Дисертації з теми "Vortex instability"
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Mao, Xuerui. "Vortex instability and transient growth." Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6442.
Повний текст джерелаAltay, Hurrem Murat. "Vortex driven flame dynamics and combustion instability." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32379.
Повний текст джерелаIncludes bibliographical references (leaves 87-93).
Combustion instability in premixed combustors mostly arises due to the coupling between heat release rate dynamics and system acoustics. It is crucial to understand the instability mechanisms to design reliable, high efficiency, low emission gas turbine combustors. In this thesis, elementary processes acting as a source of unsteady heat release rate are described. These elementary processes are acoustic wave-flame interactions, flame-vortex interactions, equivalence ratio fluctuations, flame-wall interactions and the unsteady stretch rate. To investigate the flame- vortex interaction mechanism, a parametric study is performed in single and double expansion dump combustors. 2-D simulations are performed using the random vortex method combined with thin flame model of premixed combustion. The inlet velocity of the combustor is forced sinusoidally at various amplitudes and frequencies, and the heat release rate response is evaluated. It is shown that the heat release rate dynamics are governed by the cyclical formation of a large wake vortex and its interaction with the flame. Maximum heat release rate in a cycle is reached a short time after the breakup of the vortex, which causes rapid burning of the reactants trapped within the structure. The geometry and operating conditions of the combustor control the mechanism by which the vortex breakup is initiated. For short cavities, the impingement of the large wake vortex onto the forward facing step is responsible from the vortex breakup.
(cont.) On the other hand, in long cavities, the vortex breakup is initiated as the wake vortex impinges on the upper cavity wall in single expansion dump combustor, or the vortex forming in the other half of the combustor in double expansion dump combustor. Furthermore, the effect of the air injection in the cross stream direction close to the dump plane on equivalence ratio is investigated. It is shown experimentally that high amplitude pressure oscillation in the combustor during unstable operation causes fluctuation in the injected jet velocity. The oscillatory jet velocity affects the incoming equivalence ratio depending on the momentum ratio of the jet to the primary stream. A critical momentum ratio is defined at which the amplitude of the equivalence ratio oscillations reaches a maximum.
by Hurrem Murat Altay.
S.M.
Rostami, Masoud. "Dynamical influence of diabatic processes upon developing instabilities of Earth and planetary jets and vortices." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066186.
Повний текст джерелаThe thesis is devoted to understanding dynamical influence of diabatic effects, like moist convection, on instabilities of vortices in Earth and planetary atmospheres. A vertically integrated atmospheric model with relaxational parameterisation of phase transitions and related heat release, and with convective fluxes included in mass and momentum equations, the moist-convective rotating shallow water model, was used for this purpose. The previous version of the model was improved to include precipitable water and its vaporisation and entrainment. The approach consists in 1)detailed stability analysis of idealised, or extracted from the data, vortex profiles, 2)study of nonlinear saturation of the instabilities with the help of finite-volume high-resolution numerical code. The main results of the thesis are: 1. Demonstration and quantification of strong influence of moist effects upon instabilities of synoptic vortices, including cyclone-anticyclone asymmetry of mid-latitude vortices of weak intensity, and intensification of tropical-cyclone like vortices with formation of typical cloud patterns. 2. Explanation of the dynamical origin of the Saturn's North Polar hexagon, and of the lack of similar structure at the South Pole, in terms of instability of the coupled polar vortex and circumpolar jet, and their nonlinear saturation.3. Explanation of the observed structure of Mars' winter polar vortex in terms of instability of the latter, and its saturation in the presence of radiative heating/cooling and CO2 deposition (gas-solid phase transition). A new simple parameterisation of the latter process, including the influence of deposition nuclei, was developed in the thesis
Amirante, Daria. "A numerical study of instability and vortex breakdown of swirling flow." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485518.
Повний текст джерелаQuaranta, Hugo. "Instabilities in a swirling rotor wake." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0052.
Повний текст джерелаThis work studies the instabilities associated with the wake of a rotor. These devices are used in many applications such as energy harvesting or propulsion,and their optimisation is crucial for both industry and the environment. The wakebehind a rotor is broadly defined as a system of interlaced helical vortices, whose dynamics governs the transition from the near-wake to the far-wake regime. In our first study, we investigate the wake behind different small-scale rotors in their design operating condition. We use the resulting flows in a subsequent linear stability analysis, aiming at predicting long-wavelength instability modes in the helical vortex. We find that the theoretical prediction of the modes growth-rates matches our experimental measurements. We also show that the dynamics of helical vortex filaments can be predicted from simple two-dimensional theory. In more critical flow configurations, instabilities are suspected to promote the transition to hazardous regimes such as the so called Vortex-Ring State, characterised by large-scale recirculating structures.The second part of this work is thus dedicated to the spatio-temporal evolution of localised perturbations in the rotor plane, and their potential tendency to propagate upstream in the flow
Pang, Bin. "Active suppression of vortex-driven combustion instability using controlled liquid-fuel injection." College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2958.
Повний текст джерелаThesis 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.
Waleffe, Fabian. "The 3D instability of a strained vortex and its relation to turbulence." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14221.
Повний текст джерелаMEN'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.
Повний текст джерелаKhan, Md Abdul Hakim. "Singularity analysis by summing power series." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368391.
Повний текст джерелаKim, Inchul. "Numerical study of the onset of instability in the flow past a sphere." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184809.
Повний текст джерелаChoueiri, George H. "Experimental Investigations of Flow Development, Gap Instability and Gap Vortex Street Generation in Eccentric Annular Channels." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31017.
Повний текст джерелаOno, Tomohiro. "Parametric Study of the Rossby Wave Instability in a Two-Dimensional Barotropic Disk." Kyoto University, 2018. http://hdl.handle.net/2433/232252.
Повний текст джерелаLuton, J. Alan. "Numerical simulations of vortices near free and solid surfaces." Diss., This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10052007-143040/.
Повний текст джерелаCerqueira, Stéphane. "Étude du couplage aéro-mécanique au sein des moteurs à propergol solide." Thesis, Paris, ENMP, 2012. http://www.theses.fr/2012ENMP0011/document.
Повний текст джерелаFluid Structure Interaction of an inhibitor with the internal flow induced by wall injection was studied in an axisymmetric cold flow apparatus. Experiments were carried out over a wide range of injection velocities in order to underline how the obstacle not only modifies the mean flowfield but also its entire dynamic behaviour.The resulting instability (from the interaction of the unstable shear layer with the Taylor-Culick flow) exhibits a significant shift with respect to the Taylor-Culick instability and therefore emphasizes the strong impact of the inhibitor on hydrodynamics.The mecanisms responsible of such behaviour are studied in this thesis with the help of global linear stability analysis and multi-physics numerical computations
Cornwell, Michael. "Causes of Combustion Instabilities with Passive and Active Methods of Control for practical application to Gas Turbine Engines." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1307323433.
Повний текст джерелаCastrillon, Escobar Sebastian. "Instabilité et dispersion de jets de corium liquides : analyse des processus physiques et modélisation dans le logiciel MC3D." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0102/document.
Повний текст джерелаIn the case of a severe accident in a nuclear power plant, the molten core may flow into water and interact with it. The consequences of this fuel-coolant interaction (FCI) for the follow-up of the accident may be numerous so the phenomenon needs to be described accurately, one of them called “steam explosion” can lead to the failure of the nuclear reactor containment. FCI is a complex multiphase interaction involving several physical phenomena. The premixing phase of the interaction consists in the fragmentation and dispersion of corium in the coolant pool. This phase is driven by the fragmentation process which modifies heat transfers (coolant boiling dynamics) and chemical reactions (corium oxidation and hydrogen generation). This thesis brings new elements about the corium jet and droplet breakup with the main goal of improve fragmentation models on the MC3D multiphase code, developed by the IRSN. Our study is based on a multi-scale fragmentation process where the jet fragmentation rate and final droplet dimensions are not coupled themselves. We suppose a fragmentation process resulting from a primary instability (mass transfer within jet and big droplets) depending on the large flow scales and a secondary instability depending on the small flow scales (leading to final droplet breakup). This model has been implemented in MC3D in combination with the MUSIG method recently added to MC3D. In this method, droplets are represented using several classes, each of them with their own droplet diameter, mass and energy fields. Despite new improvements on modeling corium fragmentation, there is still a lack on the comprehension and characterization on the liquid droplet fragmentation, particularly on liquid/liquid configurations. In this thesis, we study in detail droplet breakup using the computational fluid dynamics software GERRIS. As a result, we find a new droplet breakup classification in liquid/liquid configurations, we improve the droplet breakup dynamics comprehension and we analyze the droplet-vortex interaction to determine breakup regime transition
Klironomos, Alexios. "Structural transitions of the vortex lattice in anisotropic superconductors and fingering instability of electron droplets in an inhomogeneous magnetic field." [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0000723.
Повний текст джерелаChatterjee, Prateep. "A Computational Fluid Dynamics Investigation of Thermoacoustic Instabilities in Premixed Laminar and Turbulent Combustion Systems." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11209.
Повний текст джерелаPh. D.
Bolnot, Hadrien. "Instabilités des tourbillons hélicoïdaux : application au sillage des rotors." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4825/document.
Повний текст джерелаThis thesis is devoted to the stability properties of helical vortices, which are of interest for applications such as helicopter and wind turbine wakes.In a first part, the spatio-temporal development of the pairing instability is characterised for an infinite array of vortex rings, using a pseudo-spectral numerical code. We show that this axisymmetric flow model is indeed a good approximation of the helical system in the limit of large helix radius and small pitch. Under these assumptions, and by using appropriate dimensionless variables, we also show that the theoretical result concerning the spatio-temporal growth rate for a double row of point vortices represents a good prediction for the helical case.In a second part, we describe how one or several helical vortices were generated in a carefully controlled way using small-scale rotor models in the water channel of the laboratory. Introducing perturbations with well-defined amplitudes and frequencies, the growth rate of the pairing instability could be measured experimentally and compared to theoretical predictions. The non-linear evolution of these perturbations, as well as other unstable modes of smaller wavelengths, were also observed experimentally for the first time.Finally, these results were applied to helicopter wakes for the prediction of the Vortex Ring State (VRS) regime and to the transition to turbulence in wind turbine wakes
Weber, Norbert. "Modellierung von Tayler-Instabilität und Elektrowirbelströmungen in Flüssigmetallbatterien." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-199285.
Повний текст джерелаArbic, Brian K. "Generation of mid-ocean eddies : the local baroclinic instability hypothesis." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/53047.
Повний текст джерелаIncludes bibliographical references (p. 284-290).
by Brian Kenneth Arbic.
Ph.D.
Mohamed, Jainulabdeen Mohammed Abdul Kadher. "Combustion Noise and Instabilities from Confined Non-premixed Swirl Flames." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1560867354695989.
Повний текст джерелаQadri, Ubaid Ali. "Global stability and control of swirling jets and flames." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245143.
Повний текст джерелаBaey, Jean-Michel. "Instabilites d'un courant d'eau intermediaire." Grenoble 1, 1997. http://www.theses.fr/1997GRE10095.
Повний текст джерелаLeclercq, Tristan. "Flow-induced deformations and stress reduction by flexibility." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX006/document.
Повний текст джерелаThe static deflection of a flexible structure exposed to a transverse flow is classically known to reduce the drag it has to withstand. In the field of biomechanics, the flow-induced deformation of flexible plant elements leading to a reduction of the loads is referred to as `reconfiguration', in order to highlight the alleged benefits of such adaptive process. In this thesis, we investigate the mechanisms underpinning the reconfiguration in flow-structure systems featuring some spatial variability, or some dynamics arising either from the unsteadiness of the free-stream, from a flow-structure coupling leading to an instability, or from vortex-induced vibrations. We show that the ability of flexible structures to reduce the magnitude of the flow-induced loads is preserved in the presence of non-uniformities or dynamics, provided that the design of the structure is such that resistive drag dominates over inertial forces. We also show that the ability to deform has the added benefit of reducing the magnitude of the vortex-induced vibrations. Our work further indicates that light, slender structures are better suited to accommodate the flow-induced loads by reconfiguring, and that the efficiency of the process of load reduction by elastic reconfiguration is weakly sensitive to the spatial distribution of the system properties. Finally, regardless of the regime of reconfiguration, the reduction of the load always results from the concentration of the deformation on a characteristic bending length smaller than the actual length of the structure
Shankare, Gowda Vrishank Raghav. "Radial flow effects on a retreating rotor blade." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53403.
Повний текст джерелаNguyen, Quang Duy. "Numerical and Experimental Investigations of Flows over Confined Circular Cylinders." Thesis, The University of Sydney, 2022. https://hdl.handle.net/2123/29401.
Повний текст джерелаErtugrul, Suat Erdem. "The Effects Of Geometric Design Parameters On The Flow Behavior Of A Dual Pulse Solid Rocket Motor During Secondary Firing." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615184/index.pdf.
Повний текст джерелаetc.) with each other. With the selected PSD geometry alternative the effects of L/D ratio (Length/Diameter ratio) of first pulse chamber, Achamb/APSD ratio (Chamber area/PSD opening area) and APSD/Ath ratio (PSD opening area/Throat area) on the flow behavior is investigated. Flow analyses are performed by simulating the unsteady flow of second pulse operation. With the performed analyses, it is aimed to identify generic geometric definitions for a dual pulse rocket motor.
Ali, Mohamed. "Caractérisation et instabilités des tourbillons hélicoïdaux dans les sillages des rotors." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4708/document.
Повний текст джерелаThis present work is aimed to study helical vortices encountered in the wakes of rotating elements. For this, the generation of a helical wake of a one-bladed-rotor in a laminar velocity field, is simulated by the actuator line method. This method is a coupling of a Navier-Stokes (NS) solver with the Actuator Line Method where the blade is replaced by the body forces. This method has been implemented in a finite difference code, that we have written in parallel to solve the 3D incompressible NS equations written in cylindrical coordinates. The order of accuracy of the method is two both in time and space. The NS solver was validated comparing growth rates of an unstable jet, found numerically, and those of linear instability theory. A good agreement was found. A good agreement was also found comparing numerical results to analytical formulations and experimental data. It was shown that the method predicts well the blade aerodynamics . Then, the helical tip vortex is characterized for different Reynolds numbers and Tip Speed Ratios. The vorticity and the azimuthal velocity were found self-similar and the vortex core follows asymptotically the linear 2D diffusion law. A simple model for the helical vortex core was proposed. The presence of an axial velocity inside the vortex core was highlighted. Then, a stability study of the helical tip vortex was done using an angular velocity dependent on time to perturb the flow. The largest growth rates were found in good agreement with those of the (2D) pairing instability. Three types of modes were identified based on the perturbation frequency. The results are similar to those found in previous analytical and experimental works
Garnier, Elodie. "Étude numérique des instabilités de jets baroclines." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0011.
Повний текст джерелаColaciti, Alysson Kennerly. "Aeroacústica e instabilidades de uma camada de mistura compressível." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-26052009-145506/.
Повний текст джерелаTurbo-fan and turbo-jet engines are the most important noise sources during the aircraft take off, climb and acceleration segments. Owing to this fact, the jet flow noise has been studied in the past years. For the landing stage, the slat is an important sound source. In this case, the slat leading edge frequently experiences a boundary layer deattachment causing the development of a mixing layer inside the slot. Nevertheless, there are many aspects of such phenomenon that have not been studied yet. Mixing layers constitutes an usual approach for jet flow instability in aeroacoustics studies. The stategy is to study the mixing layer in order to understand the jet-flow. This strategy becomes better as the ratio between the jet diameter and mixing layer thickness becomes larger. This approach is only reazonable for the jet flow axi-symetric unstable modes. The effect of vortex modulation on the vortex pairing sound production has not been found in the literature. If such effect could cause a significant change in the sound generation patterns, an active flow control system could be developed in order to enhance the jet noise performance. The purpose of the present work was to investigate such effect. It was also possible to observe a single vortex pairing inside a wide domain without the Doppler effect. The strategy was to study the vortex pairing in a bi-dimensional mixing layer under temporal development. The method used was the direct numerical simulation (DNS) of the compressible bidimensional (2D) Navier Stokes equations written in a nonconservative form of the characteristics formulation. The results showed that the vortex modulation did not produce a significant change on the vortex pairing sound.
Costa, Junior Rubens Pereira. "Efeito combinado da relaxação da corrente e de uma camada de corrente-vórtice sobre a instabilidade magneto-rotacional." reponame:Repositório Institucional da UFABC, 2014.
Знайти повний текст джерелаDissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2014.
Neste trabalho, discutimos o efeito combinado de uma relaxção infinita para a corrente e da formação de uma camada de corrente-vórtice sobre a instabilidade magneto-rotacional em um uido condutor. Mostramos que a amplificação relativa da viscosidade magnética, desde a estabilidade marginal até a instabilidade determinada pela taxa de crescimento máxima da perturbação, é de aproximadamente 924% quando efeitos resistivos são dominantes e que ela é de aproximadamente 220% no limite ideal. Isto significa que o efeito combinado é muito mais efciente para amplicar viscosidade magnética que a simples in uência devida à tensãoo magnética usual. Os resultados apresentados aqui podem contribuir para a compreensão dos vários processos que desempenham um papel significativo no mecanismo da viscosidade anômala observada em discos de acreção keplerianos. Argumentamos que o novo efeito deve ser relevante em discos de acreação delgados. Finalmente, apresentamos uma proposta de continuidade natural deste trabalho.
Lima, Thamires Andrade. "Pico de Bóson e transições dinâmicas em água confinada em aminoácidos." reponame:Repositório Institucional da UFABC, 2014.
Знайти повний текст джерелаTese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2014.
Neste trabalho, discutimos o efeito combinado de uma relaxção infinita para a corrente e da formação de uma camada de corrente-vórtice sobre a instabilidade magneto-rotacional em um uido condutor. Mostramos que a amplificação relativa da viscosidade magnética, desde a estabilidade marginal até a instabilidade determinada pela taxa de crescimento máxima da perturbação, é de aproximadamente 924% quando efeitos resistivos são dominantes e que ela é de aproximadamente 220% no limite ideal. Isto significa que o efeito combinado é muito mais efciente para amplicar viscosidade magnética que a simples in uência devida à tensãoo magnética usual. Os resultados apresentados aqui podem contribuir para a compreensão dos vários processos que desempenham um papel significativo no mecanismo da viscosidade anômala observada em discos de acreção keplerianos. Argumentamos que o novo efeito deve ser relevante em discos de acreação delgados. Finalmente, apresentamos uma proposta de continuidade natural deste trabalho.
Gennaro, Elmer Mateus. "Análise da instabilidade hidrodinâmica de uma esteira assimétrica." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-22042008-112415/.
Повний текст джерелаIn an aircraft, high-lift devices operating at high angle of attack promote the formation wakes. Such wakes influence the aerodynamic performance. The slat wake, for example, affects the transition point of the wing main element and is the most important source of noise in the airframe. Owing to the generation of lift these wakes are asymmetries. Bodies immersed in a shear flow also produce asymmetric wakes, with important applications to the oil industry. There are aspects of such flows that need investigation. For instance, there is no consensus about whether or not the asymmetry can suppress vortex shedding or how it affects the shedding frequency. Indeed there is an apparent discrepancy between results found in literature. The aim of the present work was to contribute to this issue. The idea was to investigate the influence of asymmetry on a two-dimensional wake profile under temporal development. The asymmetric wake profile was obtained by a combination between a Gaussian wake profile and a hyperbolic tangent mixing layer profile. The bidimensional (2D) linear stability theory analysis of the profile was performed. The work also included 2D Direct Numerical Simulation (DNS) using the characteristic formulation of the compressible Navier-Stokes equations in non-conservative form. The results showed that the asymmetry reduces the shedding frequency for the range of 0 \'< OU =\' K \'< OU =\' 0,25 investigated. For small values of the asymmetric parameter the results showed that the asymmetry promotes stability. Effects of the number of Mach in asymmetric wake also were investigated. The results showed that the increase of Ma reduced the maximum rate amplification and the band unstable. Moreover, the results from literature were reconciled by taking into account the variation of the drag coefficient with the asymmetry. Therefore, a possible explanation for the controversy was offered.
Dumouchel, Fabien. "Etude expérimentale des champs dynamiques et thermiques de l'écoulement de Benard-Von Karman en aval d'un obstacle chauffé dans l'air et dans l'eau." Rouen, 1997. http://www.theses.fr/1997ROUES067.
Повний текст джерелаMoturi, Viswa Maitreyi. "Etude expérimentale d'instabilités à travers la convection turbulente de Rayleigh-Bénard et les instabilités de trajectoires de bulles en ascension." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAD030.
Повний текст джерелаThe present work focuses on two common fluid flow problems namely, Turbulent Rayleigh-Bénard Convection and Path instability of rising bubbles immersed in a liquid. Concerning Rotating Turbulent Rayleigh-Bénard Convection, the flow field and temperature field were measured respectively by Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) in a vertical plan of symmetry of our cylindrical cell of aspect ratio 1. The weakening of the Large Scale Circulation with decreasing Rossby number - leading to its complete disappearance - was confirmed as well as the formation of vortex columns in the rotation dominated regime. By doing velocity cross correlations, it has been possible to prove experimentally that the vorticity of the columns change direction in the cell’s center. The velocity fluctuations in the cell are highly anisotropic and follow a scaling of Ro0.2 in the rotation affected regime. The temperature of the vortex columns as well as of individual plumes has been estimated by LIF measurements. Concerning the Path instability of rising bubbles, small bubbles rise in straight path, whereas beyond a critical size, bubbles rise in zigzag or helical path. Some new experimental points on the marginal stability curve have been obtained by working in silicon oils of 5 and 10 cst and in water. The agreement with the most recent numerical simulations is only partial. The rise velocity, frequency and amplitude of oscillation have also been measured and suggest a supercritical Hopf bifurcation
Omowunmi, Sunday Chima. "Modelling the nonlinear dynamics of polymer solutions in complex flows." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/modelling-the-nonlinear-dynamics-of-polymer-solutions-in-complex-flows(3230a688-0ea4-4620-bda1-396346feb645).html.
Повний текст джерелаHamma, Laurence. "Etude de la diffusion de la chaleur en aval d'un cylindre chauffé à faible nombre de Reynolds (40." Rouen, 1988. http://www.theses.fr/1988ROUES031.
Повний текст джерелаCaton, François. "Écoulement de Taylor-Couette stratifié : régimes, bifurcations et transport." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10071.
Повний текст джерелаKubíček, 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.
Повний текст джерелаPeerhossaini, Hassan. "L'instabilite d'une couche limite sur une paroi concave : les tourbillons de gortler." Paris 6, 1987. http://www.theses.fr/1987PA066023.
Повний текст джерелаGardarin, Benoît. "Contrôle par générateurs de vortex d'un écoulement turbulent décollé." Palaiseau, Ecole polytechnique, 2009. http://www.theses.fr/2009EPXX0084.
Повний текст джерелаThis study deals with turbulent flow separation and its control by means of vortex generators. The experimental study is conducted downstream of a rounded ramp modeling an aircraft air intake. Due to this curvature, turbulent flow separation occurs. The first part of the work investigates the separation behavior, which involves at least three mechanisms: a mixing layer instability, a bi-dimensional beating of the recirculation bubble, and a three dimensional oscillation. The second part is devoted to the control. Both mechanical and fluidic vortex generators are used. A parametrical study allows the determination of two efficient configurations, which reduces the separated areas. Then, we show that the efficiency of this specific control strategy depends on two mechanisms: the first one is mixing, which can be characterized by the vortex circulation. The second one is vortex instability, which is responsible for the vortex disruption. Two criteria based on characteristics time scales are the constructed and validated in our experiment and other cases from the literature
forterre, yoel. "instabilités dans les écoulements granulaires." Phd thesis, Université de Provence - Aix-Marseille I, 2002. http://tel.archives-ouvertes.fr/tel-00010005.
Повний текст джерелаMeunier, Patrice. "Etude expérimentale de deux tourbillons corotatifs." Phd thesis, Université de Provence - Aix-Marseille I, 2001. http://tel.archives-ouvertes.fr/tel-00011665.
Повний текст джерелаBrun, Christophe. "Étude expérimentale et numérique de l'interaction forte entre sillages d'obstacles cylindriques." Université Joseph Fourier (Grenoble ; 1971-2015), 1998. http://www.theses.fr/1998GRE10049.
Повний текст джерелаEl, Anadouli Mohamed. "Étude des instabilités imparfaites de Couette-Taylor." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL117N.
Повний текст джерелаMoet, Henri. "Simulation numérique du comportement des tourbillons de sillage dans l'atmosphère." Toulouse, INPT, 2003. http://www.theses.fr/2003INPT007H.
Повний текст джерелаBuzík, 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.
Повний текст джерелаSelçuk, Savas Can. "Numerical study of helical vortices and their instabilities." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066138/document.
Повний текст джерелаThe work presented in this manuscript is a contribution to the numerical study of helical vortex systems and their instabilities, as encountered in the near wake of rotors (wind turbines, helicopters,~...). In this work, such flows are locally modelled within the framework of helical symmetry. Using a dedicated DNS code, helical quasi-stationary basic state solutions are obtained for several configurations, and accurate tools for their characterisation are developed: angular velocity, core size and ellipticity, structure of the velocity and vorticity fields... An Arnoldi algorithm is then coupled to a linearised version of the code. The dominant instability modes with the same symmetry as the base flow are extracted as a function of the system parameters: number of vortices, helical pitch, core size, Reynolds number, presence of a central hub vortex. Under a critical helical pitch, the instability is dominated by a global displacement mode analogous to the pairing mode of an infinite array of point vortices or vortex rings. In the nonlinear regime, this mode gives rise to complex dynamics: overtaking events, leapfrogging and merging. Another linearised code is then used to extract modes characterised by a wavelength along the helix, which break the helical symmetry of the base flow. At low wavenumbers, these modes induce local displacements of the vortices and bring together portions of neighbouring coils. At large wavenumbers, another type of mode is found, which deforms the vortex cores through the elliptical instability mechanism
Payen, Gérard. "Contribution à l'étude des régimes d'écoulement à faible nombre de Reynolds au travers d'expansions symétriques par simulations numériques instationnaires basées sur une méthode de Random Vortex hybride." Rouen, 1991. http://www.theses.fr/1991ROUES017.
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