due to the rotating vortex rope (RVR) at part load (PL) condition. Two different modes (synchronous and asynchronous) modes of vortex rope are observed at PL condition of the turbine. An asymmetry in the flow leaving the runner was detected at both design and off-design conditions, with a stronger effect during off-design operating condition. Numerical simulations of the model turbine were carried out at PL operating condition. The simulations were performed using two turbulence models, standard k-ε and SST k-ω, with high-resolution advection scheme. The numerical pressure values obtained with both standard k-ε model and SST k-ω showed a small difference with the experimental values. The amplitudes of numerical pressure values were higher (~2.8%) in the vaneless space and lower (~5.0%) in the draft tube than the experimental values. The frequencies of the RSI and RVR were well captured in the turbine but the amplitudes were overestimated. During load rejection from BEP to PL, the plunging mode of the vortex rope was observed to appear first in the system than that of the rotating mode. Whereas during the load acceptance from PL to BEP, both the modes were observed to disappear simultaneously from the system. In the velocity data, the axial velocity only contributed to the development of the plunging mode and radial velocity to the rotating mode. The region of low velocity, stagnation point, flow separation, recirculation, oscillating flow and high axial velocity gradients were well captured in the system during the transients. The induced high-velocity gradients during the load acceptance from BEP to HL was observed to develop a vortex core in the draft tube. During startup and shutdown, the guide vanes angular position was moved from one to another steady state condition to achieve the minimum load condition of the turbine. At this condition, the generator of the turbine was magnetized at the synchronous speed during startup and shutdown, respectively. The frequency of wave propagation was observed to vary with the runner angular speed during startup and complete shutdown of the turbine. Comparatively high-pressure fluctuations in the draft tube were observed during the guide vane movement from the high discharge conditions. Some unsteady phenomena such as the formation of dead velocity zone, backward flow, and flow oscillations were observed during startup and shutdown of the turbine. The current work has been also used to continue a series of workshops, i.e., Francis-99. The first workshop was held on December 2014 with the cooperation of LTU and NTNU. The measurements performed in this work were used for the second workshop which was held on December 2016. The investigations presented in this thesis will be further explored in the third workshop scheduled for December 2018.
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Bouratsis, Polydefkis. "Scour at the Base of Hydraulic Structures: Monitoring Instrumentation and Physical Investigations Over a Wide Range of Reynolds Numbers." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/71880.
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Hydraulically induced scour of the streambed at the base of bridge piers is the leading cause of bridge failures. Despite the significant scientific efforts towards the solution of this challenging engineering problem, there are still no reliable tools for the prediction and mitigation of bridge scour. This shortcoming is attributed to the lack of understanding of the physics behind this phenomenon. The experimental studies that attempted the physical investigation of bridge scour in the past have faced two main limitations: i) The characterization of the dynamic interaction between the flow and the evolving bed that is known to drive scour, was not possible due to the limitations in the available instrumentation and the significant experimental difficulties; ii) Most of the existing literature studies are based on the findings of laboratory experiments whose scale is orders of magnitudes smaller compared to bridges in the field, while the scale effects on the scour depth have never been quantified.
The objective of this research was to enhance the existing understanding of the phenomenon by tackling the aforementioned experimental challenges. To accomplish this, the first part of this work involved the development of a new underwater photogrammetric technique for the monitoring of evolving sediment beds. This technique is able to obtain very high resolution measurements of evolving beds, thus allowing the characterization of their dynamic properties (i.e. evolving topography and scour rates) and overcoming existing experimental limitations. Secondly, the underwater photogrammetric technique was applied on a bridge scour experiment, of simple geometry, and the dynamic morphological characteristics of the phenomenon were measured. The detailed measurements along with reasonable comparisons with descriptions of the flow, from past studies, were used to provide insight on the interaction between the flow and the bed and describe quantitatively the mechanisms of scour. Finally, the scale effects on scour were studied via the performance of two experiments under near-prototype conditions. In these experiments the effects of the Reynolds number on the flow and the scour were quantified and implications concerning existing small-scale studies were discussed.<br>Ph. D.
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Legendre, César. "On the interactions of sound waves and vortices." Doctoral thesis, Universite Libre de Bruxelles, 2015. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209147.
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The effects of vortices on the propagation of acoustic waves are numerous, from simple convection effects to instabilities in the acoustic phenomena, including absorption,<p>reflection and refraction effects. This work focusses on the effects of mean flow<p>vorticity on the acoustic propagation. First, a theoretical background is presented<p>in chapters 2-5. This part contains: (i) the fluid dynamics and thermodynamics<p>relations; (ii) theories of sound generation by turbulent flows; and (iii) operators taken<p>from scientific literature to take into account the vorticity effects on acoustics. Later,<p>a family of scalar operators based on total enthalpy terms are derived to handle mean<p>vorticity effects of arbitrary flows in acoustics (chapter 6). Furthermore, analytical<p>solutions of Pridmore-Brown’s equation are featured considering exponential boundary<p>layers whose profile depend on the acoustic parameters of the problem (chapter 7).<p>Finally, an extension of Pridmore-Brown’s equation is formulated for predicting the<p>acoustic propagation over a locally-reacting liner in presence of a boundary layer of<p>linear velocity profile superimposed to a constant cross flow (chapter 8).<p><br>Doctorat en Sciences de l'ingénieur<br>info:eu-repo/semantics/nonPublished
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Karlsson, Mikael. "Aeroacoustics Studies of Duct Branches with Application to Silencers." Doctoral thesis, KTH, MWL Strömningsakustik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-29568.
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New methodologies and concepts for developing compact and energy efficient automotive exhaust systems have been studied. This originates in the growing concern for global warming, to which road transportation is a major contributor. The focus has been on commercial vehicles—most often powered by diesel engines—for which the emission legislation has been dramatically increased over the last decade. The emissions of particulates and nitrogen oxides have been successfully reduced by the introduction of filters and catalytic converters, but the fuel consumption, which basically determines the emissions of carbon dioxides, has not been improved accordingly. The potential reduction of fuel consumption by optimising the exhaust after-treatment system (assuming fixed after-treatment components) of a typical heavy-duty commercial vehicle is ~4%, which would have a significant impact on both the environment and the overall economy of the vehicle. First, methodologies to efficiently model complex flow duct networks such as exhaust systems are investigated. The well-established linear multiport approach is extended to include flow-acoustic interaction effects. This introduces an effective way of quantifying amplification and attenuation of incident sound, and, perhaps more importantly, the possibility of predicting nonlinear phenomena such as self-sustained oscillations—whistling—using linear models. The methodology is demonstrated on T-junctions, which is a configuration well known to be prone to self-sustained oscillations for grazing flow past the side branch orifice. It is shown, and validated experimentally, that the existence and frequency of self-sustained oscillations can be predicted using linear theory. Further, the aeroacoustics of T-junctions are studied. A test rig for the full determination of the scattering matrix defining the linear three-port representing the T-junction is developed, allowing for any combination of grazing-bias flow. It is shown that the constructive flow-acoustic coupling not only varies with the flow configuration but also with the incidence of the acoustic disturbance. Configurations where flow from the side branch joins the grazing flow are still prone to whistling, while flow bleeding off from the main branch effectively cancels any constructive flow-acoustic coupling. Two silencer concepts are evaluated: first the classic Herschel-Quincke tube and second a novel modified flow reversal silencer. The Herschel-Quincke tube is capable of providing effective attenuation with very low pressure loss penalty. The attenuation conditions are derived and their sensitivity to mean flow explained. Two implementations have been modelled using the multiport methodology and then validated experimentally. The first configuration, where the nodal points are composed of T-junctions, proves to be an example where internal reflections in the system can provide sufficient feedback for self-sustained oscillation. Again, this is predicted accurately by the linear theory. The second implementation, with nodal points made from Y-junctions, was designed to allow for equal flow distribution between the two parallel ducts, thus allowing for the demonstration of the passive properties of the system. Experimental results presented for these two configurations correlate well with the derived theory. The second silencer concept studied consists of a flow reversal chamber that is converted to a resonator by acoustically short-circuiting the inlet and outlet ducts. The eigenfrequency of the resonator is easily shifted by varying the geometry of the short circuit, thus making the proposed concept ideal for implementation as a semi-active device. Again the concept is modelled using the multiport approach and validated experimentally. It is shown to provide significant attenuation over a wide frequency range with a very compact design, while adding little or no pressure loss to the system.<br>QC 20110208
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Li, Ye. "Development of a procedure for power generated from a tidal current turbine farm." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/2690.
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A tidal current turbine is a device functioning in a manner similar to wind turbine for harnessing energy from tidal currents, a group of which is called a farm. The existing approaches used to predict power from tidal current turbine farms oversimplify the hydrodynamic interactions between turbines, which significantly affects the results. The major focus of this dissertation is to study the relationship between turbine distribution (the relative position of the turbines) and the hydrodynamic interactions between turbines, and its impact on the power from a farm.
A new formulation of the discrete vortex method (DVM-UBC) is proposed to describe the behavior of turbines and unsteady flow mathematically, and a numerical model is developed to predict the performance, the unsteady wake and acoustic emission of a stand-alone turbine using DVM-UBC. Good agreement is obtained between the results obtained with DVM-UBC and published numerical and experimental results. Then, another numerical model is developed to predict the performance, wake and acoustic emission of a two-turbine system using DVM-UBC. The results show that the power of a two-turbine system with optimal relative position is about 25% more than two times that of a stand-alone turbine under the same conditions. The torque such a system may fluctuate 50% less than that of a stand-alone turbine. The acoustic emission of such a system may be 35% less than that of a stand-alone turbine. As an extension, a numerical procedure is developed to estimate the efficiency of an N-turbine system by using a linear theory together with the two-turbine system model.
By integrating above hydrodynamic models for predicting power and a newly-developed Operation and Maintenance (O&M) model for predicting the cost, a system model is framed to estimate the energy cost using a scenario-based cost-effectiveness analysis. This model can estimate the energy cost more accurately than the previous models because it breaks down turbine’s components and O&M strategies in much greater detail when studying the hydrodynamics and reliability of the turbine.
This dissertation provides a design tool for farm planners, and shed light on other disciplines such as environmental sciences and oceanography.
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Joy, Jesline. "Mitigation of Pressure Pulsations in Francis Turbine Draft Tube with a GuideVane System : A Numerical Investigation." Licentiate thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-83990.
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The use of renewable energy such as water and wind to produce electricity has been proven extremely effective in Sweden. The ability of these renewable resources to produce clean output energy counters the adversities caused by non-renewable resources. The use of hydraulic turbines is a good example of favoured technique for energy and power production using renewable resources. The hydro-turbines are designed to operate at best efficiency point (BEP). Varying energy demands in recent years implies on the need of flexible operation of hydraulic turbines. The issue of pressure pulsations in the draft tube of hydro-turbines, observed at lower operating conditions has been unresolved for many years. These pressure pulsations are related to the ‘rotating vortex rope’ (RVR) observed at part load operation and, affects the lifespan and performance of the hydro-turbine adversely. Several techniques have been investigated in the past to reduce the pressure pulsations in the draft tube at part load operation and enhance the flexibility of the turbine. During the present research study, a passive flow control technique was investigated numerically by implementing a guide vane system in the draft tube of the Francis-99model turbine. Guide vanes are mechanical devices that can direct the flow in a desired direction. The current study presents the possibility of reducing the pressure pulsations in the draft tube by mitigating the RVR using a guide vane system in the draft tube. At the initial stages of the research study, a reduced numerical model of the Francis model turbine was developed by only considering the draft tube domain. The motive was to develop a reduced model to perform the parametric analysis for the guide vane system in the draft tube with reduced computational time, power, and storage. The results obtained from the numerical study were found to be in good agreement with theFrancis-99 semi-model with passage domains. A parametric study was performed to achieve a guide vane system design that could mitigate RVR with minimum losses. During this study, the number of guide vanes, the chord and the span of the guide vanes were investigated. It was found that a set of three guide vane system with chord of 86% of runner radius and leading-edge span of 30% of runner radius is an ideal design that mitigates RVR above 95%.
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da, Cunha Daise Nunes Queiroz. "Properties of Flow Through the Ascending Aorta in Boxer Dogs with Mild Aortic Stenosis: Momentum, Energy, Reynolds Number, Womersley’s, Unsteadiness Parameter, Vortex Shedding, and Transfer Function of Oscillations from Aorta to Thoracic Wall." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1243910694.
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Kranenbarg, Jelle. "Techniques to inject pulsating momentum." Thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79097.
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Hydro power plants are an essential part of the infrastructure in Sweden as they stand for a large amount of the produced electricity and are used to regulate supply and demand on the electricity grid. Other renewable energy sources, such as wind and solar power, have become more popular as they contribute to a fossil free society. However, wind and solar power are intermittent energy sources causing the demand for regulating power on the grid to increase. Hydro power turbines are designed to operate at a certain design point with a specific flow rate. The plants are operated away from the design point when used to regulate the supply and demand of electricity. This can cause a specific flow phenomenon to arise in the draft tube at part load conditions called a Rotating Vortex Rope (RVR) which causes dangerous pressure fluctuation able to damage blades and bearings. A solution to mitigate a RVR is to inject pulsating momentum into the draft tube by using an actuator operating at a certain frequency. A literature study was conducted and three techniques were numerically simulated using ANSYS Workbench 19.0 R3; a fluidic oscillator, a piston actuator and a synthetic jet actuator. A dynamic mesh was used to simulate the movement of the piston actuator and diaphragm of the synthetic actuator whilst the mesh of the fluidic oscillator was stationary. The relative errors of the three numerical models were all below 3 %. All devices showed promising results and could potentially be used to mitigate a RVR because they all have the ability to produce high energy jets. The fluidic oscillator had an external supply of water, whereas the other two did not, which means that it could inject the largest mass flow. The piston actuator required a driving motor to move the piston. The diaphragm of the synthetic jet actuator was moved by a Piezoelectric element. Advantages of the fluidic oscillator are that it has no moving parts, in contrary to the two other devices, it can directly be connected to the penstock or draft tube to obtain the required water supply and it is easy to install. It will most likely also be smaller compared to the other two for the same mass flow rate. It does however not generate a pulsating jet, but rather an oscillating jet. The other two devices generate pulsating jets, but have problems with low pressure areas during the intake stroke which can cause cavitation problems. These areas cause the formation of vortex rings close to the outlet. Simulations showed that a coned piston together with a coned cylinder outlet could decrease losses by almost 16 % compared to a normal piston and cylinder. It also decreased the risk for cavitation and the required force to move the piston. Otherwise, a shorter stroke length for a constant cylinder diameter or a longer stroke length for a constant volume displacement also decreased the risk for cavitation and required force. The gasket between the piston and cylinder is a potential risk for leakage. A solution to avoid critical low pressure areas is to install an auxiliary fluid inlet or valve which opens at a certain pressure for the piston actuator as well as the synthetic jet actuator. This will also allow larger mass flow rates and a higher injected momentum. Both devices are more complicated to install and require likely more maintenance compared to the fluidic oscillator. However, there exist many possible design options for the piston actuator. The design of the synthetic jet is more limited because of the diaphragm. The amplitude of the diaphragm also has a direct effect on the pressure levels. The losses increased proportional to the mass flow to the power of three which suggests that it is better to install many small actuators instead of a few large ones.
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Liewkongsataporn, Wichit. "A numerical study of pulse-combustor jet impingement heat transfer." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22651.
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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2008.<br>Committee Co-Chair: Ahrens, Fred; Committee Co-Chair: Patterson, Tim; Committee Member: Aidun, Cyrus; Committee Member: Empie, Jeff; Committee Member: Frederick, Jim.
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Glesser, Martin. "Sons auto-entretenus produits par l'interaction d'un jet plan avec une plaque fendue : étude expérimentale et modélisation du couplage avec un résonateur." Phd thesis, Université de La Rochelle, 2006. http://tel.archives-ouvertes.fr/tel-00260176.
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Des sons auto-entretenus peuvent être générés par l'interaction d'un jet plan avec une plaque fendue, et se coupler avec les résonances acoustiques du conduit de soufflage. L'étude s'intéresse aux conditions optimales de production de la source aéroacoustique ainsi créée et à l'influence du couplage sur cette production. Un dispositif expérimental, basé essentiellement sur des mesures microphoniques et vélocimétriques est utilisé. Il est associé à un modèle basé sur la théorie du son tourbillonnaire (``vortex-sound''). Des informations obtenues expérimentalement sur la convection des tourbillons et leur synchronisation avec le champ acoustique permettent de compléter les données d'entrée du modèle. Une loi d'évolution de la fréquence d'émission de type ``Rossiter'' est également obtenue expérimentalement. Les résultats de modélisation permettent d'interpréter cette loi d'évolution comme la condition optimale de production de la source aéroacoustique. Le couplage entre cette source et les résonances du conduit de soufflage est également étudié. Il se fait avec les modes plans du conduit lorsque l'angle d'inclinaison de l'obstacle par rapport à la sortie du jet est faible et avec des modes non-plans dans le cas contraire. L'influence de l'admittance d'entrée du conduit sur le couplage est de plus mise en évidence dans le cas plan. Finalement, l'évolution des fréquences d'émission mesurée est expliquée par un compromis entre les conditions optimales de production de la source aéroacoustique et les conditions optimales de couplage avec le conduit de soufflage.
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Kubíček, Radek. "CFD simulace vibrací vyvolaných prouděním." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-403865.
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The presented diploma thesis focuses on flow-induced vibrations of a tube. The main aim and benefit is the analysis of tube stiffness in contact with the other one and the following use of obtained values and characteristics in CFD simulations. The work can be divided into three parts. The first part is about the current state of knowledge of flow-induced vibrations. It introduces the basic mechanisms of vibration and methods for their suppression. The second part deals with the determination of stiffness of defined geometry tube including the collision with the other tube. The final part demonstrates and evaluates the application of obtained characteristics in CFD simulations.
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Fischer, Jeoffrey. "Identification de sources aéroacoustiques au voisinage de corps non profilés par formation de voies fréquentielle et temporelle." Thesis, Poitiers, 2014. http://theses.univ-poitiers.fr/62768/2014-Fischer-Jeoffrey-These.
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La localisation de sources aéroacoustiques sur les corps automobiles est actuellement un sujet d’intérêt majeur pour les industriels. Le traitement d’antenne microphonique par formation de voies (beamforming) est une méthode robuste, classiquement utilisée dans ce cadre. L’objectif principal de ce manuscrit concerne ainsi la détection de sources aéroacoustiques sur des corps non profilés. Deux configurations expérimentales sont envisagées : une marche montante qui représente un cas académique, et un corps tridimensionnel générant des structures tourbillonnaires de type montant de baie se rapprochant du cadre de l’industrie automobile. La localisation de sources par formation de voies classique a permis d’identifier, pour différentes gammes de fréquence, les principales régions d’émission acoustique, à savoir : les zones tourbillonnaires amont et aval sur la marche et les montants de baie latéraux sur le corps tridimensionnel. De plus, des tendances similaires dans les mesures de pression pariétale fluctuante et de pression acoustique en champ lointain ont été observées. L’étude s’est ensuite dirigée vers la détection d’intermittences acoustiques afin de déterminer dans quelle mesure, à l’instar du bruit de jet, le bruit d’écoulement en présence d’obstacle présente un caractère intermittent. Un processus de seuillage sur le champ lointain mesuré a permis de sélectionner des événements représentant 80% de l’énergie du signal original et 20% de sa durée sur les deux configurations. Une méthode de formation de voies temporelle, en lien direct avec la technique de retournement temporel, a été développée afin de réaliser une imagerie de sources aéroacoustiques en fonction du temps.L’utilisation de cette technique permet de montrer que les événements sélectionnés à partir du seuillage correspondent à des sources intermittentes dont on peut déterminer les lieux et les instants d’émission (obéissant à une distribution statistique Gamma). Le bruit aéroacoustique généré par les corps non profilés considérés dans cette étude peut donc être vu comme une succession d’événements intermittents identifiables. Enfin, la reconstruction des signaux acoustiques à partir d’une famille d’ondelettes a été effectué. Les spectres du signal original et filtré sont fortement semblables, une différence de l’ordre de 10% ayant été observée entre eux pour les deux maquettes, confirmant l’importance des événements intermittents dans le rayonnement aéroacoustique des corps non profilés<br>The localization of aeroacoustic sources of automotive bodies is currently a topic of major interest to industry. Beamforming is a robust method typically used in this context. The main objective of this thesis relates to the detection of aeroacoustic sources on bluff bodies. Two experimental configurations are considered : a forwardfacing step that is an academic event, and a three dimensional bluff body generating A-pillar vortices approaching the automotive industry. Source localization through classical beamforming has enabled to detect the main regions of acoustic emission for different frequency ranges, namely : upstream and downstream vortices around thestep and A-pillar vortices generated on both sides of the 3D bluff body. In addition, relationships have been observed between wall pressure fluctuations and acoustic field radiated. The study was then directed to the detection of intermittent acoustic events to determine whether, like jet noise, the noise radiated by an obstacle in the flow is composed of intermittent signatures. A thresholding process on the far field measurements was used to select events representing 80% of the energy of the original signal and 20% of its time for both configurations. A time-domain beamforming algorithm, directly linked to the time reversal technique, has been developed to achieve a spatio-temporal information about the intermittent noise sources. The use of this technique has proved that the events selected with the tresholding technique correspond to intermittent acoustic sources which space and time informations canbe determined (they follow a Gamma distribution). The aeroacoustic noise radiated by the bluff bodies considered in this study can therefore be seen as a succession of intermittent events that can be identified. Finally, the reconstruction of intermittent acoustic signals using a family of wavelets was performed. The Fourier spectra of the original and reconstructed signals are highly similar, a difference of about 10% was observed, confirming the importance of intermittent events in the noise radiated by bluff bodies
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Merlin, Cindy. "Simulation numérique de la combustion turbulente : Méthode de frontières immergées pour les écoulements compressibles, application à la combustion en aval d’une cavité." Thesis, Rouen, INSA, 2011. http://www.theses.fr/2011ISAM0020/document.
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Une méthode de frontières immergées est développée pour la simulation d’écoulements compressibles et validée au travers de cas-tests spécifiques (réflexion d’ondes acoustiques et quantification de la conservation de la masse dans des canaux inclinés). La simulation aux grandes échelles (LES) d’une cavité transsonique est ensuite présentée. Le bouclage aéro-acoustique, très sensible aux conditions aux limites, est reproduit avec précision par la LES dans le cas où les parois sont immergées dans un maillage structurée. La comparaison des stratégies de modélisation de sous-maille pour cet écoulement transsonique et l’adaptation des filtres en présence de frontières immergées sont également discutées. Le rôle, souvent sous-estimé, du schéma de viscosité artificiel, est quantifié.Dans la dernière partie du manuscrit, des études sont réalisées pour aider au dimensionnement d’un nouveau concept de chambre de combustion où la flamme est stabilisée par la recirculation de gaz brûlés dans une cavité (chambre TVC pour Trapped Vortex Combustor). La modélisation de la combustion turbulente est basée sur une chimie tabulée, couplée à une fonction densité de probabilité présumée (PCM-FPI). L’étude de la dynamique de la flamme est réalisée pour diverses conditions de fonctionnement (débit de l’écoulement principal et présence ou non d’un swirl). Les spécificités de mise en œuvre de la simulation d’un écoulement de ce type sont discutées et un soin particulier est apporté au traitement de la condition de sortie, qui constitue un point sensible de la chaîne de modélisation. Les phénomènes d’instabilités et de retour de la flamme sont mis en évidence ainsi que les modifications à apporter au dispositif afin de minimiser ces effets. L’existence d’un cycle limite acoustique est souligné et une formule permettant d’anticiper le niveau des fluctuations de pression est proposée et validée. Une correction au modèle PCM-FPI est présentée afin de préserver la vitesse de flamme et d’assurer une reproduction plus précise de la dynamique de flamme<br>An immersed boundary method has been developed for the simulation of compressible flow and validated with reference test cases (pressure wave reflection and quantification of mass conservation for various inclined channels). Large Eddy Simulation (LES) of a transonic cavity is then presented. The aeroacoustic feedback loop, which is highly sensitive to the boundary conditions, was accurately reproduced where the walls are immersed inside a structured grid. The comparison between the modeling approaches for this transonic flow and the correction of the filtering operation near immersed boundaries are also discussed. The often underestimated role of the numerical artificial dissipation is also quantified.In the last part of this manuscript, many studies are realized to help in the design of a new combustion chamber for Trapped Vortex Combustor (TVC). The turbulent combustion model is based on tabulated chemistry and a presumed probability density function (PCM-FPI) method.The flame dynamics is studied for various operating conditions (flowrate of the main flow and presence of swirl motion). Details concerning the realization of such a flow are discussed and special care is taken for the treatment of the most sensitive outlet boundary condition. The phenomena of combustion instabilities and of flame backflow are highlighted along with the modifications to be made for the device to minimize these effects. The existence of a acoustic limit cycle is emphasized and a formula is proposed and validated to anticipate the level of pressure fluctuations. Finally a correction to the PCM-FPI model is suggested to preserve the flame front speed and to ensure a more accurate description of the flame dynamics
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Jaouani, Nassim. "Modelling of installation effects on the tonal noise radiated by counter-rotating open rotors." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC002.
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The Counter-Rotating Open Rotors (CROR) are identified as a possible alternative to turbofan engines for middle-range aircrafts. Providing significant fuel savings and reducing the green-house gas emissions, they may lead however to an increased noise radiation due to the absence of nacelle shielding. To properly predict the acoustic radiation of such systems is then mandatory both to reduce the source mechanisms of the isolated engine and to offer an optimal noise installation solution. Such an objective is tackled in the present thesis in two steps. In a first part, the research aims at predicting the tonal noise radiated from the first propeller of CROR mounted on the rear fuselage by means of a pylon (pusher configuration), considering both the pylon-wake and the uniform ow effects. From the Ffowcs Williams & Hawkings' formalism, three noise sources are identified. First the unsteady loading is computed using a similar procedure to the one used for the rotor-rotor wake interaction noise prediction. The velocity deficit in the pylon wake is locally expanded in two-dimensional Fourier gusts in a reference frame attached to the front rotor. The unsteady lift induced by each gust on a blade segment is calculated using a linearized analytical response function that accounts for a realistic geometry. The steady loading is the second source contribution and is evaluated using both a software based on the lifting-line theory and some numerical simulations for different reference source surfaces. Finally the thickness noise due to the blade volume displacement is included in the analysis using Isom's formulation. From the linear acoustic assumptions, all these sources modelled as equivalent acoustic dipoles rotating in a uniformly moving atmosphere are then summed to calculate the far-field noise. The whole methodology is assessed against wind-tunnel test data and reference software predictions. A parametric study considering several pylon positionings and pylon-wake configurations with blowing is performed in order to emphasize the relative contribution of the three noise sources. Secondly, the rotor- rotor wake interaction noise being recognized as the most significant contribution in isolated configuration, its modelling is completed by introducing the dynamics of the vortex occurring near the rear-rotor leading edge. A semi-analytical methodology is developed to determine a vortex attached over a at plate embedded in a uniform ow with incidence. Applied to the case of a rear blade going through a front-rotor wake, it provides a first estimate of the noise contribution of the vortex<br>Les hélices contrarotatives constituent une alternative possible aux turboréacteurs pour les avions moyens- courriers. Réduisant significativement la consommation de carburant et les émissions de gaz à effet de serre, ils peuvent néanmoins conduire à un rayonnement sonore accru de par l'absence de carénage. Prédire correctement le rayonnement sonore de telles motorisations est donc indispensable pour réduire les mécanismes sources propres au moteur isolé ou assurer une solution d'installation acoustique optimale. Un tel objectif est abordé dans cette thèse en deux temps. Dans un premier temps, l’étude vise à prédire le bruit tonal rayonné par la première hélice d'un moteur monté à l'arrière du fuselage (configuration dite en pousseur), en considérant les effets du sillage du pylône supportant le moteur et de l'écoulement moyen. Partant du formalisme de Ffowcs Williams & Hawkings, trois sources sonores sont identifiées à cet effet. La charge instationnaire, tout d'abord, est calculée en s'appuyant sur une méthodologie similaire à celle utilisée pour la prédiction du bruit d'interaction de sillages entre les deux rotors. Le déficit de vitesse dans le sillage du mât est décomposé localement en rafales bidimensionnelles dans un repère attaché au rotor amont. La portance instationnaire induite par chaque rafale sur un segment de pale est calculée en utilisant une fonction de réponse analytique linéarisée considérant une géométrie réaliste. Deuxième contribution, la charge stationnaire est évaluée au moyen d'un logiciel s'appuyant sur la théorie de la ligne portante mais également via des simulations numériques pour différentes surfaces sources de référence. Enfin, le bruit d'épaisseur associé au déplacement du volume de la pale est inclus dans l'analyse à partir de la formulation d'Isom. D'après les hypothèses de l'acoustique linéaire, toutes ces sources modélisées comme des dipôles acoustiques tournant dans une atmosphère uniforme en mouvement sont ensuite sommées pour calculer le bruit en champ lointain. L'ensemble de la méthodologie est comparé à des données d'essai et des prédictions d'un logiciel de référence. Une étude paramétrique considérant plusieurs positionnements du pylône et des configurations avec soufflage est effectuée afin de bien mettre en évidence les contributions relatives des trois sources sonores. Dans un deuxième temps, le bruit d'interaction de sillages étant reconnu comme la contribution majoritaire en configuration isolée, sa modélisation est complétée en introduisant la dynamique du tourbillon se développant au voisinage du bord d'attaque du rotor aval. Une méthodologie semi-analytique est développée pour déterminer un tourbillon attaché au-dessus d'une plaque plane plongée dans un écoulement uniforme avec incidence. Appliquée au cas d'une pale aval traversant le sillage du rotor amont, elle fournit une première estimation de la contribution sonore du tourbillon
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Alkheir, Marwan. "Contrôle du champ acoustique des sons auto-entretenus via la dynamique tourbillonnaire : application au jet plan heurtant une plaque fendue." Thesis, La Rochelle, 2020. http://www.theses.fr/2020LAROS018.
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Une étude expérimentale d’un jet d’air plan heurtant une plaque fendue a été menée. Cette étude a été réalisée pour deux nombres de Reynolds Re=5900 et Re=6700, avec un rapport d’impact L/H=4. Les écoulements associés produisent des sons auto-entretenus. Leurs dynamiques tourbillonnaires ainsi que les champs acoustiques rayonnés présentent des comportements atypiques. Afin de réduire les nuisances sonores dues à l’installation de sons auto-entretenus, un mécanisme de contrôle (tige de 4 mm) a été installé dans l’écoulement pour perturber la dynamique tourbillonnaire responsable de l’installation du son auto-entretenu. L’influence de 1085 positions de la tige entre la sortie du jet et la plaque fendue a été étudiée. Des moyens et des codes spécifiques ont été développés pour des investigations appropriées notamment une technique laser optique spécifique de double SPIV en un seul plan « D-SPIV » a été conçue réalisée. En absence de la tige, pour se renseigner sur la dynamique tourbillonnaire des écoulements pour les deux Reynolds Re=5900 et Re=6700, des mesures SPIV ont été réalisées permettant ainsi de caractériser les états de références des deux écoulements. Pour le premier nombre de Reynolds (Re=5900), deux boucles de sons auto-entretenus ont été mises en évidence. Une à la fréquence de 160 Hz et l’autre à la fréquence de 320 Hz. Ces deux boucles, installées, sont caractérisées respectivement par les organisations tourbillonnaires symétriques et antisymétriques du jet qui alternent dans le temps d’une façon aléatoire. Cependant, le régime antisymétrique à la fréquence 320 Hz est plus persistant dans le temps. Pour le deuxième nombre de Reynolds (Re=6700), l’étude dynamique de l’écoulement a montré que le jet est antisymétrique avec une fréquence de détachement tourbillonnaire de 380 Hz alors que la fréquence la plus énergétique qui caractérise le son auto-entretenu de l’écoulement est de 168 Hz. Lors de la mise en place du mécanisme de contrôle par l’installation de la tige, pour les deux nombres de Reynolds étudiés, il a été trouvé deux zones de contrôle. La première zone est sur l’axe du jet. Lorsque la tige est positionnée dans cette zone, le niveau de pression acoustique baisse d’environ 20 dB. De plus, il y a une disparition de la boucle de sons auto-entretenus. Lorsque la tige occupe des positions dans la deuxième zone qui est située aux environs de la tangente inférieure du jet, le niveau acoustique augmente d’environ de 12 dB. Cependant, il y a disparition de la boucle de sons auto-entretenus. Pour les deux nombres de Reynolds, l’étude de la dynamique des écoulements en présence de la tige, montre que lorsque la tige est installée dans la zone 2, le jet est dévié et une partie des structures tourbillonnaires passe directement par la fente sans se déformer expliquant ainsi la disparition de la boucle d’auto-entretien et l’augmentation de 12 dB du niveau acoustique du champ rayonné, alors que le débit à travers la fente est réduit d’environ 50 %. Lorsque la tige est installée dans la zone 1, aucune structure ne passe par la fente ce qui explique la disparition de la boucle d’auto-entretien et la baisse du niveau de pression acoustique d’environ 20 dB. L’activité tourbillonnaire installée de part et d’autre de la fente crée des zones de recirculations inversant ainsi le débit à travers la fente<br>An experimental study of a rectangular jet of air impinging on a slotted plate is considered in this work. This study is performed for two Reynolds numbers Re = 5900 and Re = 6700, with an impact ratio L/H=4, where L is the plate-to-nozzle distance and H is the height of the slot. This configuration consists of a flow producing self-sustaining tones. Atypical behavior of the flow through its vortices and acoustic field is found in this study. In order to reduce the noise generation, a control mechanism comprising a 4mm rod is installed in the flow to disturb the vortex dynamics responsible for the loop of self-sustaining tones installed along the jet. A total of 1085 rod positions are tested between the nozzle and the impinged plate in order to find optimal positions. Specific metrologies and codes are developed for appropriate investigations. In particular, a laser technique consisting of double Stereoscopic PIV in a plane « D-SPIV » is employed.In the absence of the rod, in order to visualize the vortex dynamics for both Reynolds numbers Re = 5900 and Re = 6700, SPIV measurements are performed. This allows to characterize these flows in their reference states. For the first Reynolds number (Re = 5900), two self-sustaining tones loops are highlighted. The first has a frequency of 160 Hz and the second has a frequency of 320 Hz. These two loops characterize respectively a symmetric and an asymmetric vortex organization of the jet and alternate in a random pattern with respect to time. The asymmetric regime (f=320 Hz) is more persistent over time. For the second Reynolds number (Re = 6700), the dynamic study of the flow shows that the jet is asymmetric with a vortex shedding frequency equal to 380 Hz, while the more energetic frequency which characterizes the self-sustaining tones of the flow is equal to 168 Hz.When control mechanism is employed through the rod, for both Reynolds numbers, two control zones could be distinguished. The first one is on the axis of the jet. Once the rod is positioned in this zone, the sound pressure level drops by approximately 20 dB. Moreover, the self-sustaining tones loop disappears. When the rod is positioned in the second zone which is located around the lower mixing layer of the jet, the sound pressure level increases by about 12 dB and the self-sustaining tones loop disappears.The study of the dynamics of the flow in the presence of the control mechanism for both Reynolds numbers shows a deflection of the jet when the rod is installed in the second zone (near from the lower mixing layer of the jet). Actually, a part of the vortices escape directly through the slot of the plate without deformation, what explains the disappearance of the self-sustaining loop and the increase of the acoustic level by 12 dB. At the same time, the flow rate through the slot is reduced by about 50%. When the rod is installed in the first zone (on the axis of the jet), no vortices are found to escape through the slot of the plate what explains the disappearance of the self-sustaining loop and the drop in sound pressure level by approximately 20 dB. The vortex activity on both sides of the slot creates recirculation zones in such a way that the flow through the slot is reversed
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Buzík, Jiří. "Analýza cyklické únavy trubkového svazku vlivem proudění pracovního média." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-371777.
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The aim of the dissertation thesis is the control of the tube bundle on the cyclic fatigue caused by the flow past tube bundle. Fatigue due to flow is caused by flow-induced vibrations. Examined vibrations are caused by the mutual interaction of two phases (solid and liquid). The present work is focused mainly on the interaction of tube bundles with fluid. The current level of knowledge in this field allows to predict mainly static respectively quazi-static loading. These predictions are based on methods of comparing key vibration variables such as frequencies, amplitudes or speeds (see TEMA [1]). In this way, it is possible to determine quickly and relatively precisely the occurrence of a vibrational phenomenon, but it is not possible to quantitatively assess the effect of these vibrations on the damage of to the tube beam and to predict its lifespan, which would require the determination of the temperature field and the distribution of forces from the fluid on the beam. The aim of the work is to evaluate the-state-of-the-art, to perform a numerical simulation of the flow of fluids in the area of shell side under the inlet nozzle. Current methods of numerical analyses very well solve this problem, but at the expense of computing time, devices and expensive licences. The benefit of this work is the use of user-defined function (UDF) as a method for simulating interaction with fluid and structure in ANSYS Fluent software. This work places great emphasis on using the current state of knowledge for verifying and validation. Verifying and validation of results include, for example, experimentally measured Reynolds and Strouhal numbers, the drag coefficients and for example magnitude of pressure coefficient around the tube. At the same time, it uses the finite element method as a tool for the stress-strain calculation of a key part on tube such as a pipe-tube joint. Another benefit of this work is the extension of the graphical design of heat exchanger according to Poddar and Polley by vibration damages control according to the method described in TEMA [1]. In this section, the author points out the enormous influence of flow velocity on both the tube side and the shell side for design of the heat exchanger to ensure faultless operation. As an etalon of damage, the author chose a heat exchanger designated 104 from the Heat Exchanger Tube Vibration Data Bank [3]. With this heat exchanger, vibrational damage has been proven to be due to cutting of the tubes over the baffles. The last part outlines the possibilities and limits of further work.
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Blaette, Lutz. "Vortex Driven Acoustic Flow Instability." 2011. http://trace.tennessee.edu/utk_graddiss/951.
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Most combustion machines feature internal flows with very high energy densities. If a small fraction of the total energy contained in the flow is diverted into oscillations, large mechanical or thermal loads on the structure can be the result, which are potentially devastating if not predicted correctly. This is particularly the case for lightweight high performing devices like rockets. The problem is commonly known as "Combustion Instability". Several mechanisms have been identified in the past that link the flow field to the acoustics inside a combustion chamber and thereby drive or dampen oscillations, one of them being vortex shedding. The interaction between the highly sheared flow behind an obstacle and longitudinal acoustic oscillations inside a solid rocket booster is investigated both analytically and experimentally.The analytical approach is developed based on modeling of the second order acoustic energy. The energy model is applied to the specific flow conditions just downstream of a single baffle protruding into the flow. The mean flow profile is assumed to be of the form of a hyperbolic tangent, the unsteady acoustic velocities are assumed to be sinusoidally oscillating. Solutions for the unsteady rotational velocities and the unsteady vorticity are derived. The resulting flow field is utilized in stability calculations for a simplified two-dimensional axial-symmetric geometry. This yields to linear growth rates of the (longitudinal) oscillation modes. The growth rates are functions of the chamber geometry, the mean flow properties and the properties of the shear layer created by the flow restriction.A cold flow experiment is designed, tested and performed in order to validate the analytical findings. Flow is injected radially into a tube with acoustic closed-closed end conditions. A single baffle is installed in the tube, the axial position of the baffle is varied as well as its inner diameter. Frequency spectra of pressure oscillations are recorded. The experimental data is then compared qualitatively to the analytical growth rates. Those longitudinal Normal Modes, which feature the highest theoretical growth rates, are expected to be most prominent in the experimental data. This behavior is clearly observable.
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Sathaye, Abhijit. "An acoustic vortex generator for microfluidic particle entrapment." 2002. http://catalog.hathitrust.org/api/volumes/oclc/50484631.html.
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Thesis (M.S.)--University of Wisconsin--Madison, 2002.<br>Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 73-76).
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Batterson, Joshua Will. "The Biglobal Instability of the Bidirectional Vortex." 2011. http://trace.tennessee.edu/utk_graddiss/1056.
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State of the art research in hydrodynamic stability analysis has moved from classic one-dimensional methods such as the local nonparallel approach and the parabolized stability equations to two-dimensional, biglobal, methods. The paradigm shift toward two dimensional techniques with the ability to accommodate fully three-dimensional base flows is a necessary step toward modeling complex, multidimensional flowfields in modern propulsive applications. Here, we employ a two-dimensional spatial waveform with sinusoidal temporal dependence to reduce the three-dimensional linearized Navier-Stokes equations to their biglobal form. Addressing hydrodynamic stability in this way circumvents the restrictive parallel-flow assumption and admits boundary conditions in the streamwise direction. Furthermore, the following work employs a full momentum formulation, rather than the reduced streamfunction form, accounting for a nonzero tangential mean flow velocity. This approach adds significant complexity in both formulation and implementation but renders a more general methodology applicable to a broader spectrum of mean flows. Specifically, we consider the stability of three models for bidirectional vortex flow. While a complete parametric study ensues, the stabilizing effect of the swirl velocity is evident as the injection parameter, kappa, is closely examined.
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Stephenson, James Harold. "Extraction of blade-vortex interactions from helicopter transient maneuvering noise." Thesis, 2014. http://hdl.handle.net/2152/25066.
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Time-frequency analysis techniques are proposed as a necessary tool for the analysis of acoustics generated by helicopter transient maneuvering flight. Such techniques are necessary as the acoustic signals related to transient maneuvers are inherently unsteady. The wavelet transform is proposed as an appropriate tool, and it is compared to the more standard short-time Fourier transform technique through an investigation using several appropriately sized interrogation windows. It is shown that the wavelet transform provides a consistent spectral representation, regardless of employed window size. The short-time Fourier transform, however, provides spectral amplitudes that are highly dependent on the size of the interrogation window, and so is not an appropriate tool for this situation. An extraction method is also proposed to investigate blade-vortex interaction noise emitted during helicopter transient maneuvering flight. The extraction method allows for the investigation of blade-vortex interactions independent of other sound sources. The method is based on filtering the spectral data calculated through the wavelet transform technique. The filter identifies blade-vortex interactions through their high amplitude, high frequency impulsive content. The filtered wavelet coefficients are then inverse transformed to create a pressure signature solely related to blade-vortex interactions. This extraction technique, along with a prescribed wake model, is applied to experimental data extracted from three separate flight maneuvers performed by a Bell 430 helicopter. The maneuvers investigated include a steady level flight, fast- and medium-speed advancing side roll maneuvers. A sensitivity analysis is performed in order to determine the optimal tuning parameters employed by the filtering technique. For the cases studied, the optimized tuning parameters were shown to be frequencies above 7 main rotor harmonics, and amplitudes stronger than 25% (−6 dB) of the energy in the main rotor harmonic. Further, it is shown that blade-vortex interactions can be accurately extracted so long as the blade-vortex interaction peak energy signal is greater or equal to the energy in the main rotor harmonic. An in-depth investigation of the changes in the blade-vortex interaction signal during transient advancing side roll maneuvers is then conducted. It is shown that the sound pressure level related to blade-vortex interactions, shifts from the advancing side, to the retreating side of the vehicle during roll entry. This shift is predicted adequately by the prescribed wake model. However, the prescribed wake model is shown to be inadequate for the prediction of blade-vortex interaction miss distance, as it does not respond to the roll rate of the vehicle. It is further shown that the sound pressure levels are positively linked to the roll rate of the vehicle. Similar sound pressure level directivities and amplitudes can be seen when vehicle roll rates are comparable. The extraction method is shown to perform admirably throughout each maneuver. One limitation with the technique is identified, and a proposal to mitigate its effects is made. The limitation occurs when the main rotor harmonic energy drops below an arbitrary threshold. When this happens, a decreased spectral amplitude is required for filtering; which leads to the extraction of high frequency noise unrelated to blade-vortex interactions. It is shown, however, that this occurs only when there are no blade-vortex interactions present. Further, the resulting sound pressure level is identifiable as it is significantly less than the peak blade-vortex interaction sound pressure level. Thus the effects of this limitation are shown to be negligible.<br>text
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Santhosh, R. "Transition and Acoustic Response of Vortex Breakdown Modes in Unconfined Coaxial Swirling Flow and Flame." Thesis, 2015. http://etd.iisc.ernet.in/2005/3856.
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The efficient and enhanced mixing of heat and incoming reactants is achieved in modern gas turbine systems by employing swirling flows. This is realized by a low velocity region (internal recirculation zone -IRZ) zone resulting from vortex breakdown phenomenon. Besides, IRZ acts as effective flame holder/stabilization mode. Double concentric swirling jet is employed in plethora of industrial applications such as heat exchange, spray drying and combustion. As such, understanding essential features of vortex breakdown induced IRZ and its acoustic response in swirling flow/flame is important in thermo-acoustic instability studies.
The key results of the present experimental investigation are discussed in four parts. In the first part, primary transition (sub-critical states) from a pre-vortex breakdown (Pre-VB) flow reversal to a fully-developed central toroidal recirculation zone (CTRZ) in a non-reacting, double-concentric swirling jet configuration is discussed when the swirl number is varied in the range 0.592 S 0.801. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially-penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. The second part describes a secondary transition from an open-bubble type axisymmetric vortex breakdown (sub-critical states) to partially-open bubble mode (super-critical states) through an intermediate, critical regime of conical sheet formation for flow modes Rom ≤ 1 is discussed when the swirl number (S) is increased beyond 0.801.
In the third part, amplitude dependent acoustic response of above mentioned sub and supercritical flow states is discussed. It was observed that the global acoustic response of the sub-critical VB states was fundamentally different from their corresponding super-critical modes. In particular, with a stepwise increase in excitation amplitude till a critical value, the sub-critical VB topology moved downstream and radially outward. Beyond a critical magnitude, the VB bubble transited back upstream and finally underwent radial shrinkage at the threshold
excitation amplitude. On the other hand, the topology of the super-critical VB state continuously moved downstream and radially outwards and finally widened/fanned-out at threshold amplitude.
In the final part, transition in time-averaged flame global flame structure is reported as a function of geometric swirl number. In particular, with a stepwise increase in swirl intensity, primary transition is depicted as a transformation from zero-swirl straight jet flame to lifted flame with blue base and finally to swirling seated flame. Further, a secondary transition is reported which consists of transformation from swirling seated flame to swirling flame with a conical tailpiece and finally to highly-swirled near blowout ultra-lean flame. For this purpose, CH* chemiluminescence imaging and 2D PIV in meridional planes were employed. Three baseline fuel flow rates through the central fuel injection pipe were considered. For each of the fuel flow cases (Ref), six different co-airflow rate settings (Rea) were employed. The geometric swirl number (SG) was increased in steps from zero till blowout for a particular fuel and co-airflow setting. A regime map (SG vs Rea) depicting different regions of flame stabilization were then drawn for each fuel flow case. The secondary transformation is explained on the basis of physical significance of Rom.
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Smith, Duane A. "An Experimental Study of Acoustically Excited, Vortex Driven, Combustion Instability within a Rearward Facing Step Combustor." Thesis, 1985. https://thesis.library.caltech.edu/1163/1/Smith_da_1985.pdf.
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<p>An internal feedback mechanism, capable of sustaining combustion instabilities, is investigated inside a small laboratory combustor in which the flame is stabilized behind a rearward facing step. Pressure and optical measurements are employed to define the acoustic field and heat release rate within the combustor, while shadowgraph records are used to visualize the reacting, kinematic flow field.</p>
<p>The acoustic flow field creates an unsteady flow inside the combustor, which produces an unsteady heat addition. When this fluctuating heat release is in the appropriate phase relationship with the pressure oscillation, energy is supplied to the acoustic field, and the strong acoustic oscillations are sustained.</p>
<p>As a result of the strong acoustic oscillations present during combustion instability, the flow surges into the combustor periodically, and large vortices are formed at the acoustic frequency which produce the large velocity fluctuation in the vicinity of the flameholder. The magnitude of the velocity fluctuation, relative to the mean flow speed, determines whether or not the vortex will form. The frequency of the combustion instability appears to be directly proportional to the amplitude of the velocity fluctuation so that the actual magnitude of the velocity fluctuation determines the instability frequency. The dependence of the instability frequency upon the velocity fluctuation creates the possibility of exciting a large range of frequencies.</p>
<p>Continued existence of the combustion instability depends upon the mean flow speed, fuel type, and fuel-air ratio.</p>
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Blazewicz, Antoni Michal. "On the relation between fluid flow over bluff bodies and accompanying acoustic radiation." 2008. http://hdl.handle.net/2440/47983.
Full textAbstract:
The relationship between distinctive characteristic fluid-flow regimes and the sound radiation generated by them has been investigated, over a range of Reynolds numbers, for various single plates and two-plate arrays in nominally two-dimensional flows. In preliminary experiments, the characteristics of flow over single plates with rectangular cross-section and faired leading edges and over tandem arrays of an upstream plate with rectangular cross-section and faired leading edges and a downstream plate of rectangular cross-section were investigated, together with the sound radiation produced. However, the main investigation has been concentrated on single plates of rectangular cross-section with various chord-to-thickness ratios C and on arrays of two plates of rectangular cross-section in tandem having various chord-to-thickness ratios C₁ and C₂ and a range of gaps (with gap-to-thickness ratios G) between them. The range of Reynolds number based on plate thickness t and free-stream velocity U, Re[subscript]t = Ut/ν (where ν is the kinematic viscosity of fluid) covered in the measurements is 3.2 x 10[superscript]3 ≤ Re[subscript]t 53 x 10[superscript]3. Spectra of velocity fluctuations in the flow and radiated sound have been measured and their characteristic frequencies related. An attempt has been made to measure force fluctuations on surfaces of the plates in order to relate them to flow characteristics and radiated sound power. Mean and fluctuating pressures associated with the force fluctuations on the plates have also been obtained. The lengths of separation bubbles on long rectangular plates have also been determined. In most cases, the measurements have been complemented by flow-visualisation in a water tunnel to provide additional detailed insight into the flow patterns. Three flow regimes have been identified for single plates of rectangular cross-section. In the first regime (1 ≤ C ≤ 3.13), shear layers separated from the leading edges form a vortex street downstream of the plate without reattachment to it. Associated force fluctuations on the plate are the main source of acoustic radiation. In the second regime (3.05 ≤ C ≤ 9.65), the separated shear layers reattach intermittently to the streamwise plate surfaces. Vortex formation in the shear layer is the dominant cause of sound radiation but the effect becomes weaker as C increases. In the third regime (6.52 ≤ C ≤ 68), the separated shear layers form closed leading-edge separation bubbles. Weak vortex shedding, with only a small contribution to the sound radiation, occurs only at the trailing edges of the plate. Bistable behaviour of the flow over a plate, with random switching between the regimes, occurs for C ≈ 3 and 6.52 ≤ C ≤ 9.65. A proposed classification of possible flow regimes for the flow around two plates of rectangular cross-section in tandem has been confirmed experimentally. For small G, the flow in the gap between the plates is isolated from the external flow. When the gap G between the plates is increased to or beyond a critical value (between 2 and 3.5), the shear layers separated from the upstream plate form a von Karman vortex street in the gap before interacting with the downstream plate. Flow and acoustic measurements indicate that this transition is associated with dramatic changes in the flow character.<br>http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1320474<br>Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 2008
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Dekkers, Willem Arthur. "Long slender cylinders in axial and near-axial flow." 2005. http://hdl.handle.net/2440/37995.
Full textAbstract:
An experimental investigation of axial and near - axial flow over long slender cylinders, which involved both flow visualisation and hot - wire anemometry, is detailed. The investigation of this type of flow was instigated by the current interest in towed underwater sonar arrays. The need to discriminate between background noise of mechanical origin and the flow - induced noise generated on a moving underwater soundrecording device has produced a requirement for a greater understanding of the larger scale, lower frequency, turbulent flow processes in the wake and the boundary layer of a cylinder in both axial and near - axial flow. Of particular interest are any regular periodic fluid - dynamic processes. Thick axisymmetric boundary layers with the ratio of outer - layer length scale ( the boundary - layer thickness δ ) to cylinder radius a in the range 31 [approximately equal to or less than] δ / a [approximately equal to or less than] 38 and the corresponding ratio of cylinder radius to the inner - layer length scale ( the viscous length v / U [subscript τ] ) in the range 22 [approximately equal to or less than] aU [subscript τ] / v = a [superscript +] [approximately equal to or less than] 41 have been investigated. In accord with previous experimental results their mean - flow and turbulence properties are found to be strongly influenced by transverse curvature and to diverge significantly from those of flat - plate boundary layers. A characteristic feature of such thick axisymmetric layers is the occurrence of " spots " of low - speed fluid which are attributed to displacement of inner - layer fluid by large - scale turbulent cross - flows. A front of low - speed fluid which propagates radially across the boundary layer is identified as the primary large - scale, low - frequency, coherent structure within the boundary layer turbulence. A flow mechanism that describes the process by which these fronts are formulated on the basis of the experimental evidence formed from low - speed spots is obtained. The stripping of low - speed fluid from the cylinder surface by large - scale crossflows within the turbulent boundary layer is seen as an additional vorticity - and turbulence - generating mechanism, which cannot occur in a flat - plate layer. When the cylinder is yawed to the free - stream, an attached boundary layer persists over a small range of yaw angle, before flow separation occurs. In this range the boundary layer becomes extremely asymmetric, even at yaw angles less than 1 °. The asymmetry and mean - flow properties of such layers have been investigated for yaw angles of 0.25 ° and 0.5 ° at several Reynolds numbers in the range 300 [approximately equal to or less than] Re [subscript a] [approximately equal to or less than] 600. At somewhat larger yaw angles, a new regime of regular vortex - shedding in near - axial flow has been identified. From the experimental results, an empirical relation for the vortex - shedding frequency ( in terms of yaw angle, vortex - shedding angle, and a Reynolds number based on the component of free - stream velocity normal to the vortex axes ) has been derived as an extension of the Roshko formula for the frequency of vortex shedding from cylinders with their axes normal to the flow. The results presented advance the current understanding of the fundamental fluid mechanics of cylinders in axial and near - axial flow, and thereby have the potential to contribute to the advancement of the signal - processing techniques applied to towed underwater sonar arrays.<br>Thesis (Ph.D.)--School of Mechanical Engineering, 2005.
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Janzen, Ryan E. "Hydraulophones: Acoustic Musical Instruments and Expressive User Interfaces." Thesis, 2007. http://hdl.handle.net/1807/25712.
Full textAbstract:
Fluid flow creates an expansive range of acoustic possibilities, particularly in the case of water, which has unique turbulence and vortex shedding properties as compared with the air of ordinary wind instruments. Sound from water flow is explained with reference to a new class of musical instruments, hydraulophones, in which oscillation originates directly from matter in its liquid state. Several hydraulophones which were realized in practical form are described. A unique user-interface consisting of a row of water jets is presented, in terms of its expressiveness, tactility, responsiveness to derivatives and integrals of displacement, and in terms of the direct physical interaction between a user and the physical process of sound production. Signal processing algorithms are introduced, which extract further information from turbulent water flow, for industrial applications as well as musical applications.