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Dissertations / Theses on the topic 'Vorticity'
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1
Ho, Ho San. "Vorticity and vorticity balance in the South China Sea circulation /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MATH%202007%20HO.
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Carroll, John B. "Free-surface/vorticity interaction." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA273263.
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Thesis (M.S. in Mechanical Engineering and Mechanical Engineer) Naval Postgraduate School, September 1993.Thesis advisor(s): Turgut Sarpkaya. "September 1993." Bibliography: p. 46-47. Also available online.
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Birkett, Hannah Rachel. "Reduced upper-tropospheric potential vorticity." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299301.
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Berrisford, Paul. "Potential vorticity in extratropical cyclones." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233686.
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Davis, Christopher A. (Christopher Alfred). "Cyclogenesis diagnosed with potential vorticity." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/51476.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1990.Includes bibliographic references (p. 188-194).
by Christopher A. Davis.
Ph.D.
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Anderson, Jamie Marie. "Vorticity control for efficient propulsion." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10570.
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Boss, Emmanuel. "Dynamics of potential vorticity fronts /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/11031.
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Neves, Alberto P. C. "Unbalanced frontogenesis with constant potential vorticity." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1996. http://handle.dtic.mil/100.2/ADA326390.
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Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, December 1996.Thesis advisor(s): Roger T. Williams, Melinda S. Peng. "December 1996." Includes bibliographical references (p. 75-76). Also available online.
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Mathioulakis, Dimitri. "Vorticity shedding over two-dimensional bodies." Diss., This resource online, 1985. http://scholar.lib.vt.edu/theses/available/etd-09162005-115000/.
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Wibawa, Martin Sulaiman. "Vorticity transfer through rapid area change." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62791.
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Thesis (S.M. in Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 77-81).
Extensive studies have been conducted on the use of biomimetic foils for propulsion and maneuvering of vehicles. These studies, however, mostly focuses on the use of sinusoidal motion similar to bird flapping or fish swimming to generate the necessary forces. Few studies have been conducted to investigate the generation of maneuvering forces by using rapid vorticity transfer into the fluid through a rapid motion as observed in some animals. In this study a NACA 0012 foil was towed steadily at Reynolds number of 14000, then the foil is rapidly accelerated in the transverse direction. Two different cases were tested: One where the area decreases and one where it increases, referred to as vanishing foil and emerging foil, respectively. Various angle of attacks were tested, and in all the cases the circulation is conserved. The method of Particle Image Velocimetry and flow visualization were used to map out the three-dimensional vortical structure after the rapid motion. In the emerging foil experiment the flow structure is similar to the case of accelerating wing. From the vanishing foil experiment, however, we managed to discover a phenomenon called global separation, where separation happens instantaneously over the entire surface of the body. This global separation allows a more effective and rapid transfer of vorticity, at about one order of magnitude faster than vorticity transfer through conventional means.
by Martin Sulaiman Wibawa.
S.M.in Naval Architecture and Marine Engineering
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Long, Dana Marie. "Excitation of Low-Level Energy Wave Accumulations and Tropical Cyclone Formation." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7282.
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A spectral shallow water model is used at the 850 mb level to investigate the effects of cyclonic vorticity on heating in the lower troposphere and how this in turn causes an increase in cyclonic vorticity generation, creating a nonlinear vorticity feedback mechanism.
The model is initialized with NCEP-NCAR reanalysis data from the period 1990-2003 and then used to simulate a heating forcing function centered in east Africa. The model is simulated using a Gaussian damped basic state, a zonally symmetric basic state, and a zero basic state. The heating forcing function is applied to these different basic states with a scaled mass sink to simulate heating in the atmosphere. The heating forcing function creates a vorticity feedback mechanism that increases cyclonic vorticity.
The analysis of these different basic states shows that the Gaussian damped basic state reduces the amplitude of the observational fields at the poles, increases the observational fields in the tropical region and increases the stability of the model at shallow depths. The zero basic state does have a significant effect on cyclonic vorticity generation, but does not improve the capability of the wave to propagate westward into the Atlantic Ocean. The zonally symmetric basic state succeeds in increasing the amount of cyclonic vorticity generated. The zonally symmetric basic state, once the vorticity non-feedback region is extended, is also very effective at increasing the amount of cyclonic vorticity generated and increasing the propagation of this wave westward into the Atlantic Ocean. The analysis suggests that the vorticity feedback mechanism created by the heating forcing function is affected by cyclonic vorticity when a zero and zonally symmetric basic state are used.
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Petropoulos, Ilias. "Study of high-order vorticity confinement schemes." Thesis, Paris, ENSAM, 2018. http://www.theses.fr/2018ENAM0001/document.
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Les tourbillons sont des structures importantes pour une large gamme d'écoulements de fluides, notamment les sillages, l'interaction fluide-structure, les décollements de couche limite et la turbulence. Cependant, les méthodes numériques classiques n'arrivent généralement pas à donner une représentation précise des tourbillons. Ceci est principalement lié à la dissipation numérique des schémas qui, si elle n'est pas spécifiquement calibrée pour le calcul des écoulements tourbillonnaires, conduit à une diffusion artificielle très rapide des tourbillons dans les calculs. Parmi d'autres approches, la méthode "Vorticity Confinement" (VC) de J. Steinhoff permet de compenser la dissipation des schémas au sein des tourbillons en introduisant une anti-dissipation non-linéaire, mais elle n’est précise qu’au premier ordre. D’autre part, des progrès significatifs ont récemment été accomplis dans le développement de méthodes numériques d’ordre élevé. Celles-ci permettent de réduire ce problème de dissipation excessive, mais la diffusion des tourbillons reste importante pour de nombreuses applications. La présente étude vise à développer des extensions d’ordre élevé de la méthode VC pour réduire cette dissipation excessive des tourbillons, tout en préservant la précision d'ordre élevé des schémas. Tout d'abord, les schémas de confinement sont analysés dans le cas de l'équation de transport linéaire, à partir de discrétisations couplées et découplées en espace et en temps. Une analyse spectrale de ces schémas est effectuée analytiquement et numériquement en raison de leur caractère non linéaire. Elle montre des propriétés dispersives et dissipatives améliorées par rapport aux schémas linéaires de base à tous les ordres de précision. Dans un second temps, des schémas VC précis au troisième et cinquième ordre sont développés pour les équations de Navier-Stokes compressibles. Les termes correctifs restent conservatifs, invariants par rotation et indépendants du schéma de base, comme la formulation originale VC2. Les tests numériques valident l'ordre de précision et la capacité des extensions VC d’ordre élevé à réduire la dissipation dans les tourbillons. Enfin, les schémas avec VC sont appliqués au calcul des écoulements turbulents, dans une approche de simulation de grandes échelles implicite (ILES). Les schémas numériques avec VC présentent une résolvabilité améliorée par rapport à leur version linéaire de base, et montrent leur capacité à décrire de façon cohérente ces écoulements tourbillonnaires complexesVortices are flow structures of primary interest in a wide range of fluid dynamics applications including wakes, fluid-structure interaction, flow separation and turbulence. Albeit their importance, standard Computational Fluid Dynamics (CFD) methods very often fail to provide an accurate representation of vortices. This is primarily related to the schemes’ numerical dissipation which, if inadequately tuned for the calculation of vortical flows, results in the artificial spreading and diffusion of vortices in numerical simulations. Among other approaches, the Vorticity Confinement (VC) method of J. Steinhoff allows balancing the baseline dissipation within vortices by introducing non-linear anti-dissipation in the discretization of the flow equations, but remains at most first-order accurate. At the same time, remarkable progress has recently been made on the development of high-order numerical methods. These allow reducing the problem of excess dissipation, but the diffusion of vortices remains important for many applications. The present study aims at developing high-order extensions of the VC method to reduce the excess dissipation of vortices, while preserving the accuracy of high-order methods. First, the schemes are analyzed in the case of the linear transport equation, based on time-space coupled and uncoupled formulations. A spectral analysis of nonlinear schemes with VC is performed analytically and numerically, due to their nonlinear character. These schemes exhibit improved dispersive and dissipative properties compared to their linear counterparts at all orders of accuracy. In a second step, third- and fifth-order accurate VC schemes are developed for the compressible Navier-Stokes equations. These remain conservative, rotationally invariant and independent of the baseline scheme, as the original VC2 formulation. Numerical tests validate the increased order of accuracy and the capability of high-order VC extensions to balance dissipation within vortices. Finally, schemes with VC are applied to the calculation of turbulent flows, in an implicit Large Eddy Simulation (ILES) approach. In these applications, numerical schemes with VC exhibit improved resolvability compared to their baseline linear version, while they are capable of producing consistent results even in complex vortical flows
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Salman, Hayder. "Numerical simulation of streamwise vorticity enhanced mixing." Thesis, Loughborough University, 2001. https://dspace.lboro.ac.uk/2134/7386.
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The goal of the present work is a detailed and comprehensive study to assess the accuracy of the numerical simulation of the mixing processes in a lobed mixer flow field via a Reynolds-averaged solution method. To meet this goal, the first objective of the current work was to establish the suitability of various meshing strategies that would allow the complex mixer geometries found in current gas-turbine engine designs to be captured, together with the associated convoluted shear layers. A second objective was targeted at providing further insight and understanding of the capability of eddy-viscosity-based turbulence models in capturing the convoluted shear layers. Simplified mixer configurations selected from the literature were studied under incompressible isothermal flow conditions. Two solution algorithms were employed to model the mixer flow fields. The first consisted of a pressure-based structured grid methodology developed for incompressible flows. A density-based mixed-unstructured grid algorithm for compressible flows was also used, with extensions to low Mach number flows made possible through a low Mach number preconditioner. The effects of turbulence were modelled using ak-e turbulence model. The absence of this model in the code made available for the unstructured algorithm necessitated its implementation as a first step in the current work. The effects of unstructured mesh type on the prediction of flows with internal mixing layers were first assessed for an incompressible planar mixing layer. This simplified case was used as a benchmark case to help understand the effects on the convoluted shear layers arising within the lobed mixer flows. To quantify the capability of a Reynolds-averaged approach in simulating the turbulent mixer flow field, two variants of the two equation k-e model were employed. The first constituted the standard linear high Reynolds number k-e model of Launder and Spalding [62]. The second model was a quadratic non-linear version developed by Speziale [99] for the prediction of secondary flows in non-circular ducts. The relative merits of these two models was assessed through detailed comparisons with experimental data taken from the literature. Of particular importance in the mixer flow was the formation and subsequent evolution of the vorticity field. Consequently, this motivated a detailed study of the evolving vorticity field. The investigations thus far were based on a simplified mixer configuration with no temperature differences between the two streams. Therefore, as a final step, a realistic scarfed mixer was modelled in an attempt to model the temperature mixing. The main contribution of the present work is the assessment of a grid-based Reynolds-averaged solution procedure for the prediction of lobed mixer flows. The study revealed that capturing the initial mixing region proved to be most difficult. Firstly, unstruc-tured meshes employing non-hexahedral elements were very inefficient at simulating the mixing layer in the early stages. Secondly, the initial mixing region presented significant difficulties for the Reynolds-averaged solution method in which neither turbulence model was capable of correctly reproducing the turbulence field. Despite this, global parameters such as momentum thickness and streamwise circulation were well captured in the predictions.
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Steele, Stephanie Chin. "Global vorticity shedding for a vanishing foil." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78192.
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Thesis (S.M. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 59-60).
We explore several aspects of the phenomenon we call global vorticity shedding. Global vorticity shedding occurs when an object in viscous fluid suddenly vanishes, shedding the entire boundary layer vorticity into the wake at once. In our experiments we approximate the disappearance of a towed foil by rapidly retracting the foil in the span-wise direction. Global vorticity shedding is in distinct contrast with conventional shedding, in which vorticity is shed from a body from only a few separation points into the fluid. In this work, we show that for a square-tipped vanishing foil at an angle of attack, the globally shed boundary layer vorticity forms into primary vortices, which evolve and eventually amalgamate with secondary vortices to leave two lasting vortices in the wake. The secondary vortices are a result of three-dimensionality in the flow. For a streamlined-end foil, we achieve a simpler and less three-dimensional wake with no secondary vortices, arid only one lasting vortex dominating the wake. However, due to the initial vorticity distribution near the streamlined end of the foil, the initial circulation is reduced. We also show that the lasting vortices are capable of producing reasonably large forces on a body through simple potential flow estimations, aid that vortex formation times are small, with vortices fully formed nearly instantaneously in the flow. These features are promising for a force transducer using global vorticity shedding to impart large and fast maneuvering forces on an underwater vehicle.
by Stephanie Chin Steele.
S.M.in Ocean Engineering
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Haydon, Thomas Richard. "Turbulence and vorticity generated by breaking waves." Thesis, University of Edinburgh, 1998. http://hdl.handle.net/1842/14031.
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Experiments have been performed on the flow generated after the breaking of laboratory-generated water waves. Digital Particle Image Velocimetry (DPIV) was employed to make flow-field measurements in the post-breaking region of both spilling and plunging breakers, for a range of times close to breaking. The development of the technique in order to study the temporal evolution of the flow with high resolution CCD cameras is outlined. The visual record generated by PIV is presented in the form of a large set of vorticity and velocity maps. This information is used to describe the flow and its evolution over time. The raw data is then further processed in order to demonstrate the effectiveness of PIV in measuring complex turbulent characteristics. Energy and velocity profiles, temporal decay of turbulent kinetic energy and power spectra are calculated and the results compared with other experimental, numerical and theoretical work. Similarities and differences are considered and explanations offered.
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MOZER, JOEL BARNEY. "LEE VORTICITY PRODUCTION BY TROPICAL MOUNTAIN RANGES." Diss., The University of Arizona, 1994. http://hdl.handle.net/10150/186600.
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Numerical simulations using the Penn State University/NCAR MM4 model are performed to examine a stably stratified, zonal easterly flow past large scale three-dimensional mountain ranges in a rotating, initially barotropic, atmosphere. Upstream blocking by the mountain range diverts the flow primarily to the south and around the mountain. Conservation of potential vorticity results in the formation of a horizontal jet at low levels south of the mountain. This jet is barotropically unstable and leads to a continuous production of synoptic scale vorticity maxima which separate from the mountain and propagate downstream. Numerical simulations using topography representative of the Sierra Madre in Mexico imply that this mechanism may be important in providing some of the initial disturbances which grow into tropical cyclones in the eastern North Pacific Ocean. The wave train produced in the simulations corresponds to waves with 3-7 day periods which have been identified observationally in the eastern North Pacific region. The sensitivity of this effect to the stability of the basic state and the upstream wind speed is investigated. Simulations are also performed which show that the Hoggar and Atlas mountains of west-central Africa block the low-level easterlies resulting in a barotropically unstable jet and a train of vorticity maxima which separate from the mountain and propagate downstream. The spacing of these disturbances is roughly 1600 km and they propagate to the east with a period of about 2.5 days. These characteristics correspond to those of observed waves in the Africa/Atlantic region. It will also be shown that the unique topography of north-central Africa results in a mid-tropospheric easterly jet which has a maximum between 0-10°E and 15-20°N. The location and magnitude of this jet correspond to the so-called African easterly jet which is usually attributed to the strong surface temperature gradients over the continent of Africa. The numerical simulations presented in this work suggest that the mechanical effect of the topography may provide a constant source of energy for the maintenance of the African easterly jet.
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Lokharu, Evgeniy. "Small-amplitude steady water waves with vorticity." Doctoral thesis, Linköpings universitet, Matematik och tillämpad matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-134243.
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The problem of describing two-dimensional traveling water waves is considered. The water region is of finite depth and the interface between the region and the air is given by the graph of a function. We assume the flow to be incompressible and neglect the effects of surface tension. However we assume the flow to be rotational so that the vorticity distribution is a given function depending on the values of the stream function of the flow. The presence of vorticity increases the complexity of the problem and also leads to a wider class of solutions. First we study unidirectional waves with vorticity and verify the Benjamin-Lighthill conjecture for flows whose Bernoulli constant is close to the critical one. For this purpose it is shown that every wave, whose slope is bounded by a fixed constant, is either a Stokes or a solitary wave. It is proved that the whole set of these waves is uniquely parametrised (up to translation) by the flow force which varies between its values for the supercritical and subcritical shear flows of constant depth. We also study large-amplitude unidirectional waves for which we prove bounds for the free-surface profile and for Bernoulli’s constant. Second, we consider small-amplitude waves over flows with counter currents. Such flows admit layers, where the fluid flows in different directions. In this case we prove that the initial nonlinear free-boundary problem can be reduced to a finite-dimensional Hamiltonian system with a stable equilibrium point corresponding to a uniform stream. As an application of this result, we prove the existence of non-symmetric wave profiles. Furthermore, using a different method, we prove the existence of periodic waves with an arbitrary number of crests per period.
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Freire, José Arruda de Oliveira. "Dynamics and nucleation of vorticity in superfluids /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9726023.
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Bogdanoff, Alec Setnor. "Global evolution of synoptic-scale vorticity maxima." Tallahassee, Fla. : Florida State University, 2008. http://purl.fcla.edu/fsu/lib/digcoll/undergraduate/honors-theses/341790.
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Hall, Ian Melvyn. "Quasi-modes and the evolution of coherent planar vortices." Thesis, University of Exeter, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269719.
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Montenegro, Gonzalo. "Three dimensional vorticity field in the California current." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA276951.
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Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, March 1993.Thesis advisor(s): Chu, Peter. "March 1993." Cover title: Three ... current system. Bibliography: p. 92-93. Also available online.
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Wang, Yuhui. "The potential vorticity budget of mean winter anomalies." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0029/MQ55097.pdf.
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Wang, Yuhui 1970. "The potential vorticity budget of mean winter anomalies /." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=29930.
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NCEP reanalyses have been used to compute the climatological isentropic potential vorticity (IPV) budget at the 315K level for 39 winters and for those winters with a North Atlantic Oscillation (NAO) as well as winters with a Pacific/North American (PNA) pattern.The climatology shows two main IPV sources, each being upstream of the two main centers of positive PV on the east coasts of North America and Asia. The results for the winters with a NAO (PNA) anomaly show, in particular, that the mean-winter IPV anomalies associated with these patterns also have upstream sources. The importance of the latter is not as clear as that of the continential sources that maintain the climatological centers.
The mean-winter IPV advection that balances the IPV sources/sinks is composed of the advection by the time-mean flow and by the transient eddies (decomposed into high- and low-frequency components), where the former is the dominant component. The latter are found to produce a negative feedback in that they act to reduce the amplitude of the IPV anomaly. For the NAO anomaly, low-frequency transient advection is more important, while high-frequency transient advection is more statistically significant for the PNA anomaly. Both the high and low-frequency advection have comparable contributions in maintaining the climatological distribution of the stationary eddy IPV.
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Griffiths, R. M. "The interaction between vorticity and internal gravity waves." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599729.
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Our dissertation investigates the interaction between a localised region of vorticity and internal gravity waves, using only analytical methods. We aim to understand further the mechanism by which internal gravity waves radiate vorticity and to address the validity of applying an analogy of Lighthill's sound generation theory to the generation of internal gravity waves. We consider an initial value problem for a two-dimensional incompressible density-stratified fluid. The buoyancy frequency is taken to be constant and the Boussinesq approximation is imposed. To make the analysis as general as possible, and more importantly to assess the importance of nonlinear mechanisms in the generation of internal gravity waves, we include nonlinear terms in the equations of motion. To make further analytical progress we consider the case of a large internal Froude number Fr, which is more often realised in physical scenarios. We attempt solutions to the equations of motion via asymptotic expansions in the small parameter ε = 1/Fr2. We consider the main results of the dissertation to be twofold. First we see the appearance of distinct regions in space-time where different dominant balances occur in the equations of motion. In particular we have an inner region, a far field and a wave region, and we have been able to perform an asymptotic matching of the different solutions in these regions successfully. The magnitude of these regions is characterised by the small parameter ε. It is hoped that the existence of such regions could be confirmed experimentally. Such space-time regions do not occur in the linear analysis of this problem, but are only evident when nonlinear terms are retained in the equations of motion. The second part of our analysis that we consider to be important arises through the study of the dynamics of vorticity transfer in our problem. The introduction of stratification destroys conservation of vorticity; the non-conservation of vorticity is observed in the inner region and the far field.
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Gutierrez-Camacho, Jorge Arturo. "Vorticity production in flows associated with mesoscale mountains." Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360754.
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Norton, Warwick Alexander. "Balance and potential vorticity inversion in atmospheric dynamics." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293018.
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Koh, Yang-Moon. "Numerical solution of three-dimensional vorticity transport equations." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/46971.
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Manning, Ted Adam. "Experimental studies of mixing flows with streamwise vorticity." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13048.
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Louch, Derek Stanley. "Vorticity and turbulent transport in premixed turbulent combustion." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625005.
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Wang, Xiaolin. "A numerical study of vorticity-enhanced heat transfer." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54017.
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In this work, we have numerically studied the effect of the vorticity on the enhancement of heat transfer in a channel flow. In the first part of the work, we focus on the investigation of a channel flow with a vortex street as the incoming flow. We propose a model to simulate the fluid dynamics. We find that the flow exhibits different properties depending on the value of four dimensionless parameters. In particularly, we can classify the flows into two types, active and passive vibration, based on the sign of the incoming vortices. In the second part of the work, we discuss the heat transfer process due to the flows just described and investigate how the vorticity in the flow improves the efficiency of the heat transfer. The temperature shows different characteristics corresponding to the active and passive vibration cases. In active vibration cases, the vortex blob improves the heat transfer by disrupting the thermal boundary layer and preventing the decay of the wall temperature gradient throughout the channel, and by enhancing the forced convection to cool down the wall temperature. The heat transxfer performance is directly related to the strength of the vortex blobs and the background flow. In passive vibration cases, the corresponding heat transfer process is complicated and varies dramatically as the flow changes its properties. We also studied the effect of thermal parameters on heat transfer performance. Finally, we propose a more realistic optimization problem which is to minimize the maximum temperature of the solids with a given input energy. We find that the best heat transfer performance is obtained in the active vibration case with zero background flow.
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Reasons, Scott. "Singularities of the stochastic Burgers equation with vorticity." Thesis, Swansea University, 2004. https://cronfa.swan.ac.uk/Record/cronfa43010.
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Huo, Zonghui. "Numerical prediction and potential vorticity diagnosis of extratropical cyclones." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ29963.pdf.
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Pesce, Matthew M. "Unsteady pressure and vorticity fields in blade-vortex interactions." Thesis, This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-03122009-040643/.
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Huo, Zonghui. "Numerical prediction and potential vorticity diagnosis of extratropical cyclones." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=42058.
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By combining numerical simulations with different diagnostic tools, this thesis examines the various aspects of two explosively deepening cyclones--the superstorm of March 12-14 1993 and a storm that occurred during the Intensive Observation Period 14 (IOP-14) of the Canadian Atlantic Storm Program (CASP). Using conventional observations, the general aspects of the storms are documented and the dynamical and physical mechanisms are discussed. Then the life cycles are simulated with the Canadian Regional Finite-Element model. To improve the model initial conditions, a methodology is proposed on the basis of potential vorticity thinking, and is tested to be successful in the simulation of the March 1993 superstorm. Using the successful simulations as control runs, a series of numerical sensitivity experiments are conducted to study the impacts of model physics on the development of the two rapidly deepening cyclones.The deepening mechanisms of both storms are examined within the context of PV thinking, i.e., using piecewise potential vorticity inversion diagnostics. In both cases, the upper-level PV anomalies contribute the most to the surface cyclone, followed by the lower-level thermal anomalies and diabatic heating related moist PV anomaly. It is found that a favorable phase tilt between the upper- and lower-level PV anomalies allows a mutual interaction between them, in which the circulations associated with the upper-level anomalies enhance the lower-level anomalies, which in turn feedback positively into the upper-level PV anomalies. In addition to the vertical interactions, there also exist lateral interactions between the upper-level PV anomalies for the March 1993 superstorm. The upper-level PV features (troughs) are isolated with the piecewise PV inversion. By removing or changing the intensity of the trough in the initial conditions, the RFE model is integrated to examine the impact of each trough and its interaction with the other trough on the superstorm development.
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Kimbell, Peter. "Heat, moisture and vorticity budgets of CASP storm #14." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=64021.
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Woollings, Tim. "Entropy and potential vorticity in dynamical core atmosphere models." Thesis, University of Reading, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412174.
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Beare, Robert J. "Potential vorticity sensitivity maps and the predictability of cyclones." Thesis, University of Reading, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394128.
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Tew, David Early. "Streamwise vorticity enhanced compressible mixing downstream of lobed mixers." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10719.
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Underwood, David Scott. "Effect of heat release on streamwise vorticity enhanced mixing." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/47390.
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Krishnan, Anantha. "Numerical study of vorticity-combustion interactions in shear flow." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14188.
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Qin, Lihai. "Vorticity Modeling for the Flow Over Surface-Mounted Prisms." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31859.
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Vorticity modeling is used to simulate the flow around a surface-mounted prism. The objective is
to examine whether vorticity modeling can give satisfactory information about surface pressure
fluctuations which are mostly due to the outer or inviscid flow. Differences between results
obtained with vorticity modeling and what one should expect from DNS and LES are pointed
out. These include the difference between the governing equations, the shortcomings of having a
2-D simulation and the realization of introducing and convecting vorticity to simulate some
turbulence aspects. All necessary details needed for the setup of vorticity modeling for complex
flows, such as the one considered here are given. These details include choice of elements, the
calculation of velocities, the application of boundary conditions and calculation of pressure. The
numerical procedure and our use of parallelization in the code are explained. The results
presented on velocity magnitude, vorticity and pressure show important characteristics of the
flow field in terms of interaction of positive and negative vorticities and their effects on the
surface pressure. The calculated peak and mean values for the pressure coefficients at the leading
edge are close to those measured in separating flows over prisms.Master of Science
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Geiman, Joe D. "Vorticity dynamics in the presence of shallow water waves." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 138 p, 2008. http://proquest.umi.com/pqdweb?did=1650510201&sid=7&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Kamm, James Russell Saffman P. G. "Shape and stability of two-dimensional uniform vorticity regions /." Diss., Pasadena, Calif. : California Institute of Technology, 1987. http://resolver.caltech.edu/CaltechETD:etd-06302004-093810.
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Butsuntorn, Nawee. "Time spectral method for rotorcraft flow with vorticity confinement /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Akkala, James. "Understanding and controlling vorticity transport in unsteady, separated flows." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1947.
Full textAbstract:
Vortices interacting with the solid surface of aerodynamic bodies are prevalent across a broad range of geometries and applications, such as dynamic stall on wind turbine and helicopter rotors, the separated flows over flapping wings of insects, birds and micro-air vehicles, formation of the vortex wakes of bluff bodies, and the lift-producing vortices formed by aircraft leading-edge extensions and delta wings. This study provides fundamental insights into the formation and evolution of such vortices by considering the leading-edge vortices formed in variations of a canonical flapping wing problem.
Specifically, the vorticity transport within three distinct experimental cases--2D plunging airfoil, 3D plunging airfoil and 2D plunging airfoil with suction applied at the leading edge--were analyzed in order to characterize the formation and evolution of the leading-edge vortex (LEV).
Three-dimensional representations of the velocity and vorticity fields were obtained via multi-plane particle image velocimetry (PIV) measurements and used to perform a vorticity flux analysis that served to identify the sources and sinks of vorticity within the flow. Time-resolved pressure measurements were obtained from the surface of the airfoil and used to characterize the flux of vorticity diffusing from the solid surface, and a method for correcting dynamic pressure data was developed and validated for the application within the current study.
Upon characterizing all of the sources and sinks of vorticity, the circulation budget was found to be fully accounted for. Interpretation of the individual vorticity balance terms demonstrated vorticity generation and transport characteristics that were consistent among all three cases that were investigated. Three-dimensional vorticity fluxes were found to be an almost negligible contributor to the overall circulation budget, mostly due to the individual terms canceling each other out. In all cases, the diffusive flux of vorticity from the surface of the airfoil was shown to act primarily as a sink of LEV vorticity, with a magnitude roughly half that of the flux of vorticity emanating from the leading-edge shear layer.
Inspection of the chordwise distribution of the diffusive flux within the 2D case showed it to correlate very well with the evolution of the flow field. Specifically, the diffusive flux experienced a major increase during the phase interval in which the LEV remained attached to the downstream boundary layer. It was also noted that the accumulation of secondary vorticity near the leading edge prevented the diffusive flux from continuing to increase after the roll-up of the LEV. This result was validated within the 3D case, which demonstrated that maintaining an LEV that stays attached to the downstream boundary layer produces a larger diffusive flux of vorticity--presumably enhancing both lift and thrust.
Through the use of a spanwise array of suction ports, the suction case was able to successfully alter the total circulation of the flow by removing positive vorticity from the opposite-signed vortex (OSV) that formed beneath the LEV. This removal of positive vorticity produced a measured increase in the total lift, and it was noted that weakening this region of secondary vorticity allowed the LEV to impose more suction on the surface of the airfoil. However, it was also noted that weakening the OSV resulted in a loss of thrust, which was attributed to the loss of suction that occurred near the leading edge when the removal of secondary vorticity caused the energetic OSV to be reverted into a low energy region of separated flow.
The physical insights provided by this work can form the basis of novel flow control strategies for enhancing the aerodynamic loads produced in unsteady, separated flows.
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Eslam, Panah Azar. "Flow structure and vorticity transport on a plunging wing." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/4623.
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The structure and dynamics of the flow field created by a plunging flat plate airfoil are investigated at a chord Reynolds number of 10,000 while varying plunge amplitude and Strouhal number. Digital particle image velocimetry measurements are used to characterize the shedding patterns and the interactions between the leading and trailing edge vortex structures (LEV and TEV), resulting in the development of a wake classification system based on the nature and timing of interactions between the leading- and trailing-edge vortices. The convection speed of the LEV and its resulting interaction with the TEV is primarily dependent on reduced frequency; however, at Strouhal numbers above approximately 0.4, a significant influence of Strouhal number (or plunge amplitude) is observed in which LEV convection is retarded, and the contribution of the LEV to the wake is diminished. It is shown that this effect is caused by an enhanced interaction between the LEV and the airfoil surface, due to a significant increase in the strength of the vortices in this Strouhal number range, for all plunge amplitudes investigated. Comparison with low-Reynolds-number studies of plunging airfoil aerodynamics reveals a high degree of consistency and suggests applicability of the classification system beyond the range examined in the present work. Some important differences are also observed.
The three-dimensional flow field was characterized for a plunging two-dimensional flat-plate airfoil using three-dimensional reconstructions of planar PIV data. Whereas the phase-averaged description of the flow field shows the secondary vortex penetrating the leading-edge shear layer to terminate LEV formation on the airfoil, time-resolved, instantaneous PIV measurements show a continuous and growing entrainment of secondary vorticity into the shear layer and LEV. A planar control volume analysis on the airfoil indicated that the generation of secondary vorticity produced approximately one half the circulation, in magnitude, as the leading-edge shear layer flux. A small but non-negligible vorticity source was also attributed to spanwise flow toward the end of the downstroke.
Preliminary measurements of the structure and dynamics of the leading-edge vortex (LEV) are also investigated for plunging finite-aspect-ratio wings at a chord Reynolds number of 10,000 while varying aspect ratio and root boundary condition. Stereoscopic particle image velocimetry (SPIV) measurements are used to characterize LEV dynamics and interactions with the plate in multiple chordwise planes. The relationship between the vorticity field and the spanwise flow field over the wing, and the influence of root boundary conditions on these quantities has been investigated. The viscous symmetry plane is found to influence this flow field, in comparison to other studies \cite{YiRo:2010,Vi:2011b,CaWaGuVi:2012}, by influencing tilting of the LEV near the symmetry wall, and introducing a corewise root-to-tip flow near the symmetry plane. Modifications in the root boundary conditions are found to significantly affect this. LEV circulations for the different aspect ratio plates are also compared. At the bottom of the downstroke, the maximum circulation is found at the middle of the semi-span in each case. The circulation of the $sAR=2$ wing is found to significantly exceed that of the $sAR=1$ wing and, surprisingly, the maximum circulation value is found to be independent of root boundary conditions for the $sAR=2$ case and also closely matched that of the quasi-2D case.
Furthermore, the 3-D flow field of a finite wing of $sAR=2$ was characterized using three-dimensional reconstructions of planar PIV data after minimizing the gap between the plunging plate and the top stationary wall. The LEV on the finite wing rapidly evolved into an arch structure centered at approximately the 50\% spanwise position, similar to previous observations by Calderon et al. \cite{CaWaGu:2010}, and Yilmaz and Rockwell \cite{YiRo:2010}. At that location, the circulation contribution due to spanwise flow was approximately half that of the shear layer flux because of the significantly greater three-dimensionality in the flow. Increased tilting at the 25\% and 75\% spanwise locations suggests increasing three-dimensionality at those locations compared to the symmetry plane of the arch (50\% spanwise location). The deviation between the LEV circulation and integrated convective vorticity fluxes at the 50\% spanwise location suggests that entrainment of secondary vorticity plays a similar role in regulating LEV circulation as in the 2D case. While the wing surface flux of vorticity could not be measured in that case, the significant difference between LEV circulation and the known integrated fluxes is comparable to that for the 2D plate, suggesting that a significant boundary flux of secondary vorticity may exist.
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Day, Kate. "On the relationship between deep circulation and a dynamical tracer over the global ocean." Thesis, University of Liverpool, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367708.
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Levine, Andrew S. "Intensity changes or recurving typhoons from a potential vorticity perspective." Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/6980.
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Potential vorticity (PV) interactions are evaluated in fourteen recurving typhoons to assess its usefulness as a forecast tool for intensity change. PV fields are derived from the large scale data in the ECMWF Global Advanced Operational Analysis data set. A deformation of the 1 potential vorticity unit contour around the typhoon on the 330 K isentropic surface coincides with the weakening of three typhoons, and may prove to be a useful forecast guideline for all recurving typhoons. Five typhoons have a trough with high PV on the 345 K isentropic surface approach within 10° radial distance. For these five typhoons, PV is not useful for forecasting intensity in isolation from other variables. The PV fields are too subtle by themselves to show a significant difference among typhoons which intensify, weaken or remain steady. Because of this, vertical shear of the horizontal wind and maximum potential intensity (MPI) are included with PV to examine intensity changes. Vertical shear of the horizontal wind calculated between 850-200 hPa in an intensifying typhoon is ≤ 15 mis, while shear in a weakening typhoon is ≥ 25 m/s. Shear increases as a PV anomaly propagates closer to the typhoon center. Weakening is associated with the upper PV anomaly passing within 50 from the center of the typhoon. When over fairly constant sea surface temperature (change of ≤ 1 °C ), two typhoons close to their MPI weakened. The typhoon which was far from its MPI intensified. Guidelines for forecasting intensity change using these parameters are presented.x, 84 leaves
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Choboter, Paul F. "Forced Rossby waves in a zero absolute vorticity gradient environment." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ37107.pdf.
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Mohamed, Kaveh. "Convergence acceleration for detached-eddy simulation via vorticity preserving limiters." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103576.
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A slope limiting algorithm for second-order Monotone Upstream-centered Schemes for Conservation Laws (MUSCL) is introduced in order to reduce the dissipation of vortices in flow simulations. The algorithm is based on the reconstruction of velocity components along the principle axes of the vortex and the augmentation of the central gradients' weight for the interpolation of velocity components on the swirl plane of the vortex. The performance of the scheme in different vortical flow problems is investigated. The proposed limiting algorithm has been able to considerably reduce the dissipation of vortices provided that the spatial and temporal discretization of the problem have been fine enough to resolve the length and time scales of the corresponding vortical motion. In particular, the scheme has significantly outperformed the conventional van Albada limiter to resolve the the second peak in the lift coefficient spectra in the case of a NACA0021 airfoil at post a stall condition. The eddy preserving scheme results in, on average, a two fold faster convergence rate as compared to the baseline DES scheme.On propose une nouvelle stratégie pour limiter les pentes des schémas du second ordre type MUSCL afin de réduire la dissipation des tourbillons pour des cas tests comportant des couches limites. L'algorithme est basé sur la reconstruction des composantes du vecteur vitesse le long des axes principaux du tourbillon et l'accroissement du gradient central des composantes de la vitesse sur le plan du tourbillon. Le schéma a bien performé dans différents problèmes d'écoulement tourbillonnaire. L'algorithme proposé a pu réduire considérablement la dissipation des tourbillons lorsque les discrétisations spaciale et temporelle sont suffisament fines pour résoudre les échelles de temps et d'espace du mouvement tourbillonnaire. En particulier le schéma est nettement moins precis en utilisant le limiteur de pentes Van Albada pour résoudre le deuxième pic du spectre du coefficient de la portance dans le cas de la simulation d'écoulement autour du profil NACA0021 avec décrochage. Les résultats du schéma préservant les tourbillons sont en moyenne deux fois plus rapides par rapport au schéma de référence DES.