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1
Heidarinejad, Ghassem. « Vortex simulation of the reacting shear layer ». Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14432.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1989.Title as it appears in M.I.T. Graduate List, Feb. 1989: Numerical simulation of reacting shear layer using vortex method.
Includes bibliographical references.
by Ghassem Heidarinejad.
Ph.D.
2
Krishna, Vikas. « Numerical simulation of vortex shedding in oscillatory flows ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1995. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq25859.pdf.
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3
Vines, Neuwirth Mauricio Alfredo. « Vortex Methods for Fluid Simulation in Computer Graphics ». Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23647.
Texte intégralRésumé :
Fluid simulations for computer graphics applications have attracted the attention of many researchers and practitioners due to the enhanced realism that natural phenomena simulation adds to graphical applications. Vortex methods are receiving increasing attention from the computer graphics community for simple and direct modeling of complex flow phenomena such as turbulence. However, vortex methods have not been developed yet to the level of other techniques for fluid simulation in computer graphics. In this work we present a novel simulation framework to model inviscid flows using Lagrangian vortex particle methods. We introduce novel stable methods to solve the vorticity flow equations that produce highly detailed visual fluid simulations. We incorporate the full interplay of solids and fluids in our framework. The coupling between free-form solids, represented by arbitrary surface meshes and fluids simulated with vortex methods, leads to visually rich simulations. Previous vortex simulators only focus on modeling the solid as a boundary for the flow. We model solid boundaries using an extended potential flow at the solid surface coupled with a boundary layer simulation. This allows the accurate simulation of two processes of visual interest. The first is the introduction of surface vorticity in the main flow as turbulence (vortex shedding). The second is the motion of the solid induced by fluid forces, which is calculated from the dynamics of vorticity in the flow and the rate of vorticity creation at solid surfaces. We demonstrate high quality results of our methods simulating flows around solid objects and solid object propulsion due to flows. This work ameliorates one of the important omissions in the development of vortex methods for computer graphics, which is the simulation of two-way coupling of solids and fluids.
4
Sheikh, Amer Hussain. « The numerical simulation of compressible blade vortex interaction ». Thesis, Imperial College London, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399771.
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5
Radler, Karl Simon [Verfasser]. « Periodic Free Vortex Wake Simulation / Karl Simon Radler ». München : Verlag Dr. Hut, 2018. http://d-nb.info/1156510422/34.
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6
Takeda, Kenji. « Parallel discrete vortex methods for viscous flow simulation ». Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287340.
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Pérez, Sánchez Jorge Manuel. « Numerical simulation of deceleration of an axisymmetric vortex ». Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/39023.
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Mohammad, Abrar Hasan. « Numerical simulation of three dimensional vortex-dominated flows ». [Ames, Iowa : Iowa State University], 2008.
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9
Stein, Peter. « Numerical simulation and investigation of draft tube vortex flow ». Thesis, Coventry University, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.549077.
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10
Asyikin, Muhammad Tedy. « CFD Simulation of Vortex Induced Vibration of a Cylindrical Structure ». Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for bygg, anlegg og transport, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18814.
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This thesis presents the investigation of the flow characteristic and vortex induced vibration (VIV) of a cylindrical structure due to the incompressible laminar and turbulent flow at Reynolds number 40, 100, 200 and 1000. The simulations were performed by solving the steady and transient (unsteady) 2D Navier-Stokes equation. For Reynolds number 40, the simulations were set as a steady and laminar flow and the SIMPLE and QUICK were used as the pressure-velocity coupling scheme and momentum spatial discretization respectively. Moreover, the transient turbulent flow was set for Re 100, 200 and 1000 and SIMPLE and LES (large Eddies Simulation) were selected as the pressure-velocity coupling solution and the turbulent model respectively. The drag and lift coefficient (Cd and Cl) were obtained and verified to the previous studies and showed a good agreement. Whilst the vibration frequency (fvib), the vortex shedding frequency (fv), the Strouhal number (St) and the amplitude of the vibration (A) were also measured.
11
Watson, John Paul. « Numerical simulation of vortex breakdown in an enclosed circular cylinder ». Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/16868.
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Prendergast, John Michael. « Simulation of unsteady 2-D wind by a vortex method ». Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612179.
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13
Xu, G. « Numerical simulation of two-dimensional vortex shedding for marine applications ». Thesis, University College London (University of London), 2013. http://discovery.ucl.ac.uk/1398681/.
Texte intégralRésumé :
The velocity potential theory has been adopted to investigate the two-dimensional vortex shedding problems in marine hydrodynamics. The theory can find its applications to the lifting body problems such as a hydrofoil advancing near the free surface, the flow passing through an orifice of a damaged compartment, the vortex shedding at sharp edges of a marine structure. Since the viscosity of the fluid is assumed to be confined within a thin boundary layer along the surface of the structure, the fluid flow can be described by velocity potential theory. Literature review on vortex shedding has been presented. The development of relevant theories and their applications have been discussed. The challenges and suitable methodologies are investigated. When the steady motion and small amplitude unsteady motion of a hydrofoil advancing near free surface is considered, a flat vortex sheet is introduced and imposed behind the trailing edge; linear free surface conditions are imposed to study the free surface effects. Free surface Green functions, which satisfy free surface boundary conditions, are adopted to account for the free surface effects which are found to be highly significant. To study the non-linear effects of body surface boundary condition and vortex wake when the attack angle or the motion amplitude becomes moderately large, we introduce a time stepping scheme. The vortices shed from the trailing edge are approximated by introducing point vortex. The non-linear effects of body surface condition and vortex wake are investigated. Further studies on the submerged foil and surface piercing structures with vortex shedding are presented; efforts are made to investigate the non-linear wave-body interaction problems with vortex shedding. The non-linear free surface and non-linear vortex wake are found to have significant effects on the fluid flow and the hydrodynamic force.
14
El, Hamraoui Mohammed. « Contributions à la simulation d'écoulement tridimensionnel par méthode de vortex ». Toulouse 3, 1999. http://www.theses.fr/1999TOU30101.
Texte intégralRésumé :
Ce travail est consacré au développement d'une méthode de couplage particules-grille en écoulement tridimensionnel d'un fluide incompressible visqueux ou non visqueux. La méthode consiste a faire cohabiter des techniques euleriennes et lagrangiennes dans le même domaine de calcul tripériodique. Dans la première partie, nous définissons l'algorithme ainsi que les différents outils mathématiques et numériques associés. Les différentes manière de traiter les opérateurs de convection, d'étirement et de diffusion sont exposées. Dans la seconde partie, la validation de la méthode est fait pour les anneaux tourbillons isolés. Nous utilisons les invariants et les diagnostiques pour comparer les résultats numériques avec les prévisions théoriques. Dans la troisième partie, nous testons la méthode sur deux problèmes classiques sur lesquels des résultats d'expériences sont connus : - La reconnection de deux anneaux tourbillonnaires. - Les tourbillons contrarotatifs (Instabilité de Crow). Pour ces études, nous avons implémenté une méthode de visualisation objective basée sur un critère cinématique (critère dit de 'λ2'). Dans la dernière partie, nous proposons une implémentation parallèle de la méthode. Le parallélisme est fondé sur un approche de décomposition de domaine. Des tests de validation et d'évaluation des performances sont présentés
15
Misra, Ashish Pullin Dale Ian. « Large-eddy simulation using a vortex-based subgrid stress model / ». Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-08102005-134328.
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Xia, Jianjun. « Large-eddy simulation of a three-dimensional compressible tornado vortex ». Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2216.
Texte intégralRésumé :
Thesis (Ph. D.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xviii, 130 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 98-104).
17
Bos, Fedderik van der. « Contributions to non-uniform large-eddy simulation for vortex dominated flows ». Enschede : University of Twente [Host], 2006. http://doc.utwente.nl/57450.
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Lou, Guang Ping. « Three-dimensional simulation of N₂O transport and antarctic vortex evolution ». Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/25760.
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Qian, Ling. « Towards numerical simulation of vortex-body interaction using vorticity-based methods ». Thesis, University of Glasgow, 2001. http://theses.gla.ac.uk/4902/.
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Saghbini, Jean-Claude J. « Simulation of vorticity dynamics in swirling flows, mixing and vortex breakdown ». Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39391.
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Shiels, Doug Leonard Anthony. « Simulation of controlled bluff body flow with a viscous vortex method / ». Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-03162004-133652.
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22
Weiler, Justin D. « Numerical Simulation of Flame-Vortex Interactions in Natural and Synthetic Gas Mixtures ». Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4774.
Texte intégralRésumé :
The interactions between laminar premixed flames and counter-rotating vortex pairs in natural and synthetic gas mixtures have been computationally investigated through the use of Direct Numerical Simulations and parallel processing. Using a computational model for premixed combustion, laminar flames are simulated for single- and two-component fuel mixtures of methane, carbon monoxide, and hydrogen. These laminar flames are forced to interact with superimposed laminar vortex pairs, which mimic the effects of a pulsed, two-dimensional slot-injection. The premixed flames are parameterized by their unstretched laminar flame speed, heat release, and flame thickness. The simulated vortices are of a fixed size (relative to the flame thickness) and are parameterized, solely, by their rotational velocity (relative to the flame speed). Strain rate and surface curvature measurements are made along the stretched flame surfaces to study the effects of additive syngas species (CO and H2) on lean methane-air flames. For flames that share the same unstretched laminar flame speed, heat release, and flame thickness, it is observed that the effects of carbon monoxide on methane-air mixtures are essentially negigible while the effects of hydrogen are quite substantial. The dynamics of stretched CH4/Air and CH4/CO/Air flames are nearly identical to one another for interactions with both strong and weak vortices. However, the CH4/H2/Air flames demonstrate a remarkable tendency toward surface area growth. Over comparable interaction periods, the flame surface area produced during interactions with CH4/H2/Air flames was found to be more than double that of the pure CH4/Air flames. Despite several obvious differences, all of the interactions revealed the same basic phenomena, including vortex breakdown and flame pinch-off (i.e. pocket formation). In general, the strain rate and surface curvature magnitudes were found to be lower for the CH4/H2/Air flames, and comparable between CH4/Air and CH4/CO/Air flames. Rates of flame stretching are not explicitely determined, but are, instead, addressed through observation of their individual components. Two different models are used to determine local displacement speed values. A discrepancy between practical and theoretical definitions of the displacement speed is evident based on the instantaneous results for CH4/Air and CH4/H2/Air flames interacting with weak and strong vortices.
23
Sreedhar, Madhu K. « Large eddy simulation of turbulent vortices and mixing layers ». Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-163324/.
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24
Youssef, Khaled Saad II. « Numerical Investigation of the Wake of a Rectangular Wing ». Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30347.
Texte intégralRésumé :
Wakes of lifting bodies contain vortex sheets that roll up into strong streamwise vortices. The long time behavior of such vortices depends on the turbulence in the wake and the stability characteristics of the vortices themselves.
In the near wake of a rectangular wing the flow field consists of a spiraling wake that winds around a pair of vortex cores. The study of the turbulence structure and life of wing tip vortices is of great importance to air traffic control in congested airports. In this dissertation a computer code is developed for the temporal as well as spatial simulations of trailing vortices.
A sixth-order compact finite-difference method is used in the cross plane. The streamwise derivatives are represented either by a Fourier series for temporal simulations (periodic flow) or by a sixth-order compact scheme for spatial simulations. The time marching scheme is a third-order Runge-Kutta method. The code is used to study the nonlinear development of temporal helical instability waves in a trailing vortex.
Contours of a passive scalar are used to study the entrainment process that redistributes angular and axial momenta between the core and its surroundings. Such a process leads to quenching of the instability waves in the vortex core. The code is also used to predict the spatial development of mean flow in the wake of a rectangular wing. New treatment of the outflow boundary condition on the pressure is formulated so that a strong streamwise vortex can exit the computational domain without distortion.
Temporal large-eddy simulation (LES) is performed to study the development of large scale structures in the wake and their interaction with the tip vortex. A modified MacCormack scheme developed by Gottlieb and Turkel(1976) has been used to solve the LES equations. A model of the initial conditions in the near wake of a rectangular wing is devised to investigate mechanisms of turbulence production in the spiral wake around the core of a tip vortex. The model consists of a streamwise vortex sheet whose strength is found from Prandtl lifting line theory. A Gaussian streamwise velocity profile is superimposed on the field of the vortex sheet.
This profile represents the spanwise vorticity. The integrated spanwise vorticity of this profile is zero. A novel feature of this study is that the mean flow contains both streamwise and spanwise vorticity. The model is then used to initialize the flow field for temporal LES of the instabilities of the spanwise vorticity during roll up.
The results show that the sinuous mode prevails in the spiral wake around the core. The strength and streamwise length scale of the instability vary along the span because of the continuous variation of the wake thickness due to stretching by the tip vortex. The large scale structures produced by the instability of the spiral wake cause the formation of undulations on the core - consistent with the hypothesis of Devenport et al. (1996).Ph. D.
25
Gsell, Simon. « Vortex-induced vibrations of a rigid circular cylinder ». Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/17430/1/gsell.pdf.
Texte intégralRésumé :
When a flexible body with bluff cross-section is immersed in a flow, the unsteady fluid forces accompanying the vortex-shedding phenomenon may lead to structural vibrations. These vortexinduced vibrations (VIV) occur through a mechanism of synchronization between flow unsteadiness and body displacement, referred to as lock-in. VIV are detrimental to many industrial systems, but may also be used as mechanical energy converter in the context of flow energy harvesting. In the present work, the VIV of a rigid circular cylinder mounted on a elastic support are investigated in various configurations on the basis of direct numerical simulations. Four aspects are studied. (i) The interaction mechanisms are first examined in the early turbulent regime, where VIV have been rarely studied numerically. The Reynolds number, based on the cylinder diameter and oncoming flow velocity, is set to 3900. A combined analysis of the structural responses and fluid forcing in the case where the cylinder is free to oscillate in the in-line and cross-flow directions, i.e. the directions parallel and perpendicular to the oncoming flow, is performed over a range of the reduced velocity (inverse of the oscillator natural frequency). (ii) The system behavior when the body is free to oscillate in a single direction only is also explored, shedding some light on the possible interactions between in-line and cross-flow motions in the two-degree-of-freedom (2-dof) case; the analysis shows for instance how large-amplitude in-line oscillations may be induced by cross-flow motion. (iii) The three-dimensional wake developing downstream of the oscillating body is analyzed in the 2-dof case as well as in the fixed body case. The spanwise flow patterns, which are analyzed quantitatively in terms of wavelength and amplitude of vorticity fluctuations, are differently altered in the shear-layer and wake regions, when the body oscillates. (iv) The last physical configuration involves a cylinder immersed in a flow linearly sheared in the cross-flow direction. The impact of the symmetry breaking induced by the shear, on the flow-structure system behavior, is explored. Different interaction regimes are uncovered in the shear rate - reduced velocity domain. Some of them are associated with a profound reconfiguration of the wake and a major alteration of the fluid forces.
26
Carullo, Francesco. « Analysis, simulation and control of the Von Karman vortex street behind a circular cylinder ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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This work focuses on studying the 2D wake pattern behind a bluff body/airfoil immersed in a fluid. Within a specific Reynolds number range, a repeating pattern of swirling vortices shows up: the "Von Karman Vortex Street". To suppress Vortex-Induced Vibration which can cause the structure resonating, a suitable control method has to be adopted. Furthermore, this work
aims at designing a control technique for a flapping airfoil able to produce the desired "Reverse Von Karman Vortex Street": a thrust-generating wake created by the birds flapping wings.
27
Sheen, Shaw-Ching. « Large eddy simulation of subsonic mixing layers ». Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40183.
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Meneghini, Julio Romano. « Numerical simulation of bluff body flow control using a discrete vortex method ». Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/8441.
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Ribera, Maria. « Helicopter flight dynamics simulation with a time-accurate free-vortex wake model ». College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6876.
Texte intégralRésumé :
Thesis (Ph. D.) -- University of Maryland, College Park, 2007Thesis 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.
30
Saban, Deborah. « Wake Vortex Modelling and Simulation for Air Vehicles in Close Formation Flight ». Thesis, Cranfield University, 2010. http://hdl.handle.net/1826/4414.
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The aim of this research is to develop realistic models of aerodynamic cross-coupling
e ects that can be incorporated in real-time or near real-time simulations of Unmanned
Aerial Vehicles (UAVs) in close formation flight. These would permit the assessment of
the risks and issues associated with wake vortex evolution and encounter and the analysis
of their consequences on the design of automatic control systems and the development
of safe and reliable operating procedures. A number of wake vortex modelling
techniques that can be used in formation flight simulations are reviewed. A novel Wake
Vortex Model (WVM) is developed, implemented, verified, validated and successfully
integrated within a Matlab/Simulink simulation environment. The code, named ELL
because it is based on Weissinger’s extended lifting line theory, meets the following
requirements: (i) it is generic and can easily be adapted to accomodate any wing planform
and air vehicle configuration; (ii) it is computationally rapid enough to be used in
real-time or near real-time simulations; (iii) and it is sufficiently representative to support
studies of aerodynamic interaction between multiple air vehicles during formation
reconfiguration and air-to-air refuelling simulations. Simulink test scenarios of two
Aerosonde UAVs are developed to test and validate the use of ELL within simulation
models, and the simulation environment is interfaced with visualisation tools in order
to facilitate the evaluation of multiple air vehicle dynamic interaction.
31
Clarke, Nicholas Richard. « Two dimensional flow simulation using discrete vortex methods on MIND processor arrays ». Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336148.
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32
Daniels, Steven. « An evaluation of vortex shedding over slender structures using large-eddy simulation ». Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/397164/.
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Turbulent flows around slender structures are common in nature and occur in many applications, including flows around tall buildings and long-span bridges. Understanding and predicting the properties of these flows are necessary for a safe, effective and economical engineering design. Experimental techniques are expensive and often provide data that is not sufficiently detailed for the structural engineer. With increasing computational power it has become possible to investigate these flows using numerical techniques. A number of numerical approaches have been proposed over the last half century. Of these, one of the most effective techniques, that is currently on the verge of being viable for common use in industry, is that of Large-Eddy Simulation (LES). This thesis illustrates the appealing aspects of LES for the use in wind engineering. Measurement of forces on a bluff body placed in a flow is of considerable importance to the wind engineer. It is well established in the literature that the peak pressures on the body are due to large coherent structures in the flow, denoted vortices. The atmospheric boundary layer, in which all civil engineering structures are situated, is almost always turbulent, and it has a strong influence on vortex formation. In the present work, to generate in flow turbulence for LES, a synthetic in flow condition was utilised to analyse the effects of freestream turbulence over the CAARC standard tall model building. With the use of pressure statistics and conditional sampling, the sensitivity of the peak loading to the freestream turbulence effects were analysed, showing a marked increase for both turbulence intensity and length scale of the flow. The formation of vortices over a long-span bridges can incur severe aeroelastic instabilities. A fluid-structure coupling method was proposed for the study of freely-vibrating cylinder (simulating a bridge section) undergoing Vortex-Induced Vibration (VIV) and torsional flutter. The Motion Induced Vortex was identified as the fundamental cause of both cases. Spanwise correlations and pressure statistics were used to determine the effects of the motion and freestream turbulence on both phenomena. It was found that small-scale turbulence (length scales size of the cylinder) had a diminishing effect on the cylinder's response (compared to smooth flow). When the length scales were increased to those found in atmospheric wind, the cylinder's response was increased for the torsional motion.
33
Mulvaney, Daniel. « Numerical simulation of vortex dipole formation and evolution in stably stratified fluid ». Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/397199/.
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Direct numerical simulation has been used to study how axisymmetric vertical flow structures evolve whilst propagating horizontally in both homogeneous fluid and in fluid with a linear stable density stratification in the vertical direction. The structures studied were initially toroidal vortex rings and impulsive jets formed from a brief, horizontal injection of fluid into a quiescent domain. Previous experimental studies have demonstrated that when these initially axisymmetric structures are allowed to evolve under the influence of stable stratification, acceleration due to buoyancy acts to suppress vertical displacement of fluid particles, eventually reducing the flow to a pair of contra-rotating, planar vortices, commonly referred to as a vortex dipole. The numerical simulations documented in this thesis demonstrate the process by which the initially axisymmetric structures are transformed into late time dipoles in a stratified fluid, with the stages of this transformation categorised both through visual changes in the flow field as well as characteristic variations in kinetic energy and buoyancy variance histories that are inaccessible to the experimental work, thus allowing the energetics and vorticity fields of these flows to be directly correlated for the first time. Additionally, it has been demonstrated that while different means of imparting horizontal momentum to the fluid through an initial solution or different profiles of momentum injection may generate distinct vorticity fields at the early time, the energetics, scaling behaviours and agreement with theoretical models appear universal across the late time dipoles formed from these cases, which has not been addressed directly in previous literature.
34
Roa, Perez Julio Alberto. « Development of Aircraft Wake Vortex Dynamic Separations Using Computer Simulation and Modeling ». Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/96199.
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This dissertation presents a research effort to evaluate wake vortex mitigation procedures and technologies in order to decrease aircraft separations, which could result in a runway capacity increase. Aircraft separation is a major obstacle to increasing the operational efficiency of the final approach segment and the runway.
An aircraft in motion creates an invisible movement of air called wake turbulence, which has been shown to be dangerous to aircraft that encounter it. To avoid this danger, aircraft separations were developed in the 1970s, that allows time for wake to be dissipated and displaced from an aircraft's path. Though wake vortex separations have been revised, they remain overly conservative.
This research identified 16 concepts and 3 sub-concepts for wake mitigation from the literature. The dissertation describes each concept along with its associated benefits and drawbacks. All concepts are grouped, based on common dependencies required for implementation, into four categories: airport fleet dependent, parallel runway dependent, single runway dependent, and aircraft or environmental condition dependent.
Dynamic wake vortex mitigation was the concept chosen for further development because of its potential to provide capacity benefit in the near term and because it is initiated by air traffic control, not the pilot. Dynamic wake vortex mitigation discretizes current wake vortex aircraft groups by analyzing characteristics for each individual pair of leader and follower aircraft as well as the environment where the aircraft travel. This results in reduced aircraft separations from current static separation standards.
Monte Carlo simulations that calculate the dynamic wake vortex separation required for a follower aircraft were performed by using the National Aeronautics and Space Administration (NASA) Aircraft Vortex Spacing System (AVOSS) Prediction Algorithm (APA) model, a semi-empirical wake vortex behavior model that predicts wake vortex decay as a function of atmospheric turbulence and stratification. Maximum circulation capacities were calculated based on the Federal Aviation Administration's (FAA) proposed wake recategorization phase II (RECAT II) 123 x 123 matrix of wake vortex separations.
This research identified environmental turbulence and aircraft weight as the parameters with the greatest influence on wake vortex circulation strength. Wind has the greatest influence on wake vortex lateral behavior, and aircraft mass, environmental turbulence, and wind have the greatest influence on wake vortex vertical position.
The research simulated RECAT II and RECAT III dynamic wake separations for Chicago O'Hare International (ORD), Denver International Airport (DEN) and LaGuardia Airport (LGA). The simulation accounted for real-world conditions of aircraft operations during arrival and departure: static and dynamic wake vortex separations, aircraft fleet mix, runway occupancy times, aircraft approach speeds, aircraft wake vortex circulation capacity, environmental conditions, and operational error buffers. Airport data considered for this analysis were based on Airport Surface Detection Equipment Model X (ASDE-X) data records at ORD during a 10-month period in the year 2016, a 3-month period at DEN, and a 4-month period at LGA.
Results indicate that further reducing wake vortex separation distances from the FAA's proposed RECAT II static matrix, of 2 nm and less, shifts the operational bottleneck from the final approach segment to the runway. Consequently, given current values of aircraft runway occupancy time under some conditions, the airport runway becomes the limiting factor for inter-arrival separations.
One of the major constraints of dynamic wake vortex separation at airports is its dependence on real-time or near-real-time data collection and broadcasting technologies. These technologies would need to measure and report temperature, environmental turbulence, wind speed, air humidity, air density, and aircraft weight, altitude, and speed.PHD
35
Memory, Curtis Lynn. « Numerical Simulation of Vortex Generating Jets in Zero and Adverse Pressure Gradients ». Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd2098.pdf.
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Delyagin, Kirill V. « Steady-state simulation of a premixed flame in axisymmetric channels in the presence of vortex breakdown / ». Thesis, Connect to this title online ; UW restricted, 1998. http://hdl.handle.net/1773/9981.
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Jiang, Ming. « A feature-based approach to visualizing and mining simulation data ». Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1119020006.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xvi, p. 116; also includes graphics. Includes bibliographical references (p. 108-116). Available online via OhioLINK's ETD Center
38
Ward, Jami. « REDUCTION OF VORTEX-DRIVEN OSCILLATIONS IN A SOLID ROCKET MOTOR COLD FLOW SIMULATION THROUGH ACTIVE CONTROL ». Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4310.
Texte intégralRésumé :
Control of vortex-driven instabilities was demonstrated via a scaled-down, cold-flow simulation that modeled closed-end acoustics. When vortex shedding frequencies couple with the natural acoustic modes of a choked chamber, potentially damaging low-frequency instabilities may arise. Although passive solutions can be effective, an active control solution is preferable. An experiment was performed to demonstrate an active control scheme for the reduction of vortex-driven oscillations. A non-reacting experiment using a primary flow of air, where both the duct exit and inlet are choked, simulated the closed-end acoustics. Two plates, separated by 1.27 cm, produced the vortex shedding phenomenon at the chamber's first longitudinal mode. Two active control schemes, closed-loop and open-loop, were studied via a cold-flow simulation for validating the effects of reducing vortex shedding instabilities in the system. Actuation for both control schemes was produced by using a secondary injection method. The actuation system consisted of pulsing compressed air from a modifed, 2-stroke model airplane engine, controlled and powered by a DC motor. The use of open-loop only active control was not highly effective in reducing the amplitude of the first longitudinal acoustic mode, near 93 Hz, when the secondary injection was pulsed at the same modal frequency. This was due to the uncontrolled phasing of the secondary injection system. A Pulse Width Modulated (PWM) signal was added to the open-loop control scheme to correct for improper phasing of the secondary injection flow relative to the primary flow. This addition allowed the motor speed to be intermittently increased to a higher RPM before returning to the desired open-loop control state. This proved to be effective in reducing the pressure disturbance by approximately 46%. A closed-loop control scheme was then test for its effectiveness in controlling the phase of the secondary injection. Feedback of the system's state was determined by placing a dynamic pressure transducer near the chamber exit. Closed-loop active control, using the designed secondary injection system, was proven as an effective means of reducing the problematic instabilities. A 50% reduction in the FFT RMS amplitude was realized by utilizing a Proportional-Derivative controller to modify the phase of the secondary injection.M.S.A.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Aerospace Engineering
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McMullin, Nathan K. « Numerical simulation of plasma-based actuator vortex control of a turbulent cylinder wake / ». Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1558.pdf.
Texte intégral
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YAGAMI, Hisanori, et Tomomi UCHIYAMA. « Numerical Simulation of Particle-Laden Plane Mixing Layer by Three-Dimensional Vortex Method ». The Japan Society of Mechanical Engineers, 2006. http://hdl.handle.net/2237/9219.
Texte intégral
41
Di, Scala Nicolas. « TRANSITION DE DÉPIÉGEAGE DANS LES RÉSEAUX DE VORTEX SUPRACONDUCTEURS : ÉTUDE PAR SIMULATION NUMÉRIQUE ». Phd thesis, Université François Rabelais - Tours, 2012. http://tel.archives-ouvertes.fr/tel-00741545.
Texte intégralRésumé :
Cette étude traite du dépiégeage et de la dynamique des systèmes élastiques désordonnés. Ce cadre regroupe une large classe de systèmes allant des interfaces (telles que les parois de domaines dans les systèmes magnétiques ou ferroélectriques) aux systèmes périodiques (comme les réseaux de vortex dans les supraconducteur de type II, les colloïdes ou encore les cristaux de Wigner). Dans ces systèmes, la compétition entre l'élasticité de la structure qui veut imposer un ordre parfait et le désordre induit une grande richesse dans le diagramme de phase. L'étude est menée par simulations numériques à grande échelle, dans lesquelles nous nous intéresserons spéci fiquement aux réseaux 2D de vortex supraconducteurs. Deux types de dépiégeage sont observés lorsque l'on met en mouvement ces réseaux à l'aide d'une force extérieure : un dépiégeage plastique et un dépiégeage élastique. Nous portons notre attention sur la transition de dépiégeage élastique obtenue dans le cas d'un piégeage faible. A travers une analyse en loi d'échelle à température nulle et à température nie nous montrons le caractère continu de la transition. Divers exposants critiques sont déterminés dont l'exposant et caractérisant la dépendance en force et en température de la vitesse ou bien l'exposant caractérisant la divergence de la longueur de corrélation du système. Un modèle visco-élastique simple permettant de décrire la plasticité dans les systèmes périodiques évoluant sur un potentiel de piégeage en présence de désordre fort est également développé. Une grande variété de comportements dynamiques, similaires à ceux observés à plus grande échelle dans des systèmes périodiques, peuvent être extraits d'un tel modèle. Un dépiégeage élastique ou plastique est observé, de l'hystérésis est mesurée dans le cas du dépiégeage élastique, et du chaos est détecté pour le dépiégeage plastique.
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Pashias, Christos. « Propeller tip vortex simulation using adaptive grid refinement based on flow feature identification ». Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427353.
Texte intégral
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Balakrishnan, Shankar Kumar. « A numerical study of some vortex ring phenomena using direct numerical simulation (DNS) ». Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355700/.
Texte intégralRésumé :
Direct numerical simulation (DNS) is used to study some aspects of the dynamics of vortex rings in viscous, incompressible ow at Reynolds numbers (defined as the ratio of the initial circulation to the kinematic viscosity) in the range of 103 to 104. Firstly, the effect of the particular initial core azimuthal vorticity profile of a vortex ring on its subsequent evolution in unbounded ow is studied. Vortex rings with a wide range of initial core vorticity profiles are shown to relax to a common equilibrium state. Additionally the behaviour of the equilibrium vortex ring at large times is studied. When the slenderness ratio of the vortex rings increases beyond a particular limit, the vortex rings diverge from the common equilibrium state and follow paths determined by the viscosity of the uid. Secondly, the interaction of a laminar vortex ring with a non-deformable, free-slip surface at an oblique angle of incidence leading to the phenomenon of vortex reconnection is investigated. Specifically the effect of Reynolds number on the dynamics of the reconnection process is studied. The scaling of the reconnection timescale with the Reynolds number is obtained. At high Reynolds numbers the reconnection process leads to a breakdown of the entire vortex ring structure to a turbulent-like ow. This phenomenon is shown to be related to the mechanics of the reconnection process. Finally, the dynamics of vortex rings with swirl in unbounded ow is studied. Two different types of vortex rings with swirl were considered: i) Vortex rings with Gaussian distributions of core azimuthal vorticity and core azimuthal velocity and ii) Steady state solutions of the Euler equations for vortex rings with swirl. Both types of vortex rings develop an elongated axial vortex after initialisation. The existence of a maximum limit for the swirl on a vortex ring is shown above which the vortex rings undergo a rapid de-swirling readjustment. A helical instability occurring in vortex rings due to swirl at high Reynolds numbers is presented. A relation is shown to exist between one of the modes of the helical instability and the geometric parameters of the vortex ring.
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McMullin, Nathan Keith. « Numerical Simulation of Plasma-Based Actuator Vortex Control of a Turbulent Cylinder Wake ». BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/783.
Texte intégralRésumé :
A numerical study has been performed to investigate the mechanics of the turbulent wake of a circular cylinder that is controlled by a plasma actuator. The numerical investigation implements a straightforward moving wall boundary condition to model the actuator's effects on the flow. Validations of the moving wall for this simulation are set forth with the understanding that the moving wall can model the plasma actuator bulk flow effects at a distance downstream and not in a region near or on the plasma actuator. The moving wall boundary condition is then applied to a circular cylinder at a Reynolds number of 8,000. At this unsteady transitional flow regime, a large eddy simulation solver is utilized to resolve flow features. The moving walls are placed at the top and bottom ninety degree points of the cylinder and alternately activated at a frequency to produce lock-in behavior. Investigation into the flowfield mechanics reveals that a harmonic frequency of the forced frequency occurs from the creation of sub-vortices from the instantaneous starting and stopping of the moving-wall actuators. With the forcing frequency close to the natural shedding frequency it is found that the aerodynamic drag increases due to the moving wall creating an average low pressure region on to the downstream side of the cylinder. It is also found that drag can be reduced when the forcing frequency is closer to half the natural shedding frequency. This happens because of a decrease in the average pressure on the downstream side of the cylinder.
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Matin, Nikoo Hamid. « Passive Control and Numerical Simulation of Vortex-Induced Vibration (VIV) of Marine Structures ». Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/77405.
Texte intégralRésumé :
This thesis proposes three new passive VIV suppression techniques. Analytical and numerical studies are carried out to examine the effectiveness of the proposed methods, and the results show that they are effective for VIV control. The proposed systems are based on or modified from the existing practices and can suppress the VIV without change too much of the existing designs, therefore, they are believed have potential applications.
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Alatawi, Eid. « Simulation of axisymmetric round jet with and without coflow using vortex-in-cell method ». Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/27662.
Texte intégralRésumé :
The vortex-in-cell is developed to simulate an axisymmetric round jet with and without coflow. For an incompressible and viscous jet, the method consists in three fractional steps. The first fractional step describes the convection of interacting vortex elements. The second and third fractional steps simulate the diffusion of vorticity using the diffusion velocity method and the deterministic diffusion, respectively.
For the jet with no coflow, the methodology is tested by initializing the vorticity field with one vortex sheet, multiple vortex sheets and with the Stokes stream function using one and multiple vortex sheets. Two inflow profiles are tested, the top hat profile and the jet self similar profiles. The sensitivity of the results to the number of vortex elements and grid size are presented and compared. Also, the effect of perturbing the top hat inflow velocity profile is investigated. The jet with coflow is investigated using top hat inflow velocity profile with one and multiple vortex sheets. The mean centerline velocity, streamwise mean velocity profile, vorticity contour, instantaneous distribution of vortex elements, root-mean-square longitudinal and lateral velocity fluctuations, cross-stream correlation are presented. The results are compared with previous experimental measurements and numerical simulation using vortex method.
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Dong, Bonian. « Numerical simulation of wakes, blade-vortex interaction, flutter, and flutter suppression by feedback control ». Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134810/.
Texte intégral
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Ghadiri, Dehkordi Behzad. « Numerical simulation of the viscous flow around bluff bodies via the random Vortex method ». Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41598.
Texte intégralRésumé :
The viscous, incompressible and laminar flow around bluff bodies is analysed via a random vortex method using a hybrid (Eulerian-Lagrangian) scheme. The Navier-Stokes equations, written in the form of vorticity equations, are split into nonlinear convection and linear diffusion parts according to a fractional step method. Vorticity is modelled by discrete point vortices. Vortices are created on the surface to satisfy the zero tangential velocity boundary condition. Random walks are applied to the vortices to simulate the diffusion equation. Vortices are then convected in an inviscid calculation in the Lagrangian scheme to simulate the convection equation. The velocity of each vortex is calculated using the Clould-in-Cell method.The random vortex method is developed to simulate the flow around a circular cylinder with a splitter plate. A conformal transformation is used to map the cylinder with a splitter plate to a unit circular cylinder. The force coefficients and Strouhal number are presented for various lengths of the splitter plate and are in good agreement with experiments.
The random vortex method has also been developed for the flow around a circular cylinder vibrating transverse to the flow in a channel. The results are presented for various values of Reynolds number, forcing frequency and vibration amplitudes. The effect of blockage on the drag coefficient is presented. The drag coefficient and vortex shedding frequency are shown to compare favourably with experimental results. The flow around a vibrating cylinder with a splitter plate is also simulated. The results are presented for various values of forcing frequency and lengths of the splitter plate.
The flow around multiple stationary cylinders is also simulated. Also, results are presented for the flow around two cylinders, one of which is forced to oscillate in a transverse direction. The numerical results of Strouhal number are in reasonable agreement with experiments.
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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.
Texte intégralRésumé :
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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Hoinville, Eric. « Etude du sillage de rotors d'hélicoptère en configuration de Vortex Ring ». Phd thesis, Orléans, 2007. http://www.theses.fr/2007ORLE2070.
Texte intégralRésumé :
Les études sur le Vortex Ring State ont récemment reçu un regain d'intérêt suite à la mise en place de trajectoires d'approche à forte pente pour les atterrissages en ville qui conduisent à des conditions de vol proches des frontières du VRS. Dans les années antérieures, les aspects numériques ont été étudiés grâce à des méthodes empiriques ou des modèles analytiques, et des expériences ont été effectuées dans le but de mieux comprendre la physique du phénomène. Dans cette étude, le code CFD elsA a été utilisé dans le but de résoudre les équations d'Euler. Un balayage en vitesse de descente verticale avec différents maillages a été réalisé afin d'étudier la capacité du solveur à capturer le Vortex Ring State. Dans un premier temps, la précision de la représentation de l'écoulement a été évalué en fonction d'hypothèses numériques (stratégies et précision des maillages, consistance en temps des simulations,. . . ) et physiques (périodicité de l'écoulement, cinématique du rotor,. . . ). Ceci permet d'extraire les options pour effectuer, dans un second temps, des simulations les plus représentatives possible de l'état de VRS afin d'étudier et de pouvoir décrire les mécanismes d'apparition et d'évolution de ce phénomène.