Vortex dynamics Research Papers - Academia.edu (original) (raw)

We discuss the close link between intermittent events ('quakes') and extremal noise fluctuations which has been advocated in recent numerical and theoretical work. From the idea that record-breaking noise fluctuations trigger the quakes, an approximate analytical description of non-equilibrium aging as a Poisson process with logarithmic time arguments can be derived. Theoretical predictions for measurable statistical properties of mesoscopic fluctuations are emphasized, and supporting numerical evidence is included from simulations of short-ranged Ising spin-glass models, of the ROM model of vortex dynamics in type II superconductors, and of the Tangled Nature model of biological evolution.

- by
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- Vortex dynamics, Complex System, Superconductors, Spin Glass

Spin dynamics with the Landau-Lifshitz equation has provided topics for a wealth of research endeavors. We introduce here a numerical integration method which explicitly uses the precession motion of a spin about the local field, thus intrinsically conserving spin lengths, and therefore allowing for relatively quick results for a large number of situations with varying temperatures and couplings. This method is applied to the effect of long-range dipole-dipole interactions in two-dimensional clusters of spins with nearest-neighbor XY-Heisenberg exchange interactions on a square lattice at finite temperature. The structures thus obtained are analyzed through orientational correlations functions. Magnon dispersion curves, different from those of the standard Heisenberg model, are obtained and discussed. The number of vortices in the system is discussed as a function of temperature and typical examples of vortex dynamics are shown.

- by Franz Mertens
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- Materials Engineering, Condensed Matter Physics, Nanotechnology, Vortex dynamics

Axisymmetric solution of radial, axial and tangential components of velocity of flow through a cylindrical chamber with an inflow containing swirl and outflow is investigated numerically using Finite Volume Method. An in-house developed computer code for solving the three components of velocity and pressure is developed and validated using experimental data available from literature on the problem of axial vortex breakdown of confined flow in a cylinder due to rotation of one of the end walls. The code uses a staggered approach and fractional step projection method for decoupling the velocity and pressure. The convection and diffusion terms are approximated using a second-order accurate central difference scheme. This paper discusses the characteristics features of flow such as mixing streams, streams of fluid flowing close to the solid walls(cooling streams), swirl motion and development of flow structures.

- by Anil Lal S
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- Computational Fluid Dynamics, Vortex dynamics, Swirling Flow
- by Rodolfo Bontempo and +1
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- Aerospace Engineering, Fluid Mechanics, Aeronautical Engineering, Aerodynamics

The flow about a body placed inside a channel differs from its unbounded counterpart because of the effects of wall confinement, shear in the incoming velocity profile, and separation of vorticity from the channel walls. The case of a circular cylinder placed between two parallel walls is here studied numerically with a finite element method based on the vorticity-streamfunction formulation for values of the Reynolds number consistent with a two-dimensional assumption.

- by Gianni Pedrizzetti
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- Engineering, Fluid Mechanics, Finite element method, Vortex dynamics

Decaying homogeneous isotropic turbulence in inertial and rotating reference frames is investigated to evaluate the capability of the lattice Boltzmann method in turbulence. In the inertial frame case, the decay exponents of kinetic energy and dissipation and the low wave-number scaling of the spectrum are studied. The results are in agreement with classical ones. In the frame-rotation case, simulations show that the energy decay rate decreases with decreasing Rossby number as the energy cascade is inhibited by rotation, again in agreement with turbulence physics. These results clearly indicate that the lattice Boltzmann method captures important features of decaying turbulence.

- by Li-Shi Luo and +1
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- Engineering, Turbulent Flows, Vortex dynamics, Mathematical Sciences

The vortex shedding characteristics and the drag force acting on a circular cylinder, attached with an oscillating splitter plate, are investigated by solving the two-dimensional Navier–Stokes equations. The splitter plate is forced to exhibit harmonic oscillation about its attachment point, and the Reynolds number (Re) of the flow is 100. In order to facilitate easy handling of the plate oscillations inside the computational domain, the equations are solved in a Cartesian grid, and the concept of immersed boundary method is used to impose the boundary conditions on the body surface. The characteristic feature of this problem is the complex interaction between the vortices shed from the splitter plate and the cylinder. Three different patterns of vortex shedding are observed in the wake of the circular cylinder depending upon the frequency and amplitude of plate oscillation: normal shedding, chain of vortices and shedding from splitter plate. It is found that the inverse relationship between the vortex formation length and Strouhal number is not applicable when the splitter plate is subjected to oscillation. Additional related interesting fluid dynamics features are also presented.► Three shedding patterns: normal shedding, chain of vortices and shedding from plate. ► To completely suppress shedding oscillating plate can be much shorter than fixed one. ► Inverse relationship between vortex formation length and St is not applicable. ► Drag coefficient is less than that of fixed plate configuration. ► Use of immersed boundary method to model plate oscillations in fixed Cartesian grid.

- by Sudhakar Yogaraj
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- Flow Control, Vortex dynamics, Immersed Boundary Methods, Vortex shedding
- by stefanus tobing
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- Vortex dynamics, Vortex

Enhancing heat transfer surface are used in many engineering applications such as heat exchanger, air conditioning, chemical reactor and refrigeration systems, hence many techniques have been investigated on enhancement of heat transfer rate and decrease the size and cost of the involving equipment especially in heat exchangers. One of the most important techniques used are passive heat transfer technique. These techniques when adopted in Heat exchanger proved that the overall thermal performance was improved significantly. This experimental works can be taken by researchers on Augmentation Technique such as Twisted Tape. So, Researchers tried to increase the effective surface area Contact with fluid to increases the heat transfer rate in the heat exchanger. We tried to enhance the Heat transfer rate with the help of Twisted Tape insert with Wiry Metallic Sponge and find out the effect of Metallic Wiry Sponge on Flow of Fluid.

- by International Journal IJRITCC
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- Heat Exchanger, Vortex dynamics, Pre-swirl, Tube

Strömungslenkung mit kleinen EInbauten (Instream River Training) statt harter Uferverbau

- by Niels Werdenberg
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- Flood Risk Management, River Engineering, Fluid Dynamics, Vortex dynamics

The equations governing the evolution of quantum vortex defects subject to twist are derived in standard hydrodynamic form. Vortex defects emerge as solutions of the Gross-Pitaevskii equation, that by Madelung transformation admits a hydrodynamic description. Here, we consider a vortex defect subject to superposed twist due to the rotation of the phase of the wave function. We prove that, when twist is present, the corresponding Hamiltonian is non-Hermitian and determine the effect of twist on the energy expectation value of the system. We show how twist diffusion may trigger linear instability, a property directly related to the non-Hermiticity of the Hamiltonian. We derive the correct continuity equation and, by applying defect theory, we obtain the correct momentum equation. Finally, by coupling twist kinematics and vortex dynamics we determine the full set of hydrodynamic equations governing quantum vortex evolution subject to twist.

- by Matteo Foresti and +1
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- Vortex dynamics, Topological Defects, Bose Einstein Condensates

We present in this communication further details to justify the new theory on Aerodynamics, discussing the D'Alembert's Paradox with intuitive and direct application on a cutted short aerodynamic body, vortex stabilizer, developed industrially on a golf club with results tested in wind tunnels, robotic machine and obviously in competition, having reached wins in the European Tour. In addition, we report experiment on possible aerodynamic properties of the hair of certain mammals

The demand for power has been increased nowadays in many folds and the need for a better, reliable
and cleaner source of energy has become essential. Ultimately our aim is to fulfill the requirements of power
demand. By research it is found that atmospheric vortex engine (AVE), the twin of solar chimney, seems to be a
promising source and has many advantages than the latter. Through this research it is possible generating power
from the residual heat source from the industries/thermal power plants. The AVE model is designed using
computerized modeling and analyzed it using computational fluid dynamics. By varying the parameters, that
influence the performance of AVE, it is studied to obtain an optimum design and operating conditions. Also the
AVE scaled model is fabricated and passed the flow to study about the vortex practically. It is found that it has
enough strength to rotate a small turbine placed inside it. Also the smoke has been passed and small particles to
visualize the flow. In this research the results of the CFD analysis to show that AVE is capable of producing a
sustained vortex, to generate power. This paper also serves as a base for future research.
Keywords: AVE, Alternate power, Updraft, Vortex

- by IJRAME Journal
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- Design, Vortex dynamics

It is my great honour to welcome you on behalf of the Bureau of IUTAM to this Symposium on Hamiltonian dynamics, vortex structures and turbulence. The Symposium has been in preparation for two years, and I congratulate our hosts here at the Steklov Institute of the Russian Academy of Sciences for having prepared an excellent and wide-ranging programme, and for having succeeded in attracting such a distinguished gathering to debate problems in ﬂuid dynamics many of which have a long history, yet still today present many challenges of a fundamental nature. The letters IUTAM, as you all know, stand for the International Union of Theoretical and Applied Mechanics. This Union is one of the International Scientiﬁc Union members of ICSU, the International Council for Science, which this year celebrates its 75th anniversary. The roots of IUTAM itself go back to the early Congresses in Mechanics, the ﬁrst of which was held in Delft in the Netherlands, in 1924. IUTAM was formally established as an International Union at the 7th Congress, which was held in London in 1948. The 13th Congress of Theoretical and Applied Mechanics was held here in Moscow in 1972, under the Presidency of the great Mushkhelishvili. The most recent 21st Congress was held in Warsaw in 2004, and the next will be held in Adelaide, South Australia, in 2008.
Professor Keith Moﬀatt, Vice-President, IUTAM

- by Mikhail A Sokolovskiy and +2
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- Hamiltonian dynamics, Stability, Vortex dynamics, ocean eddies

The definition of a vortex is a topic of much discussion in fluid mechanics . The common intuitive features of a vortex are a pressure minimum, closed or spiraling streamlines, and iso-surfaces of constant vorticity. [Jeong & Hussain] have proposed a definition of a vortex as a pressure minimum in the absence of unsteady straining and viscous effects. According to [Majumdar] , decreasing μ and increasing the fluid velocity, disintegrate the fluid parcel moving along U. into smaller parcels moving in arbitrary directions with random velocities. This is where the vortices are generated.

- by Ideen Sadrehaghighi
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- Vortex dynamics, Vortex shedding

Pull the plug on a sink full of water, and it bubbles as it labors down the drain. But in a moment the water begins to swirl, accelerating at the center, and the surface punctures into a vortex that spirals smoothly away. This distinctive phenomenon, common yet extraordinary, caught the eye of entrepreneur and inventor Paul Kouris when he was considering the world energy crisis in 1975. He thought, "Wow, that's it." Franz Zotloterer came up with the same idea when he was exploring ways to aerate water. The concept was to use the kinetic energy of a water vortex to generate clean renewable energy.

- by Bryan Graczyk
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- Physics, Renewable Energy, Ecology, Environmental Justice

The Lorentz transformations are best known for the relativistic Lorentz factor, γ = 1/√(1 – v^2/c^2), which appears in the equations of special relativity, and it is also known that the Lorentz transformations can be used to derive both the Biot-Savart law in the form B = γv×E/c^2, and the magnetic force in the form E = γv×B.
It could therefore be argued that magnetism is a relativistic effect, even though it is observed at laboratory speeds. This article will now examine how the physical structure of the luminiferous medium enables the existence of magnetism. The aim will be to identify the latent presence of the speed of light within the fabric of a laboratory magnetic field. On establishing this, the Lorentz factor will then be exposed as an asymptotic coefficient which only becomes significant at speeds close to the speed of light.

- by Frederick David Tombe
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- Electromagnetism, Æther Physics, Special Relativity, Vortex dynamics

Vortex filament statement of Helmholtz's vortex theorems, Biot-Savart Law, starting, bound & trailing vortices of wings, Lanchester's experiment, Prandtl's Lifting line theory-downwash and induced drag, Elliptic loading & wings of elliptic platforms, expression for induced drag, minimum induced drag for Elliptic platform. Source and vortex panel methods for airfoils. Replacement of an airfoil by a concentrated vortex at quarter-chord point, importance of three-quarter chord point for discretization, use of quarter chord and three-quarter chord points in vortex panel method for wings.

This paper presents a previously unreported method of laryngeal vocal sound production that is capable of producing pitches even higher than the whistle register (M3). Colloquially known as the glottal whistle (here referred to as M4), this method has a wider range than M3 and features frequent instances of biphonation, which is of interest for those involved with contemporary and improvised music. Pitch profile analyses of M4 have found the majority of fundamental frequency (f0) activity to be between 1 and 3 kHz, while the most frequently seen range was between 1000 to 1,500 Hz. Remarkably, multiple singers were able to produce f0 higher than the highest tone on the piano.

- by Michael Edgerton
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- Music, Musicology, Composition (Music), Voice (Music)

This research focuses on the gravitational creation of a water vortex stream, which is a novel technique in hydropower engineering. The water enters a wide straight inlet and then through a vertical conical tube, creating a vortex that exits at the shallow basin's centre floor. The blades of the turbine can spin in the vortex, which generates electricity from a generator. The gravitational vortex turbine is the name for this kind of turbine. The turbine is driven by the vortex's dynamic force rather than the pressure differential. Since no discretization of the flow domain is needed, this study relies on simulation to provide the specifics of water vortex creation. The computational fluid dynamics (CFD) models' boundary conditions are added depending on the experiment configuration. Two different hole sizes for water discharge were tested in two different environments. The first condition's effect shows that the vortex heights in the experiment and CFD agree. The final vortex height of the CFD model differs from the experiment outcome in the second condition. More turbulent flow has set in as the discharge hole becomes larger, creating more errors in the CFD model's prediction of water vortex formation.

In Section 1.1 of this chapter we explain the subject of Geophysical Fluid Dynamics, and give the description of main vortex structures that have become objects of the present book: (a) Heton – a two-layer vortex with opposite rotations in different layers, and (b)Intrathermocline lens, which is studied in this work as a vortex patch in the intermediate layer of a three-layer ocean model. In this section, we propose also a short review of works in the related topics. Section 1.2 is a mathematical introduction. It contains all main formulae which are used furher in Chapters 2 and 3.

- by Mikhail A Sokolovskiy
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- Vortex dynamics

This thesis presents an experimental study of hydrodynamical phenomena of a laser propagating nonlinearly. For a medium presenting an intensity-dependent refractive index, and in the frame of the paraxial approximation, the intensity of the laser beam is equivalent to a density of a fluid, the propagation direction is seen as a time evolution of the fluid as well as the phase gradient of the laser beam defines a flow velocity and the nonlinear refractive index change allows defining a sound velocity of the fluid. Under this analogy, we call the propagating laser beam a fluid of light. In this thesis, we provide a study of the superfluidity concept of a fluid of light in a self-defocusing regime of the nonlinearity. It is defined as the absence of diffraction when the fluid of light encounters an obstacle. The parameters which control the superfluid transition are: the flow velocity as well as the sound velocity. They are monitored respectively through the wave vector and the intensity of the laser beam. In the frame of this analogy, we also present in this manuscript a study of vortex shedding regime as a result of the interaction between the fluid of light and the obstacle. Here, the obstacle is considered being strong. When twice the flow velocity at the poles of the obstacle is larger than the sound velocity, pairs of vortex/anti-vortex are emitted demonstrating a hydrodynamical behaviour of the fluid of light. In order to underline the nonlinear refractive index change, we also report in this thesis a study of the photorefractive nonlinearity using the self-phase modulation effect.

- by Omar Boughdad
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- Nonlinear Optics, Superfluidity, Vortex dynamics, Bose Einstein Condensation

The present work considers the turbulent flow inside a high-speed rotor-stator cavity with or without superimposed throughflow. New extensive measurements made at IRPHE by a two-component laser Doppler anemometer technique and by pressure transducers are compared to numerical predictions based on one-point statistical modeling using a low-Reynolds-number second-order full stress transport closure. The advanced second-order model provides good predictions for the mean flow as well as for the turbulent field and so is the adequate level of closure to describe such complex flows. A better insight into the dynamics of such flows is also gained from this study. Indeed the transition between a Batchelor type of flow with two boundary layers separated by a central rotating core and a Stewartson type of flow with only one boundary layer on the rotating disk is characterized in the (r*,Ro) plane, where r* is the dimensionless radial location and Ro a modified Rossby number. The 5/7 power-law of Poncet et al. (2005) describing the mean centripetal flow in a rotor-stator system is extended to different aspect ratios and to the case of centrifugal Batchelor type of flows.

- by Sebastien Poncet
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- Engineering, Vortex dynamics, Mathematical Sciences, Power Law
- by Mikhail A Sokolovskiy
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- Stability, Vortex dynamics, Numerical Methods
- by Lionel Larchevêque and +1
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- Engineering, Fluid Mechanics, Large Eddy Simulation, Vortex dynamics

Empedocles' cyclical attractions/separations of the two eternal principles highlight the role played by the vortex as an agent of both unity and dissolution:
“When Νεῖκος has reached the deepest depth/ of the vortex (ἐπεὶ Νεῖκος μὲν ἐνέρτατον ἵκητο βένθος δίνης), and Φιλότης has come to be in the center of the whirl (ἐν δὲ μέσῃ Φιλότης στροφάλιγγι γένηται),/ under her dominion all these [i.e., the elements] come together to be only one.” (B35.20-22)
My goal here is to examine the type of authority of Empedocles' δίνη and στροφάλιγξ over the cosmic alternations and the constant interaction between the cosmic elements. Furthermore, I will consider Empedocles' differentiated usage of δίνη (as instrument for the alternating and cyclical exercise of Νεῖκος' authority) and στροφάλιγξ (for Φιλία's modus operandi) through a careful comparison with the Homeric occurrences of δίνη and of στροφαλιγξ in the climactic scenes of the Battle of the Gods in Iliad 21. My hypothesis is that the dialectic confrontation of Empedocles' two cosmic principles has the Theomachy (νεῖκος!) of Iliad 21 as poetic model. If Empedocles uses two different words to refer to the two vortices, it is to emphasize the fundamental difference between the two cosmic principles and between the modalities by which each of them, alternately and cyclically, manifests and implements its cosmic authority.

- by Gabriela Cursaru
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- Classics, Greek Literature, Homer, Greek Language

Globalization has led to an increase in the use of small copters for different activities such as geo-referencing, agricultural fields monitoring, survillance, among others. This is the main reason why there is a strong interest in the performance of small-scale propellers used in unmanned aerial vehicles. The flow developed by rotors is complex and the estimation of its aerodynamic performance is not a trivial process besides, viscous effects, when the rotor operates at low Reynolds, affect its performance. In the present paper, two different computational methods, Computational Fluid Dynamics (CFD) and the Unsteady Vortex Lattice Method (UVLM) with a viscous correction, were used to study the performance of an isolated rotor of a quadcopter flying at hover. The Multi Reference Frame model and transition SST (kappa-omega) turbulence model were used in the CFD simulations. The tip vortex core growth was used to account for the viscous effects in the UVLM. The wake structure, pressure coefficient, thrust and torque predictions from both methods are compared. Thrust and torque results from simulations were validated by means of experimental results of a characterization of a single rotor. Finally, figure of merit of the rotor is evaluated showing that UVLM overestimates the efficiency of the rotor, meanwhile CFD predictions are close to experimental values.}

Flow separation over a surface-mounted obstacle is prevalent in numerous applications. Previous studies of 3D sepa- ration around protuberances have been limited to steady ow. In biological and geophysical ows, pulsatile conditions are fre- quently encountered, yet this situation has not been extensively studied. Primarily motivated by our previous studies of the ow patterns observed in various human vocal fold pathologies such as polyps, our research aimed to ll this gap in the knowledge concerning unsteady 3D ow separation. This is achieved by characterizing velocity elds surrounding the obstacle, focused primarily on the vortical ow structures and dynamics that occur around a hemispheroid in pulsatile ow. As part of this study, two- dimensional, instantaneous and phase-averaged particle image velocimetry data in both steady and pulsatile ows are presented and compared. Coherent vortical ow structures have been identi- ed by their swirling strength. This analysis revealed ow struc- tures with dynamics dependent on the pulsatile forcing function. A mechanism to explain the formation and observed dynamics of these ow structures based on the self-induced velocity of vortex rings interacting with the unsteady ow is proposed.

- by Ian Carr
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- Biofluids, Biofluid Mechanics, Vortex dynamics, Bluff Body Aerodynamics
- by Doç. Dr. Bahar Aşcı
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- Scenario planning, Vortex dynamics, Vortex

We investigate equilibrium solutions for tripolar vortices in a two-layer quasi-geostrophic flow. Two of the vortices are like-signed and lie in one layer. An opposite-signed vortex lies in the other layer. The families of equilibria can be spanned by the distance (called separation) between the two like-signed vortices. Two equilibrium configurations are possible when the opposite-signed vortex lies between the two other vortices. In the first configuration (called ordinary roundabout), the opposite signed vortex is equidistant to the two other vortices. In the second configuration (eccentric roundabouts), the distances are unequal. We determine the equilibria numerically and describe their characteristics for various internal deformation radii. The two branches of equilibria can co-exist and intersect for small deformation radii. Then, the eccentric roundabouts are stable while unstable ordinary roundabouts can be found. Indeed, ordinary roundabouts exist at smaller separations than eccentric roundabouts do, thus inducing stronger vortex interactions. However, for larger deformation radii, eccentric roundabouts can also be unstable. Then, the two branches of equilibria do not cross. The branch of eccentric roundabouts only exists for large separations. Near the end of the branch of eccentric roundabouts (at the smallest separation), one of the like-signed vortices exhibits a sharp inner corner where instabilities can be triggered. Finally, we investigate the nonlinear evolution of a few selected cases of tripoles. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4978806]

- by Mikhail A Sokolovskiy
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- Vortex dynamics, Quasi Stationary States

A novel numerical configuration has been devised in order to investigate active control of separated airfoil flows in a comprehensive and systematic manner. The configuration consists of a flat plate at zero degrees angle-of-attack in a freestream on which a separation bubble of prescribed size is created at a prescribed location through blowing and suction on the top boundary of the computational domain. Numerical simulations of this configuration show that these canonical separated airfoil flows exhibit three distinct characteristic time scales corresponding to the shear layer, the separation zone and the wake vortex shedding. The vortex dynamics associated with these distinct phenomena are described. Preliminary simulations of this flow subjected to zero-net-mass-flux perturbation are also presented.

- by Louis Cattafesta
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- Flow Control, Vortex dynamics, Numerical Simulation, Active Control

The flame structure of unsteady flickering partially premixed flames is numerically investigated, and detailed results are provided for a flame established at Fr = 0.5, Re = 500, and overall ~b = 1. A numerical study is conducted in an inverse configuration in which a fuel-rich (CHa-air) annular jet is sandwiched between an axisymmetric air jet (on the inside) and coflowing air (on the outside). The computations involve a time-dependent, axisymmetric model based on a direct numerical simulation methodology, and a detailed 52-step mechanism to model the CH4-air chemistry. The calculations show that the flame structure of the partially premixed flames differs from that of a typical nonpremixed laminar jet flame. The fuel-rich annular ring close to the nozzle exit undergoes premixed combustion, but once oxygen is depleted inside the annular ring, diffusion flames are established on both sides of it due to excess fuel emerging from the premixed zone. The two high temperature nonpremixed regions later merge into a single surface in the plume. Subsequently, buoyant acceleration of hot gases outside the diffusion flame surface causes shear-layer rollup, leading to the formation of toroidal vortex rings, which then interact with the plume surface. While the premixed flame exhibits relatively steep temperature gradients, and is thin, the two diffusion flames display broader gradients, and are thicker. The carbon monoxide and molecular hydrogen formed due to premixed combustion provide "fuel" for two nonpremised flames connected to either wing of the premixed flame. The oxygen present in the fuel-rich annulus is completely consumed in the premixed zone, primarily by atomic hydrogen through the reaction H + O 2 ~* OH + O. Considering the dominant reactions, the premixed region can be characterized by the overall reaction CH 4 + O2 -(H) ¢* (CO + 2H 2 + OH). Oxygen consumption in the nonpremixed region is due to the O-H chemistry. Adding the significant reactions in the nonpremixed region and eliminating the steady-state intermediate species, the overall reaction (CO + 2H 2 + OH) + O2 ¢* CO2 + 2H20 + (H) describes combustion in that zone. The effect of unsteadiness on flame structure is investigated by comparing the scalar profiles at different times with respect to a conserved scalar. The predictions do not reveal significant effects of unsteadiness on the flame structure, although buoyant convection may influence the heat transfer to the unreacted flow. This is because the rollup process essentially affects the postflame, or plume, region and not the actual "flame." The vortex rollup process can be delayed by increasing either the Froude (Fr) or Reynolds (Re) numbers. The shortest roilup length is for the flame corresponding to the lowest values of Fr and Re. The "flame" flicker frequency increases as the Froude number is decreased, but the qualitative nature of the flame (plume)-vortex dynamics remains essentially the same. Detailed numerical simulations of analogous counterflow flames were performed using a more detailed chemical mechanism for the sake of comparison. There is remarkable similarity between the steady counterflow profiles and those of the unsteady co-annular flame.

- by suresh aggarwal
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- Mechanical Engineering, Chemical Engineering, Kinetics, Combustion

The interaction between a swept shock and the secondary flows present in the corners of a supersonic channel flow is experimentally investigated. Such an interaction presents an additional type of unit problem different than the isolated fin-type swept shock/boundary layer interaction. Stereo PIV measurements were conducted perpendicular to the principal flow direction in order to capture the secondary flows characteristic of such an interaction. Various parameters, such as vorticity, probability of flow separation, separation strength and friction coefficient are evaluated. The region of strongest separation in the flowfield generated by a coupled 3D SBLI was found to be at the location of the interaction between the vortex induced by the swept shock and the corner vortex developed in the corner of the channel. In this study, we attempt at explaining the mechanisms responsible for the observed separation.

- by Rohan Morajkar
- •
- Turbulent Flows, Vortex dynamics, Shock Waves, Experimental Fluid Dynamics

ABSTRACT This chapter summarizes the main results obtained in the book, defines possible generalizations and evokes perspectives for future investigation as well as related problems.

- by Mikhail A Sokolovskiy
- •
- Vortex dynamics

An axial flow fan, which is applied for ventilation in underground spaces such as tunnels, features a medium-large size, and most of the blades go through the casting process in consideration of mass production and cost. In the casting process, post-work related to roughness treatment is essential, and this is a final operation to determine the thickness profile of an airfoil which is designed from the empirical equation. In this study, the effect of the thickness profile of an airfoil on the performance and aerodynamic characteristics of the axial fan was examined through numerical analysis with the commercial code, ANSYS CFX. In order to conduct the sensitivity analysis on the effect of the maximum thickness position for each span on the performance at the design flow rate, the design of experiments (DOE) method was applied with a full factorial design as an additional attempt. The energy loss near the shroud span was confirmed with a quantified value for the tip leakage flow (TLF) rate through the tip clearance, and the trajectory of the TLF was observed on the two-dimensional (2D) coordinates system. The trajectory of the TLF matched well with the tendency of the calculated angle and correlated with the intensity of the turbulence kinetic energy (TKE) distribution. However, a correlation between the TLF rate and TKE could not be established. Meanwhile, the Q-criterion method was applied to specifically initiate the distribution of flow separation and inlet recirculation. The location accompanying the energy loss was mutually confirmed with the axial coordinates. Additionally, the nonuniform blade loading distribution, which was more severe as the maximum thickness position moved toward the leading edge (LE), could be improved significantly as the thickness near the trailing edge (TE) became thinner. The validation for the numerical analysis results was performed through a model-sized experimental test.

Mangrove forests along the Mekong delta estuaries are usually observed to degrade together with the increasing extension of fish farms. In this limited-width condition, the formation of coherent structures, their interactions with mangroves, the role of the width of the mangrove forest, and their effects on the exchange processes between the open channel and the adjacent floodplain are still not well examined. In order to obtain more insight, a unique laboratory experiment of a vegetated compound channel mimicking estuarine mangroves has been conducted. The results show that in a compound vegetated channel with a very gentle transverse slope, the vegetated shear layer dynamics resembled that associated with vegetation rather than that associated with a depth differential. Furthermore, the flow field under the effect of large horizontal coherent structures (LHCSs) shows a spatially and temporally cycloid motion with associated flow events, namely, sweep, ejection, stagnant, and reverse flows. It is also suggested that the coherent structures can have an influence on a broader area than the vegetation area into which the eddy structures can penetrate. In terms of the exchange processes, the momentum transfer and the intensity of transverse fluctuations induced by the LHCSs can be related to this phenomenon. Consequently, decreasing the mangrove width can significantly affect the pattern of the LHCSs, disturb the transverse exchange processes induced by these structures, and thereby changing the shear layer, creating unfavorable conditions for sedimentation inside forests and for river bank stability.

- by S.H. Truong
- •
- Climate Change Adaptation, Turbulent Flows, Ecohydraulics, Vortex dynamics
- by Blair Perot
- •
- Engineering, Fluid Mechanics, Vortex dynamics, Mathematical Sciences

Using micro-bridge technique, we have studied the vortex dynamics in a very low temperature region (i.e. T/Tc -> 0) of the B-T phase diagram of Bi_2Sr_2Ca_1Cu_2O_{8+\delta} single crystal. We distinguish two types of vortex dynamics near the depinning threshold depending on the magnitude of the vortex-vortex interactions. For 0.01 <= \mu_0H <= 1T, we show that current-voltage characteristics (I-V) are

- by Alex Ruyter
- •
- Vortex dynamics, Magnetic field, Power Law, Single Crystal

We study the spatial and temporal evolution of kinetic energy flux at different scales using direct numerical simulations of isotropic turbulence. The correlation coefficients at different times, between the molecular energy dissipation and local energy fluxes across inertial-range scales, are computed in both Eulerian and Lagrangian frames. The Eulerian correlation coefficients are found to decay monotonically backward in time. However, the Lagrangian correlation coefficients peak after a certain time delay. The peak time delay is found to be proportional to the local eddy turnover time ͑it scales with wave number k according to k −2/3 ͒, consistent with Kolmogorov's theory. Conditional sampling is used to isolate effects of strong rotation. The results presented provide strong evidence of the Lagrangian nature of turbulent energy cascade.

- by Gregory Eyink
- •
- Engineering, Physics, Direct Numerical Simulation, Numerical Analysis

The influence of different wing kinematic models on the aerodynamic performance of a hovering insect is investigated by means of two-dimensional time-dependent Navier-Stokes simulations. For this, simplified models are compared with averaged representations of the hovering fruit fly wing kinematics. With increasing complexity, a harmonic model, a Robofly model and two more-realistic fruit fly models are considered, all dynamically scaled at Re = 110. To facilitate the comparison, the parameters of the models were selected such that their mean quasi-steady lift coefficients were matched. Details of the vortex dynamics, as well as the resulting lift and drag forces, were studied.

- by Hester Bijl and +1
- •
- Engineering, Fluid Mechanics, Vortex dynamics, Mathematical Sciences

We consider surface-tension driven convection in a rotating fluid layer. For nearly insulating boundary conditions we derive a long-wave equation for the convection planform. Using a Galerkin method and direct numerical simulations we study the stability of the steady hexagonal patterns with respect to general side-band instabilities. In the presence of rotation steady and oscillatory instabilities are identified. One of them leads to stable, homogeneously oscillating hexagons. For sufficiently large rotation rates the stability balloon closes, rendering all steady hexagons unstable and leading to spatio-temporal chaos.

- by H. Riecke and +1
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- Applied Mathematics, Direct Numerical Simulation, Fluid Dynamics, Finite Element

A parametric study has been carried out to elucidate the characteristics of flow past a square cylinder inclined with respect to the main flow in the laminar flow regime. Reynolds number and angle of incidence are the key parameters which determine the flow characteristics. Location of separation point is greatly affected by angle of incidence, thus determining the flow field around the square cylinder. The critical Reynolds number for periodic vortex shedding at each angle of incidence considered is obtained by using Stuart-Landau equation. Attempt is made to classify the related flow patterns from a topological point of view, resulting in three distinct patterns in total. A comprehensive analysis of the effects of Reynolds number and angle of incidence on flow-induced forces on the square cylinder is presented. Collecting all the results obtained, contour diagrams of force and moment coefficients, Strouhal number, rms of lift-coefficient fluctuation, as well as a flow-pattern diagram are proposed for the ranges of the two parameters considered in the current investigation. Finally, a Floquet stability analysis is presented to detect the onset of the secondary instability leading to three-dimensional flow. The proposed diagrams and the Floquet stability analysis shed light on better physical understanding of the flow past a square cylinder, which should be useful in many engineering applications.

- by Choon-Bum Choi
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- Engineering, Pattern Formation, Fluid Dynamics, Vortex dynamics

For investigating vortex formation in rotating superfluid 3 He-B at high velocities of vortex-free superflow, the usual geometry is a cylindrical sample, which is connected via an orifice and a liquid 3 He column to the heat exchanger on the refrigerator. The orifice prevents vortices, created in the heat exchanger, from flowing into the sample until the rotation velocity reaches a critical value O c : We describe NMR measurements of O c as a function of temperature and discuss the results in terms of vortex-line pinning at the rim of the orifice. r

- by M. Krusius
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- Condensed Matter Physics, Quantum Physics, Heat Exchanger, Vortex dynamics

An experimental study was conducted to explore the effect of surface flexibility at the leading and trailing edges on the near-wake flow dynamics of a sinusoidal heaving foil. Midspan particle image velocimetry (PIV) measurements were taken in a closed-loop wind tunnel at a Reynolds number of 25,000 and at a range of reduced frequencies (k ¼ fc/U) from 0.09 to 0.20. Time-resolved and phase-locked measurements are used to describe the mean flow characteristics and phase-averaged vortex structures and their evolution. Large-eddy scale (LES) decomposition and swirling strength analysis are used to quantify the vortical structures. The results demonstrate that trailing edge flexibility has minimal influence on the mean flow characteristics. The mean velocity deficit for the flexible trailing edge and rigid foils remains constant for all reduced frequencies tested. However, the trailing edge flexibility increases the swirling strength of the small-scale structures, resulting in enhanced cross-stream dispersion. Flexibility at the leading edge is shown to generate a large-scale leading edge vortex (LEV) for k ! 0.18. This results in a reduction in the swirling strength due to vortex interactions when compared to the flexible trailing edge and rigid foils. Furthermore, it is shown that the large-scale LEV is responsible for extracting a significant portion of energy from the mean flow, reducing the mean flow momentum in the wake. The kinetic energy loss in the wake is shown to scale with the energy content of the LEV.

- by Firas Siala
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- Fluid Mechanics, Fluid structure interaction, Vortex dynamics, Flapping Flight