Vortex formation with a snapping shrimp claw.

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David Hess

Full Text Available Snapping shrimp use one oversized claw to generate a cavitating high speed water jet for hunting, defence and communication. This work is an experimental investigation about the jet generation. Snapping shrimp (Alpheus-bellulus were investigated by using an enlarged transparent model reproducing the closure of the snapper claw. Flow inside the model was studied using both High-Speed Particle Image Velocimetry (HS-PIV and flow visualization. During claw closure a channel-like cavity was formed between the plunger and the socket featuring a nozzle-type contour at the orifice. Closing the mechanism led to the formation of a leading vortex ring with a dimensionless formation number of approximate ΔT*≈4. This indicates that the claw might work at maximum efficiency, i.e. maximum vortex strength was achieved by a minimum of fluid volume ejected. The subsequent vortex cavitation with the formation of an axial reentrant jet is a reasonable explanation for the large penetration depth of the water jet. That snapping shrimp can reach with their claw-induced flow. Within such a cavitation process, an axial reentrant jet is generated in the hollow cylindrical core of the cavitated vortex that pushes the front further downstream and whose length can exceed the initial jet penetration depth by several times.

Vortex formation and instability in the left ventricle

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Le, Trung Bao; Sotiropoulos, Fotis; Coffey, Dane; Keefe, Daniel

2012-09-01

We study the formation of the mitral vortex ring during early diastolic filling in a patient-specific left ventricle (LV) using direct numerical simulation. The geometry of the left ventricle is reconstructed from Magnetic Resonance Imaging (MRI) data of a healthy human subject. The left ventricular kinematics is modeled via a cell-based activation methodology, which is inspired by cardiac electro-physiology and yields physiologic LV wall motion. In the fluid dynamics videos, we describe in detail the three-dimensional structure of the mitral vortex ring, which is formed during early diastolic filling. The ring starts to deform as it propagates toward the apex of the heart and becomes inclined. The trailing secondary vortex tubes are formed as the result of interaction between the vortex ring and the LV wall. These vortex tubes wrap around the circumference and begin to interact with and destabilize the mitral vortex ring. At the end of diastole, the vortex ring impinges on the LV wall and the large-scale intraventricular flow rotates in clockwise direction. We show for the first time that the mitral vortex ring evolution is dominated by a number of vortex-vortex and vortex-wall interactions, including lateral straining and deformation of vortex ring, the interaction of two vortex tubes with unequal strengths, helicity polarization of vortex tubes and twisting instabilities of the vortex cores.

Vortex-induced buckling of a viscous drop impacting a pool

KAUST Repository

Li, Erqiang; Beilharz, Daniel; Thoroddsen, Sigurdur T

2017-01-01

on the inner side of the vortex ring, while their folds can be stretched and straightened on the outside edge. We characterize the total stretching from high-speed video imaging and use particle image velocimetry to track the formation and evolution

Vortex Formation and Foraging in Polyphenic Spadefoot Toad Tadpoles.

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Bazazi, Sepideh; Pfennig, Karin S; Handegard, Nils Olav; Couzin, Iain D

2012-06-01

Animal aggregations are widespread in nature and can exhibit complex emergent properties not found at an individual level. We investigate one such example here, collective vortex formation by congeneric spadefoot toad tadpoles: Spea bombifrons and S. multiplicata. Tadpoles of these species develop into either an omnivorous or a carnivorous (cannibalistic) morph depending on diet. Previous studies show S. multiplicata are more likely to develop into omnivores and feed on suspended organic matter in the water body. The omnivorous morph is frequently social, forming aggregates that move and forage together, and form vortices in which they adopt a distinctive slowly-rotating circular formation. This behaviour has been speculated to act as a means to agitate the substratum in ponds and thus could be a collective foraging strategy. Here we perform a quantitative investigation of the behaviour of tadpoles within aggregates. We found that only S. multiplicata groups exhibited vortex formation, suggesting that social interactions differ between species. The probability of collectively forming a vortex, in response to introduced food particles, increased for higher tadpole densities and when tadpoles were hungry. Individuals inside a vortex moved faster and exhibited higher (by approximately 27%) tailbeat frequencies than those outside the vortex, thus incurring a personal energetic cost. The resulting environmental modification, however, suggests vortex behaviour may be an adaptation to actively create, and exploit, a resource patch within the environment.

Numerical investigation on nonlinear effect and vortex formation of oscillatory flow throughout a short tube in a thermoacoustic Stirling engine

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Yang, Peng; Chen, Hui; Liu, Yingwen

2017-06-01

In this paper, a two-dimensional axisymmetric model of a thermoacoustic Stirling engine with a short tube where the cross section narrows has been developed. The transient streamlines and vortex formation through short tubes with different diameters in oscillatory flow have been investigated visually by computational fluid dynamics. Three dimensionless parameters, Reynolds number (Re), Keulegan-Carpenter number (KC), and Womersley number (Wo), are used to describe the flow regime and vortex characteristic throughout the short tube. High Re and Wo numbers indicate that the oscillatory flow develops into the turbulent flow through the short tube. The KC number has a direct effect on the transition of streamlines and the development of the vortex. For a small cross section where KC ≈ 1, streamlines rotate and the vortex forms at both sides of the short tube. The vortex stays in the main flow region, and intensity varies as streamlines are convected downstream. The velocity along the radius presents a Poiseuille profile within the influence of the vortex. For a large cross section where KC < 1, streamlines pass the short tube with little rotation and the vortex disappears in the main flow region and confines near the short tube. The velocity profile tends to be flat. The nonlinear effects including instantaneous pressure drop and power dissipation throughout the short tube are also discussed. It shows that the time averaged pressure drop is generated at the cost of power dissipation. Finally, the "effectiveness" is applied to evaluate the performance of the short tube. The results suggest that increasing the diameter of the short tube is in favor of reducing power dissipation, which is beneficial to improve "effectiveness."

Vortex Formation During Unsteady Boundary-Layer Separation

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Das, Debopam; Arakeri, Jaywant H.

1998-11-01

Unsteady laminar boundary-layer separation is invariably accompanied by the formation of vortices. The aim of the present work is to study the vortex formation mechanism(s). An adverse pressure gradient causing a separation can be decomposed into a spatial component ( spatial variation of the velocity external to the boundary layer ) and a temporal component ( temporal variation of the external velocity ). Experiments were conducted in a piston driven 2-D water channel, where the spatial component could be be contolled by geometry and the temporal component by the piston motion. We present results for three divergent channel geometries. The piston motion consists of three phases: constant acceleration from start, contant velocity, and constant deceleration to stop. Depending on the geometry and piston motion we observe different types of unsteady separation and vortex formation.

Blood drop patterns: Formation and applications.

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Chen, Ruoyang; Zhang, Liyuan; Zang, Duyang; Shen, Wei

2016-05-01

The drying of a drop of blood or plasma on a solid substrate leads to the formation of interesting and complex patterns. Inter- and intra-cellular and macromolecular interactions in the drying plasma or blood drop are responsible for the final morphologies of the dried patterns. Changes in these cellular and macromolecular components in blood caused by diseases have been suspected to cause changes in the dried drop patterns of plasma and whole blood, which could be used as simple diagnostic tools to identify the health of humans and livestock. However, complex physicochemical driving forces involved in the pattern formation are not fully understood. This review focuses on the scientific development in microscopic observations and pattern interpretation of dried plasma and whole blood samples, as well as the diagnostic applications of pattern analysis. Dried drop patterns of plasma consist of intricate visible cracks in the outer region and fine structures in the central region, which are mainly influenced by the presence and concentration of inorganic salts and proteins during drying. The shrinkage of macromolecular gel and its adhesion to the substrate surface have been thought to be responsible for the formation of the cracks. Dried drop patterns of whole blood have three characteristic zones; their formation as functions of drying time has been reported in the literature. Some research works have applied engineering treatment to the evaporation process of whole blood samples. The sensitivities of the resultant patterns to the relative humidity of the environment, the wettability of the substrates, and the size of the drop have been reported. These research works shed light on the mechanisms of spreading, evaporation, gelation, and crack formation of the blood drops on solid substrates, as well as on the potential applications of dried drop patterns of plasma and whole blood in diagnosis. Crown Copyright © 2016. Published by Elsevier B.V. All rights reserved.

The Effect of Uniform Background Flow on Vortex Ring Formation and Pinch-off

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Krueger, Paul S.; Dabiri, John O.; Gharib, Morteza

2002-11-01

Experimental investigations of vortex ring formation are extended to include the effects of a uniform background flow, in a manner relevant to the locomotion of aquatic animals utilizing jet propulsion. Gharib et. al. [J. Fluid Mech. 360, 121 (1998)] generated vortex rings using a piston/cylinder apparatus with relatively large discharge times to demonstrate that the vortex ring at the leading edge of the jet attains its maximum circulation at a piston stroke-to-diameter ratio L/D of 4. This "formation number" is robust over a range of piston motions and cylinder boundary conditions, and can be explained in terms of the Kelvin-Benjamin variational principle. To determine the effect of background flow on formation number and pinch-off of the leading vortex ring, uniform co-flow is established in a large annulus surrounding the vortex generator. The ratio of co-flow velocity to piston velocity is varied between 0 and 1. In addition, the co-flow is initiated at times both before and after the start of vortex ring formation. We present results for stroke ratios L/D = 2 and L/D = 8, in order to discern effects of the co-flow on the leading vortex ring in isolation and in the presence of a trailing jet.

Unsteady aerodynamics and vortex-sheet formation of a two-dimensional airfoil

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Xia, X.; Mohseni, K.

2017-11-01

Unsteady inviscid flow models of wings and airfoils have been developed to study the aerodynamics of natural and man-made flyers. Vortex methods have been extensively applied to reduce the dimensionality of these aerodynamic models, based on the proper estimation of the strength and distribution of the vortices in the wake. In such modeling approaches, one of the most fundamental questions is how the vortex sheets are generated and released from sharp edges. To determine the formation of the trailing-edge vortex sheet, the classical Kutta condition can be extended to unsteady situations by realizing that a flow cannot turn abruptly around a sharp edge. This condition can be readily applied to a flat plate or an airfoil with cusped trailing edge since the direction of the forming vortex sheet is known to be tangential to the trailing edge. However, for a finite-angle trailing edge, or in the case of flow separation away from a sharp corner, the direction of the forming vortex sheet is ambiguous. To remove any ad-hoc implementation, the unsteady Kutta condition, the conservation of circulation, as well as the conservation laws of mass and momentum are coupled to analytically solve for the angle, strength, and relative velocity of the trailing-edge vortex sheet. The two-dimensional aerodynamic model together with the proposed vortex-sheet formation condition is verified by comparing flow structures and force calculations with experimental results for airfoils in steady and unsteady background flows.

Formation and interference of two pairs of vortex streets

International Nuclear Information System (INIS)

Kamemoto, Kyoji

1976-01-01

A series of theoretical analysis were made on the mechanism of the formation and interference of two pairs of vortex streets appearing behind a pair of two long bars placed perpendicularly to uniform flow. In the first part, the flow model used for this study is explained. It was assumed that two pairs of vortex sheets having the same interval (h) were placed at the distance of g in non-viscous flow. Then small disturbance was given to the flow, and the behavior of the vortex sheets in course of time was analyzed by solving a set of linear simultaneous differential equations. Eight fundamental modes of small displacement were obtained as the independent solutions of the equations. The fundamental modes and the associated parameters are presented. In the second part, a set of non-linear differential equations were derived by substituting the vortex sheets with vortex streets with finite intensity. The set of equations were solved numerically. The results of numerical solutions for various conditions are presented. Main conclusions drawn from this study are that the condition of the existence of two pairs of vortex sheets is g/h >= 1, and that the mutual interference between two pairs of vortex streets becomes conspicuous for g/h <= 2. Some discussions made by other researchers and the author are also presented at the end of this paper. (Aoki, K.)

Drop impact entrapment of bubble rings

KAUST Repository

Thoraval, M.-J.

2013-04-29

We use ultra-high-speed video imaging to look at the initial contact of a drop impacting on a liquid layer. We observe experimentally the vortex street and the bubble-ring entrapments predicted numerically, for high impact velocities, by Thoraval et al. (Phys. Rev. Lett., vol. 108, 2012, article 264506). These dynamics mainly occur within 50 -s after the first contact, requiring imaging at 1 million f.p.s. For a water drop impacting on a thin layer of water, the entrapment of isolated bubbles starts through azimuthal instability, which forms at low impact velocities, in the neck connecting the drop and pool. For Reynolds number Re above -12 000, up to 10 partial bubble rings have been observed at the base of the ejecta, starting when the contact is -20% of the drop size. More regular bubble rings are observed for a pool of ethanol or methanol. The video imaging shows rotation around some of these air cylinders, which can temporarily delay their breakup into micro-bubbles. The different refractive index in the pool liquid reveals the destabilization of the vortices and the formation of streamwise vortices and intricate vortex tangles. Fine-scale axisymmetry is thereby destroyed. We show also that the shape of the drop has a strong influence on these dynamics. 2013 Cambridge University Press.

PREFACE: Special section on vortex rings Special section on vortex rings

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Fukumoto, Yasuhide

2009-10-01

This special section of Fluid Dynamics Research includes five articles on vortex rings in both classical and quantum fluids. The leading scientists of the field describe the trends in and the state-of-the-art development of experiments, theories and numerical simulations of vortex rings. The year 2008 was the 150th anniversary of 'vortex motion' since Hermann von Helmholtz opened up this field. In 1858, Helmholtz published a paper in Crelle's Journal which put forward the concept of 'vorticity' and made the first analysis of vortex motion. Fluid mechanics before that was limited to irrotational motion. In the absence of vorticity, the motion of an incompressible homogeneous fluid is virtually equivalent to a rigid-body motion in the sense that the fluid motion is determined once the boundary configuration is specified. Helmholtz proved, among other things, that, without viscosity, a vortex line is frozen into the fluid. This Helmholtz's law immediately implies the preservation of knots and links of vortex lines and its implication is enormous. One of the major trends of fluid mechanics since the latter half of the 20th century is to clarify the topological meaning of Helmholtz's law and to exploit it to develop theoretical and numerical methods to find the solutions of the Euler equations and to develop experimental techniques to gain an insight into fluid motion. Vortex rings are prominent coherent structures in a variety of fluid motions from the microscopic scale, through human and mesoscale to astrophysical scales, and have attracted people's interest. The late professor Philip G Saffman (1981) emphasized the significance of studies on vortex rings. One particular motion exemplifies the whole range of problems of vortex motion and is also a commonly known phenomenon, namely the vortex ring or smoke ring. Vortex rings are easily produced by dropping drops of one liquid into another, or by puffing fluid out of a hole, or by exhaling smoke if one has the skill

Drop impact into a deep pool: vortex shedding and jet formation

NARCIS (Netherlands)

Agbaglah, G.; Thoraval, Marie-Jean; Thoroddsen, S.T.; Zhang, L.V.; Fezzaa, K.; Deegan, R.D.

2015-01-01

One of the simplest splashing scenarios results from the impact of a single drop on a deep pool. The traditional understanding of this process is that the impact generates an axisymmetric sheet-like jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of

Complex 3D Vortex Lattice Formation by Phase-Engineered Multiple Beam Interference

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Jolly Xavier

2012-01-01

Full Text Available We present the computational results on the formation of diverse complex 3D vortex lattices by a designed superposition of multiple plane waves. Special combinations of multiples of three noncoplanar plane waves with a designed relative phase shift between one another are perturbed by a nonsingular beam to generate various complex 3D vortex lattice structures. The formation of complex gyrating lattice structures carrying designed vortices by means of relatively phase-engineered plane waves is also computationally investigated. The generated structures are configured with both periodic as well as transversely quasicrystallographic basis, while these whirling complex lattices possess a long-range order of designed symmetry in a given plane. Various computational analytical tools are used to verify the presence of engineered geometry of vortices in these complex 3D vortex lattices.

Vortex ring formation at the open end of a shock tube: A particle image velocimetry study

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Arakeri, J. H.; Das, D.; Krothapalli, A.; Lourenco, L.

2004-04-01

The vortex ring generated subsequent to the diffraction of a shock wave from the open end of a shock tube is studied using particle image velocimetry. We examine the early evolution of the compressible vortex ring for three-exit shock Mach numbers, 1.1, 1.2, and 1.3. For the three cases studied, the ring formation is complete at about tUb/D=2, where t is time, Ub is fluid velocity behind shock as it exits the tube and D is tube diameter. Unlike in the case of piston generated incompressible vortex rings where the piston velocity variation with time is usually trapezoidal, in the shock-generated vortex ring case the exit fluid velocity doubles from its initial value Ub before it slowly decays to zero. At the end of the ring formation, its translation speed is observed to be about 0.7 Ub. During initial formation and propagation, a jet-like flow exists behind the vortex ring. The vortex ring detachment from the tailing jet, commonly referred to as pinch-off, is briefly discussed.

Aerosol Effects on Microphysical Processes, Storm Structure, and Cold Pool Strength in Simulated Supercell Thunderstorms from VORTEX-2 and VORTEX-SE

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Guo, M.; Dawson, D. T., II; Baldwin, M. E.; Mansell, E. R.

2017-12-01

The cloud condensation nuclei (CCN) concentration has been found to strongly affect microphysical, dynamical and thermodynamical processes in supercells and other deep convective storms. Moreover, recent simulation studies have shown aerosols effects differ between higher- and lower-CAPE environments. Owing to the known sensitivity of severe storms to microphysical differences, studying the impact of aerosols supercell storms different environments is of clear societal importance. Tornadic environments in the southwastern U.S. are generally characterized by lower magnitudes CAPE and deeper tropospheric moisture than those in the Great Plains. These two regions were the focus of Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX)-2 and VORTEX-Southeast (SE) field campaigns, respectively. In our study, we simulate several cases from VORTEX-2 and -SE with the Advanced Regional Prediction System (ARPS) Model at 6 different CCN concentrations (100-3000 cm-3). We use NSSL 3-moment microphysics parameterization schemeto explicitly predict precipitation particle size distributions and microphysirocess rates. Overall, storms under the higher-CAPE VORTEX-2 environments are more sensitiveto the change of CCN than those under the lower-CAPE VORTEX-SE environments. Updraft volume decreases as CCN increases for the VORTEX-2 cases, whereas the opposite is true but with a much weaker trend for the VORTEX-SE cases. Moreover, the cold pool strength drops dramatically as CCN surpasses 1000 cm-3n the VORTEX-2 cases but barely changes for the VORTEX-SE cases. Through a microphysics budget analysis, we show the change of the importance of ice processes is key to the differing sensitivities. in the VORTEX-2 cases, deposition to ice nuclei, cloud drop freezing and rain drop freezing in the upper levels (5-11km) contribute more to latent heating since more rain and cloud drops are lifted above the freezing level due to stronger updrafts. For CCN concentration over 1000

Intrinsic and extrinsic mechanisms of vortex formation in superfluid 3He-B

International Nuclear Information System (INIS)

Ruutu, V.M.H.; Parts, Ue.; Krusius, M.

1997-01-01

The authors report on the first comprehensive measurements of critical superflow velocities in 3 He-B which allow different mechanisms of vortex formation to be identified. As a function of temperature T and pressure P, they measure the critical angular velocity Ω c (T,P) at which vortices start to form in slowly accelerating rotation in a cylindrical container filled with 3 He-B. Owing to the long coherence length ξ(T,P) ∼ 10-100 nm, either trapped remanent vorticity or intrinsic nucleation may dominate vortex formation, depending on the roughness of the container wall and the presence of loaded traps. NMR measurement with a resolution of one single vortex line allows the authors to distinguish between different processes: (1) Three extrinsic mechanisms of vortex formation have been observed. One of them is the vortex mill, a continuous periodic source which is activated in a rough-walled container well below the limit for intrinsic nucleation. (2) In a closed smooth-walled container intrinsic nucleation is the only mechanism available, with a critical velocity v c (T,P) = Ω c (T,P) R, where R is the radius of the container. The authors find v c (T,P) to be related to the calculated intrinsic stability limit v c (T,P) of homogeneous superflow. The existence of this connection in the form of a scaling law implies that nucleation takes place at an instability, rather than by thermal activation or quantum tunneling which become impossible because of an inaccessibly high energy barrier

Drop formation of black liquor spraying; Mustalipeaen pisaroituminen

Energy Technology Data Exchange (ETDEWEB)

Fogelholm, C J; Kankkunen, A; Nieminen, K; Laine, J; Miikkulainen, P [Helsinki Univ. of Technology, Otaniemi (Finland): Lab. of Energy Technology and Environmental Protection

1997-10-01

Black liquor is a spent liquor of the pulp and paper industry. It is burned in kraft recovery boilers for chemical and energy recovery. The high dry solids content and viscosity of black liquor require a high spraying temperature. This affects the performance of the boiler. Kraft recovery boiler deposit formation, emissions and chemical recovery are strongly affected by the drop size and the velocity of the black liquor spray formed by a splashplate nozzle. The sheet breakup mechanism is studied with a system based on a video and image-analysis. The drop size of mill-scale nozzles was measured also with an image-analysis-system. Measurements were carried out in a spray test chamber. The sheet breakup mechanism and drop size tests were carried out both below and over the boiling point of black liquor. Special attention was paid to the effect of flashing on drop formation. Temperature increase normally decreases drop size. In the temperature where the wavy-sheet disintegration changes to perforated-sheet disintegration the drop size increases. Spray velocity rises when the temperature is increased above the boiling point. (orig.)

Vortex Formation and Acceleration of a Fish-Inspired Robot Performing Starts from Rest

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Devoria, Adam; Bapst, Jonathan; Ringuette, Matthew

2009-11-01

We investigate the unsteady flow of a fish-inspired robot executing starts from rest, with the objective of understanding the connection among the kinematics, vortex formation, and acceleration performance. Several fish perform ``fast starts,'' where the body bends into a ``C'' or ``S'' shape while turning (phase I), followed by a straightening of the body and caudal fin and a linear acceleration (phase II). The resulting highly 3-D, unsteady vortex formation and its relationship to the acceleration are not well understood. The self-propelled robotic model contains motor-driven joints with programmable motion to emulate phase II of a simplified C-start. The experiments are conducted in a water tank, and the model is constrained to 1 direction along rails. The velocity is measured using digital particle image velocimetry (DPIV) in multiple planes. Vortex boundaries are identified using the finite-time Lyapunov exponent, then the unsteady vortex circulation is computed. The thrust is estimated from the identified vortices, and correlated with the circulation and model acceleration for different kinematics.

Heat transfer and pressure drop characteristics of the tube bank fin heat exchanger with fin punched with flow redistributors and curved triangular vortex generators

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Liu, Song; Jin, Hua; Song, KeWei; Wang, LiangChen; Wu, Xiang; Wang, LiangBi

2017-10-01

The heat transfer performance of the tube bank fin heat exchanger is limited by the air-side thermal resistance. Thus, enhancing the air-side heat transfer is an effective method to improve the performance of the heat exchanger. A new fin pattern with flow redistributors and curved triangular vortex generators is experimentally studied in this paper. The effects of the flow redistributors located in front of the tube stagnation point and the curved vortex generators located around the tube on the characteristics of heat transfer and pressure drop are discussed in detail. A performance comparison is also carried out between the fins with and without flow redistributors. The experimental results show that the flow redistributors stamped out from the fin in front of the tube stagnation points can decrease the friction factor at the cost of decreasing the heat transfer performance. Whether the combination of the flow redistributors and the curved vortex generators will present a better heat transfer performance depends on the size of the curved vortex generators. As for the studied two sizes of vortex generators, the heat transfer performance is promoted by the flow redistributors for the fin with larger size of vortex generators and the performance is suppressed by the flow redistributors for the fin with smaller vortex generators.

Theory of Vortex Crystal Formation in Two-Dimensional Turbulence

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Jin, D. Z.

1999-11-01

The free relaxation of inviscid, incompressible 2D turbulence is often dominated by strong vortices (coherent patches of intense vorticity) that move chaotically and merge. However, recent experiments(K.S. Fine et al., Phys. Rev. Lett. 75), 3277 (1995). with pure electron plasmas have found that freely relaxing turbulent flows with a single sign of vorticity can spontaneously form ``vortex crystals'' -- symmetric, stable arrays of strong vortices that are immersed in a low vorticity background. In this talk we discuss how these complex equilibria can form from 2D turbulence. First, we formulate a statistical theory of the vortex crystals. We show that vortex crystals are well described as ``regional'' maximum fluid entropy (RMFE) states, which are equilibrium states reached through ergodic mixing of the background by the strong vortices.(D.Z. Jin and D.H.E. Dubin, Phys. Rev. Lett. 80), 4434 (1998). Given the dynamically conserved quantities as well as the number and the vorticity distributions of the strong vortices, the theory predicts the positions of the strong vortices and the coarse-grained vorticity distribution of the background. These predictions agree well with the observed vortex crystals. Second, we examine the formation process of the vortex crystals in more detail. In the RMFE theory, the vortex crystal equilibrium can only be predicted if the number Nc of the strong vortices in the final state is given. Here, we estimate Nc from the characteristics of the early turbulent flow. The estimate relies on the idea that vortex crystals form because the chaotic motions of the strong vortices are ``cooled'' due to mixing of the background by the vortices. When the rate of cooling is faster than the rate of pairwise mergers, the vortices fall into a crystal pattern before they can merge. We estimate the merger rate from the observed power law decay of the number of strong vortices in the early stages of the flow, and the cooling rate from the rate of mixing of

Altered left ventricular vortex ring formation by 4-dimensional flow magnetic resonance imaging after repair of atrioventricular septal defects.

Science.gov (United States)

Calkoen, Emmeline E; Elbaz, Mohammed S M; Westenberg, Jos J M; Kroft, Lucia J M; Hazekamp, Mark G; Roest, Arno A W; van der Geest, Rob J

2015-11-01

During normal left ventricular (LV) filling, a vortex ring structure is formed distal to the left atrioventricular valve (LAVV). Vortex structures contribute to efficient flow organization. We aimed to investigate whether LAVV abnormality in patients with a corrected atrioventricular septal defect (AVSD) has an impact on vortex ring formation. Whole-heart 4D flow MRI was performed in 32 patients (age: 26 ± 12 years), and 30 healthy subjects (age: 25 ± 14 years). Vortex ring cores were detected at peak early (E-peak) and peak late filling (A-peak). When present, the 3-dimensional position and orientation of the vortex ring was defined, and the circularity index was calculated. Through-plane flow over the LAVV, and the vortex formation time (VFT), were quantified to analyze the relationship of vortex flow with the inflow jet. Absence of a vortex ring during E-peak (healthy subjects 0%, vs patients 19%; P = .015), and A-peak (healthy subjects 10% vs patients 44%; P = .008) was more frequent in patients. In 4 patients, this was accompanied by a high VFT (5.1-7.8 vs 2.4 ± 0.6 in healthy subjects), and in another 2 patients with abnormal valve anatomy. In patients compared with controls, the vortex cores had a more-anterior and apical position, closer to the ventricular wall, with a more-elliptical shape and oblique orientation. The shape of the vortex core closely resembled the valve shape, and its orientation was related to the LV inflow direction. This study quantitatively shows the influence of abnormal LAVV and LV inflow on 3D vortex ring formation during LV inflow in patients with corrected AVSD, compared with healthy subjects. Copyright © 2015. Published by Elsevier Inc.

Vortex rings

CERN Document Server

Akhmetov, D G

2009-01-01

This text on vortex rings covers their theoretical foundation, systematic investigations, and practical applications such as the extinction of fires at gushing oil wells. It pays special attention to the formation and motion of turbulent vortex rings.

Experimental validation of plugging during drop formation in a T-junction.

Science.gov (United States)

Abate, Adam R; Mary, Pascaline; van Steijn, Volkert; Weitz, David A

2012-04-21

At low capillary number, drop formation in a T-junction is dominated by interfacial effects: as the dispersed fluid flows into the drop maker nozzle, it blocks the path of the continuous fluid; this leads to a pressure rise in the continuous fluid that, in turn, squeezes on the dispersed fluid, inducing pinch-off of a drop. While the resulting drop volume predicted by this "squeezing" mechanism has been validated for a range of systems, as of yet, the pressure rise responsible for the actual pinch-off has not been observed experimentally. This is due to the challenge of measuring the pressures in a T-junction with the requisite speed, accuracy, and localization. Here, we present an empirical study of the pressures in a T-junction during drop formation. Using Laplace sensors, pressure probes we have developed, we confirm the central ideas of the squeezing mechanism; however, we also uncover other findings, including that the pressure of the dispersed fluid is not constant but rather oscillates in anti-phase with that of the continuous fluid. In addition, even at the highest capillary number for which monodisperse drops can be formed, pressure oscillations persist, indicating that drop formation in confined geometries does not transition to an entirely shear-driven mechanism, but to a mechanism combining squeezing and shearing.

Vortex lattice formation in 2D magnetized plasmas

International Nuclear Information System (INIS)

Kono, M.

1998-01-01

Formation or self-organization of coherent structures play a crucial role to the macroscopic properties of the system. Observations of long-lived ordered (crystallization) motion of well-defined vortices suggest that the relaxation to the ordered states may be described by introducing a point vortices. The structure of vortex lattice which is intimately related to the profile of the linear eigen function may be controlled by the unperturbed density profile. In experiments the density profile is rather sensitive to the plasma production. (M. Tanaka)

Vortex lattice matching effects in a washboard pinning potential induced by Co nanostripe arrays

International Nuclear Information System (INIS)

Dobrovolskiy, Oleksandr V.; Begun, Evgeniya; Huth, Michael; Shklovskij, Valerij A.; Tsindlekht, Menachem I.

2011-01-01

We furnish superconducting Nb thin films with linearly-extended uniaxial pinning nanostructures. An array of Co stripes is deposited by focused electron beam-induced deposition. Nanostructures are designed to be commensurate with the vortex lattice at small magnetic fields. We investigate vortex lattice matching effects by magneto-transport measurements. Drops in ρ(B) are observed only when the vortex lattice parameter matches the nanostructure period. No matching effects corresponding to the Co stripe width have been observed. Drops in ρ(B) are more pronounced for the vortex motion perpendicular to the Co stripes. An advanced mask-less nanofabrication technique, focused electron beam-induced deposition (FEBID), has been employed on epitaxial Nb thin films to prepare ferromagnetic decorations in the form of an array of Co stripes. These substantially modify the non-patterned films' superconducting properties, providing a washboard-like pinning potential landscape for the vortex motion. At small magnetic fields B ≤ 0.1 T, vortex lattice matching effects have been investigated by magneto-transport measurements. Step-like drops in the field dependencies of the films resistivity ρ(B) have been observed in particular for the vortex motion perpendicular to the Co stripes. The field values, corresponding to the middle points of these drops in ρ(B), meet the vortex lattice parameter matching the pinning structure's period. These disagree with the results of Jaque et al. (2002) , who observed matching effects corresponding to the stripe width in Nb films grown on periodically distributed submicrometric lines of Ni.

Role of vortices in cavitation formation in the flow across a mechanical heart valve.

Science.gov (United States)

Li, Chi-Pei; Lu, Po-Chien; Liu, Jia-Shing; Lo, Chi-Wen; Hwang, Ned H

2008-07-01

Cavitation occurs during mechanical heart valve closure when the local pressure drops below vapor pressure. The formation of stable gas bubbles may result in gaseous emboli, and secondarily cause transient ischemic attacks or strokes. It is noted that instantaneous valve closure, occluder rebound and high-speed leakage flow generate vortices that promote low-pressure regions in favor of stable bubble formation; however, to date no studies have been conducted for the quantitative measurement and analysis of these vortices. A Björk-Shiley Monostrut (BSM) monoleaflet valve was placed in the mitral position of a pulsatile mock circulatory loop. Particle image velocimetry (PIV) and pico coulomb (PCB) pressure measurements were applied. Flow field measurements were carried out at t = -5, -3, -1, -0.5, 0 (valve closure), 0.3, 0.5, 0.75, 1.19, 1.44, 1.69, 1.94, 2, 2.19, 2.54, 2.79, 3.04, 3.29, 3.54, 5 and 10 ms. The vortices were quantitatively analyzed using the Rankine vortex model. A single counter-clockwise vortex was The instantaneous formation of cavitation bubbles at mechanical heart valve (MHV) closure, which subsequently damage blood cells and valve integrity, is a well-known and widely studied phenomenon (1-4). Contributing factors seem to include the water-hammer, squeeze flow and Venturi effects, all of which are short-lived. Both, Dauzat et al. (5) and Sliwka et al. (6) have detected high-intensity transient signals (HITS) with transcranial Doppler ultrasound in the carotid and cerebral arteries of MHV recipients, while Deklunder (7) observed clinical occurrences of cerebral gas emboli that were not seen with bioprosthetic valves. These detected over the major orifice, while a pair of counter-rotating vortices was found over the minor orifice. Velocity profiles were consistent with Rankine vortices. The vortex strength and magnitude of the pressure drop peaked shortly after initial occluder-housing impact and rapidly decreased after 0.5 ms, indicating viscous

Vortex Formation and Foraging in Polyphenic Spadefoot Toad Tadpoles

OpenAIRE

Bazazi, Sepideh; Pfennig, Karin S.; Handegard, Nils Olav; Couzin, Iain D.

2012-01-01

Animal aggregations are widespread in nature and can exhibit complex emergent properties not found at an individual level. We investigate one such example here, collective vortex formation by congeneric spadefoot toad tadpoles: Spea bombifrons and S. multiplicata. Tadpoles of these species develop into either an omnivorous or a carnivorous (cannibalistic) morph depending on diet. Previous studies show S. multiplicata are more likely to develop into omnivores and feed on suspended organic matt...

Vortex cutting in superconductors

Science.gov (United States)

Vlasko-Vlasov, Vitalii K.; Koshelev, Alexei E.; Glatz, Andreas; Welp, Ulrich; Kwok, Wai-K.

2015-03-01

Unlike illusive magnetic field lines in vacuum, magnetic vortices in superconductors are real physical strings, which interact with the sample surface, crystal structure defects, and with each other. We address the complex and poorly understood process of vortex cutting via a comprehensive set of magneto-optic experiments which allow us to visualize vortex patterns at magnetization of a nearly twin-free YBCO crystal by crossing magnetic fields of different orientations. We observe a pronounced anisotropy in the flux dynamics under crossing fields and the filamentation of induced supercurrents associated with the staircase vortex structure expected in layered cuprates, flux cutting effects, and angular vortex instabilities predicted for anisotropic superconductors. At some field angles, we find formation of the vortex domains following a type-I phase transition in the vortex state accompanied by an abrupt change in the vortex orientation. To clarify the vortex cutting scenario we performed time-dependent Ginzburg-Landau simulations, which confirmed formation of sharp vortex fronts observed in the experiment and revealed a left-handed helical instability responsible for the rotation of vortices. This work was supported by the U.S. Department of Energy, Office of Science, Materials Sciences and Engineering Division.

Vortex Ring Dynamics in Radially Confined Domains

Science.gov (United States)

Stewart, Kelley; Niebel, Casandra; Jung, Sunghwan; Vlachos, Pavlos

2010-11-01

Vortex ring dynamics have been studied extensively in semi-infinite quiescent volumes. However, very little is known about vortex-ring formation in wall-bounded domains where vortex wall interaction will affect both the vortex ring pinch-off and propagation velocity. This study addresses this limitation and studies vortex formation in radially confined domains to analyze the affect of vortex-ring wall interaction on the formation and propagation of the vortex ring. Vortex rings were produced using a pneumatically driven piston cylinder arrangement and were ejected into a long cylindrical tube which defined the confined downstream domain. A range of confinement domains were studied with varying confinement diameters Velocity field measurements were performed using planar Time Resolved Digital Particle Image Velocimetry (TRDPIV) and were processed using an in-house developed cross-correlation PIV algorithm. The experimental analysis was used to facilitate the development of a theoretical model to predict the variations in vortex ring circulation over time within confined domains.

Swarming and complex pattern formation in Paenibacillus vortex studied by imaging and tracking cells

Directory of Open Access Journals (Sweden)

Jacob Eshel

2008-02-01

Full Text Available Abstract Background Swarming motility allows microorganisms to move rapidly over surfaces. The Gram-positive bacterium Paenibacillus vortex exhibits advanced cooperative motility on agar plates resulting in intricate colonial patterns with geometries that are highly sensitive to the environment. The cellular mechanisms that underpin the complex multicellular organization of such a simple organism are not well understood. Results Swarming by P. vortex was studied by real-time light microscopy, by in situ scanning electron microscopy and by tracking the spread of antibiotic-resistant cells within antibiotic-sensitive colonies. When swarming, P. vortex was found to be peritrichously flagellated. Swarming by the curved cells of P. vortex occurred on an extremely wide range of media and agar concentrations (0.3 to 2.2% w/v. At high agar concentrations (> 1% w/v rotating colonies formed that could be detached from the main mass of cells by withdrawal of cells into the latter. On lower percentage agars, cells moved in an extended network composed of interconnected "snakes" with short-term collision avoidance and sensitivity to extracts from swarming cells. P. vortex formed single Petri dish-wide "supercolonies" with a colony-wide exchange of motile cells. Swarming cells were coupled by rapidly forming, reversible and non-rigid connections to form a loose raft, apparently connected via flagella. Inhibitors of swarming (p-Nitrophenylglycerol and Congo Red were identified. Mitomycin C was used to trigger filamentation without inhibiting growth or swarming; this facilitated dissection of the detail of swarming. Mitomycin C treatment resulted in malcoordinated swarming and abortive side branch formation and a strong tendency by a subpopulation of the cells to form minimal rotating aggregates of only a few cells. Conclusion P. vortex creates complex macroscopic colonies within which there is considerable reflux and movement and interaction of cells. Cell

An experimental study of low Re cavity vortex formation embedded in a laminar boundary layer

Science.gov (United States)

Gautam, Sashank; Lang, Amy; Wilroy, Jacob

2016-11-01

Laminar boundary layer flow across a grooved surface leads to the formation of vortices inside rectangular cavities. The nature and stability of the vortex inside any single cavity is determined by the Re and cavity geometry. According to the hypothesis, under low Re and stable vortex conditions a single cavity vortex leads to a roller-bearing effect which results in a decrease in drag as quantified by velocity profiles measured within the boundary layer. At higher Re once the vortex becomes unstable, drag should increase due to the mixing of low-momentum fluid within the cavity and the outer boundary layer flow. The primary objective of this experiment is to document the phenomenon using DPIV in a tow tank facility. This study focuses on the transition of the cavity flow from a steady to an unsteady state as the Re is increased above a critical value. The change in boundary layer momentum and cavity vortex characteristics are documented as a function of Re and boundary layer thickness. Funding from NSF CBET fluid dynamics Grant 1335848 is gratefully acknowledged.

Translational velocity oscillations of piston generated vortex rings

Science.gov (United States)

Kumar, Manoj; Arakeri, J. H.; Shankar, P. N.

1995-11-01

Experimental results are presented that show that the translational velocities of piston generated vortex rings often undergo oscillations, similar to those recently discovered for drop generated rings. An attempt has been made to minimize uncertainties by utilizing both dye and hydrogen bubbles for visualization and carefully repeating measurements on the same ring and on different realizations under the same nominal piston conditions. The results unambiguously show that under most conditions, both for laminar and turbulent rings and for rings generated from pipes and orifices, the oscillations are present. The present results, together with the earlier results on drop generated rings, give support to the view that translational velocity oscillations are probably an inherent feature of translating vortex ring fields.

Onsager Vortex Formation in Two-component Bose-Einstein Condensates

Science.gov (United States)

Han, Junsik; Tsubota, Makoto

2018-06-01

We numerically study the dynamics of quantized vortices in two-dimensional two-component Bose-Einstein condensates (BECs) trapped by a box potential. For one-component BECs in a box potential, it is known that quantized vortices form Onsager vortices, which are clusters of same-sign vortices. We confirm that the vortices of the two components spatially separate from each other — even for miscible two-component BECs — suppressing the formation of Onsager vortices. This phenomenon is caused by the repulsive interaction between vortices belonging to different components, hence, suggesting a new possibility for vortex phase separation.

Synchronization of vortex formation frequency with the body motion frequency at high Reynolds numbers

Energy Technology Data Exchange (ETDEWEB)

Pereira, Luiz Antonio Alcantara [Federal University of Itajuba (UNIFEI), MG (Brazil). Inst. of Mechanical Engineering], E-mail: luizantp@unifei.edu.br; Hirata, Miguel Hiroo [State University of Rio de Janeiro (FAT/UERJ), Resende, RJ (Brazil). Fac. de Tecnologia], E-mail: hirata@fat.uerj.br

2010-07-01

Understanding vortex induced vibrations is of great importance in the design of a variety of offshore engineering structures, nuclear plant components and cylindrical elements in tube-bank heat exchangers, for example. If a body is placed in a flow, it experiences alternating lift and drag forces caused by the asymmetric formation of vortices, which can cause a structure to vibrate. One of the most interesting features of this flow is the phenomenon of lock-in which is observed when the vortex shedding frequency is close to the body oscillation frequency. This paper presents the results of numerical experiments on vortex shedding from a circular cylinder vibrating in-line or transversely with an incident uniform flow at Reynolds number of 1.0 x 10{sup 5}. The frequencies of the lift and drag coefficients are compared with the body motion frequency when the frequency ratio is about unity. (author)

Tripolar vortex formation in dense quantum plasma with ion-temperature-gradients

Science.gov (United States)

Qamar, Anisa; Ata-ur-Rahman, Mirza, Arshad M.

2012-05-01

We have derived system of nonlinear equations governing the dynamics of low-frequency electrostatic toroidal ion-temperature-gradient mode for dense quantum magnetoplasma. For some specific profiles of the equilibrium density, temperature, and ion velocity gradients, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. These results are relevant to understand nonlinear structure formation in dense quantum plasmas in the presence of equilibrium ion-temperature and density gradients.

Tripolar vortex formation in dense quantum plasma with ion-temperature-gradients

Energy Technology Data Exchange (ETDEWEB)

Qamar, Anisa; Ata-ur-Rahman [Institute of Physics and Electronics, University of Peshawar, Khyber Pakhtoon Khwa 25000 (Pakistan); National Center for Physics Shahdrah Valley Road, Islamabad 44000 (Pakistan); Mirza, Arshad M. [Theoretical Plasma Physics Group, Physics Department, Quaid-i-Azam University, Islamabad 45320 (Pakistan)

2012-05-15

We have derived system of nonlinear equations governing the dynamics of low-frequency electrostatic toroidal ion-temperature-gradient mode for dense quantum magnetoplasma. For some specific profiles of the equilibrium density, temperature, and ion velocity gradients, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. These results are relevant to understand nonlinear structure formation in dense quantum plasmas in the presence of equilibrium ion-temperature and density gradients.

Tripolar vortex formation in dense quantum plasma with ion-temperature-gradients

International Nuclear Information System (INIS)

Qamar, Anisa; Ata-ur-Rahman; Mirza, Arshad M.

2012-01-01

We have derived system of nonlinear equations governing the dynamics of low-frequency electrostatic toroidal ion-temperature-gradient mode for dense quantum magnetoplasma. For some specific profiles of the equilibrium density, temperature, and ion velocity gradients, the nonlinear equations admit a stationary solution in the form of a tripolar vortex. These results are relevant to understand nonlinear structure formation in dense quantum plasmas in the presence of equilibrium ion-temperature and density gradients.

Afterlife of a Drop Impacting a Liquid Pool

Science.gov (United States)

Saha, Abhishek; Wei, Yanju; Tang, Xiaoyu; Law, Chung K.

2017-11-01

Drop impact on liquid pool is ubiquitous in industrial processes, such as inkjet printing and spray coating. While merging of drop with the impacted liquid surface is essential to facilitate the printing and coating processes, it is the afterlife of this merged drop and associated mixing which control the quality of the printed or coated surface. In this talk we will report an experimental study on the structural evolution of the merged droplet inside the liquid pool. First, we will analyze the depth of the crater created on the pool surface by the impacted drop for a range of impact inertia, and we will derive a scaling relation and the associated characteristic time-scale. Next, we will focus on the toroidal vortex formed by the moving drop inside the liquid pool and assess the characteristic time and length scales of the penetration process. The geometry of the vortex structure which qualitatively indicates the degree of mixedness will also be discussed. Finally, we will present the results from experiments with various viscosities to demonstrate the role of viscous dissipation on the geometry and structure formed by the drop. This work is supported by the Army Research Office and the Xerox Corporation.

Experimental analysis of waveform effects on satellite and ligament behavior via in situ measurement of the drop-on-demand drop formation curve and the instantaneous jetting speed curve

International Nuclear Information System (INIS)

Kwon, Kye-Si

2010-01-01

In situ techniques to measure the drop-on-demand (DOD) drop formation curve and the instantaneous jetting speed curve are developed such that ligament behavior and satellite behavior of inkjet droplets can be analyzed effectively. It is known that the droplet jetting behavior differs by ink properties and the driving waveform voltage. In this study, to reduce possible droplet placement errors due to satellite drops or long ligaments during printing, waveform effects on drop formation are investigated based on the measured DOD drop formation curve and the instantaneous jetting speed curve. Experimental results show that a dwell time greater than the so-called efficient dwell time was effective in reducing placement errors due to satellite drops during the printing process

Statistical Characterization of River and Channel Network Formation in Intermittently Flowing Vortex Systems.

Science.gov (United States)

Olson, C. J.; Reichhardt, C.; Nori, F.

1997-03-01

Vortices moving in dirty superconductors can form intricate flow patterns, resembling fluid rivers, as they interact with the pinning landscape (F. Nori, Science 271), 1373 (1996).. Weaker pinning produces relatively straight nori>vortex channels, while stronger pinning results in the formation of one or more winding channels that carry all flow. This corresponds to a crossover from elastic flow to plastic flow as the pinning strength is increased. For several pinning parameters, we find the fractal dimension of the channels that form, the vortex trail density, the distance travelled by vortices as they pass through the sample, the branching ratio, the sinuosity, and the size distribution of the rivers, and we compare our rivers with physical rivers that follow Horton's laws.

Drop impact entrapment of bubble rings

KAUST Repository

Thoraval, M.-J.; Takehara, K.; Etoh, T.G.; Thoroddsen, Sigurdur T

2013-01-01

We use ultra-high-speed video imaging to look at the initial contact of a drop impacting on a liquid layer. We observe experimentally the vortex street and the bubble-ring entrapments predicted numerically, for high impact velocities, by Thoraval et

Interaction of Vortex Ring with Cutting Plate

Science.gov (United States)

Musta, Mustafa

2015-11-01

The interaction of a vortex ring impinging on a thin cutting plate was made experimentally using Volumetric 3-component Velocitmetry (v3v) technique. The vortex rings were generated with piston-cylinder vortex ring generator using piston stroke-to-diameter ratios and Re at 2-3 and 1500 - 3000, respectively. The cutting of vortex rings below center line leads to the formation of secondary vortices on each side of the plate which is look like two vortex rings, and a third vortex ring propagates further downstream in the direction of the initial vortex ring, which is previously showed by flow visualization study of Weigand (1993) and called ``trifurcation''. Trifurcation is very sensitive to the initial Reynolds number and the position of the plate with respect to the vortex ring generator pipe. The present work seeks more detailed investigation on the trifurcation using V3V technique. Conditions for the formation of trifurcation is analyzed and compared with Weigand (1993). The formed secondary vortex rings and the propagation of initial vortex ring in the downstream of the plate are analyzed by calculating their circulation, energy and trajectories.

Numerical and experimental investigation of surface vortex formation in coolant reservoirs of reactor safety systems

Energy Technology Data Exchange (ETDEWEB)

Pandazis, Peter [Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) gGmbH, Garching (Germany); Babcsany, Boglarka [Budapest Univ. of Technology and Economics (Hungary). Inst. of Nuclear Techniques

2016-11-15

The reliable operation of the emergency coolant pumps and passive gravitational injection systems are an important safety issue during accident scenarios with coolant loss in pressurized water reactors. Because of the pressure drop and flow disturbances surface vortices develops at the pump intakes if the water level decreasing below a critical value. The induced swirling flow and gas entrainment lead to flow limitation and to pump failures and damages. The prediction of the critical submergence to avoid surface vortex building is difficult because it depends on many geometrical and fluid dynamical parameters. An alternative and new method has been developed for the investigation of surface vortices. The method based on the combination of CFD results with the analytical vortex model of Burgers and Rott. For further investigation the small scale experiments from the Institute of Nuclear Techniques of the Budapest University of Technology and Economics are used which were inspired from flow limitation problems during the draining of the bubble condenser trays at a VVER type nuclear power plants.

Numerical study on drop formation through a micro nozzle

International Nuclear Information System (INIS)

Kim, Sung Il; Son, Gi Hun

2005-01-01

The drop ejection process from a micro nozzle is investigated by numerically solving the conservation equations for mass and momentum. The liquid-gas interface is tracked by a level set method which is extended for two-fluid flows with irregular solid boundaries. Based on the numerical results, the liquid jet breaking and droplet formation behavior is found to depend strongly on the pulse type of forcing pressure and the contact angle at the gas-liquid-solid interline. The negative pressure forcing can be used to control the formation of satelite droplets. Also, various nozzle shapes are tested to investigate their effect on droplet formation

Experimental formation of a fractional vortex in a superconducting bi-layer

Science.gov (United States)

Tanaka, Y.; Yamamori, H.; Yanagisawa, T.; Nishio, T.; Arisawa, S.

2018-05-01

We report the experimental formation of a fractional vortex generated by using a thin superconducting bi-layer in the form of a niobium bi-layer, observed as a magnetic flux distribution image taken by a scanning superconducting quantum interference device (SQUID) microscope. Thus, we demonstrated that multi-component superconductivity can be realized by an s-wave conventional superconductor, because, in these superconductors, the magnetic flux is no longer quantized as it is destroyed by the existence of an inter-component phase soliton (i-soliton).

Crack formation and prevention in colloidal drops

Science.gov (United States)

Kim, Jin Young; Cho, Kun; Ryu, Seul-A.; Kim, So Youn; Weon, Byung Mook

2015-08-01

Crack formation is a frequent result of residual stress release from colloidal films made by the evaporation of colloidal droplets containing nanoparticles. Crack prevention is a significant task in industrial applications such as painting and inkjet printing with colloidal nanoparticles. Here, we illustrate how colloidal drops evaporate and how crack generation is dependent on the particle size and initial volume fraction, through direct visualization of the individual colloids with confocal laser microscopy. To prevent crack formation, we suggest use of a versatile method to control the colloid-polymer interactions by mixing a nonadsorbing polymer with the colloidal suspension, which is known to drive gelation of the particles with short-range attraction. Gelation-driven crack prevention is a feasible and simple method to obtain crack-free, uniform coatings through drying-mediated assembly of colloidal nanoparticles.

Experimental Study of Shock Generated Compressible Vortex Ring

Science.gov (United States)

Das, Debopam; Arakeri, Jaywant H.; Krothapalli, Anjaneyulu

2000-11-01

Formation of a compressible vortex ring and generation of sound associated with it is studied experimentally. Impulse of a shock wave is used to generate a vortex ring from the open end of a shock-tube. Vortex ring formation process has been studied in details using particle image Velocimetry (PIV). As the shock wave exits the tube it diffracts and expands. A circular vortex sheet forms at the edge and rolls up into a vortex ring. Far field microphone measurement shows that the acoustic pressure consists of a spike due to shock wave followed by a low frequency pressure wave of decaying nature, superimposed with high frequency pressure wave. Acoustic waves consist of waves due to expansion, waves formed in the tube during diaphragm breakage and waves associated with the vortex ring and shear-layer vortices. Unsteady evolution of the vortex ring and shear-layer vortices in the jet behind the ring is studied by measuring the velocity field using PIV. Corresponding vorticity field, circulation around the vortex core and growth rate of the vortex core is calculated from the measured velocity field. The velocity field in a compressible vortex ring differs from that of an incompressible ring due to the contribution from both shock and vortex ring.

Vortex formation in Taylor-Couette flow with weakly spatial modulation

International Nuclear Information System (INIS)

Li, Z.; Khayat, R.E.

2002-01-01

The onset of the vortex structure in axisymmetric Taylor-Couette flow with spatially modulated cylinders is examined. The modulation amplitude is assumed to be small for a regular perturbation solution to be sought at small to moderate Taylor numbers. It is found that the presence of a weak modulation of the outer or inner cylinders leads unavoidably to the emergence of steady vortex flow even for a vanishingly small Taylor number. This situation is reminiscent of the onset of an imperfect bifurcation. The vortex structure of the forced TVF is found to have same periodicity when only one cylinder is modulated or the two modulations are commensurate for the Taylor number measured. The vortex structure is quasi-periodic when the two modulations are incommensurate. For a certain Taylor number, there exists a critical wavelength for the presence of the strongest vortex flow when the modulation is in the form of sinusoidal. This critical wavelength tends to the critical value predicted by the linear stability analysis when Ta approaches the supercritical value. (author)

Vortex flow during early and late left ventricular filling in normal subjects : Quantitative characterization using retrospectively-gated 4D flow cardiovascular magnetic resonance and three-dimensional vortex core analysis

NARCIS (Netherlands)

Elbaz, M.S.M.; Calkoen, E.E.; Westenberg, J.J.M.; Lelieveldt, B.P.F.; Roest, A.A.W.; Van der Geest, R.J.

2014-01-01

Background LV diastolic vortex formation has been suggested to critically contribute to efficient blood pumping function, while altered vortex formation has been associated with LV pathologies. Therefore, quantitative characterization of vortex flow might provide a novel objective tool for

Vortex ring behavior provides the epigenetic blueprint for the human heart.

Science.gov (United States)

Arvidsson, Per M; Kovács, Sándor J; Töger, Johannes; Borgquist, Rasmus; Heiberg, Einar; Carlsson, Marcus; Arheden, Håkan

2016-02-26

The laws of fluid dynamics govern vortex ring formation and precede cardiac development by billions of years, suggesting that diastolic vortex ring formation is instrumental in defining the shape of the heart. Using novel and validated magnetic resonance imaging measurements, we show that the healthy left ventricle moves in tandem with the expanding vortex ring, indicating that cardiac form and function is epigenetically optimized to accommodate vortex ring formation for volume pumping. Healthy hearts demonstrate a strong coupling between vortex and cardiac volumes (R(2) = 0.83), but this optimized phenotype is lost in heart failure, suggesting restoration of normal vortex ring dynamics as a new, and possibly important consideration for individualized heart failure treatment. Vortex ring volume was unrelated to early rapid filling (E-wave) velocity in patients and controls. Characteristics of vortex-wall interaction provide unique physiologic and mechanistic information about cardiac diastolic function that may be applied to guide the design and implantation of prosthetic valves, and have potential clinical utility as therapeutic targets for tailored medicine or measures of cardiac health.

Dynamic Stall Vortex Formation of OA-209 Airfoil at Low Reynolds Number

OpenAIRE

Aung Myo Thu; Sang Eon Jeon; Yung Hwan Byun; Soo Hyung Park

2014-01-01

The unsteady flow field around oscillating OA-209 airfoil at a Reynolds number of 3.5×105 were investigated. Three different reduced frequencies were tested in order to see how it affects the hysteresis loop of an airfoil. At a reduced frequency of 0.05 the deep dynamic stall phenomenon was observed. Lift overshooting was observed as a result of dynamic stall vortex (DSV) shedding. Further investigation was carried out to find out the cause of DSV formation and shedding over airfoil. Particle...

Vortex Formation in the Wake of Dark Matter Propulsion

Science.gov (United States)

Robertson, G. A.; Pinheiro, M. J.

Future spaceflight will require a new theory of propulsion; specifically one that does not require mass ejection. A new theory is proposed that uses the general view that closed currents pervade the entire universe and, in particular, there is a cosmic mechanism to expel matter to large astronomical distances involving vortex currents as seen with blazars and blackholes. At the terrestrial level, force producing vortices have been related to the motion of wings (e.g., birds, duck paddles, fish's tail). In this paper, vortex structures are shown to exist in the streamlines aft of a spaceship moving at high velocity in the vacuum. This is accomplished using the density excitation method per a modified Chameleon Cosmology model. This vortex structure is then shown to have similarities to spacetime models as Warp-Drive and wormholes, giving rise to the natural extension of Hawking and Unruh radiation, which provides the propulsive method for space travel where virtual electron-positron pairs, absorbed by the gravitational expansion forward of the spaceship emerge from an annular vortex field aft of the spaceship as real particles, in-like to propellant mass ejection in conventional rocket theory.

Metamorphosis of a Hairpin Vortex into a Young Turbulent Spot

Science.gov (United States)

Singer, Bart A.; Joslin, Ronald D.

1995-01-01

Direct numerical simulation was used to study the formation and growth of a hairpin vortex in a flat-plate boundary layer and its later development into a young turbulent spot. Fluid injection through a slit in the wall triggered the initial vortex. The legs of the vortex were stretched into a hairpin shape as it traveled downstream. Multiple hairpin vortex heads developed between the stretched legs. New vortices formed beneath the streamwise-elongated vortex legs. The continued development of additional vortices resulted in the formation of a traveling region of highly disturbed ow with an arrowhead shape similar to that of a turbulent spot.

Vortex rope instabilities in a model of conical draft tube

Science.gov (United States)

Skripkin, Sergey; Tsoy, Mikhail; Kuibin, Pavel; Shtork, Sergey

2017-10-01

We report on experimental studies of the formation of vortex ropes in a laboratory simplified model of hydroturbine draft tube. Work is focused on the observation of various flow patterns at the different rotational speed of turbine runner at fixed flow rate. The measurements involve high-speed visualization and pressure pulsations recordings. Draft tube wall pressure pulsations are registered by pressure transducer for different flow regimes. Vortex rope precession frequency were calculated using FFT transform. The experiments showed interesting features of precessing vortex rope like twin spiral and formation of vortex ring.

Vortex rope instabilities in a model of conical draft tube

Directory of Open Access Journals (Sweden)

Skripkin Sergey

2017-01-01

Full Text Available We report on experimental studies of the formation of vortex ropes in a laboratory simplified model of hydroturbine draft tube. Work is focused on the observation of various flow patterns at the different rotational speed of turbine runner at fixed flow rate. The measurements involve high-speed visualization and pressure pulsations recordings. Draft tube wall pressure pulsations are registered by pressure transducer for different flow regimes. Vortex rope precession frequency were calculated using FFT transform. The experiments showed interesting features of precessing vortex rope like twin spiral and formation of vortex ring.

A-DROP: A predictive model for the formation of oil particle aggregates (OPAs)

Science.gov (United States)

Zhao, Lin; Boufadel, Michel C.; Geng, Xiaolong; Lee, Kenneth; King, Thomas; Robinson, Brian; Fitzpatrick, Faith A.

2016-01-01

Oil–particle interactions play a major role in removal of free oil from the water column. We present a new conceptual–numerical model, A-DROP, to predict oil amount trapped in oil–particle aggregates. A new conceptual formulation of oil–particle coagulation efficiency is introduced to account for the effects of oil stabilization by particles, particle hydrophobicity, and oil–particle size ratio on OPA formation. A-DROP was able to closely reproduce the oil trapping efficiency reported in experimental studies. The model was then used to simulate the OPA formation in a typical nearshore environment. Modeling results indicate that the increase of particle concentration in the swash zone would speed up the oil–particle interaction process; but the oil amount trapped in OPAs did not correspond to the increase of particle concentration. The developed A-DROP model could become an important tool in understanding the natural removal of oil and developing oil spill countermeasures by means of oil–particle aggregation.

Ring vortex solitons in nonlocal nonlinear media

DEFF Research Database (Denmark)

Briedis, D.; Petersen, D.E.; Edmundson, D.

2005-01-01

We study the formation and propagation of two-dimensional vortex solitons, i.e. solitons with a phase singularity, in optical materials with a nonlocal focusing nonlinearity. We show that nonlocality stabilizes the dynamics of an otherwise unstable vortex beam. This occurs for either single...... or higher charge fundamental vortices as well as higher order (multiple ring) vortex solitons. Our results pave the way for experimental observation of stable vortex rings in other nonlocal nonlinear systems including Bose-Einstein condensates with pronounced long-range interparticle interaction....

Vortex dynamics during blade-vortex interactions

Science.gov (United States)

Peng, Di; Gregory, James W.

2015-05-01

Vortex dynamics during parallel blade-vortex interactions (BVIs) were investigated in a subsonic wind tunnel using particle image velocimetry (PIV). Vortices were generated by applying a rapid pitch-up motion to an airfoil through a pneumatic system, and the subsequent interactions with a downstream, unloaded target airfoil were studied. The blade-vortex interactions may be classified into three categories in terms of vortex behavior: close interaction, very close interaction, and collision. For each type of interaction, the vortex trajectory and strength variation were obtained from phase-averaged PIV data. The PIV results revealed the mechanisms of vortex decay and the effects of several key parameters on vortex dynamics, including separation distance (h/c), Reynolds number, and vortex sense. Generally, BVI has two main stages: interaction between vortex and leading edge (vortex-LE interaction) and interaction between vortex and boundary layer (vortex-BL interaction). Vortex-LE interaction, with its small separation distance, is dominated by inviscid decay of vortex strength due to pressure gradients near the leading edge. Therefore, the decay rate is determined by separation distance and vortex strength, but it is relatively insensitive to Reynolds number. Vortex-LE interaction will become a viscous-type interaction if there is enough separation distance. Vortex-BL interaction is inherently dominated by viscous effects, so the decay rate is dependent on Reynolds number. Vortex sense also has great impact on vortex-BL interaction because it changes the velocity field and shear stress near the surface.

Stagnation zone formation on the axis of a closed vortex flow

DEFF Research Database (Denmark)

Naumov, I. V.; Okulov, Valery; Mikkelsen, Robert Flemming

2014-01-01

The features of developing a counterflow zone (bubble-mode vortex breakdown or vortex explosion) at the center of an intensively swirled flow produced in a liquid-filled cylindrical container with a rotating endwall have been studied. The observation showed that the scenario of developing a bubbl......-mode breakdown zone with generation of counterflow is the same for cylinders with low or high aspect ratio, and it remains independent of stationary-nonstationary transition boundary for the main vortex flow....

Vortex matter stabilized by many-body interactions

Science.gov (United States)

Wolf, S.; Vagov, A.; Shanenko, A. A.; Axt, V. M.; Aguiar, J. Albino

2017-10-01

This work investigates interactions of vortices in superconducting materials between standard types I and II, in the domain of the so-called intertype (IT) superconductivity. Contrary to common expectations, the many-body (many-vortex) contribution is not a correction to the pair-vortex interaction here but plays a crucial role in the formation of the IT vortex matter. In particular, the many-body interactions stabilize vortex clusters that otherwise could not exist. Furthermore, clusters with large numbers of vortices become more stable when approaching the boundary between the intertype domain and type I. This indicates that IT superconductors develop a peculiar unconventional type of the vortex matter governed by the many-body interactions of vortices.

Roughness Effects on the Formation of a Leading Edge Vortex

Science.gov (United States)

Elliott, Cassidy; Lang, Amy; Wahidi, Redha; Wilroy, Jacob

2017-11-01

Microscopic scales cover the wings of Monarch butterflies, creating a patterned surface that acts as a natural energy capture mechanism. This patterning is thought to delay the growth of the leading edge vortex (LEV) produced by the flapping motion of a wing. Increased skin friction caused by the scales leads to a weaker LEV being shed into the butterfly's wake, lessening drag and increasing flight efficiency. To test how this roughness effects LEV formation, a plate of random roughness was designed in SolidWorks and printed on the Objet 30 Pro 3D printer. A 2x3x5 cubic foot tow tank was used to test the rough plate at Reynold's numbers of 1500, 3000, and 6000 (velocities of 8, 16, and 32 mm/s) at an angle of attack of 45 degrees. Images were captured of the LEV generated when the plate was towed upwards through the particle-seeded flow. These images were used to determine the XY velocity of the particles using a technique called Digital Particle Image Velocimetry (DPIV). Codes written in MATLAB were used to track and measure the strength of the LEV. Circulation values for the randomly-rough plate were then compared to the same values generated in a previous experiment that used a smooth plate and a grooved plate to determine the effect of the patterning on vortex development. Funding for this research project was provided by the National Science Foundation under the Research Experience for Undergraduates (REU) program (REU Supplement CBET 1628600 under CBET 1335848).

Rewritable ferroelectric vortex pairs in BiFeO3

Science.gov (United States)

Li, Yang; Jin, Yaming; Lu, Xiaomei; Yang, Jan-Chi; Chu, Ying-Hao; Huang, Fengzhen; Zhu, Jinsong; Cheong, Sang-Wook

2017-08-01

Ferroelectric vortex in multiferroic materials has been considered as a promising alternative to current memory cells for the merit of high storage density. However, the formation of regular natural ferroelectric vortex is difficult, restricting the achievement of vortex memory device. Here, we demonstrated the creation of ferroelectric vortex-antivortex pairs in BiFeO3 thin films by using local electric field. The evolution of the polar vortex structure is studied by piezoresponse force microscopy at nanoscale. The results reveal that the patterns and stability of vortex structures are sensitive to the poling position. Consecutive writing and erasing processes cause no influence on the original domain configuration. The Z4 proper coloring vortex-antivortex network is then analyzed by graph theory, which verifies the rationality of artificial vortex-antivortex pairs. This study paves a foundation for artificial regulation of vortex, which provides a possible pathway for the design and realization of non-volatile vortex memory devices and logical devices.

Non-Abelian vortex lattices

Science.gov (United States)

Tallarita, Gianni; Peterson, Adam

2018-04-01

We perform a numerical study of the phase diagram of the model proposed in [M. Shifman, Phys. Rev. D 87, 025025 (2013)., 10.1103/PhysRevD.87.025025], which is a simple model containing non-Abelian vortices. As per the case of Abrikosov vortices, we map out a region of parameter space in which the system prefers the formation of vortices in ordered lattice structures. These are generalizations of Abrikosov vortex lattices with extra orientational moduli in the vortex cores. At sufficiently large lattice spacing the low energy theory is described by a sum of C P (1 ) theories, each located on a vortex site. As the lattice spacing becomes smaller, when the self-interaction of the orientational field becomes relevant, only an overall rotation in internal space survives.

Vorticity and vortex dynamics

CERN Document Server

Wu, Jie-Zhi; Zhou, M-D

2006-01-01

The importance of vorticity and vortex dynamics has now been well rec- nized at both fundamental and applied levels of ?uid dynamics, as already anticipatedbyTruesdellhalfcenturyagowhenhewrotethe?rstmonograph onthesubject, The Kinematics of Vorticity(1954);andasalsoevidencedby the appearance of several books on this ?eld in 1990s. The present book is characterizedbythefollowingfeatures: 1. A basic physical guide throughout the book. The material is directed by a basic observation on the splitting and coupling of two fundamental processes in ?uid motion, i.e., shearing (unique to ?uid) and compre- ing/expanding.Thevorticityplaysakeyroleintheformer,andavortex isnothingbuta?uidbodywithhighconcentrationofvorticitycompared to its surrounding ?uid. Thus, the vorticity and vortex dynamics is - cordinglyde?nedasthetheoryofshearingprocessanditscouplingwith compressing/expandingprocess. 2. A description of the vortex evolution following its entire life.Thisbegins from the generation of vorticity to the formation of thi...

On angled bounce-off impact of a drop impinging on a flowing soap film

Science.gov (United States)

Basu, Saikat; Yawar, Ali; Concha, Andres; Bandi, M. M.

2017-12-01

Small drops impinging obliquely on thin flowing soap films frequently demonstrate the rare emergence of bulk elastic effects working in-tandem with the more commonplace hydrodynamic interactions. Three collision regimes are observable: (a) drop piercing through the film, (b) it coalescing with the flow, and (c) it bouncing off the film surface. During impact, the drop deforms along with a bulk elastic deformation of the film. For impacts that are close-to-tangential, the bounce-off regime predominates. We outline a reduced order analytical framework assuming a deformable drop and a deformable three-dimensional film, and the idealization invokes a phase-based parametric study. Angular inclination of the film and the ratio of post and pre-impact drop sizes entail the phase parameters. We also perform experiments with vertically descending droplets (constituted from deionized water) impacting against an inclined soap film, flowing under constant pressure head. Model-predicted phase domain for bounce-off compares well to our experimental findings. Additionally, the experiments exhibit momentum transfer to the film in the form of shed vortex dipoles, along with propagation of free surface waves. On consulting prior published work, we note that for locomotion of water-walking insects using an impulsive action, the momentum distribution to the shed vortices and waves are both significant, taking up respectively 2/3 and 1/3 of the imparted streamwise momentum. Considering the visually similar impulse actions, this theory, despite its assumption of a quiescent liquid bath of infinite depth, is applied to the drop bounce-off experiments, and the resultant shed vortex dipole momenta are compared to the momenta of the coherent vortex structures computed from particle imaging velocimetry data. The magnitudes reveal identical order (10-7 N s), suggesting that notwithstanding the disparities, the bounce-off regime may be tapped as a toy analog for impulse-based interfacial

Classical hydrodynamics of an ideal incompressible fluid and vortex motion in helium II

International Nuclear Information System (INIS)

Mamaladze, Y.G.; Kiknadze, L.V.

1982-01-01

Vortex motion in the vicinity of a protuberance at a bounding surface in rotating helium II and in plane slits is considered from the standpoint of the vortex-formation mechanism, the equilibrium spatial vortex distribution, and the possibility of supercritical quasidissipationless vortex flow

Z2 vortex strings in grand unified theories

International Nuclear Information System (INIS)

Olive, D.; Turok, N.

1982-01-01

Spontaneously broken gauge theories may display distinct vortex string solutions for the disconnected components of the exact gauge symmetry group. A type of Higgs mechanism thought to apply in grand unified theories as being responsible for fermion masses yields Z 2 vortex lines, irrespectively of the group. These could seed galaxy formation if the corresponding fermion masses are superheavy. More generally a Higgs mechanism producing Zsub(n) vortex strings is presented. (orig.)

Dynamics of levitated objects in acoustic vortex fields.

Science.gov (United States)

Hong, Z Y; Yin, J F; Zhai, W; Yan, N; Wang, W L; Zhang, J; Drinkwater, Bruce W

2017-08-02

Acoustic levitation in gaseous media provides a tool to process solid and liquid materials without the presence of surfaces such as container walls and hence has been used widely in chemical analysis, high-temperature processing, drop dynamics and bioreactors. To date high-density objects can only be acoustically levitated in simple standing-wave fields. Here we demonstrate the ability of a small number of peripherally placed sources to generate acoustic vortex fields and stably levitate a wide range of liquid and solid objects. The forces exerted by these acoustic vortex fields on a levitated water droplet are observed to cause a controllable deformation of the droplet and/or oscillation along the vortex axis. Orbital angular momentum transfer is also shown to rotate a levitated object rapidly and the rate of rotation can be controlled by the source amplitude. We expect this research can increase the diversity of acoustic levitation and expand the application of acoustic vortices.

Numerical simulation of fuel mixing with air in laminar buoyant vortex rings

International Nuclear Information System (INIS)

Prasad, M. Jogendra; Sundararajan, T.

2016-01-01

Highlights: • At large Reynolds number, small vortex ring is formed due to thin boundary layer. • At higher stroke to diameter ratio, larger vortex is formed which travels farther. • After formation, trailing stem transfers circulation and fuel to the ring by buoyancy. • Formation number of buoyant vortex ring is higher than that of non-buoyant ring. • Buoyant fuel puffs entrain more air than non-buoyant air-premixed fuel puffs. - Abstract: The formation and evolution of vortex rings consisting of methane-air mixtures have been numerically simulated for different stroke to diameter (L/D) ratios (1.5, 3.5 and 6), Reynolds numbers (1000 and 2000) and initial mixture compositions (fuel with 0%, 15% and 30% of stoichiometric air). The numerical simulations are first validated by comparing with the results of earlier computational studies and also with in-house data from smoke visualization studies. In pure methane case, buoyancy significantly aids the upward rise of the vortex ring. The increase of vortex core height with time is faster for larger L/D ratio, contributed mainly by the larger initial puff volume. The radial size of the vortex also increases rapidly with time during the formation stage; this is followed by a slight shrinkage when piston comes to a stop. Later, a slow radial growth of the ring occurs due to the entrainment of ambient air, except during vortex pinch-off. The boundary layer thickness δ_e at orifice exit decreases as Re"−"0"."5 at a fixed L/D ratio; this in turn, results in a vortex of smaller size and circulation level, at a relatively higher Reynolds number. For L/D values greater than the critical value, a trailing stem is formed behind the ring vortex which feeds circulation and fuel into the vortex ring in the later stages of vortex evolution. Mass fraction contours indicate that fuel-air mixing is more effective within the vortex than in the stem. Ambient air entrainment is larger at higher L/D ratio and lower Re, for the

IUTAM Symposium on Vortex Dynamics: Formation, Structure and Function, 10-14 March 2013, Fukuoka, Japan

Science.gov (United States)

Fukumoto, Yasuhide

2014-06-01

This special issue of Fluid Dynamics Research contains the first of a two-part publication of the papers presented at the IUTAM Symposium on Vortex Dynamics: Formation, Structure and Function, held at the Centennial Hall, Kyushu University School of Medicine, Fukuoka, Japan, during the week of 10-14 March 2013. Vortices are ubiquitous structures in fluid mechanics spanning the range of scales from nanofluidics and microfluidics to geophysical and astrophysical flows. Vortices are the key to understanding many different phenomena. As a result, the subject of vortex dynamics continues to evolve and to constantly find new applications in biology, biotechnology, industrial and environmental problems. Vortices can be created by the separation of a flow from the surface of a body or at a density interface, and evolve into coherent structures. Once formed, a vortex acquires a function, depending on its individual structure. In this way, for example, insects gain lift and fish gain thrust. Surprisingly, despite the long history of vortex dynamics, only recently has knowledge about formation, structure and function of vortices been combined to yield new perspectives in the subject, thereby helping to solve outstanding problems brought about by modern advances in computer technology and improved experimental techniques. This symposium is a continuation, five years on, of the IUTAM Symposium '50 Years of Vortex Dynamics', Lyngby, Denmark that took place between 12-16 October 2008, organized by the late Professor Hassan Aref. Originally, Professor Aref was a member of the International Scientific Committee of this symposium and offered his enthusiasm and great expertise, to support its organization. To our shock, he suddenly passed away on 9 September 2011. Furthermore, Professor Slava Meleshko, a leading scientist of fluid and solid mechanics and an intimate friend of Professor Aref, was expected to make an eminent contribution to the symposium. Soon after this sad loss

Capillary Thinning of Particle-laden Drops

Science.gov (United States)

Wagoner, Brayden; Thete, Sumeet; Jahns, Matt; Doshi, Pankaj; Basaran, Osman

2015-11-01

Drop formation is central in many applications such as ink-jet printing, microfluidic devices, and atomization. During drop formation, a thinning filament is created between the about-to-form drop and the fluid hanging from the nozzle. Therefore, the physics of capillary thinning of filaments is key to understanding drop formation and has been thoroughly studied for pure Newtonian fluids. The thinning dynamics is, however, altered completely when the fluid contains particles, the physics of which is not well understood. In this work, we explore the impact of solid particles on filament thinning and drop formation by using a combination of experiments and numerical simulations.

Air-sea interaction and formation of the Asian summer monsoon onset vortex over the Bay of Bengal

Energy Technology Data Exchange (ETDEWEB)

Wu, Guoxiong; Liu, Yimin; Mao, Jiangyu [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, P.O. Box 9804, Beijing (China); Guan, Yue [Chinese Academy of Sciences, State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), Institute of Atmospheric Physics, P.O. Box 9804, Beijing (China); Graduate University of Chinese Academy of Sciences, Beijing (China); Yan, Jinghui [China Meteorological Administration, National Climate Center, Beijing (China)

2012-01-15

In spring over the southern Bay of Bengal (BOB), a vortex commonly develops, followed by the Asian summer monsoon onset. An analysis of relevant data and a case study reveals that the BOB monsoon onset vortex is formed as a consequence of air-sea interaction over BOB, which is modulated by Tibetan Plateau forcing and the land-sea thermal contrast over the South Asian area during the spring season. Tibetan Plateau forcing in spring generates a prevailing cold northwesterly over India in the lower troposphere. Strong surface sensible heating is then released, forming a prominent surface cyclone with a strong southwesterly along the coastal ocean in northwestern BOB. This southwesterly induces a local offshore current and upwelling, resulting in cold sea surface temperatures (SSTs). The southwesterly, together with the near-equatorial westerly, also results in a surface anticyclone with descending air over most of BOB and a cyclone with ascending air over the southern part of BOB. In the eastern part of central BOB, where sky is clear, surface wind is weak, and ocean mixed layer is shallow, intense solar radiation and low energy loss due to weak surface latent and sensible heat fluxes act onto a thin ocean layer, resulting in the development of a unique BOB warm pool in spring. Near the surface, water vapor is transferred from northern BOB and other regions to southeastern BOB, where surface sensible heating is relatively high. The atmospheric available potential energy is generated and converted to kinetic energy, thereby resulting in vortex formation. The vortex then intensifies and moves northward, where SST is higher and surface sensible heating is stronger. Meanwhile, the zonal-mean kinetic energy is converted to eddy kinetic energy in the area east of the vortex, and the vortex turns eastward. Eventually, southwesterly sweeps over eastern BOB and merges with the subtropical westerly, leading to the onset of the Asian summer monsoon. (orig.)

Large-scale vortex structures and local heat release in lean turbulent swirling jet-flames under vortex breakdown conditions

Science.gov (United States)

Chikishev, Leonid; Lobasov, Aleksei; Sharaborin, Dmitriy; Markovich, Dmitriy; Dulin, Vladimir; Hanjalic, Kemal

2017-11-01

We investigate flame-flow interactions in an atmospheric turbulent high-swirl methane/air lean jet-flame at Re from 5,000 to 10,000 and equivalence ratio below 0.75 at the conditions of vortex breakdown. The focus is on the spatial correlation between the propagation of large-scale vortex structures, including precessing vortex core, and the variations of the local heat release. The measurements are performed by planar laser-induced fluorescence of hydroxyl and formaldehyde, applied simultaneously with the stereoscopic particle image velocimetry technique. The data are processed by the proper orthogonal decomposition. The swirl rate exceeded critical value for the vortex breakdown resulting in the formation of a processing vortex core and secondary helical vortex filaments that dominate the unsteady flow dynamics both of the non-reacting and reacting jet flows. The flame front is located in the inner mixing layer between the recirculation zone and the annular swirling jet. A pair of helical vortex structures, surrounding the flame, stretch it and cause local flame extinction before the flame is blown away. This work is supported by Russian Science Foundation (Grant No 16-19-10566).

Vortex wake investigation behind a wing-flap model with jet simulations

NARCIS (Netherlands)

Veldhuis, L.L.M.; De Kat, R.

2008-01-01

To get a better insight in the effect of jets on vortex development and decay, stereo-PIV measurements were performed in a towing tank behind a flapped aircraft model. The experimental data set yields the wake vortex behavior in a range that extends from the vortex formation stage up to the

AC electric field induced vortex in laminar coflow diffusion flames

KAUST Repository

Xiong, Yuan

2014-09-22

Experiments were performed by applying sub-critical high-voltage alternating current (AC) to the nozzle of laminar propane coflow diffusion flames. Light scattering, laser-induced incandescence and laser-induced fluorescence techniques were used to identify the soot zone, and the structures of OH and polycyclic aromatic hydrocarbons (PAHs). Particle image velocimetry was adopted to quantify the velocity field. Under certain AC conditions of applied voltage and frequency, the distribution of PAHs and the flow field near the nozzle exit were drastically altered, leading to the formation of toroidal vortices. Increased residence time and heat recirculation inside the vortex resulted in appreciable formation of PAHs and soot near the nozzle exit. Decreased residence time along the jet axis through flow acceleration by the vortex led to a reduction in the soot volume fraction in the downstream sooting zone. Electromagnetic force generated by AC was proposed as a viable mechanism for the formation of the toroidal vortex. The onset conditions for the vortex formation supported the role of an electromagnetic force acting on charged particles in the flame zone. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

AC electric field induced vortex in laminar coflow diffusion flames

KAUST Repository

Xiong, Yuan; Cha, Min; Chung, Suk-Ho

2014-01-01

Experiments were performed by applying sub-critical high-voltage alternating current (AC) to the nozzle of laminar propane coflow diffusion flames. Light scattering, laser-induced incandescence and laser-induced fluorescence techniques were used to identify the soot zone, and the structures of OH and polycyclic aromatic hydrocarbons (PAHs). Particle image velocimetry was adopted to quantify the velocity field. Under certain AC conditions of applied voltage and frequency, the distribution of PAHs and the flow field near the nozzle exit were drastically altered, leading to the formation of toroidal vortices. Increased residence time and heat recirculation inside the vortex resulted in appreciable formation of PAHs and soot near the nozzle exit. Decreased residence time along the jet axis through flow acceleration by the vortex led to a reduction in the soot volume fraction in the downstream sooting zone. Electromagnetic force generated by AC was proposed as a viable mechanism for the formation of the toroidal vortex. The onset conditions for the vortex formation supported the role of an electromagnetic force acting on charged particles in the flame zone. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Formation of vortex pairs with hinged rigid flaps at the nozzle exit

Science.gov (United States)

Das, Prashant; Govardhan, Raghuraman; Arakeri, Jaywant

2013-11-01

Biological flows related to aquatic propulsion using pulsed jets, or flow through the valves in a human heart, have received considerable attention in the last two decades. Both these flows are associated with starting jets that occur through biological tissue/membranes that are flexible. Motivated by these flows, we explore in the present work, the effect of passive flexibility of the nozzle exit on vortex generation from a starting jet. The starting jet is generated using a two-dimensional piston cylinder mechanism, the cross-section of the cylinder being rectangular with large aspect ratio. The fluid is pushed out of this cylinder or channel using a computer controlled piston. We introduce flexibility at the channel exit by hinging rigid flaps, which are initially parallel to the channel. The hinge used is such that it provides negligible stiffness or damping, thus allowing for the maximum opening of the flaps due to fluid forces. Using this system, we study both the flap kinematics and the vorticity dynamics downstream of the channel exit. Visualizations show large flap motions as the piston starts and this dramatically changes the vorticity distribution downstream of the flaps, with the formation of up to three different kinds of vortex pairs. This idealized configuration opens new opportunities to look at the effect of flexibility in such biological flows.

Vortex line topology during vortex tube reconnection

Science.gov (United States)

McGavin, P.; Pontin, D. I.

2018-05-01

This paper addresses reconnection of vortex tubes, with particular focus on the topology of the vortex lines (field lines of the vorticity). This analysis of vortex line topology reveals key features of the reconnection process, such as the generation of many small flux rings, formed when reconnection occurs in multiple locations in the vortex sheet between the tubes. Consideration of three-dimensional reconnection principles leads to a robust measurement of the reconnection rate, even once instabilities break the symmetry. It also allows us to identify internal reconnection of vortex lines within the individual vortex tubes. Finally, the introduction of a third vortex tube is shown to render the vortex reconnection process fully three-dimensional, leading to a fundamental change in the topological structure of the process. An additional interesting feature is the generation of vorticity null points.

The effect of surface pressure modification on the speed of vortex rings

Energy Technology Data Exchange (ETDEWEB)

Partridge, Matthew; Davis, Frank; Higson, Seamus P J [Centre of Biomedical Imaging, Cranfield University, Cranfield MK43 0AL (United Kingdom); James, Stephen W; Tatam, Ralph P, E-mail: f.davis@cranfield.ac.uk [Engineering Photonics, School of Engineering, Cranfield University, Cranfield MK43 0AL (United Kingdom)

2014-10-01

A series of experiments investigating the relationship between surface pressure, monolayer elasticity and the speed of vortex rings is presented. A drop of water, when touched to the surface of a larger body of water, will coalesce and form a vortex ring that moves perpendicularly to the surface of the water. The speed of the vortex ring movement away from the surface of the water has been seen to be sensitive to the presence of monolayer materials. Here we explore the influence of four monolayer forming materials, stearic acid, tricosanoic acid, 4-tert butyl calix[4]arene and calix[4]resorcarene (C11), on the properties of vortex rings. For each material, the speed of the vortex rings through the water was measured at a range of surface pressures. The speed was found to increase in a linear fashion until surface pressures greater than 30 mN m{sup −1}, where the ring’s speed decreased towards the value measured in the absence of a monolayer. Analysis of the results suggests a future route toward a better understanding of the mechanisms involved.

Direct visualization of the vortex distributions in a superconducting film with a Penrose array of magnetic pinning centers: Symmetry induced giant vortex state

International Nuclear Information System (INIS)

Kramer, R.B.G.; Silhanek, A.V.; Van de Vondel, J.; Raes, B.; Moshchalkov, V.V.

2010-01-01

Using scanning Hall probe microscopy a direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained. We demonstrate that stable vortex configurations can be found for fields H ∼ 0.8H 1 , H 1 and 1.6H 1 , where H 1 corresponds to one flux quantum per pinning site. The vortex pattern at 0.8H 1 corresponds to one vacancy in one of the vertices of the thin tiles whereas at 1.6H 1 the vortex structure can be associated with one interstitial vortex inside each thick tile. Strikingly, for H = 1.6H 1 interstitial and pinned vortices arrange themselves in ring-like structures ('vortex corrals') which favor the formation of a giant vortex state at their center.

Phenomena, dynamics and instabilities of vortex pairs

International Nuclear Information System (INIS)

Williamson, C H K; Asselin, D J; Leweke, T; Harris, D M

2014-01-01

Our motivation for studying the dynamics of vortex pairs stems initially from an interest in the trailing wake vortices from aircraft and the dynamics of longitudinal vortices close to a vehicle surface. However, our motivation also comes from the fact that vortex–vortex interactions and vortex–wall interactions are fundamental to many turbulent flows. The intent of the paper is to present an overview of some of our recent work concerning the formation and structure of counter-rotating vortex pairs. We are interested in the long-wave and short-wave three-dimensional instabilities that evolve for an isolated vortex pair, but also we would like to know how vortex pairs interact with a wall, including both two-dimensional interactions, and also the influence of the surface on the three-dimensional instabilities. The emphasis of this presentation is on physical mechanisms by which vortices interact with each other and with surfaces, principally from an experimental approach, but also coupled with analytical studies. (paper)

Vortex profiles and vortex interactions at the electroweak crossover

OpenAIRE

Chernodub, M. N.; Ilgenfritz, E. -M.; Schiller, A.

1999-01-01

Local correlations of Z-vortex operators with gauge and Higgs fields (lattice quantum vortex profiles) as well as vortex two-point functions are studied in the crossover region near a Higgs mass of 100 GeV within the 3D SU(2) Higgs model. The vortex profiles resemble certain features of the classical vortex solutions in the continuum. The vortex-vortex interactions are analogous to the interactions of Abrikosov vortices in a type-I superconductor.

On the evolution of vortex rings with swirl

International Nuclear Information System (INIS)

Naitoh, Takashi; Okura, Nobuyuki; Gotoh, Toshiyuki; Kato, Yusuke

2014-01-01

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions

On the evolution of vortex rings with swirl

Energy Technology Data Exchange (ETDEWEB)

Naitoh, Takashi, E-mail: naitoh.takashi@nitech.ac.jp [Department of Engineering Physics, Electronics and Mechanics, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Okura, Nobuyuki, E-mail: ohkura@meijo-u.ac.jp [Department of Vehicle and Mechanical Engineering, Meijo University, 1-501 Shiogamaguchi Tempaku-ku, Nagoya 468-8502 (Japan); Gotoh, Toshiyuki, E-mail: gotoh.toshiyuki@nitech.ac.jp [Department of Scientific and Engineering Simulation, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555 (Japan); Kato, Yusuke [Controller Business Unit Engineering Division 1, Engineering Department 3, Denso Wave Incorporated, 1 Yoshiike Kusagi Agui-cho, Chita-gun Aichi 470-2297 (Japan)

2014-06-15

A laminar vortex ring with swirl, which has the meridional velocity component inside the vortex core, was experimentally generated by the brief fluid ejection from a rotating outlet. The evolution of the vortex ring was investigated with flow visualizations and particle image velocimetry measurements in order to find the influence of swirling flow in particular upon the transition to turbulence. Immediately after the formation of a vortex ring with swirl, a columnar strong vortex along the symmetric axis is observed in all cases of the present experiment. Then the characteristic fluid discharging from a vortex ring with swirl referred to as “peeling off” appears. The amount of discharging fluid due to the “peeling off” increases with the angular velocity of the rotating outlet. We conjectured that the mechanism generating the “peeling off” is related to the columnar strong vortex by close observations of the spatio-temporal development of the vorticity distribution and the cutting 3D images constructed from the successive cross sections of a vortex ring. While a laminar vortex ring without swirl may develop azimuthal waves around its circumference at some later time and the ring structure subsequently breaks, the swirling flow in a vortex ring core reduces the amplification rate of the azimuthal wavy deformation and preserved its ring structure. Then the traveling distance of a vortex ring can be extended using the swirl flow under certain conditions.

Formation Mechanism and Characteristics Research of Ball Lightning Based on Vortex Model

International Nuclear Information System (INIS)

Li Zicheng; Yang Guohua

2011-01-01

The strange characteristics of ball lightning are considered as a question hard to explain. In order to solve the problem, in this paper a complete model of plasma vortex is presented for the ball lightning. By ideal MHD equations, through imposing disturbance to plasma column, the possibility of sausage and kink instability of the lightning channel is analyzed from the perspective the minimum potential energy. The conclusion is that the kink instability (m = 1) is most prone to occur. And when instability occurs, because of the difference of the magnetic field in the twisted area, the magnetic pressure makes the trend further and therefore forming the plasma vortex that may eventually turn into ball lightning if the energy of the vortex is large enough. The existence of the vortex makes ball lightning have a short period of time stability. By the proposed model, the ball lightning features that are hard to understand in the past are explained. In this paper, the reason for bead lightning is also explained from the perspective of the sausage instability. (physics of gases, plasmas, and electric discharges)

Vortex flow in rotating superfluid .sup.3./sup.He-B

Czech Academy of Sciences Publication Activity Database

Skrbek, Ladislav; Blaauwgeers, R.; Eltsov, V. B.; Finne, A. P.; Kopnin, N. B.; Krusius, M.

329-333, - (2003), s. 106-107 ISSN 0921-4526 Institutional research plan: CEZ:AV0Z1010914 Keywords : superfluid 3 He * vortex dynamics * vortex formation * critical velocity * counterflow * magnus force * mutual friction Subject RIV: BK - Fluid Dynamics Impact factor: 0.908, year: 2003

Inhomogeneous vortex tangles in counterflow superfluid turbulence: flow in convergent channels

Directory of Open Access Journals (Sweden)

Saluto Lidia

2016-06-01

Full Text Available We investigate the evolution equation for the average vortex length per unit volume L of superfluid turbulence in inhomogeneous flows. Inhomogeneities in line density L andincounterflowvelocity V may contribute to vortex diffusion, vortex formation and vortex destruction. We explore two different families of contributions: those arising from asecondorder expansionofthe Vinenequationitself, andthose whichare notrelated to the original Vinen equation but must be stated by adding to it second-order terms obtained from dimensional analysis or other physical arguments.

Vortex Ring Interaction With a Coaxially Aligned Cylinderical Rod

Science.gov (United States)

Arakeri, Jaywant H.; Rajmanoharan, P.; Koochesfahani, Manoochehr

1998-11-01

We present results of experiments of a fully developed vortex ring interacting with a cylinderical rod, having a rounded nose, placed coaxially in line with the motion of the ring. The pressure field of the translating ring causes unsteady boundary layer separation and results in the formation of one or more ( secondary ) vortex rings, that subsequently interact. The nature and strength of the interaction depends on the ratio of the cylinder diameter to the ring diameter. For the larger diameter cylinders the vortex ring travels a few ring diameters before it breaks up. For the smaller diameter cylinders the vortex ring speed decreases slowly and, simultaneously, its diameter increases.

Vortex rings from Sphagnum moss capsules

Science.gov (United States)

Whitaker, Dwight; Strassman, Sam; Cha, Jung; Chang, Emily; Guo, Xinyi; Edwards, Joan

2010-11-01

The capsules of Sphagnum moss use vortex rings to disperse spores to suitable habitats many kilometers away. Vortex rings are created by the sudden release of pressurized air when the capsule ruptures, and are an efficient way to carry the small spores with low terminal velocities to heights where they can be carried by turbulent wind currents. We will present our computational model of these explosions, which are carried out using a 2-D large eddy simulation (LES) on FLUENT. Our simulations can reproduce the observed motion of the spore clouds observed from moss capsules with high-speed videos, and we will discuss the roles of bursting pressure, cap mass, and capsule morphology on the formation and quality of vortex rings created by this plant.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

Energy Technology Data Exchange (ETDEWEB)

Galvis, J.A. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Departamento de Ciencias Naturales, Facultad de ingeniería y Ciencias Básicas, Universidad Central, Bogotá (Colombia); National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310 (United States); Herrera, E.; Guillamón, I.; Vieira, S. [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain); Suderow, H., E-mail: hermann.suderow@uam.es [Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid (Spain); Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid (Spain)

2017-02-15

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

International Nuclear Information System (INIS)

Galvis, J.A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.

2017-01-01

Highlights: • The observation of vortex cores is reviewed, with emphasis in new experiments. • Vortex cores are follow superconducting gap and Fermi surface shapes. • The vortex core shape influences vortex dynamics. - Abstract: Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

Vortex methods and vortex statistics

International Nuclear Information System (INIS)

Chorin, A.J.

1993-05-01

Vortex methods originated from the observation that in incompressible, inviscid, isentropic flow vorticity (or, more accurately, circulation) is a conserved quantity, as can be readily deduced from the absence of tangential stresses. Thus if the vorticity is known at time t = 0, one can deduce the flow at a later time by simply following it around. In this narrow context, a vortex method is a numerical method that makes use of this observation. Even more generally, the analysis of vortex methods leads, to problems that are closely related to problems in quantum physics and field theory, as well as in harmonic analysis. A broad enough definition of vortex methods ends up by encompassing much of science. Even the purely computational aspects of vortex methods encompass a range of ideas for which vorticity may not be the best unifying theme. The author restricts himself in these lectures to a special class of numerical vortex methods, those that are based on a Lagrangian transport of vorticity in hydrodynamics by smoothed particles (''blobs'') and those whose understanding contributes to the understanding of blob methods. Vortex methods for inviscid flow lead to systems of ordinary differential equations that can be readily clothed in Hamiltonian form, both in three and two space dimensions, and they can preserve exactly a number of invariants of the Euler equations, including topological invariants. Their viscous versions resemble Langevin equations. As a result, they provide a very useful cartoon of statistical hydrodynamics, i.e., of turbulence, one that can to some extent be analyzed analytically and more importantly, explored numerically, with important implications also for superfluids, superconductors, and even polymers. In the authors view, vortex ''blob'' methods provide the most promising path to the understanding of these phenomena

Vortex formation during rf heating of plasma

International Nuclear Information System (INIS)

Motley, R.W.

1980-05-01

Experiments on a test plasma show that the linear theory of waveguide coupling to slow plasma waves begins to break down if the rf power flux exceeds approx. 30 W/cm 2 . Probe measurements reveal that within 30 μs an undulation appears in the surface plasma near the mouth of the twin waveguide. This surface readjustment is part of a vortex, or off-center convective cell, driven by asymmetric rf heating of the plasma column

Vortex-vortex interactions in toroidally trapped Bose-Einstein condensates

OpenAIRE

Schulte, T.; Santos, L.; Sanpera, A.; Lewenstein, M.

2002-01-01

We analyze the vortex dynamics and vortex-vortex interactions in Bose-Einstein condensates confined in toroidal traps. We show that this particular geometry strongly distorts the vortex dynamics. The numerically calculated vortex trajectories are well explained by an analytical calculation based on image method and conformal mapping. Finally, the dissipation effects are discussed.

Vortex coupling in trailing vortex-wing interactions

Science.gov (United States)

Chen, C.; Wang, Z.; Gursul, I.

2018-03-01

The interaction of trailing vortices of an upstream wing with rigid and flexible downstream wings has been investigated experimentally in a wind tunnel, using particle image velocimetry, hot-wire, force, and deformation measurements. Counter-rotating upstream vortices exhibit increased meandering when they are close to the tip of the downstream wing. The upstream vortex forms a pair with the vortex shed from the downstream wing and then exhibits large displacements around the wing tip. This coupled motion of the pair has been found to cause large lift fluctuations on the downstream wing. The meandering of the vortex pair occurs at the natural meandering frequency of the isolated vortex, with a low Strouhal number, and is not affected by the frequency of the large-amplitude wing oscillations if the downstream wing is flexible. The displacement of the leading vortex is larger than that of the trailing vortex; however, it causes highly correlated variations of the core radius, core vorticity, and circulation of the trailing vortex with the coupled meandering motion. In contrast, co-rotating vortices do not exhibit any increased meandering.

Vortex flow during early and late left ventricular filling in normal subjects: quantitative characterization using retrospectively-gated 4D flow cardiovascular magnetic resonance and three-dimensional vortex core analysis.

Science.gov (United States)

Elbaz, Mohammed S M; Calkoen, Emmeline E; Westenberg, Jos J M; Lelieveldt, Boudewijn P F; Roest, Arno A W; van der Geest, Rob J

2014-09-27

LV diastolic vortex formation has been suggested to critically contribute to efficient blood pumping function, while altered vortex formation has been associated with LV pathologies. Therefore, quantitative characterization of vortex flow might provide a novel objective tool for evaluating LV function. The objectives of this study were 1) assess feasibility of vortex flow analysis during both early and late diastolic filling in vivo in normal subjects using 4D Flow cardiovascular magnetic resonance (CMR) with retrospective cardiac gating and 3D vortex core analysis 2) establish normal quantitative parameters characterizing 3D LV vortex flow during both early and late ventricular filling in normal subjects. With full ethical approval, twenty-four healthy volunteers (mean age: 20±10 years) underwent whole-heart 4D Flow CMR. The Lambda2-method was used to extract 3D LV vortex ring cores from the blood flow velocity field during early (E) and late (A) diastolic filling. The 3D location of the center of vortex ring core was characterized using cylindrical cardiac coordinates (Circumferential, Longitudinal (L), Radial (R)). Comparison between E and A filling was done with a paired T-test. The orientation of the vortex ring core was measured and the ring shape was quantified by the circularity index (CI). Finally, the Spearman's correlation between the shapes of mitral inflow pattern and formed vortex ring cores was tested. Distinct E- and A-vortex ring cores were observed with centers of A-vortex rings significantly closer to the mitral valve annulus (E-vortex L=0.19±0.04 versus A-vortex L=0.15±0.05; p=0.0001), closer to the ventricle's long-axis (E-vortex: R=0.27±0.07, A-vortex: R=0.20±0.09, p=0.048) and more elliptical in shape (E-vortex: CI=0.79±0.09, A-vortex: CI=0.57±0.06; vortex. The circumferential location and orientation relative to LV long-axis for both E- and A-vortex ring cores were similar. Good to strong correlation was found between vortex shape and

Interpreting Brightness Asymmetries in Transition Disks: Vortex at Dead Zone or Planet-carved Gap Edges?

Science.gov (United States)

Regály, Zs.; Juhász, A.; Nehéz, D.

2017-12-01

Recent submillimeter observations show nonaxisymmetric brightness distributions with a horseshoe-like morphology for more than a dozen transition disks. The most-accepted explanation for the observed asymmetries is the accumulation of dust in large-scale vortices. Protoplanetary disks’ vortices can form by the excitation of Rossby wave instability in the vicinity of a steep pressure gradient, which can develop at the edges of a giant planet–carved gap or at the edges of an accretionally inactive zone. We studied the formation and evolution of vortices formed in these two distinct scenarios by means of two-dimensional locally isothermal hydrodynamic simulations. We found that the vortex formed at the edge of a planetary gap is short-lived, unless the disk is nearly inviscid. In contrast, the vortex formed at the outer edge of a dead zone is long-lived. The vortex morphology can be significantly different in the two scenarios: the vortex radial and azimuthal extensions are ∼1.5 and ∼3.5 times larger for the dead-zone edge compared to gap models. In some particular cases, the vortex aspect ratios can be similar in the two scenarios; however, the vortex azimuthal extensions can be used to distinguish the vortex formation mechanisms. We calculated predictions for vortex observability in the submillimeter continuum with ALMA. We found that the azimuthal and radial extent of the brightness asymmetry correlates with the vortex formation process within the limitations of α-viscosity prescription.

A PDMS-Based Microfluidic Hanging Drop Chip for Embryoid Body Formation.

Science.gov (United States)

Wu, Huei-Wen; Hsiao, Yi-Hsing; Chen, Chih-Chen; Yet, Shaw-Fang; Hsu, Chia-Hsien

2016-07-06

The conventional hanging drop technique is the most widely used method for embryoid body (EB) formation. However, this method is labor intensive and limited by the difficulty in exchanging the medium. Here, we report a microfluidic chip-based approach for high-throughput formation of EBs. The device consists of microfluidic channels with 6 × 12 opening wells in PDMS supported by a glass substrate. The PDMS channels were fabricated by replicating polydimethyl-siloxane (PDMS) from SU-8 mold. The droplet formation in the chip was tested with different hydrostatic pressures to obtain optimal operation pressures for the wells with 1000 μm diameter openings. The droplets formed at the opening wells were used to culture mouse embryonic stem cells which could subsequently developed into EBs in the hanging droplets. This device also allows for medium exchange of the hanging droplets making it possible to perform immunochemistry staining and characterize EBs on chip.

A PDMS-Based Microfluidic Hanging Drop Chip for Embryoid Body Formation

Directory of Open Access Journals (Sweden)

Huei-Wen Wu

2016-07-01

Full Text Available The conventional hanging drop technique is the most widely used method for embryoid body (EB formation. However, this method is labor intensive and limited by the difficulty in exchanging the medium. Here, we report a microfluidic chip-based approach for high-throughput formation of EBs. The device consists of microfluidic channels with 6 × 12 opening wells in PDMS supported by a glass substrate. The PDMS channels were fabricated by replicating polydimethyl-siloxane (PDMS from SU-8 mold. The droplet formation in the chip was tested with different hydrostatic pressures to obtain optimal operation pressures for the wells with 1000 μm diameter openings. The droplets formed at the opening wells were used to culture mouse embryonic stem cells which could subsequently developed into EBs in the hanging droplets. This device also allows for medium exchange of the hanging droplets making it possible to perform immunochemistry staining and characterize EBs on chip.

Flame-Vortex Interactions Imaged in Microgravity - To Assess the Theory Flame Stretch

Science.gov (United States)

Driscoll, James F.

2001-01-01

The goals of this research are to: 1) Assess the Theory of Flame Stretch by operating a unique flame-vortex experiment under microgravity conditions in the NASA Glenn 2.2 Second Drop Tower (drops to identify operating conditions have been completed); 2) Obtain high speed shadowgraph images (500-1000 frames/s) using the drop rig (images were obtained at one-g, and the NASA Kodak RO camera is being mounted on the drop rig); 3) Obtain shadowgraph and PIV images at 1-g while varying the effects of buoyancy by controlling the Froude number (completed); 4) Numerically model the inwardly-propagating spherical flame that is observed in the experiment using full chemistry and the RUN 1DL code (completed); 5) Send images of the flame shape to Dr. G. Patniak at NRL who is numerically simulating the entire flame-vortex interaction of the present experiment (data transfer completed); and 6) Assess the feasibility of obtaining PIV velocity field images in the drop rig, which would be useful (but not required) for our assessment of the Theory of Flame Stretch (PIV images were obtained at one-g using same low laser power that is available from fiber optic cable in drop tower). The motivation for the work is to obtain novel measurement needed to develop a physically accurate model of turbulent combustion that can help in the control of engine pollutants. The unique experiment allows, for the first time, the detailed study of a negatively-curved (negatively stretched) flame, which is one of the five fundamental types of premixed flames. While there have been studies of flat flames, positively-curved (outwardly-propagating) cases and positively-strained (counterflow) cases, this is the first detailed study of a negatively-curved (inwardly-propagating) flame. The first set of drops in the 2.2 Second Drop Tower showed that microgravity provides more favorable conditions for achieving inwardly-propagating flames (IPFs) than 1-g. A vortex interacts with a flame and creates a spherical

Satellite Formation during Coalescence of Unequal Size Drops

KAUST Repository

Zhang, F. H.

2009-03-12

The coalescence of a drop with a flat liquid surface pinches off a satellite from its top, in the well-known coalescence cascade, whereas the coalescence of two equally sized drops does not appear to leave such a satellite. Herein we perform experiments to identify the critical diameter ratio of two drops, above which a satellite is produced during their coalescence. We find that the critical parent ratio is as small as 1.55, but grows monotonically with the Ohnesorge number. The daughter size is typically about 50% of the mother drop. However, we have identified novel pinch-off dynamics close to the critical size ratio, where the satellite does not fully separate, but rather goes directly into a second stage of the coalescence cascade, thus generating a much smaller satellite droplet.

Satellite Formation during Coalescence of Unequal Size Drops

KAUST Repository

Zhang, F. H.; Li, E. Q.; Thoroddsen, Sigurdur T

2009-01-01

The coalescence of a drop with a flat liquid surface pinches off a satellite from its top, in the well-known coalescence cascade, whereas the coalescence of two equally sized drops does not appear to leave such a satellite. Herein we perform experiments to identify the critical diameter ratio of two drops, above which a satellite is produced during their coalescence. We find that the critical parent ratio is as small as 1.55, but grows monotonically with the Ohnesorge number. The daughter size is typically about 50% of the mother drop. However, we have identified novel pinch-off dynamics close to the critical size ratio, where the satellite does not fully separate, but rather goes directly into a second stage of the coalescence cascade, thus generating a much smaller satellite droplet.

Spontaneous Formation of Anti-ferromagnetic Vortex Lattice in a Fast Rotating BEC with Dipole Interactions

International Nuclear Information System (INIS)

Yang Shijie; Feng Shiping; Wen Yuchuan; Yu Yue

2007-01-01

When a Bose-Einstein condensate is set to rotate, superfluid vortices will be formed, which finally condense into a vortex lattice as the rotation frequency further increases. We show that the dipole-dipole interactions renormalize the short-range interaction strength and result in a distinction between interactions of parallel-polarized atoms and interactions of antiparallel-polarized atoms. This effect may lead to a spontaneous breakdown of the rapidly rotating Bose condensate into a novel anti-ferromagnetic-like vortex lattice. The upward-polarized Bose condensate forms a vortex lattice, which is staggered against a downward-polarized vortex lattice. A phase diagram related to the coupling strength is obtained.

Self-organized vortex multiplets in swirling flow

DEFF Research Database (Denmark)

Okulov, Valery; Naumov, Igor; Sørensen, Jens Nørkær

2008-01-01

The possibility of double vortex multiplet formation at the center of an intensively swirling cocurrent flow generated in a cylindrical container by its rotating lid is reported for the first time. The boundary of the transition to unsteady flow regimes, which arise as a result of the equilibrium...... rotation of self-organized vortex multiplets (triplet, double triplet, double doublet, and quadruplet), has been experimentally determined for cylinders with the aspect (height to radius) ratios in a wider interval than that studied previously....

Evaluation of Aircraft Wing-Tip Vortex Using PIV

Science.gov (United States)

Alsayed, Omer A.; Asrar, Waqar; Omar, Ashraf A.

2010-06-01

The formation and development of a wing-tip vortex in a near and extended near filed were studied experimentally. Particle image velocimetry was used in a wind tunnel to measure the tip vortex velocity field and hence investigate the flow structure in a wake of aircraft half-wing model. The purpose of this investigation is to evaluate the main features of the lift generated vortices in order to find ways to alleviate hazardous wake vortex encounters for follower airplanes during start and approach such that the increase in airport capacity can be achieved. First the wake structure at successive downstream planes crosswise to the axis of the wake vortices was investigated by measuring parameters such as core radius, maximum tangential velocities, vorticities and circulation distributions. The effect of different angles of attack setting on vortex parameters was examined at one downstream location. In very early stages the vortex sheet evolution makes the tip vortex to move inward and to the suction side of the wing. While the core radius and circulation distributions hardly vary with the downstream distance, noticeable differences for the same vortex parameters at different angles of attack settings were observed. The center of the wing tip vortices scatter in a circle of radius nearly equal to 1% of the mean wing chord and wandering amplitudes shows no direct dependence on the vortex strength but linearly increase with the downstream distance.

Impact of a drop onto a wetted wall: description of crown formation and propagation

Science.gov (United States)

Roisman, I. V.; Tropea, C.

2002-12-01

The impact of a drop onto a liquid film with a relatively high impact velocity, leading to the formation of a crown-like ejection, is studied theoretically. The motion of a kinematic discontinuity in the liquid film on the wall due to the drop impact, the formation of the upward jet at this kinematic discontinuity and its elevation are analysed. Four main regions of the drop and film are considered: the perturbed liquid film on the wall inside the crown, the unperturbed liquid film on the wall outside the crown, the upward jet forming a crown, and the free rim bounding this jet. The theory of Yarin & Weiss (1995) for the propagation of the kinematic discontinuity is generalized here for the case of arbitrary velocity vectors in the inner and outer liquid films on the wall. Next, the mass, momentum balance and Bernoulli equations at the base of the crown are considered in order to obtain the velocity and the thickness of the jet on the wall. Furthermore, the dynamic equations of motion of the crown are developed in the Lagrangian form. An analytical solution for the crown shape is obtained in the asymptotic case of such high impact velocities that the surface tension and the viscosity effects can be neglected in comparison to inertial effects. The edge of the crown is described by the motion of a rim, formed due to the surface tension.

Effect of temperature, pH, and water activity on biofilm formation by Salmonella enterica enteritidis PT4 on stainless steel surfaces as indicated by the bead vortexing method and conductance measurements.

Science.gov (United States)

Giaouris, E; Chorianopoulos, N; Nychas, G J E

2005-10-01

An assay was developed in an effort to elucidate the effect of important environmental parameters (temperature, pH, and water activity [aw]) on Salmonella Enteritidis biofilm formation on stainless steel surfaces. To achieve this, a modified microbiological technique used for biofilm studying (the bead vortexing method) and a rapid method based on conductivity measurements were used. The ability of the microorganism to generate biofilm on the stainless surfaces was studied at three temperatures (5, 20, and 37 degrees C), four pH values (4.5, 5.5, 6.5, and 7.4), and four aw values (0.5, 1.5, 5.5, and 10.5% NaCl). Results obtained by the bead vortexing method show that maximum numbers of adherent bacteria per square centimeter (106 CFU/cm2) were attained in 6 days at 20 degrees C. Biofilm formation after 7 days of incubation at 20 degrees C was found to be independent of the pH value. In addition, the high concentration of sodium chloride (10.5% NaCl, aw = 0.94) clearly inhibited the adherence of cells to the coupons. Conductance measurements were used as a supplementary tool to measure indirectly the attachment and biofilm formation of bacterial cells on stainless steel surfaces via their metabolic activity (i.e., changes in the conductance of the growth medium due to microbial growth or metabolism). Results obtained by conductance measurements corresponded well to those of the bead vortexing method. Furthermore, we were able to detect cells that remained attached on the metal surfaces even after vortexing via their metabolic activity. The results, except for demonstrating environmental-dependent Salmonella Enteritidis biofilm formation, indicated that traditional vortexing with beads did not remove completely biofilm cells from stainless steel; hence, conductance measurements seem to provide a more sensitive test capable to detect down to one single viable organism.

Vortex-Breakdown-Induced Particle Capture in Branching Junctions.

Science.gov (United States)

Ault, Jesse T; Fani, Andrea; Chen, Kevin K; Shin, Sangwoo; Gallaire, François; Stone, Howard A

2016-08-19

We show experimentally that a flow-induced, Reynolds number-dependent particle-capture mechanism in branching junctions can be enhanced or eliminated by varying the junction angle. In addition, numerical simulations are used to show that the features responsible for this capture have the signatures of classical vortex breakdown, including an approach flow aligned with the vortex axis and a pocket of subcriticality. We show how these recirculation regions originate and evolve and suggest a physical mechanism for their formation. Furthermore, comparing experiments and numerical simulations, the presence of vortex breakdown is found to be an excellent predictor of particle capture. These results inform the design of systems in which suspended particle accumulation can be eliminated or maximized.

384 hanging drop arrays give excellent Z-factors and allow versatile formation of co-culture spheroids.

Science.gov (United States)

Hsiao, Amy Y; Tung, Yi-Chung; Qu, Xianggui; Patel, Lalit R; Pienta, Kenneth J; Takayama, Shuichi

2012-05-01

We previously reported the development of a simple, user-friendly, and versatile 384 hanging drop array plate for 3D spheroid culture and the importance of utilizing 3D cellular models in anti-cancer drug sensitivity testing. The 384 hanging drop array plate allows for high-throughput capabilities and offers significant improvements over existing 3D spheroid culture methods. To allow for practical 3D cell-based high-throughput screening and enable broader use of the plate, we characterize the robustness of the 384 hanging drop array plate in terms of assay performance and demonstrate the versatility of the plate. We find that the 384 hanging drop array plate performance is robust in fluorescence- and colorimetric-based assays through Z-factor calculations. Finally, we demonstrate different plate capabilities and applications, including: spheroid transfer and retrieval for Janus spheroid formation, sequential addition of cells for concentric layer patterning of different cell types, and culture of a wide variety of cell types. Copyright © 2011 Wiley Periodicals, Inc.

Diagnostics of spatial structure of vortex multiplets in a swirl flow

DEFF Research Database (Denmark)

Naumov, I. V.; Okulov, Valery; Sørensen, Jens Nørkær

2011-01-01

Results on investigation of vortex unstable breakdown are presented. The structure of vortex multiplets was visualized in a vertical cylindrical container made of transparent organic glass of the optic quality with the inner diameter of 288 mm and rotating upper lid. Visualization was performed....... Visualization of flow structure for unstable swirl flows and cylinder aspect ratios from 3.2 to 5.5 allowed first identification of these regimes as multispiral breakdowns with formation of helical-like vortex duplets, triplets and quadruplets....

The interaction of counter-rotating strained vortex pairs with a third vortex

International Nuclear Information System (INIS)

Higgins, Keith; Ooi, Andrew; Chong, M S; Ruetten, Markus

2009-01-01

The vortex dynamics caused by the interaction of counter-rotating Burgers vortex pairs with a third Burgers vortex in a straining flow is investigated numerically. These interactions blend vortex merging and cancellation effects, and the aim is to investigate how the third vortex might influence the evolution of the vortex pair. Many different choices of initial conditions for the pair and third vortex exist, so attention is restricted to a class of initial conditions in which the vortex pair initially moves in the general direction of vortex 3, and the distance from vortex 3 to the line of free propagation of the vortex pair is the 'offset' parameter δ. A series of calculations with 0≤δ≤4 reveals three types of intermediate-time vortex dynamics that are called merging, swapping and switching. The evolution of the vortex core separation and core vorticity level diagnostics are used to determine the points of transition from merging to swapping and switching. In the longer term, vortex merging, cancellation and straining reduces the three vortices to a single vortex. Other diagnostics of interest are also monitored, including the spatial distributions of the rate of viscous dissipation and terms contributing to the vorticity transport equation. During the merging phase for the case with δ=0, double-peak and double-trough structures are observed in the dissipation-rate contours. In addition, the diffusion of vorticity dominates the vortex-stretching effect near vortex 1 during its absorbtion by vortex 3. Finally, the dynamics of the three vortices are also examined by computing a co-rotating angular velocity and stream function. A series of peaks in the co-rotating angular velocity is found to be associated with the conservation of angular momentum and interactions with a 'ghost' vortex in the co-rotating stream function.

A parametric study of AC electric field-induced toroidal vortex formation in laminar nonpremixed coflow flames

KAUST Repository

Xiong, Yuan

2017-05-02

This study presents an experimental work investigating the controlling parameters on the formation of an electrically-induced inner toroidal vortex (ITV) near a nozzle rim in small, laminar nonpremixed coflow flames, when an alternating current is applied to the nozzle. A systematic parametric study was conducted by varying the flow parameters of the fuel and coflowing-air velocities, and the nozzle diameter. The fuels tested were methane, ethylene, ethane, propane, n-butane, and i-butane, each representing different ion-generation characteristics and sooting tendencies. The results showed that the fluid dynamic effects on ITV formation were weak, causing only mild variation when altering flow velocities. However, increased fuel velocity resulted in increased polycyclic aromatic hydrocarbon (PAH) formation, which promoted ITV formation. When judging the ITV-formation tendency based on critical applied voltage and frequency, it was qualitatively well correlated with the PAH concentration and the relative location of PAHs to the nozzle rim. The sooting tendency of the fuels did not affect the results much. A change in the nozzle diameter highlighted the importance of the relative distance between the PAH zone and the nozzle rim, indicating the role of local electric-field intensity on ITV formation. Detailed onset conditions, characteristics of near-nozzle flow patterns, and PAH distributions are also discussed.

Vortex Induced Vibrations of Cylinders: Experiments in Reducing Drag Force and Amplitude of Motion

National Research Council Canada - National Science Library

Farrell, David E

2007-01-01

.... The second series of tests are the rigid cylinder, PIV experiments. These rests measure both the drag force on the cylinder and the oscillating component of the lift force, the latter of which is a good indication of vortex formation. The Chapter 3 tests also image the test section wake-providing helpful insight into the physical process of vortex formations.

ABOUT TEMPERATURE FIELDS AND CONDITIONS OF GASEOUS CONDENSATION OF NEBULAES IN THE PLANETARY VORTEX

Directory of Open Access Journals (Sweden)

L. V. Klyuchinskaya

2014-01-01

Full Text Available New exact solution of the spherically-axissymmetric Eiler's equations, called as plan­etary vortex, is applied to the problem of formation in planetary nebula germs of planets due to the condensation of gases in the areas of vortex instability which calls the rings of planetary vortex. It is shown that the vortex perturbations causes changes in preassure and temperature at which the gases of nebula condense themselves, forming the germs of the planets.

Compressible Vortex Ring

Science.gov (United States)

Elavarasan, Ramasamy; Arakeri, Jayawant; Krothapalli, Anjaneyulu

1999-11-01

The interaction of a high-speed vortex ring with a shock wave is one of the fundamental issues as it is a source of sound in supersonic jets. The complex flow field induced by the vortex alters the propagation of the shock wave greatly. In order to understand the process, a compressible vortex ring is studied in detail using Particle Image Velocimetry (PIV) and shadowgraphic techniques. The high-speed vortex ring is generated from a shock tube and the shock wave, which precedes the vortex, is reflected back by a plate and made to interact with the vortex. The shadowgraph images indicate that the reflected shock front is influenced by the non-uniform flow induced by the vortex and is decelerated while passing through the vortex. It appears that after the interaction the shock is "split" into two. The PIV measurements provided clear picture about the evolution of the vortex at different time interval. The centerline velocity traces show the maximum velocity to be around 350 m/s. The velocity field, unlike in incompressible rings, contains contributions from both the shock and the vortex ring. The velocity distribution across the vortex core, core diameter and circulation are also calculated from the PIV data.

IUTAM Symposium on Hamiltonian Dynamics, Vortex Structures, Turbulence

CERN Document Server

Borisov, Alexey V; Mamaev, Ivan S; Sokolovskiy, Mikhail A; IUTAM BOOKSERIES : Volume 6

2008-01-01

This work brings together previously unpublished notes contributed by participants of the IUTAM Symposium on Hamiltonian Dynamics, Vortex Structures, Turbulence (Moscow, 25-30 August 2006). The study of vortex motion is of great interest to fluid and gas dynamics: since all real flows are vortical in nature, applications of the vortex theory are extremely diverse, many of them (e.g. aircraft dynamics, atmospheric and ocean phenomena) being especially important. The last few decades have shown that serious possibilities for progress in the research of real turbulent vortex motions are essentially related to the combined use of mathematical methods, computer simulation and laboratory experiments. These approaches have led to a series of interesting results which allow us to study these processes from new perspectives. Based on this principle, the papers collected in this proceedings volume present new results on theoretical and applied aspects of the processes of formation and evolution of various flows, wave a...

Vortex configuration and vortex-vortex interaction in nano-structured superconductors

International Nuclear Information System (INIS)

Kato, Masaru; Niwa, Yuhei; Suematsu, Hisataka; Ishida, Takekazu

2012-01-01

We study the vortex structures and quasi-particle structures in nano-structured superconductors. We used the Bogoliubov-de Gennes equation and the finite element method and obtained stable magnetic flux structures and the quasi-particle states. We found the vortex configurations are affected by the interference of the quasi-particle bound states around the vortices. In order to clarify the interference between the quasi-particle wave-functions around two vortices we have developed a numerical method using the elliptic coordinates and the Mathieu functions. We apply this method to two singly quantized vortex state in a conventional s-wave superconductor and a pair of half-quantum vortices in a chiral p-wave superconductor.

Effect of vortex generators on the closing transient flow of bileaflet mechanical heart valves

Science.gov (United States)

Murphy, David; Dasi, Lakshmi; Yoganathan, Ajit; Glezer, Ari

2006-11-01

The time-periodic closing of bileaflet mechanical heart valves is accompanied by a strong flow transient that is associated with the formation of a counter-rotating vortex pair near the b-datum line of leaflet edges. The strong transitory shear that is generated by these vortices may be damaging to blood elements and may result in platelet activation. In the present work, these flow transients are mitigated using miniature vortex generator arrays that are embedded on the surface of the leaflets. Two vortex generator designs were investigated: one design comprised staggered rectangular fins and the other one staggered hemispheres. The closing transients in the absence and presence of the passive vortex generators are characterized using phase locked PIV measurements. The study utilizes a 25 mm St. Jude Medical valve placed in the aortic position of the Georgia Tech left heart simulator. Measurements of the velocity field in the center plane of the leaflets demonstrate that the dynamics of the transient vortices that precede the formation of the leakage jets can be significantly altered and controlled by relatively simple passive modifications of existing valve designs. Human blood experiments validated the effectiveness of miniature vortex generators in reducing thrombus formation by over 42 percent.

Drift wave coherent vortex structures in inhomogeneous plasmas

International Nuclear Information System (INIS)

Su, X.N.

1992-01-01

Nonlinear drift wave vortex structures in magnetized plasmas are studied theoretically and numerically in the various physical environments. The effects of density and temperature gradients on drift wave vortex dynamics are analyzed using a fully nonlinear model with the Boltzmann density distribution. The equation, based on the full Boltzmann relation, possess no localized monopole solution in the short wavelength (∼ρ s ) region, while in the longer wavelength (∼(ρ s (r) n ) 1/2 ) region the density profile governs the existence of monopole-like solutions. In the longer wavelength regime, however, the monopoles cannot be localized sufficiently to avoid coupling to propagating drift waves due to the inhomogeneity of the plasma. Thus, the monopole vortex is a long lived coherent structure, but it is not precisely a stationary structure since the coupling results in a open-quote flapping close-quote tail. The tail causes energy of the vortex to leak out, but the effect of the temperature gradient is to reduce the leaking of this energy. Nonlinear coherent structures governing by the coupled drift wave-ion acoustic mode equations in sheared magnetic field are studied analytically and numerically. A solitary vortex equation that includes the effects of density and temperature gradients and magnetic shear is derived and analyzed. The results show that for a plasma in a sheared magnetic field, there exist the solitary vortex solutions. The new vortex structures are dipole-like in their symmetry, but not the modon type of dipoles. The numerical simulations are performed in 2-D with the coupled vorticity and parallel mass flow equations. The vortex structures in an unstable drift wave system driven by parallel shear flow are studied. The nonlinear solitary vortex solutions are given and the formation of the vortices from a turbulent state is observed from the numerical simulations

A study of the vortex structures around circular cylinder mounted on vertical heated plate

Science.gov (United States)

Malah, Hamid; Chumakov, Yurii S.; Levchenya, Alexander M.

2018-05-01

In recent years, studies of natural convection boundary layer interacting with obstacles draw much of attention, because of its practical applications. Pressure gradient resulting from this interaction leads to separation of the boundary layer. The formation of vortex structure around obstacle is characteristic to any kind of convection flow. In this paper, we describe the formation of three-dimensional vortex structure for the case of natural convection flow around the circular cylinder mounted on vertical heated plate. Navier-Stokes equations were used for numerical computations. The results proved the presence of a horseshoe vortex system in the case of natural convection flow as in the forced convection flow.

Chemical-Reaction-Controlled Phase Separated Drops: Formation, Size Selection, and Coarsening

Science.gov (United States)

Wurtz, Jean David; Lee, Chiu Fan

2018-02-01

Phase separation under nonequilibrium conditions is exploited by biological cells to organize their cytoplasm but remains poorly understood as a physical phenomenon. Here, we study a ternary fluid model in which phase-separating molecules can be converted into soluble molecules, and vice versa, via chemical reactions. We elucidate using analytical and simulation methods how drop size, formation, and coarsening can be controlled by the chemical reaction rates, and categorize the qualitative behavior of the system into distinct regimes. Ostwald ripening arrest occurs above critical reaction rates, demonstrating that this transition belongs entirely to the nonequilibrium regime. Our model is a minimal representation of the cell cytoplasm.

Calcium-Phosphate-Osteopontin Particles Reduce Biofilm Formation and pH Drops in in situ-Grown Dental Biofilms

DEFF Research Database (Denmark)

Schlafer, Sebastian; Ibsen, Casper Jon Steenberg; Birkedal, Henrik

2017-01-01

This 2-period crossover study investigated the effect of calcium-phosphate-osteopontin particles on biofilm formation and pH in 48-h biofilms grown in situ. Bovine milk osteopontin is a highly phosphorylated glycoprotein that has been shown to interfere with bacterial adhesion to salivary......-coated surfaces. Calcium-phosphate-osteopontin particles have been shown to reduce biofilm formation and pH drops in a 5-species laboratory model of dental biofilm without affecting bacterial viability. Here, smooth surface biofilms from 10 individuals were treated ex vivo 6 times/day for 30 min with either...... calcium-phosphate-osteopontin particles or sterile saline. After growth, the amount of biofilm formed was determined by confocal microscopy, and pH drops upon exposure to glucose were monitored using confocal-microscopy-based pH ratiometry. A total of 160 biofilms were analysed. No adverse effects...

Quantum-Size Dependence of the Energy for Vacancy Formation in Charged Small Metal Clusters. Drop Model

Science.gov (United States)

Pogosov, V. V.; Reva, V. I.

2018-04-01

Self-consistent computations of the monovacancy formation energy are performed for Na N , Mg N , and Al N (12 < N ≤ 168) spherical clusters in the drop model for stable jelly. Scenarios of the Schottky vacancy formation and "bubble vacancy blowing" are considered. It is shown that the asymptotic behavior of the size dependences of the energy for the vacancy formation by these two mechanisms is different and the difference between the characteristics of a charged and neutral cluster is entirely determined by the difference between the ionization potentials of clusters and the energies of electron attachment to them.

Vortex formation at the open end of an acoustic waveguide

Science.gov (United States)

Martinez Del Rio, Leon; Rendon, Pablo L.; Malaga, Carlos; Zenit, Roberto

2017-11-01

For high enough levels of acoustic pressure inside a cylindrical tube, a nonlinear mechanism is responsible for the formation of annular vortices at the open end of the tube, which results in energy loss. Higher sound pressure levels in the tube lead, in turn, to larger values of the acoustic velocity at the exit, and thus to higher Reynolds numbers. It has been observed [Buick et al., 2011] that, provided the magnitude of the acoustic velocity is large enough, two nonlinear regimes are possible: in the first regime, the vorticity appears only in the immediate vicinity of the tube; for higher velocities, vortex rings are formed at the open end of the tube and are advected outwards. We use a Lattice Boltzmann Method (LBM) to simulate the velocity and the pressure fields at the exit of the tube in 3D, with Reynolds numbers based on the acoustic boundary layer thickness 18 >Rδ > 1.8 . We also conduct experiments with phase-locked particle image velocimetry (PL-PIV) 2D within a range of 25.5 >Rδ > 10.2 . Experimental and numerical results are compared for a range of Womersley numbers. The effects of varying both the tube geometry and the end shape are addressed.

Composite vortex ordering in superconducting films with arrays of blind holes

International Nuclear Information System (INIS)

Berdiyorov, G R; Milosevic, M V; Peeters, F M

2009-01-01

The pinning properties of a superconducting thin film with a square array of blind holes are studied using the nonlinear Ginzburg-Landau theory. Although blind holes provide a weaker pinning potential than holes (also called antidots), several novel vortex structures are predicted for different size and thickness of the blind holes. Orientational dimer and trimer vortex states as well as concentric vortex shells can nucleate in the blind holes. In addition, we predict the stabilization of giant vortices that may be located both in the pinning centers and/or at the interstitial sites, as well as the combination of giant vortices with sets of individual vortices. For large blind holes, local vortex shell structures inside the blind holes may transfer their symmetry to interstitial vortices as well. The subtle interplay of shell formation and traditional Abrikosov vortex lattices inside the blind holes is also studied for different numbers of trapped vortices.

Structure formation in soft nanocolloids: liquid-drop model.

Science.gov (United States)

Doukas, A-K; Likos, C N; Ziherl, P

2018-04-25

Using a model where soft nanocolloids such as spherical polymer brushes and star polymers are viewed as compressible liquid drops, we theoretically explore contact interactions between such particles. By numerically minimizing the phenomenological free energy consisting of bulk and surface terms, we find that at small deformations the drop-drop interaction is pairwise additive and described by a power law. We also propose a theory to describe the small-deformation regime, and the agreement is very good at all drop compressibilities. The large-deformation regime, which is dominated by many-body interactions, is marked by a rich phase diagram which includes the face- and body-centered-cubic, σ, A15, and simple hexagonal lattice as well as isostructural and re-entrant transitions. Most of these features are directly related to the non-convex deformation free energy emerging from many-body effects in the partial-faceting regime. The phase diagram, which depends on just two model parameters, contains many of the condensed phases observed in experiments. We also provide statistical-mechanical arguments that relate the two model parameters to the molecular architecture of the polymeric nanocolloids, chain rigidity, and solvent quality. The model represents a generic framework for the overarching features of the phase behavior of polymeric nanocolloids at high compressions.

Intraventricular vortex properties in nonischemic dilated cardiomyopathy

Science.gov (United States)

Benito, Yolanda; Alhama, Marta; Yotti, Raquel; Martínez-Legazpi, Pablo; del Villar, Candelas Pérez; Pérez-David, Esther; González-Mansilla, Ana; Santa-Marta, Cristina; Barrio, Alicia; Fernández-Avilés, Francisco; del Álamo, Juan C.

2014-01-01

Vortices may have a role in optimizing the mechanical efficiency and blood mixing of the left ventricle (LV). We aimed to characterize the size, position, circulation, and kinetic energy (KE) of LV main vortex cores in patients with nonischemic dilated cardiomyopathy (NIDCM) and analyze their physiological correlates. We used digital processing of color-Doppler images to study flow evolution in 61 patients with NIDCM and 61 age-matched control subjects. Vortex features showed a characteristic biphasic temporal course during diastole. Because late filling contributed significantly to flow entrainment, vortex KE reached its maximum at the time of the peak A wave, storing 26 ± 20% of total KE delivered by inflow (range: 1–74%). Patients with NIDCM showed larger and stronger vortices than control subjects (circulation: 0.008 ± 0.007 vs. 0.006 ± 0.005 m2/s, respectively, P = 0.02; KE: 7 ± 8 vs. 5 ± 5 mJ/m, P = 0.04), even when corrected for LV size. This helped confining the filling jet in the dilated ventricle. The vortex Reynolds number was also higher in the NIDCM group. By multivariate analysis, vortex KE was related to the KE generated by inflow and to chamber short-axis diameter. In 21 patients studied head to head, Doppler measurements of circulation and KE closely correlated with phase-contract magnetic resonance values (intraclass correlation coefficient = 0.82 and 0.76, respectively). Thus, the biphasic nature of filling determines normal vortex physiology. Vortex formation is exaggerated in patients with NIDCM due to chamber remodeling, and enlarged vortices are helpful for ameliorating convective pressure losses and facilitating transport. These findings can be accurately studied using ultrasound. PMID:24414062

ProFile Vortex and Vortex Blue Nickel-Titanium Rotary Instruments after Clinical Use.

Science.gov (United States)

Shen, Ya; Zhou, Huimin; Coil, Jeffrey M; Aljazaeri, Bassim; Buttar, Rene; Wang, Zhejun; Zheng, Yu-feng; Haapasalo, Markus

2015-06-01

The aim of this study was to analyze the incidence and mode of ProFile Vortex and Vortex Blue instrument defects after clinical use in a graduate endodontic program and to examine the impact of clinical use on the instruments' metallurgical properties. A total of 330 ProFile Vortex and 1136 Vortex Blue instruments from the graduate program were collected after each had been used in 3 teeth. The incidence and type of instrument defects were analyzed. The lateral surfaces and fracture surfaces of the fractured files were examined by using scanning electron microscopy. Unused and used instruments were examined by full and partial differential scanning calorimetry. No fractures were observed in the 330 ProFile Vortex instruments, whereas 20 (6.1%) revealed bent or blunt defects. Only 2 of the 1136 Vortex Blue files fractured during clinical use. The cause of fracture was shear stress. The fractures occurred at the tip end of the spirals. Only 1.8% (21 of 1136) of the Vortex Blue files had blunt tips. Austenite-finish temperatures were very similar for unused and used ProFile Vortex files and were all greater than 50°C. The austenite-finish temperatures of used and unused Vortex Blue files (38.5°C) were lower than those in ProFile Vortex instruments (P Vortex Blue files had an obvious 2-stage transformation, martensite-to-R phase and R-to-austenite phase. The trends of differential scanning calorimetry plots of unused Vortex Blue instruments and clinically used instruments were very similar. The risk of ProFile Vortex and Vortex Blue instrument fracture is very low when instruments are discarded after clinical use in the graduate endodontic program. The Vortex Blue files have metallurgical behavior different from ProFile Vortex instruments. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Effects of streamwise vortex breakdown on supersonic combustion.

Science.gov (United States)

Hiejima, Toshihiko

2016-04-01

This paper presents a numerical simulation study of the combustion structure of streamwise vortex breakdown at Mach number 2.48. Hydrogen fuel is injected into a combustor at sonic speed from the rear of a hypermixer strut that can generate streamwise vortices. The results show that the burning behavior is enhanced at the points of the shock waves that are incident on the vortex and therefore the vortex breakdown in the subsonic region occurs due to combustion. The breakdown domain in the mainstream is found to form a flame-holding region suited to combustion and to lead to a stable combustion field with detached flames. In this way, streamwise vortex breakdown has an essential role in combustion enhancement and the formation of flames that hold under supersonic inflow conditions. Finally, the combustion property defined here is shown to coincide with the produced-water mass flow. This property shows that the amount of combustion is saturated at equivalence ratios over 0.4, although there is a slight increase beyond 1.

Collapsing vortex filaments and the spectrum of quantum turbulence

Science.gov (United States)

Andryushchenko, V. A.; Nemirovskii, S. K.

2017-01-01

The method of correlation functions and the method of quantum vortex configurations are used to calculate the energy spectrum of a three-dimensional velocity field that is induced by collapsing (immediately before reconnection) vortex filaments. The formulation of this problem is motivated by the idea of modeling classical turbulence by a set of chaotic quantized vortex filaments. Among the various arguments that support the idea of quasi-classical behavior for quantum turbulence, the most persuasive is probably the resulting Kolmogorov energy spectrum resembling E ( k ) ∝ k - 5 / 3 that was obtained in a number of numerical studies. Another goal is associated with an important and intensely studied theme that relates to the role of hydrodynamic collapse in the formation of turbulence spectra. Calculations have demonstrated that vortex filaments create a velocity field at the moment of contact, which has a singularity. This configuration of vortex filaments generates the spectrum E(k), which bears the resemblance to the Kolmogorov law. A possible cause for this observation is discussed, as well as the likely reasons behind any deviations. The obtained results are discussed from the perspective of both classical and quantum turbulence.

Transitions in the vortex wake behind the plunging profile

Science.gov (United States)

Kozłowski, Tomasz; Kudela, Henryk

2014-12-01

In this study we investigate numerically the vortex wake formation behind the profile performing simple harmonic motion known in the literature as plunging. This research was inspired by the flapping motion which is appropriate for birds, insects and fishes. We assume the two dimensional model of flow. Depending on the parameters such as plunging amplitude, frequency and the Reynolds number, we demonstrate many different types of vortex street behind the profile. It is well known that the type of vortex wake determines the hydrodynamic forces acting on the profile. Dependences of the plunging amplitude, the Strouhal number and various topology vortices are established by constructing the phase transition diagram. The areas in the diagram related to the drag, thrust, and lift force generation are captured. We notice also the areas where the vorticity field is disordered. The disordered vorticity field does not allow maintenance of the periodic forces on the profile. An increase in the Reynolds number leads to the transition of the vortex wake behind the profile. The transition is caused by the phenomenon of boundary layer eruption. Further increase of the Reynolds number causes the vortex street related to the generation of the lift force to vanish.

Vortex Dynamics of Asymmetric Heave Plates

Science.gov (United States)

Rusch, Curtis; Maurer, Benjamin; Polagye, Brian

2017-11-01

Heave plates can be used to provide reaction forces for wave energy converters, which harness the power in ocean surface waves to produce electricity. Heave plate inertia includes both the static mass of the heave plate, as well as the ``added mass'' of surrounding water accelerated with the object. Heave plate geometries may be symmetric or asymmetric, with interest in asymmetric designs driven by the resulting hydrodynamic asymmetry. Limited flow visualization has been previously conducted on symmetric heave plates, but flow visualization of asymmetric designs is needed to understand the origin of observed hydrodynamic asymmetries and their dependence on the Keulegan-Carpenter number. For example, it is hypothesized that the time-varying added mass of asymmetric heave plates is caused by vortex shedding, which is related to oscillation amplitude. Here, using direct flow visualization, we explore the relationship between vortex dynamics and time-varying added mass and drag. These results suggest potential pathways for more advanced heave plate designs that can exploit vortex formation and shedding to achieve more favorable hydrodynamic properties for wave energy converters.

Vortex rings and jets recent developments in near-field dynamics

CERN Document Server

Yu, Simon

2015-01-01

In this book, recent developments in our understanding of fundamental vortex ring and jet dynamics will be discussed, with a view to shed light upon their near-field behaviour which underpins much of their far-field characteristics. The chapters provide up-to-date research findings by their respective experts and seek to link near-field flow physics of vortex ring and jet flows with end-applications in mind. Over the past decade, our knowledge on vortex ring and jet flows has grown by leaps and bounds, thanks to increasing use of high-fidelity, high-accuracy experimental techniques and numerical simulations. As such, we now have a much better appreciation and understanding on the initiation and near-field developments of vortex ring and jet flows under many varied initial and boundary conditions. Chapter 1 outlines the vortex ring pinch-off phenomenon and how it relates to the initial stages of jet formations and subsequent jet behaviour, while Chapter 2 takes a closer look at the behaviour resulting from vor...

Point vortex modelling of the wake dynamics behind asymmetric vortex generator arrays

NARCIS (Netherlands)

Baldacchino, D.; Simao Ferreira, C.; Ragni, D.; van Bussel, G.J.W.

2016-01-01

In this work, we present a simple inviscid point vortex model to study the dynamics of asymmetric vortex rows, as might appear behind misaligned vortex generator vanes. Starting from the existing solution of the in_nite vortex cascade, a numerical model of four base-vortices is chosen to represent

Generation of shockwave and vortex structures at the outflow of a boiling water jet

Science.gov (United States)

Alekseev, M. V.; Lezhnin, S. I.; Pribaturin, N. A.; Sorokin, A. L.

2014-12-01

Results of numerical simulation for shock waves and generation of vortex structures during unsteady outflow of boiling liquid jet are presented. The features of evolution of shock waves and vortex structures formation during unsteady outflow of boiling water are compared with corresponding structures during unsteady gas outflow.

Population imbalance as a vortex catalyst in Fermi superfluids

International Nuclear Information System (INIS)

Tempere, J.; Devreese, J.T.

2008-01-01

Pairing leads to superfluidity in ultracold atomic gases, but this pairing can be frustrated when a population imbalance is present between the pairing partners. Here we investigate how vortices in the fermionic superfluid are affected by imbalance. We show that the vortex core radius is increased by imbalance, accommodating excess component atoms. This has two intriguing consequences. Firstly, a small imbalance acts as a catalyst for vortex formation, decreasing the critical rotation frequency. Secondly, imbalanced gases near critical imbalance can exhibit rotationally induced superfluidity

Vortex pair production and decay of a two-dimensional supercurrent by a quantum-field-theory approach

International Nuclear Information System (INIS)

Iengo, R.; Jug, G.

1995-01-01

We investigate the phenomenon of the decay of a supercurrent through homogeneous nucleation of vortex-antivortex pairs in a two-dimensional (2D) like superconductor or superfluid by means of a quantum electrodynamic formulation for the decay of the 2D vacuum. The case in which both externally driven current and Magnus force are present is treated exactly, taking the vortex activation energy and its inertial mass as independent parameters. Quantum dissipation is included through the formulation introduced by Caldeira and Leggett. The most relevant consequence of quantum dissipation is the elimination of the threshold for vortex production due to the Magnus force. In the dissipation-dominated case, corresponding formally to the limit of zero intertial mass, an exact formula for the pair production rate is given. If however the inertial mass is strictly zero we find that vortex production is inhibited by a quantum effect related to the Magnus force. The possibility of including vortex pinning is investigated by means of an effective harmonic potential. While an additional term in the vortex activation energy can account for the effect of a finite barrier in the direction perpendicular to the current, pinning along the current depresses the role of the Magnus force in the dissipation-dominated dynamics, except for the above-mentioned quantum effect. A possible description of vortex nucleation due to the combined effects of temperature and externally driven currents is also presented along with an evaluation of the resulting voltage drop

Independent control of the vortex chirality and polarity in a pair of magnetic nanodots

Energy Technology Data Exchange (ETDEWEB)

Li, Junqin; Wang, Yong, E-mail: wangyong@sinap.ac.cn; Cao, Jiefeng; Meng, Xiangyu; Zhu, Fangyuan; Wu, Yanqing; Tai, Renzhong

2017-08-01

Independent control of the vortex chirality and polarity is realized by changing the in-plane magnetic field direction in nanodot pair through Object Oriented Micromagnetic Framework (OOMMF) simulation. The two magnetic circles are close to each other and have magnetic interaction. The two circles always have the same polarity and opposite chirality at every remanent state. There are totally four predictable magnetic states in the nanodot pair which can be obtained in the remanent state relaxed from the saturation state along all possible directions. An explanation on the formation of vortex states is given by vortex dynamics. The vortex states are stable in large out-of-plane magnetic field which is in a direction opposite to the vortex polarity. The geometry of the nanodot pair gives a way to easily realize a vortex state with specific polarity and chirality.

A Coaxial Vortex Ring Model for Vortex Breakdown

OpenAIRE

Blackmore, Denis; Brons, Morten; Goullet, Arnaud

2008-01-01

A simple - yet plausible - model for B-type vortex breakdown flows is postulated; one that is based on the immersion of a pair of slender coaxial vortex rings in a swirling flow of an ideal fluid rotating around the axis of symmetry of the rings. It is shown that this model exhibits in the advection of passive fluid particles (kinematics) just about all of the characteristics that have been observed in what is now a substantial body of published research on the phenomenon of vortex breakdown....

Data Fusion to Estimate Vortex Location for Drag Reduction in Formation Flight

Data.gov (United States)

National Aeronautics and Space Administration — NASA is investigating the potential benefits of flying aircraft in the aerodynamic wake vortex emanating from a lead aircraft's wing tip. Analytic studies predict...

Left ventricular fluid dynamics in heart failure: echocardiographic measurement and utilities of vortex formation time.

Science.gov (United States)

Poh, Kian Keong; Lee, Li Ching; Shen, Liang; Chong, Eric; Tan, Yee Leng; Chai, Ping; Yeo, Tiong Cheng; Wood, Malissa J

2012-05-01

In clinical heart failure (HF), inefficient propagation of blood through the left ventricle (LV) may result from suboptimal vortex formation (VF) ability of the LV during early diastole. We aim to (i) validate echocardiographic-derived vortex formation time (adapted) (VFTa) in control subjects and (ii) examine its utility in both systolic and diastolic HF. Transthoracic echocardiography was performed in 32 normal subjects and in 130 patients who were hospitalized with HF [91, reduced ejection fraction (rEF) and 39, preserved ejection fraction (pEF)]. In addition to biplane left ventricular ejection fraction (LVEF) and conventional parameters, the Tei index and tissue Doppler (TD) indices were measured. VFTa was obtained using the formula: 4 × (1 - β)/π × α³ × LVEF, where β is the fraction of total transmitral diastolic stroke volume contributed by atrial contraction (assessed by time velocity integral of the mitral E- and A-waves) and α is the biplane end-diastolic volume (EDV)(1/3) divided by mitral annular diameter during early diastole. VFTa was correlated with demographic, cardiac parameters, and a composite clinical endpoint comprising cardiac death and repeat hospitalization for HF. Mean VFTa was 2.67 ± 0.8 in control subjects; reduced in HF, preserved EF HF, 2.21 ± 0.8; HF with reduced EF, 1.25 ± 0.6 (PTD early diastolic myocardial velocities (E', septal, r = 0.46; lateral, r = 0.43), systolic myocardial velocities (S', septal, r = 0.47; lateral, r = 0.41), and inversely with the Tei index (r = -0.41); all Ps < 0.001. Sixty-two HF patients (49%) met the composite endpoint. VFTa of <1.32 was associated with significantly reduced event-free survival (Kaplan Meier log rank = 16.3, P= 0.0001) and predicted the endpoint with a sensitivity and specificity of 65 and 72%, respectively. VFTa, a dimensionless index, incorporating LV geometry, systolic and diastolic parameters, may be useful in the diagnosis and prognosis of HF.

The effect of butterfly-scale inspired patterning on leading-edge vortex growth

Science.gov (United States)

Wilroy, Jacob Aaron

Leading edge vortices (LEVs) are important for generating thrust and lift in flapping flight, and the surface patterning (scales) on butterfly wings is hypothesized to play a role in the vortex formation of the LEV. To simplify this complex flow problem, an experiment was designed to focus on the alteration of 2-D vortex development with a variation in surface patterning. Specifically, the secondary vorticity generated by the LEV interacting at the patterned surface was studied, as well as the subsequent effect on the LEV's growth rate and peak circulation. For this experiment, rapid-prototyped grooves based on the scale geometry of the Monarch butterfly (Danaus plexippus) were created using additive manufacturing and were attached to a flat plate with a chordwise orientation, thus increasing plate surface area. The vortex generated by the grooved plate was then compared to a smooth plate case in an experiment where the plate translated vertically through a 2 x 3 x 5 cubic foot tow tank. The plate was impulsively started in quiescent water and flow fields at Rec = 1416, 2833, and 5667 are examined using Digital Particle Image Velocimetry (DPIV). The maximum vortex formation number is 2.8 and is based on the flat plate travel length and chord length. Flow fields from each case show the generation of a secondary vortex whose interaction with the shear layer and LEV caused different behaviors depending upon the surface type. The vortex development process varied for each Reynolds number and it was found that for the lowest Reynolds number case a significant difference does not exist between surface types, however, for the other two cases the grooves affected the secondary vortex's behavior and the LEV's ability to grow at a rate similar to the smooth plate case.

Mapping degenerate vortex states in a kagome lattice of elongated antidots via scanning Hall probe microscopy

Science.gov (United States)

Xue, C.; Ge, J.-Y.; He, A.; Zharinov, V. S.; Moshchalkov, V. V.; Zhou, Y. H.; Silhanek, A. V.; Van de Vondel, J.

2017-07-01

We investigate the degeneracy of the superconducting vortex matter ground state by directly visualizing the vortex configurations in a kagome lattice of elongated antidots via scanning Hall probe microscopy. The observed vortex patterns, at specific applied magnetic fields, are in good agreement with the configurations obtained using time-dependent Ginzburg-Landau simulations. Both results indicate that the long-range interaction in this nanostructured superconductor is unable to lift the degeneracy between different vortex states and the pattern formation is mainly ruled by the nearest-neighbor interaction. This simplification makes it possible to identify a set of simple rules characterizing the vortex configurations. We demonstrate that these rules can explain both the observed vortex distributions and the magnetic-field-dependent degree of degeneracy.

Transitions in the vortex wake behind the plunging profile

Energy Technology Data Exchange (ETDEWEB)

Kozłowski, Tomasz; Kudela, Henryk, E-mail: tomasz.kozlowski@pwr.wroc.pl, E-mail: henryk.kudela@pwr.wroc.pl [Department of Numerical Modelling of Flows, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

2014-12-01

In this study we investigate numerically the vortex wake formation behind the profile performing simple harmonic motion known in the literature as plunging. This research was inspired by the flapping motion which is appropriate for birds, insects and fishes. We assume the two dimensional model of flow. Depending on the parameters such as plunging amplitude, frequency and the Reynolds number, we demonstrate many different types of vortex street behind the profile. It is well known that the type of vortex wake determines the hydrodynamic forces acting on the profile. Dependences of the plunging amplitude, the Strouhal number and various topology vortices are established by constructing the phase transition diagram. The areas in the diagram related to the drag, thrust, and lift force generation are captured. We notice also the areas where the vorticity field is disordered. The disordered vorticity field does not allow maintenance of the periodic forces on the profile. An increase in the Reynolds number leads to the transition of the vortex wake behind the profile. The transition is caused by the phenomenon of boundary layer eruption. Further increase of the Reynolds number causes the vortex street related to the generation of the lift force to vanish. (paper)

Transitions in the vortex wake behind the plunging profile

International Nuclear Information System (INIS)

Kozłowski, Tomasz; Kudela, Henryk

2014-01-01

In this study we investigate numerically the vortex wake formation behind the profile performing simple harmonic motion known in the literature as plunging. This research was inspired by the flapping motion which is appropriate for birds, insects and fishes. We assume the two dimensional model of flow. Depending on the parameters such as plunging amplitude, frequency and the Reynolds number, we demonstrate many different types of vortex street behind the profile. It is well known that the type of vortex wake determines the hydrodynamic forces acting on the profile. Dependences of the plunging amplitude, the Strouhal number and various topology vortices are established by constructing the phase transition diagram. The areas in the diagram related to the drag, thrust, and lift force generation are captured. We notice also the areas where the vorticity field is disordered. The disordered vorticity field does not allow maintenance of the periodic forces on the profile. An increase in the Reynolds number leads to the transition of the vortex wake behind the profile. The transition is caused by the phenomenon of boundary layer eruption. Further increase of the Reynolds number causes the vortex street related to the generation of the lift force to vanish. (paper)

Structures of single vortex and vortex lattice in a d-wave superconductor

International Nuclear Information System (INIS)

Xu, J.; Ren, Y.; Ting, C.

1996-01-01

The structures of a single vortex and vortex lattice in a superconductor with d x 2 -y 2 symmetry are studied self-consistently employing a recently developed Ginzburg-Landau theory. Near a single vortex, we found that an s-wave component of the order parameter is always induced, and it causes the local magnetic-field distribution and the d-wave order parameter to have a fourfold anisotropy. It is shown that there is a strong correlation between the structure of a single vortex and the shape of the vortex lattice. Our numerical calculation indicates that the structure of the vortex lattice is always oblique except for temperatures very close to T c where it becomes triangular. The possible connection of the result with experiment is also discussed. copyright 1996 The American Physical Society

Beating motion of a circular cylinder in vortex-induced vibrations

Science.gov (United States)

Shen, Linwei; Chan, Eng-Soon; Wei, Yan

2018-04-01

In this paper, beating phenomenon of a circular cylinder in vortex-induced vibration is studied by numerical simulations in a systematic manner. The cylinder mass coefficients of 2 and 10 are considered, and the Reynolds number is 150. Two distinctive frequencies, namely cylinder oscillation and vortex shedding frequencies, are obtained from the harmonic analysis of the cylinder displacement. The result is consistent with that observed in laboratory experiments. It is found that the cylinder oscillation frequency changes with the natural frequency of the cylinder while the reduced velocity is varied. The added-mass coefficient of the cylinder in beating motion is therefore estimated. Meanwhile, the vortex shedding frequency does not change dramatically in the beating situations. In fact, it is very close to 0.2. Accordingly, the lift force coefficient has two main components associated with these two frequencies. Besides, higher harmonics of the cylinder oscillation frequency appear in the spectrum of the lift coefficient. Moreover, the vortex shedding timing is studied in the beating motion by examining the instantaneous flow fields in the wake, and two scenarios of the vortex formation are observed.

"Self-Shaping" of Multicomponent Drops.

Science.gov (United States)

Cholakova, Diana; Valkova, Zhulieta; Tcholakova, Slavka; Denkov, Nikolai; Smoukov, Stoyan K

2017-06-13

In our recent study we showed that single-component emulsion drops, stabilized by proper surfactants, can spontaneously break symmetry and transform into various polygonal shapes during cooling [ Denkov Nature 2015 , 528 , 392 - 395 ]. This process involves the formation of a plastic rotator phase of self-assembled oil molecules beneath the drop surface. The plastic phase spontaneously forms a frame of plastic rods at the oil drop perimeter which supports the polygonal shapes. However, most of the common substances used in industry appear as mixtures of molecules rather than pure substances. Here we present a systematic study of the ability of multicomponent emulsion drops to deform upon cooling. The observed trends can be summarized as follows: (1) The general drop-shape evolution for multicomponent drops during cooling is the same as with single-component drops; however, some additional shapes are observed. (2) Preservation of the particle shape upon freezing is possible for alkane mixtures with chain length difference Δn ≤ 4; for greater Δn, phase separation within the droplet is observed. (3) Multicomponent particles prepared from alkanes with Δn ≤ 4 plastify upon cooling due to the formation of a bulk rotator phase within the particles. (4) If a compound, which cannot induce self-shaping when pure, is mixed with a certain amount of a compound which induces self-shaping, then drops prepared from this mixture can also self-shape upon cooling. (5) Self-emulsification phenomena are also observed for multicomponent drops. In addition to the three recently reported mechanisms of self-emulsification [ Tcholakova Nat. Commun. 2017 , ( 8 ), 15012 ], a new (fourth) mechanism is observed upon freezing for alkane mixtures with Δn > 4. It involves disintegration of the particles due to a phase separation of alkanes upon freezing.

Numerical Simulation of the Aircraft Wake Vortex Flowfield

Science.gov (United States)

Ahmad, Nashat N.; Proctor, Fred H.; Perry, R. Brad

2013-01-01

The near wake vortex flowfield from a NACA0012 half-wing was simulated using a fully unstructured Navier-Stokes flow solver in three dimensions at a chord Reynolds number of 4.6 million and a Mach number of approximately 0.15. Several simulations were performed to examine the effect of boundary conditions, mesh resolution and turbulence scheme on the formation of wingtip vortex and its downstream propagation. The standard Spalart-Allmaras turbulence model was compared with the Dacles-Mariani and Spalart-Shur corrections for rotation and curvature effects. The simulation results were evaluated using the data from experiment performed at NASA Ames' 32in x 48in low speed wind tunnel.

Scaling during capillary thinning of particle-laden drops

Science.gov (United States)

Thete, Sumeet; Wagoner, Brayden; Basaran, Osman

2017-11-01

A fundamental understanding of drop formation is crucial in many applications such as ink-jet printing, microfluidic devices, and atomization. During drop formation, the about-to-form drop is connected to the fluid hanging from the nozzle via a thinning filament. Therefore, the physics of capillary thinning of filaments is key to understanding drop formation and has been thoroughly studied for pure Newtonian fluids using theory, simulations, and experiments. In some of the applications however, the forming drop and hence the thinning filament may contain solid particles. The thinning dynamics of such particle-laden filaments differs radically from that of particle-free filaments. Moreover, our understanding of filament thinning in the former case is poor compared to that in the latter case despite the growing interest in pinch-off of particle-laden filaments. In this work, we go beyond similar studies and experimentally explore the impact of solid particles on filament thinning by measuring both the radial and axial scalings in the neck region. The results are summarized in terms of a phase diagram of capillary thinning of particle-laden filaments.

COLLECTIVE VORTEX BEHAVIORS: DIVERSITY, PROXIMATE, AND ULTIMATE CAUSES OF CIRCULAR ANIMAL GROUP MOVEMENTS.

Science.gov (United States)

Delcourt, Johann; Bode, Nikolai W F; Denoël, Mathieu

2016-03-01

Ant mill, caterpillar circle, bat doughnut, amphibian vortex, duck swirl, and fish torus are different names for rotating circular animal formations, where individuals turn around a common center. These "collective vortex behaviors" occur at different group sizes from pairs to several million individuals and have been reported in a large number of organisms, from bacteria to vertebrates, including humans. However, to date, no comprehensive review and synthesis of the literature on vortex behaviors has been conducted. Here, we review the state of the art of the proximate and ultimate causes of vortex behaviors. The ubiquity of this behavioral phenomenon could suggest common causes or fundamental underlying principles across contexts. However, we find that a variety of proximate mechanisms give rise to vortex behaviors. We highlight the potential benefits of collective vortex behaviors to individuals involved in them. For example, in some species, vortices increase feeding efficiency and could give protection against predators. It has also been argued that vortices could improve collective decision-making and information transfer. We highlight gaps in our understanding of these ubiquitous behavioral phenomena and discuss future directions for research in vortex studies.

Spatially resolved resistivity near the vortex lattice phase transition in Bi 2Sr 2CaCu 2O 8+δ single crystals

Science.gov (United States)

Berseth, V.; Indenbom, M. V.; van der Beek, C. J.; D'Anna, G.; Benoit, W.

1997-08-01

Using a multiterminal contact configuration, we investigate the local variations of the resistivity drop near the vortex lattice first order phase transition in a very homogeneous Bi2Sr2CaCu2O8+δ (BSCCO) single crystal.

Vortex structure behind highly heated two cylinders in parallel arrangements

International Nuclear Information System (INIS)

Kurita, Eiichirou; Yahagi, Yuji

2008-01-01

Vortex structures behind twin, highly heated cylinders in parallel arrangements have been investigated experimentally. The experiments were conducted under the following conditions: cylinder diameter, D=4 mm; mean flow velocity, U ∞ =1.0 m/s; Reynolds number, Re=250; cylinder clearance, S/D=0.5 - 1.4; and cylinder heat flux, q=0 - 72.6 kW/m 2 . For S/D > 1.2, the Karman vortex street is formed alternately behind each cylinder divided on the slit flow. The slit flow velocity increases with a decrease in S/D and decreases with increasing heat flux. For S/D 2 ). As a result, the increased local kinematic viscosity and S/D play a key role for the vortex structure and formation behind arrangements of two parallel cylinders. (author)

Flexible margin kinematics and vortex formation of Aurelia aurita and Robojelly.

Science.gov (United States)

Villanueva, Alex; Vlachos, Pavlos; Priya, Shashank

2014-01-01

The development of a rowing jellyfish biomimetic robot termed as "Robojelly", has led to the discovery of a passive flexible flap located between the flexion point and bell margin on the Aurelia aurita. A comparative analysis of biomimetic robots showed that the presence of a passive flexible flap results in a significant increase in the swimming performance. In this work we further investigate this concept by developing varying flap geometries and comparing their kinematics with A. aurita. It was shown that the animal flap kinematics can be replicated with high fidelity using a passive structure and a flap with curved and tapered geometry gave the most biomimetic performance. A method for identifying the flap location was established by utilizing the bell curvature and the variation of curvature as a function of time. Flaps of constant cross-section and varying lengths were incorporated on the Robojelly to conduct a systematic study of the starting vortex circulation. Circulation was quantified using velocity field measurements obtained from planar Time Resolved Digital Particle Image Velocimetry (TRDPIV). The starting vortex circulation was scaled using a varying orifice model and a pitching panel model. The varying orifice model which has been traditionally considered as the better representation of jellyfish propulsion did not appear to capture the scaling of the starting vortex. In contrast, the pitching panel representation appeared to better scale the governing flow physics and revealed a strong dependence on the flap kinematics and geometry. The results suggest that an alternative description should be considered for rowing jellyfish propulsion, using a pitching panel method instead of the traditional varying orifice model. Finally, the results show the importance of incorporating the entire bell geometry as a function of time in modeling rowing jellyfish propulsion.

Flexible margin kinematics and vortex formation of Aurelia aurita and Robojelly.

Directory of Open Access Journals (Sweden)

Alex Villanueva

Full Text Available The development of a rowing jellyfish biomimetic robot termed as "Robojelly", has led to the discovery of a passive flexible flap located between the flexion point and bell margin on the Aurelia aurita. A comparative analysis of biomimetic robots showed that the presence of a passive flexible flap results in a significant increase in the swimming performance. In this work we further investigate this concept by developing varying flap geometries and comparing their kinematics with A. aurita. It was shown that the animal flap kinematics can be replicated with high fidelity using a passive structure and a flap with curved and tapered geometry gave the most biomimetic performance. A method for identifying the flap location was established by utilizing the bell curvature and the variation of curvature as a function of time. Flaps of constant cross-section and varying lengths were incorporated on the Robojelly to conduct a systematic study of the starting vortex circulation. Circulation was quantified using velocity field measurements obtained from planar Time Resolved Digital Particle Image Velocimetry (TRDPIV. The starting vortex circulation was scaled using a varying orifice model and a pitching panel model. The varying orifice model which has been traditionally considered as the better representation of jellyfish propulsion did not appear to capture the scaling of the starting vortex. In contrast, the pitching panel representation appeared to better scale the governing flow physics and revealed a strong dependence on the flap kinematics and geometry. The results suggest that an alternative description should be considered for rowing jellyfish propulsion, using a pitching panel method instead of the traditional varying orifice model. Finally, the results show the importance of incorporating the entire bell geometry as a function of time in modeling rowing jellyfish propulsion.

Vortex mass in a superfluid

Science.gov (United States)

Simula, Tapio

2018-02-01

We consider the inertial mass of a vortex in a superfluid. We obtain a vortex mass that is well defined and is determined microscopically and self-consistently by the elementary excitation energy of the kelvon quasiparticle localized within the vortex core. The obtained result for the vortex mass is found to be consistent with experimental observations on superfluid quantum gases and vortex rings in water. We propose a method to measure the inertial rest mass and Berry phase of a vortex in superfluid Bose and Fermi gases.

Coalescence collision of liquid drops I: Off-center collisions of equal-size drops

Directory of Open Access Journals (Sweden)

Alejandro Acevedo-Malavé

2011-09-01

Full Text Available The Smoothed Particle Hydrodynamics method (SPH is used here to model off-center collisions of equal-size liquid drops in a three-dimensional space. In this study the Weber number is calculated for several conditions of the droplets dynamics and the velocity vector fields formed inside the drops during the collision process are shown. For the permanent coalescence the evolution of the kinetic and internal energy is shown and also the approaching to equilibrium of the resulting drop. Depending of the Weber number three possible outcomes for the collision of droplets is obtained: permanent coalescence, flocculation and fragmentation. The fragmentation phenomena are modeled and the formation of small satellite drops can be seen. The ligament that is formed follows the “end pinching” mechanism and it is transformed into a flat structure.

Investigating the vortex melting phenomenon in BSCCO crystals ...

Indian Academy of Sciences (India)

reveal complex patterns in the formation and evolution of the vortex solid–liquid interface ... images of the melting process in a BSCCO crystal (Tc =90 K) of area 0.35×0.27 mm2 .... For example, at 20 Oe the valley in the form of an arc along.

Interfacial Instabilities in Evaporating Drops

Science.gov (United States)

Moffat, Ross; Sefiane, Khellil; Matar, Omar

2007-11-01

We study the effect of substrate thermal properties on the evaporation of sessile drops of various liquids. An infra-red imaging technique was used to record the interfacial temperature. This technique illustrates the non-uniformity in interfacial temperature distribution that characterises the evaporation process. Our results also demonstrate that the evaporation of methanol droplets is accompanied by the formation of wave-trains in the interfacial temperature field; similar patterns, however, were not observed in the case of water droplets. More complex patterns are observed for FC-72 refrigerant drops. The effect of substrate thermal conductivity on the structure of the complex pattern formation is also elucidated.

Front propagation in a regular vortex lattice: Dependence on the vortex structure.

Science.gov (United States)

Beauvier, E; Bodea, S; Pocheau, A

2017-11-01

We investigate the dependence on the vortex structure of the propagation of fronts in stirred flows. For this, we consider a regular set of vortices whose structure is changed by varying both their boundary conditions and their aspect ratios. These configurations are investigated experimentally in autocatalytic solutions stirred by electroconvective flows and numerically from kinematic simulations based on the determination of the dominant Fourier mode of the vortex stream function in each of them. For free lateral boundary conditions, i.e., in an extended vortex lattice, it is found that both the flow structure and the front propagation negligibly depend on vortex aspect ratios. For rigid lateral boundary conditions, i.e., in a vortex chain, vortices involve a slight dependence on their aspect ratios which surprisingly yields a noticeable decrease of the enhancement of front velocity by flow advection. These different behaviors reveal a sensitivity of the mean front velocity on the flow subscales. It emphasizes the intrinsic multiscale nature of front propagation in stirred flows and the need to take into account not only the intensity of vortex flows but also their inner structure to determine front propagation at a large scale. Differences between experiments and simulations suggest the occurrence of secondary flows in vortex chains at large velocity and large aspect ratios.

Critical phenomena in magnetic vortex formation probed by noise spectroscopy

International Nuclear Information System (INIS)

Saitoh, E.; Harii, K.; Miyajima, H.; Yamaoka, T.

2004-01-01

Transition between a vortex magnetic state and a uniform magnetic state in a Ni 81 Fe 19 mesoscopic ring has been investigated in terms of resistive-noise spectroscopy. The observed low-frequency noise exhibits critical enhancement around the magnetization saturation. This noise enhancement can be argued from the viewpoint of the critical phenomena due to the chiral-symmetry breakdown of mesoscopic magnetic-structure, which can present a typical mechanism of symmetry transition of magnetic structure in mesoscopic ferromagnets

Plasmonic vortex generator without polarization dependence

Science.gov (United States)

Wang, Han; Liu, Lixia; Liu, Chunxiang; Li, Xing; Wang, Shuyun; Xu, Qing; Teng, Shuyun

2018-03-01

In view of the limitations of vortex generators with polarization dependence at present, we propose a plasmonic vortex generator composed of rectangular holes etched in silver film, in which the optical vortex can be generated under arbitrary linearly polarized light illumination. Two sets of rectangular holes are arranged equidistantly on a circle and rotate in postulate directions. Theoretical analysis provides the design principle for the vortex generator, and numerical simulations give guidance on designating the vortex generator parameters. Experimental measurements verify the performance of the proposed vortex generator. Moreover, two alternative structures for the generation of a plasmonic vortex are also provided in this paper. The resulting perfect vortex, compact structure and flexible illumination conditions will lead to wide applications of this plasmonic vortex generator.

Roughness Effects on the Formation of a Leading Edge Vortex

Science.gov (United States)

Elliott, Cassidy; Lang, Amy; Wahidi, Redha; Wilroy, Jacob

2016-11-01

Microscopic scales cover the wings of Monarch butterflies, creating a patterned surface. This patterning is an important natural flow control mechanism that is thought to delay the growth of the leading edge vortex (LEV) produced by the flapping motion of a wing. The increased skin friction caused by the scales leads to a weaker LEV being shed into the butterfly's wake, lessening drag and increasing flight efficiency. To test this theory, a plate of random roughness was designed in SolidWorks and printed on the Objet 30 Pro 3D printer. A 2x3x5 cubic foot tow tank was used to test the rough plate at Reynold's numbers of 1500, 3000, and 6000 (velocities of 8, 16, and 32 mm/s) at an angle of attack of 45 degrees. Particle Image Velocimetry (PIV) captured images of the LEV generated by the plate when towed upwards through the particle-seeded flow. Codes written in MatLab were used to automatically track and determine the strength of the LEV. Circulation values for the randomly-rough plate were then compared to the same values generated in a previous experiment that used a smooth plate and a grooved plate to determine the effect of the patterning on vortex development. Funding provided by NSF REU site Grant EEC 1358991 and CBET 1628600.

The singing vortex

Science.gov (United States)

Arndt, R.; Pennings, P.; Bosschers, J.; van Terwisga, T.

2015-01-01

Marine propellers display several forms of cavitation. Of these, propeller-tip vortex cavitation is one of the important factors in propeller design. The dynamic behaviour of the tip vortex is responsible for hull vibration and noise. Thus, cavitation in the vortices trailing from tips of propeller blades has been studied extensively. Under certain circumstances cavitating vortices have been observed to have wave-like disturbances on the surfaces of vapour cores. Intense sound at discrete frequencies can result from a coupling between tip vortex disturbances and oscillating sheet cavitation on the surfaces of the propeller blades. This research article focuses on the dynamics of vortex cavitation and more in particular on the energy and frequency content of the radiated pressures. PMID:26442147

DNS of droplet-vortex interaction with a Karman vortex street

International Nuclear Information System (INIS)

Burger, M.; Schmehl, R.; Koch, R.; Wittig, S.; Bauer, H.-J.

2006-01-01

Predicting fuel spray interaction with large scale vortex structures still is a major challenge for state-of-the-art CFD codes. In order to elucidate the mechanisms involved, a fundamental study has been carried out in which the interaction of water droplets with a Karman vortex street is investigated. The disperse two-phase flow around a cylinder has been computed taking into account the mass, momentum and heat transfer between both phases. Flow conditions are chosen such that large scale vortices are generated by periodic flow separations of the well known Karman vortex street. A homogeneous distribution of water droplets is injected into the hot air up-stream of the computational domain. The mixing process as well as the impact of the droplets on the gas phase instabilities is analyzed in the downstream region where large scale vortex structures are present

Peculiarities of binding composition production in vortex jet mill

Science.gov (United States)

Zagorodnyuk, L. Kh; Lesovik, V. S.; Sumskoy, D. A.; Elistratkin, M. Yu; Makhortov, D. S.

2018-03-01

The article investigates the disintegration of perlite production waste in a vortex jet mill; the regularities of milling were established. Binding compositions were obtained at different ratios of cement vs. perlite sand production waste in the vortex jet mill in various milling regimes. The peculiarities of milling processes were studied, and technological and physicomechanical properties of the binding compositions were determined as well. The microstructure of the cement stones made of activated Portland cement and binding compositions in the vortex jet mill was elucidated by electron microscopy. The open pores of the cement-binding compositions prepared using perlite fillers were found to be filled by newgrowths at different stages of collective growth. The microstructure of the binding compositions is dense due to rationally proportioned composition, effective mineral filler— perlite waste — that creates additional substrates for internal composite microstructure formation, mechanochemical activation of raw mixture, which allows obtaining composites with required properties.

String cavitation formation inside fuel injectors

Science.gov (United States)

Reid, B. A.; Gavaises, M.; Mitroglou, N.; Hargrave, G. K.; Garner, C. P.; McDavid, R. M.

2015-12-01

The formation of vortex or ‘string’ cavitation has been visualised at pressures up to 2000 bar in an automotive-sized optical diesel fuel injector nozzle. The multi-hole nozzle geometry studied allowed observation of the hole-to-hole vortex interaction and, in particular, that of a bridging vortex in the sac region between the holes. Above a threshold Reynolds number, their formation and appearance during a 2 ms injection event was repeatable and independent of upstream pressure and cavitation number. In addition, two different hole layouts and threedimensional flow simulations have been employed to describe how, the relative positions of adjacent holes influenced the formation and hole-to-hole interaction of the observed string cavitation vortices, with good agreement between the experimental and simulation results being achieved.

Aircraft Wake Vortex Measurement with Coherent Doppler Lidar

Directory of Open Access Journals (Sweden)

Wu Songhua

2016-01-01

Full Text Available Aircraft vortices are generated by the lift-producing surfaces of the aircraft. The variability of near-surface conditions can change the drop rate and cause the cell of the wake vortex to twist and contort unpredictably. The pulsed Coherent Doppler Lidar Detection and Ranging is an indispensable access to real aircraft vortices behavior which transmitting a laser beam and detecting the radiation backscattered by atmospheric aerosol particles. Experiments for Coherent Doppler Lidar measurement of aircraft wake vortices has been successfully carried out at the Beijing Capital International Airport (BCIA. In this paper, the authors discuss the Lidar system, the observation modes carried out in the measurements at BCIA and the characteristics of vortices.

Experimental Setup For Study of Drop Deformation In Air Flow

Directory of Open Access Journals (Sweden)

Basalaev Sergey

2017-01-01

Full Text Available Experimental study for study of deformation of drops in air flow is considered. Experimental setup includes a module for obtaining the drops, an air flow system and measuring system. Module for formation of drops is in the form of vertically arranged dropper with capillary with the possibility of formation of fixed drops. Air flow supply system comprises an air pump coupled conduit through a regulating valve with a cylindrical pipe, installed coaxially with dropper. The measuring system includes the video camera located with possibility of visualization of drop and the Pitot gage for measurement of flow rate of air located in the output section of branch pipe. This experimental setup allows to provide reliable and informative results of the investigation of deformation of drops in the air flow.

Dust grain charges in a nuclear-track plasma and the formation of dynamic vortex dust structures

International Nuclear Information System (INIS)

Rykov, V.A.; Khudyakov, A.V.; Filinov, V.S.; Vladimirov, V.I.; Deputatova, L.V.; Krutov, D.V.; Nefedov, A.P.; Fortov, V.E.

2002-01-01

Results are presented from Monte Carlo calculations of the electric charge of dust grains in a plasma produced during the slowing down of the radioactive decay products of californium nuclei in neon. The dust grain charging is explained for the first time as being due to the drift of electrons and ions in an external electric field. It is shown that the charges of the grains depend on their coordinates and strongly fluctuate with time. The time-averaged grain charges agree with the experimental data obtained on ordered liquidlike dust structures in a nuclear-track plasma. The time-averaged dust grain charges are used to carry out computer modeling of the formation of dynamic vortex structures observed in experiments. Evidence is obtained of the fact that the electrostatic forces experienced by the dust grains are potential in character

Cylindrical vortex wake model: right cylinder

DEFF Research Database (Denmark)

Branlard, Emmanuel; Gaunaa, Mac

2015-01-01

The vortex system consisting of a bound vortex disk, a root vortex and a vortex cylinder as introduced by Joukowski in 1912 is further studied in this paper. This system can be used for simple modeling of rotors (e.g. wind turbines) with infinite number of blades and finite tip-speed ratios....... For each vortex element, the velocity components in all directions and in the entire domain are computed analytically in a novel approach. In particular, the velocity field from the vortex actuator disk is derived for the first time. The induction from the entire vortex system is studied and is seen...

A vortex ring interacting with a vortex filament and its deformation near the two-dimensional stagnation point

International Nuclear Information System (INIS)

Kiya, M.; Sato, T.

1986-01-01

In this paper the interaction between vortex filaments and vortex rings and the deformation of vortex rings near the two-dimensional stagnation point are simulated by a three-dimensional vortex method. The two problems are respectively concerned with the effect of free-stream turbulence on turbulent plane mixing layers and the production of turbulence by the vortex stretching near saddles associated with large-scale coherent structures. The authors assume that the first step to understand the free-stream turbulence effect is to study the interaction between a vortex ring and a vortex filament and that the process of deformation of a vortex ring gives us a clue to understand physical processes occurring near the saddles

Imaging of artificially induced vortex structures

International Nuclear Information System (INIS)

Fasano, Yanina; Menghini, M.; Cruz, F. de la

2004-01-01

The combination of engineered pinning potentials in superconducting crystals, the detection of the liquid-solid vortex transition and the observation of the vortex structure with single vortex sensitivity allow the microscopic analysis of the response of 3D elastic systems to the presence of these potentials. In this work we review recent results obtained by a combination of those techniques studying different vortex structure induced transformations. On the one hand, we have visualized the transformation, along the vortex direction, of a bulk vortex single crystal with hexagonal symmetry into another crystal with square symmetry induced by an engineered Fe-dot lattice deposited on a surface of the vortex single crystal. On the other hand, we found an infrequent first-order phase transition where a vortex liquid under the presence of a random correlated potential (columnar defects) transforms into a vortex solid with no change of topological order

Unsteady behavior of leading-edge vortex and diffuser stall in a centrifugal compressor with vaned diffuser

Science.gov (United States)

Fujisawa, Nobumichi; Hara, Shotaro; Ohta, Yutaka

2016-02-01

The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge (i.e., the leading-edge vortex (LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading- edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.

Nanoscale strain-induced pair suppression as a vortex-pinning mechanism in high-temperature superconductors

International Nuclear Information System (INIS)

Llordes, Anna; Palau, A.; Gazquez, J.; Coll, M.; Vlad, R.; Pomar, A.; Arbiol, Jordi; Guzman, Roger; Ye, S.; Rouco, V.; Sandiumenge, Felip; Ricart, Susagna; Puig, Teresa; Varela del Arco, Maria; Chataigner, D.; Vanacken, J.; Gutierrez, J.; Moschalkov, V.; Deutscher, G.; Magen Dominguez, Cesar; Obradors, Xavier

2012-01-01

Boosting large-scale superconductor applications require nanostructured conductors with artificial pinning centres immobilizing quantized vortices at high temperature and magnetic fields. Here we demonstrate a highly effective mechanism of artificial pinning centers in solution-derived high-temperature superconductor nanocomposites through generation of nanostrained regions where Cooper pair formation is suppressed. The nanostrained regions identified from transmission electron microscopy devise a very high concentration of partial dislocations associated with intergrowths generated between the randomly oriented nanodots and the epitaxial YBa 2 Cu 3 O 7 matrix. Consequently, an outstanding vortex-pinning enhancement correlated to the nanostrain is demonstrated for four types of randomly oriented nanodot, and a unique evolution towards an isotropic vortex-pinning behaviour, even in the effective anisotropy, is achieved as the nanostrain turns isotropic. We suggest a new vortex-pinning mechanism based on the bond-contraction pairing model, where pair formation is quenched under tensile strain, forming new and effective core-pinning regions.

Persistence of metastable vortex lattice domains in MgB2 in the presence of vortex motion.

Science.gov (United States)

Rastovski, C; Schlesinger, K J; Gannon, W J; Dewhurst, C D; DeBeer-Schmitt, L; Zhigadlo, N D; Karpinski, J; Eskildsen, M R

2013-09-06

Recently, extensive vortex lattice metastability was reported in MgB2 in connection with a second-order rotational phase transition. However, the mechanism responsible for these well-ordered metastable vortex lattice phases is not well understood. Using small-angle neutron scattering, we studied the vortex lattice in MgB2 as it was driven from a metastable to the ground state through a series of small changes in the applied magnetic field. Our results show that metastable vortex lattice domains persist in the presence of substantial vortex motion and directly demonstrate that the metastability is not due to vortex pinning. Instead, we propose that it is due to the jamming of counterrotated vortex lattice domains which prevents a rotation to the ground state orientation.

Vortex survival in 3D self-gravitating accretion discs

Science.gov (United States)

Lin, Min-Kai; Pierens, Arnaud

2018-04-01

Large-scale, dust-trapping vortices may account for observations of asymmetric protoplanetary discs. Disc vortices are also potential sites for accelerated planetesimal formation by concentrating dust grains. However, in 3D discs vortices are subject to destructive `elliptic instabilities', which reduces their viability as dust traps. The survival of vortices in 3D accretion discs is thus an important issue to address. In this work, we perform shearing box simulations to show that disc self-gravity enhances the survival of 3D vortices, even when self-gravity is weak in the classic sense (e.g. with a Toomre Q ≃ 5). We find a 3D, self-gravitating vortex can grow on secular timescales in spite of the elliptic instability. The vortex aspect-ratio decreases as it strengthens, which feeds the elliptic instability. The result is a 3D vortex with a turbulent core that persists for ˜103 orbits. We find when gravitational and hydrodynamic stresses become comparable, the vortex may undergo episodic bursts, which we interpret as interaction between elliptic and gravitational instabilities. We estimate the distribution of dust particles in self-gravitating, turbulent vortices. Our results suggest large-scale vortices in protoplanetary discs are more easily observed at large radii.

Effects of hanging drop culture conditions on embryoid body formation and neuronal cell differentiation using mouse embryonic stem cells: optimization of culture conditions for the formation of well-controlled embryoid bodies.

Science.gov (United States)

Ohnuki, Yoshitsugu; Kurosawa, Hiroshi

2013-05-01

Hanging drop (HD) cultures were carried out with a drop volume of either 20 or 30 μl. An incubation period of 3 days was determined to be appropriate for the formation of well-controlled embryoid bodies (EBs), and the initial cell number was identified as the most critical factor in the growth and neuronal cell differentiation of EBs. Copyright © 2012 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.

Propagation of optical vortex beams and nucleation of vortex-antivortex pairs in disordered nonlinear photonic lattices

International Nuclear Information System (INIS)

Cho, Yeong-Kwon; Kim, Ki-Hong

2014-01-01

The propagation of optical vortex beams through disordered nonlinear photonic lattices is numerically studied. The vortex beams are generated by using a superposition of several Gaussian laser beams arranged in a radially-symmetric manner. The paraxial nonlinear Schroedinger equation describing the longitudinal propagation of the beam array through nonlinear triangular photonic lattices with two-dimensional disorder is solved numerically by using the split-step Fourier method. We find that due to the spatial disorder, the vortex beam is destabilized after propagating a finite distance and new vortex-antivortex pairs are nucleated at the positions of perfect destructive interference. We also find that in the presence of a self-focusing nonlinearity, the vortex-antivortex pair nucleation is suppressed and the vortex beam becomes more stable, while a self-defocusing nonlinearity enhances the vortex-antivortex pair nucleation.

Drop dynamics on a stretched viscoelastic filament: An experimental study

Science.gov (United States)

Peixinho, Jorge; Renoult, Marie-Charlotte; Crumeyrolle, Olivier; Mutabazi, Innocent

2016-11-01

Capillary pressure can destabilize a thin liquid filament during breakup into a succession of drops. Besides, the addition of a linear, high molecular weight, flexible and soluble polymer is enough to modify the morphology of this instability. In the time period preceding the breakup, the development of beads-on-a-string structures where drops are connected by thin threads is monitored. The drops dynamics involve drop formation, drop migration and drop coalescence. Experiments using a high-speed camera on stretched bridges of viscoelastic polymeric solutions were conducted for a range of viscosities and polymer concentrations. The rheological properties of the solutions are also quantified through conventional shear rheology and normal stress difference. The overall goal of this experimental investigation is to gain more insight into the formation and time evolution of the drops. The project BIOENGINE is co-financed by the European Union with the European regional development fund and by the Normandie Regional Council.

A Carbon Dioxide Bubble-Induced Vortex Triggers Co-Assembly of Nanotubes with Controlled Chirality.

Science.gov (United States)

Zhang, Ling; Zhou, Laicheng; Xu, Na; Ouyang, Zhenjie

2017-07-03

It is challenging to prepare co-organized nanotube systems with controlled nanoscale chirality in an aqueous liquid flow field. Such systems are responsive to a bubbled external gas. A liquid vortex induced by bubbling carbon dioxide (CO 2 ) gas was used to stimulate the formation of nanotubes with controlled chirality; two kinds of achiral cationic building blocks were co-assembled in aqueous solution. CO 2 -triggered nanotube formation occurs by formation of metastable intermediate structures (short helical ribbons and short tubules) and by transition from short tubules to long tubules in response to chirality matching self-assembly. Interestingly, the chirality sign of these assemblies can be selected for by the circulation direction of the CO 2 bubble-induced vortex during the co-assembly process. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Delayed frost growth on jumping-drop superhydrophobic surfaces.

Science.gov (United States)

Boreyko, Jonathan B; Collier, C Patrick

2013-02-26

Self-propelled jumping drops are continuously removed from a condensing superhydrophobic surface to enable a micrometric steady-state drop size. Here, we report that subcooled condensate on a chilled superhydrophobic surface are able to repeatedly jump off the surface before heterogeneous ice nucleation occurs. Frost still forms on the superhydrophobic surface due to ice nucleation at neighboring edge defects, which eventually spreads over the entire surface via an interdrop frost wave. The growth of this interdrop frost front is shown to be up to 3 times slower on the superhydrophobic surface compared to a control hydrophobic surface, due to the jumping-drop effect dynamically minimizing the average drop size and surface coverage of the condensate. A simple scaling model is developed to relate the success and speed of interdrop ice bridging to the drop size distribution. While other reports of condensation frosting on superhydrophobic surfaces have focused exclusively on liquid-solid ice nucleation for isolated drops, these findings reveal that the growth of frost is an interdrop phenomenon that is strongly coupled to the wettability and drop size distribution of the surface. A jumping-drop superhydrophobic condenser minimized frost formation relative to a conventional dropwise condenser in two respects: preventing heterogeneous ice nucleation by continuously removing subcooled condensate, and delaying frost growth by limiting the success of interdrop ice bridge formation.

A Lagrangian analysis of a two-dimensional airfoil with vortex shedding

Energy Technology Data Exchange (ETDEWEB)

Lipinski, Doug; Cardwell, Blake; Mohseni, Kamran [Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO 80309-0429 (United States)], E-mail: Mohseni@colorado.edu

2008-08-29

Using invariant material manifolds and flow topology, the flow behavior and structure of flow around a two-dimensional Eppler 387 airfoil is examined with an emphasis on vortex shedding and the time-dependent reattachment profile. The examination focuses on low Reynolds number (Re = 60 000) flow at several angles of attack. Using specialized software, we identify invariant manifolds in the flow and use these structures to illuminate the process of vortex formation and the periodic behavior of the reattachment profile. Our analysis concludes with a topological view of the flow, including fixed points and a discussion of phase plots and the frequency spectrum of several key points in the flow. The behavior of invariant manifolds directly relates to the flow topology and illuminates some aspects seen in phase space during vortex shedding. Furthermore, it highlights the reattachment behavior in ways not seen before.

A Lagrangian analysis of a two-dimensional airfoil with vortex shedding

International Nuclear Information System (INIS)

Lipinski, Doug; Cardwell, Blake; Mohseni, Kamran

2008-01-01

Using invariant material manifolds and flow topology, the flow behavior and structure of flow around a two-dimensional Eppler 387 airfoil is examined with an emphasis on vortex shedding and the time-dependent reattachment profile. The examination focuses on low Reynolds number (Re = 60 000) flow at several angles of attack. Using specialized software, we identify invariant manifolds in the flow and use these structures to illuminate the process of vortex formation and the periodic behavior of the reattachment profile. Our analysis concludes with a topological view of the flow, including fixed points and a discussion of phase plots and the frequency spectrum of several key points in the flow. The behavior of invariant manifolds directly relates to the flow topology and illuminates some aspects seen in phase space during vortex shedding. Furthermore, it highlights the reattachment behavior in ways not seen before

DEVELOPMENT OF A VORTEX CONTAINMENT COMBUSTOR FOR COAL COMBUSTION SYTEMS

Science.gov (United States)

The report describes the development of a vortex containment combustor (VCC) for coal combustion systems, designed to solve major problems facing the conversion of oil- and gas-fired boilers to coal (e.g., derating, inorganic impurities in coal, and excessive formation of NOx and...

Vortex and half-vortex dynamics in a nonlinear spinor quantum fluid.

Science.gov (United States)

Dominici, Lorenzo; Dagvadorj, Galbadrakh; Fellows, Jonathan M; Ballarini, Dario; De Giorgi, Milena; Marchetti, Francesca M; Piccirillo, Bruno; Marrucci, Lorenzo; Bramati, Alberto; Gigli, Giuseppe; Szymańska, Marzena H; Sanvitto, Daniele

2015-12-01

Vortices are archetypal objects that recur in the universe across the scale of complexity, from subatomic particles to galaxies and black holes. Their appearance is connected with spontaneous symmetry breaking and phase transitions. In Bose-Einstein condensates and superfluids, vortices are both point-like and quantized quasiparticles. We use a two-dimensional (2D) fluid of polaritons, bosonic particles constituted by hybrid photonic and electronic oscillations, to study quantum vortex dynamics. Polaritons benefit from easiness of wave function phase detection, a spinor nature sustaining half-integer vorticity, strong nonlinearity, and tuning of the background disorder. We can directly generate by resonant pulsed excitations a polariton condensate carrying either a full or half-integer vortex as initial condition and follow their coherent evolution using ultrafast imaging on the picosecond scale. The observations highlight a rich phenomenology, such as the spiraling of the half-vortex and the joint path of the twin charges of a full vortex, until the moment of their splitting. Furthermore, we observe the ordered branching into newly generated secondary couples, associated with the breaking of radial and azimuthal symmetries. This allows us to devise the interplay of nonlinearity and sample disorder in shaping the fluid and driving the vortex dynamics. In addition, our observations suggest that phase singularities may be seen as fundamental particles whose quantized events span from pair creation and recombination to 2D+t topological vortex strings.

Optimal formation of genetically modified and functional pancreatic islet spheroids by using hanging-drop strategy.

Science.gov (United States)

Kim, H J; Alam, Z; Hwang, J W; Hwang, Y H; Kim, M J; Yoon, S; Byun, Y; Lee, D Y

2013-03-01

Rejection and hypoxia are important factors causing islet loss at an early stage after pancreatic islet transplantation. Recently, islets have been dissociated into single cells for reaggregation into so-called islet spheroids. Herein, we used a hanging-drop strategy to form islet spheroids to achieve functional equivalence to intact islets. To obtain single islet cells, we dissociated islets with trypsin-EDTA digestion for 10 minutes. To obtain spheroids, we dropped various numbers of single cells (125, 250, or 500 cells/30 μL drop) onto a Petri dish, that was inverted for incubation in humidified air containing 5% CO(2) at 37 °C for 7 days. The aggregated spheroids in the droplets were harvested for further culture. The size of the aggregated islet spheroids depended on the number of single cells (125-500 cells/30 μL droplet). Their morphology was similar to that of intact islets without any cellular damage. When treated with various concentrations of glucose to evaluate responsiveness, their glucose-mediated stimulation index value was similar to that of intact islets, an observation that was attributed to strong cell-to-cell interactions in islet spheroids. However, islet spheroids aggregated in general culture dishes showed abnormal glucose responsiveness owing to weak cell-to-cell interactions. Cell-to-cell interactions in islet spheroids were confirmed with an anti-connexin-36 monoclonal antibody. Finally, nonviral poly(ethylene imine)-mediated interleukin-10 cytokine gene delivered beforehand into dissociated single cells before formation of islet spheroids increased the gene transfection efficacy and interleukin-10 secretion from islet spheroids >4-fold compared with intact islets. These results demonstrated the potential application of genetically modified, functional islet spheroids with of controlled size and morphology using an hanging-drop technique. Copyright © 2013 Elsevier Inc. All rights reserved.

Vortex generation and wave-vortex interaction over a concave plate with roughness and suction

Science.gov (United States)

Bertolotti, Fabio

1993-01-01

The generation and amplification of vortices by surface homogeneities, both in the form of surface waviness and of wall-normal velocity, is investigated using the nonlinear parabolic stability equations. Transients and issues of algebraic growth are avoided through the use of a similarity solution as initial condition for the vortex. In the absence of curvature, the vortex decays as the square root of 1/x when flowing over streamwise aligned riblets of constant height, and grows as the square root of x when flowing over a corresponding streamwise aligned variation of blowing/suction transpiration velocity. However, in the presence of wall inhomogeneities having both streamwise and spanwise periodicity, the growth of the vortex can be much larger. In the presence of curvature, the vortex develops into a Gortler vortex. The 'direct' and 'indirect' interaction mechanisms possible in wave-vortex interaction are presented. The 'direct' interaction does not lead to strong resonance with the flow conditions investigated. The 'indirect' interaction leads to K-type transition.

Manipulation of vortex rings for flow control

International Nuclear Information System (INIS)

Toyoda, Kuniaki; Hiramoto, Riho

2009-01-01

This paper reviews the dynamics of vortex rings and the control of flow by the manipulation of vortex rings. Vortex rings play key roles in many flows; hence, the understanding of the dynamics of vortex rings is crucial for scientists and engineers dealing with flow phenomena. We describe the structures and motions of vortex rings in circular and noncircular jets, which are typical examples of flows evolving into vortex rings. For circular jets the mechanism of evolving, merging and breakdown of vortex rings is described, and for noncircular jets the dynamics of three-dimensional deformation and interaction of noncircular vortex rings under the effect of self- and mutual induction is discussed. The application of vortex-ring manipulation to the control of various flows is reviewed with successful examples, based on the relationship between the vortex ring dynamics and the flow properties. (invited paper)

Optical vortex scanning inside the Gaussian beam

International Nuclear Information System (INIS)

Masajada, J; Leniec, M; Augustyniak, I

2011-01-01

We discussed a new scanning method for optical vortex-based scanning microscopy. The optical vortex is introduced into the incident Gaussian beam by a vortex lens. Then the beam with the optical vortex is focused by an objective and illuminates the sample. By changing the position of the vortex lens we can shift the optical vortex position at the sample plane. By adjusting system parameters we can get 30 times smaller shift at the sample plane compared to the vortex lens shift. Moreover, if the range of vortex shifts is smaller than 3% of the beam radius in the sample plane the amplitude and phase distribution around the phase dislocation remains practically unchanged. Thus we can scan the sample topography precisely with an optical vortex

Multiple helical modes of vortex breakdown

DEFF Research Database (Denmark)

Sørensen, Jens Nørkær; Naumov, I. V.; Okulov, Valery

2011-01-01

Experimental observations of vortex breakdown in a rotating lid-driven cavity are presented. The results show that vortex breakdown for cavities with high aspect ratios is associated with the appearance of stable helical vortex multiplets. By using results from stability theory generalizing Kelvi......’s problem on vortex polygon stability, and systematically exploring the cavity flow, we succeeded in identifying two new stable vortex breakdown states consisting of triple and quadruple helical multiplets....

Calcium-Phosphate-Osteopontin Particles Reduce Biofilm Formation and pH Drops in in situ Grown Dental Biofilms.

Science.gov (United States)

Schlafer, Sebastian; Ibsen, Casper J S; Birkedal, Henrik; Nyvad, Bente

2017-01-01

This 2-period crossover study investigated the effect of calcium-phosphate-osteopontin particles on biofilm formation and pH in 48-h biofilms grown in situ. Bovine milk osteopontin is a highly phosphorylated glycoprotein that has been shown to interfere with bacterial adhesion to salivary-coated surfaces. Calcium-phosphate-osteopontin particles have been shown to reduce biofilm formation and pH drops in a 5-species laboratory model of dental biofilm without affecting bacterial viability. Here, smooth surface biofilms from 10 individuals were treated ex vivo 6 times/day for 30 min with either calcium-phosphate-osteopontin particles or sterile saline. After growth, the amount of biofilm formed was determined by confocal microscopy, and pH drops upon exposure to glucose were monitored using confocal-microscopy-based pH ratiometry. A total of 160 biofilms were analysed. No adverse effects of repeated ex vivo treatment with calcium-phosphate-osteopontin particles were observed. Particle treatment resulted in a 32% lower amount of biofilm formed (p Biofilm pH was significantly higher upon particle treatment, both shortly after the addition of glucose and after 30 min of incubation with glucose (p biofilms as well as the remineralizing potential of the particles. © 2016 S. Karger AG, Basel.

Cryptanalysis of Vortex

DEFF Research Database (Denmark)

Aumasson, Jean-Philippe; Dunkelman, Orr; Mendel, Florian

2009-01-01

Vortex is a hash function that was first presented at ISC'2008, then submitted to the NIST SHA-3 competition after some modifications. This paper describes several attacks on both versions of Vortex, including collisions, second preimages, preimages, and distinguishers. Our attacks exploit flaws...

Mechanism of transient force augmentation varying with two distinct timescales for interacting vortex rings

Science.gov (United States)

Fu, Zhidong; Qin, Suyang; Liu, Hong

2014-01-01

The dynamics of dual vortex ring flows is studied experimentally and numerically in a model system that consists of a piston-cylinder apparatus. The flows are generated by double identical strokes which have the velocity profile characterized by the sinusoidal function of half the period. By calculating the total wake impulse in two strokes in the experiments, it is found that the average propulsive force increases by 50% in the second stroke for the sufficiently small stroke length, compared with the first stroke. In the numerical simulations, two types of transient force augmentation are revealed, there being the transient force augmentation for the small stroke lengths and the absolute transient force augmentation for the large stroke lengths. The relative transient force augmentation increases to 78% for L/D = 1, while the absolute transient force augmentation for L/D = 4 is twice as much as that for L/D = 1. Further investigation demonstrates that the force augmentation is attributed to the interaction between vortex rings, which induces transport of vortex impulse and more evident fluid entrainment. The critical situation of vortex ring separation is defined and indicated, with vortex spacing falling in a narrow gap when the stroke lengths vary. A new model is proposed concerning the limiting process of impulse, further suggesting that apart from vortex formation timescale, vortex spacing should be interpreted as an independent timescale to reflect the dynamics of vortex interaction.

An Organic Vortex Laser.

Science.gov (United States)

Stellinga, Daan; Pietrzyk, Monika E; Glackin, James M E; Wang, Yue; Bansal, Ashu K; Turnbull, Graham A; Dholakia, Kishan; Samuel, Ifor D W; Krauss, Thomas F

2018-03-27

Optical vortex beams are at the heart of a number of novel research directions, both as carriers of information and for the investigation of optical activity and chiral molecules. Optical vortex beams are beams of light with a helical wavefront and associated orbital angular momentum. They are typically generated using bulk optics methods or by a passive element such as a forked grating or a metasurface to imprint the required phase distribution onto an incident beam. Since many applications benefit from further miniaturization, a more integrated yet scalable method is highly desirable. Here, we demonstrate the generation of an azimuthally polarized vortex beam directly by an organic semiconductor laser that meets these requirements. The organic vortex laser uses a spiral grating as a feedback element that gives control over phase, handedness, and degree of helicity of the emitted beam. We demonstrate vortex beams up to an azimuthal index l = 3 that can be readily multiplexed into an array configuration.

Pattern formation due to non-linear vortex diffusion

Science.gov (United States)

Wijngaarden, Rinke J.; Surdeanu, R.; Huijbregtse, J. M.; Rector, J. H.; Dam, B.; Einfeld, J.; Wördenweber, R.; Griessen, R.

Penetration of magnetic flux in YBa 2Cu 3O 7 superconducting thin films in an external magnetic field is visualized using a magneto-optic technique. A variety of flux patterns due to non-linear vortex diffusion is observed: (1) Roughening of the flux front with scaling exponents identical to those observed in burning paper including two distinct regimes where respectively spatial disorder and temporal disorder dominate. In the latter regime Kardar-Parisi-Zhang behavior is found. (2) Fractal penetration of flux with Hausdorff dimension depending on the critical current anisotropy. (3) Penetration as ‘flux-rivers’. (4) The occurrence of commensurate and incommensurate channels in films with anti-dots as predicted in numerical simulations by Reichhardt, Olson and Nori. It is shown that most of the observed behavior is related to the non-linear diffusion of vortices by comparison with simulations of the non-linear diffusion equation appropriate for vortices.

Dynamic signatures of driven vortex motion.

Energy Technology Data Exchange (ETDEWEB)

Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M.; Safar, H.

1999-09-16

We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.

Insights from the pollination drop proteome and the ovule transcriptome of Cephalotaxus at the time of pollination drop production.

Science.gov (United States)

Pirone-Davies, Cary; Prior, Natalie; von Aderkas, Patrick; Smith, Derek; Hardie, Darryl; Friedman, William E; Mathews, Sarah

2016-05-01

Many gymnosperms produce an ovular secretion, the pollination drop, during reproduction. The drops serve as a landing site for pollen, but also contain a suite of ions and organic compounds, including proteins, that suggests diverse roles for the drop during pollination. Proteins in the drops of species of Chamaecyparis, Juniperus, Taxus, Pseudotsuga, Ephedra and Welwitschia are thought to function in the conversion of sugars, defence against pathogens, and pollen growth and development. To better understand gymnosperm pollination biology, the pollination drop proteomes of pollination drops from two species of Cephalotaxus have been characterized and an ovular transcriptome for C. sinensis has been assembled. Mass spectrometry was used to identify proteins in the pollination drops of Cephalotaxus sinensis and C. koreana RNA-sequencing (RNA-Seq) was employed to assemble a transcriptome and identify transcripts present in the ovules of C. sinensis at the time of pollination drop production. About 30 proteins were detected in the pollination drops of both species. Many of these have been detected in the drops of other gymnosperms and probably function in defence, polysaccharide metabolism and pollen tube growth. Other proteins appear to be unique to Cephalotaxus, and their putative functions include starch and callose degradation, among others. Together, the proteins appear either to have been secreted into the drop or to occur there due to breakdown of ovular cells during drop production. Ovular transcripts represent a wide range of gene ontology categories, and some may be involved in drop formation, ovule development and pollen-ovule interactions. The proteome of Cephalotaxus pollination drops shares a number of components with those of other conifers and gnetophytes, including proteins for defence such as chitinases and for carbohydrate modification such as β-galactosidase. Proteins likely to be of intracellular origin, however, form a larger component of drops

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

International Nuclear Information System (INIS)

Gerlach, Angela; Preuss, Enrico; Thamsen, Paul Uwe; Lykholt-Ustrup, Flemming

2017-01-01

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation

Numerical simulations of the internal flow pattern of a vortex pump compared to the Hamel-Oseen vortex

Energy Technology Data Exchange (ETDEWEB)

Gerlach, Angela; Preuss, Enrico; Thamsen, Paul Uwe [Institute of Fluid System Dynamics, Technische Universitaet, Berlin (Germany); Lykholt-Ustrup, Flemming [Grundfos Holding A/S, Bjerringbro (Denmark)

2017-04-15

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation.

Coherent vortex structures in fluids and plasmas

CERN Document Server

Tur, Anatoli

2017-01-01

This monograph introduces readers to the hydrodynamics of vortex formation, and reviews the last decade of active research in the field, offering a unique focus on research topics at the crossroads of traditional fluids and plasmas. Vortices are responsible for the process of macroscopic transport of momentum, energy and mass, and are formed as the result of spontaneous self-organization. Playing an important role in nature and technology, localized, coherent vortices are regularly observed in shear flows, submerged jets, afterbody flows and in atmospheric boundary layers, sometimes taking on the form of vortex streets. In addition, the book addresses a number of open issues, including but not limited to: which singularities are permitted in a 2D Euler equation besides point vortices? Which other, even more complex, localized vortices could be contained in the Euler equation? How do point vortices interact with potential waves?

Effects of parallel dynamics on vortex structures in electron temperature gradient driven turbulence

International Nuclear Information System (INIS)

Nakata, M.; Watanabe, T.-H.; Sugama, H.; Horton, W.

2011-01-01

Vortex structures and related heat transport properties in slab electron temperature gradient (ETG) driven turbulence are comprehensively investigated by means of nonlinear gyrokinetic Vlasov simulations, with the aim of elucidating the underlying physical mechanisms of the transition from turbulent to coherent states. Numerical results show three different types of vortex structures, i.e., coherent vortex streets accompanied with the transport reduction, turbulent vortices with steady transport, and a zonal-flow-dominated state, depending on the relative magnitude of the parallel compression to the diamagnetic drift. In particular, the formation of coherent vortex streets is correlated with the strong generation of zonal flows for the cases with weak parallel compression, even though the maximum growth rate of linear ETG modes is relatively large. The zonal flow generation in the ETG turbulence is investigated by the modulational instability analysis with a truncated fluid model, where the parallel dynamics such as acoustic modes for electrons is incorporated. The modulational instability for zonal flows is found to be stabilized by the effect of the finite parallel compression. The theoretical analysis qualitatively agrees with secondary growth of zonal flows found in the slab ETG turbulence simulations, where the transition of vortex structures is observed.

Two secondary drops

Indian Academy of Sciences (India)

Figure shows formation of two secondary drops of unequal size and their merger. The process is same as the earlier process until t= 0.039 Tc with necking occurring at two places, one at the bottom of the column and the other at the middle. The necking at the middle of the liquid column is due to Raleigh instability.

Aircraft Wake Vortex Deformation in Turbulent Atmosphere

OpenAIRE

Hennemann, Ingo; Holzaepfel, Frank

2007-01-01

Large-scale distortion of aircraft wake vortices appears to play a crucial role for aircraft safety during approach and landing. Vortex distortion is investigated based on large eddy simulations of wake vortex evolution in a turbulent atmosphere. A vortex identification method is developed that can be adapted to the vortex scales of interest. Based on the identified vortex center tracks, a statistics of vortex curvature radii is established. This statistics constitutes the basis for understan...

High-charge and multiple-star vortex coronagraphy from stacked vector vortex phase masks.

Science.gov (United States)

Aleksanyan, Artur; Brasselet, Etienne

2018-02-01

Optical vortex phase masks are now installed at many ground-based large telescopes for high-contrast astronomical imaging. To date, such instrumental advances have been restricted to the use of helical phase masks of the lowest even order, while future giant telescopes will require high-order masks. Here we propose a single-stage on-axis scheme to create high-order vortex coronagraphs based on second-order vortex phase masks. By extending our approach to an off-axis design, we also explore the implementation of multiple-star vortex coronagraphy. An experimental laboratory demonstration is reported and supported by numerical simulations. These results offer a practical roadmap to the development of future coronagraphic tools with enhanced performances.

Vortex rings in classical and quantum systems

International Nuclear Information System (INIS)

Barenghi, C F; Donnelly, R J

2009-01-01

The study of vortex rings has been pursued for decades and is a particularly difficult subject. However, the discovery of quantized vortex rings in superfluid helium has greatly increased interest in vortex rings with very thin cores. While rapid progress has been made in the simulation of quantized vortex rings, there has not been comparable progress in laboratory studies of vortex rings in a viscous fluid such as water. This article overviews the history and current frontiers of classical and quantum vortex rings. After introducing the classical results, this review discusses thin-cored vortex rings in superfluid helium in section 2, and recent progress in understanding vortex rings of very thin cores propagating in water in section 3. (invited paper)

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1998-12-31

In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.

On vortex shedding and prediction of vortex-induced vibrations of circular cylinders

Energy Technology Data Exchange (ETDEWEB)

Halse, Karl Henning

1997-12-31

In offshore installations, many crucial components can be classified as slender marine structures: risers, mooring lines, umbilicals and cables, pipelines. This thesis studies the vortex shedding phenomenon and the problem of predicting vortex-induced vibrations of such structures. As the development of hydrocarbons move to deeper waters, the importance of accurately predicting the vortex-induced response has increased and so the need for proper response prediction methods is large. This work presents an extensive review of existing research publications about vortex shedding from circular cylinders and the vortex-induced vibrations of cylinders and the different numerical approaches to modelling the fluid flow. The response predictions from different methods are found to disagree, both in response shapes and in vibration amplitudes. This work presents a prediction method that uses a fully three-dimensional structural finite element model integrated with a laminar two-dimensional Navier-Stokes solution modelling the fluid flow. This solution is used to study the flow both around a fixed cylinder and in a flexibly mounted one-degree-of-freedom system. It is found that the vortex-shedding process (in the low Reynolds number regime) is well described by the computer program, and that the vortex-induced vibration of the flexibly mounted section do reflect the typical dynamic characteristics of lock-in oscillations. However, the exact behaviour of the experimental results found in the literature was not reproduced. The response of the three-dimensional structural model is larger than the expected difference between a mode shape and a flexibly mounted section. This is due to the use of independent hydrodynamic sections along the cylinder. The predicted response is not unrealistic, and the method is considered a powerful tool. 221 refs., 138 figs., 36 tabs.

Wake Vortex Inverse Model User's Guide

Science.gov (United States)

Lai, David; Delisi, Donald

2008-01-01

NorthWest Research Associates (NWRA) has developed an inverse model for inverting landing aircraft vortex data. The data used for the inversion are the time evolution of the lateral transport position and vertical position of both the port and starboard vortices. The inverse model performs iterative forward model runs using various estimates of vortex parameters, vertical crosswind profiles, and vortex circulation as a function of wake age. Forward model predictions of lateral transport and altitude are then compared with the observed data. Differences between the data and model predictions guide the choice of vortex parameter values, crosswind profile and circulation evolution in the next iteration. Iterations are performed until a user-defined criterion is satisfied. Currently, the inverse model is set to stop when the improvement in the rms deviation between the data and model predictions is less than 1 percent for two consecutive iterations. The forward model used in this inverse model is a modified version of the Shear-APA model. A detailed description of this forward model, the inverse model, and its validation are presented in a different report (Lai, Mellman, Robins, and Delisi, 2007). This document is a User's Guide for the Wake Vortex Inverse Model. Section 2 presents an overview of the inverse model program. Execution of the inverse model is described in Section 3. When executing the inverse model, a user is requested to provide the name of an input file which contains the inverse model parameters, the various datasets, and directories needed for the inversion. A detailed description of the list of parameters in the inversion input file is presented in Section 4. A user has an option to save the inversion results of each lidar track in a mat-file (a condensed data file in Matlab format). These saved mat-files can be used for post-inversion analysis. A description of the contents of the saved files is given in Section 5. An example of an inversion input

Piezoelectric energy harvesting in coupling-chamber excited by the vortex-induced pressure

Science.gov (United States)

Cheng, Tinghai; Wang, Yingting; Qin, Feng; Song, Zhaoyang; Lu, Xiaohui; Bao, Gang; Zhao, Xilu

2016-08-01

The performance of a piezoelectric energy harvester with a coupling chamber was investigated under vortex-induced pressure. The harvester consisted of a power chamber, a buffer, and a storage chamber. Different types of vortex (i.e., clockwise or counter-clockwise) could be induced by changing the volume ratio between the power chamber and the storage chamber. The peak voltage of the harvester could be tuned by changing the volume ratio. For example, under a pressure of 0.30 MPa, input cycle of 2.0 s, and flow rate of 200 l/min, the peak voltage decreased from 79.20 to 70.80 V with increasing volume ratio. The optimal volume ratio was 2.03, which resulted in the formation of a clockwise vortex. The corresponding effective power through a 600 kΩ resistor was 1.97 mW.

Lift enhancement by trapped vortex

Science.gov (United States)

Rossow, Vernon J.

1992-01-01

The viewgraphs and discussion of lift enhancement by trapped vortex are provided. Efforts are continuously being made to find simple ways to convert wings of aircraft from an efficient cruise configuration to one that develops the high lift needed during landing and takeoff. The high-lift configurations studied here consist of conventional airfoils with a trapped vortex over the upper surface. The vortex is trapped by one or two vertical fences that serve as barriers to the oncoming stream and as reflection planes for the vortex and the sink that form a separation bubble on top of the airfoil. Since the full three-dimensional unsteady flow problem over the wing of an aircraft is so complicated that it is hard to get an understanding of the principles that govern the vortex trapping process, the analysis is restricted here to the flow field illustrated in the first slide. It is assumed that the flow field between the two end plates approximates a streamwise strip of the flow over a wing. The flow between the endplates and about the airfoil consists of a spanwise vortex located between the suction orifices in the endplates. The spanwise fence or spoiler located near the nose of the airfoil serves to form a separated flow region and a shear layer. The vorticity in the shear layer is concentrated into the vortex by withdrawal of fluid at the suction orifices. As the strength of the vortex increases with time, it eventually dominates the flow in the separated region so that a shear or vertical layer is no longer shed from the tip of the fence. At that point, the vortex strength is fixed and its location is such that all of the velocity contributions at its center sum to zero thereby making it an equilibrium point for the vortex. The results of a theoretical analysis of such an idealized flow field are described.

Self-excited hydrothermal waves in evaporating sessile drops

OpenAIRE

Sefiane K.; Moffat J.R.; Matar O.K.; Craster R.V.

2008-01-01

Pattern formation driven by the spontaneous evaporation of sessile drops of methanol, ethanol, and FC-72 using infrared thermography is observed and, in certain cases, interpreted in terms of hydrothermal waves. Both methanol and ethanol drops exhibit thermal wave trains, whose wave number depends strongly on the liquid volatililty and substrate thermal conductivity. The FC- 72 drops develop cellular structures whose size is proportional to the local thickness. Prior to this work, hydrotherma...

The Energy Budget of a Southwest Vortex With Heavy Rainfall over South China

Institute of Scientific and Technical Information of China (English)

FU Shenming; SUN Jianhua; ZHAO Sixiong; LI Wanli

2011-01-01

Energy budgets were analyzed to study the development of an eastward propagating southwest vortex (SWV) associated with heavy rainfall over southern China (11-13 June 2008). The results show that kinetic energy (KE) generation and a dvection were the most important KE sources, while friction and sub-grid processes were the main KE sinks. There was downward conversion from divergent to rotational wind KE consistent with the downward stretching of SWVs. The Coriolis force was important for the formation and maintenance of the SWV. Convergence was also an important factor for maintenance, as was vertical motion during the mature stage of the SWV and the formation stage of a newly formed vortex (vortex B). The conversion from available potential energy (APE) to KE of divergent wind can lead to strong convection. Vertical motion influenced APE by dynamical and thermal processes which had opposite effects.The variation of APE was related to the heavy rainfall and convection; in this case, vertical motion with direct thermal circulation was the most important way in which APE was released, while latent heat release and vertical temperature advection were important for APE generation.

A vortex dynamics perspective on stratospheric sudden warmings

OpenAIRE

Matthewman, N. J.

2009-01-01

A vortex dynamics approach is used to study the underlying mechanisms leading to polar vortex breakdown during stratospheric sudden warmings (SSWs). Observational data are used in chapter 2 to construct climatologies of the Arctic polar vortex structure during vortex-splitting and vortex-displacement SSWs occurring between 1958 and 2002. During vortex-splitting SSWs, polar vortex breakdown is shown to be typically independent of height (barotropic), whereas breakdown during vor...

Controlling vortex motion and vortex kinetic friction

International Nuclear Information System (INIS)

Nori, Franco; Savel'ev, Sergey

2006-01-01

We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcia, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves

Controlling vortex motion and vortex kinetic friction

Science.gov (United States)

Nori, Franco; Savel'ev, Sergey

2006-05-01

We summarize some recent results of vortex motion control and vortex kinetic friction. (1) We describe a device [J.E. Villegas, S. Savel'ev, F. Nori, E.M. Gonzalez, J.V. Anguita, R. Garcìa, J.L. Vicent, Science 302 (2003) 1188] that can easily control the motion of flux quanta in a Niobium superconducting film on an array of nanoscale triangular magnets. Even though the input ac current has zero average, the resulting net motion of the vortices can be directed along either one direction, the opposite direction, or producing zero net motion. We also consider layered strongly anisotropic superconductors, with no fixed spatial asymmetry, and show [S. Savel'ev, F. Nori, Nature Materials 1 (2002) 179] how, with asymmetric drives, the ac motion of Josephson and/or pancake vortices can provide a net dc vortex current. (2) In analogy with the standard macroscopic friction, we present [A. Maeda, Y. Inoue, H. Kitano, S. Savel'ev, S. Okayasu, I. Tsukada, F. Nori , Phys. Rev. Lett. 94 (2005) 077001] a comparative study of the friction force felt by vortices in superconductors and charge density waves.

Vortex dynamics in spacing-graded array of defects on a niobium film

International Nuclear Information System (INIS)

Wu, T.C.; Horng, Lance; Wu, J.C.; Hsiao, C.W.; Kolacek, Jan; Yang, T.J.

2006-01-01

We have investigated the vortex dynamics in the niobium films having a spacing-graded array of pinning sites. The samples were fabricated by using electron beam lithography through a lift-off technique. The pinning sites of 200 nm in diameter were arranged with a constant hole-defect separation in x-axis direction and graded separation in y-axis direction from 392 nm to 408 nm. The magnetoresistance measurements and current-voltage characteristics were explored with the external magnetic field applied perpendicular to the film plane. Dc current-voltage measured at matching field revealed two distinct curves resulted from the positive and negative applied current directions, respectively. This is believed to be due to an asymmetry pinning potential formed in the spacing-graded array of holes, giving rise to asymmetry Lorentz forces. Dc voltage drop measured with respect to the ac current applied along the x-axis of the sample showed two separated maxima, which can be explained using the dynamics of pinned vortex lattice and interstitial vortices in the asymmetry pinning landscape

Electric vortex in MHD flow

International Nuclear Information System (INIS)

Garcia, M.

1995-01-01

An electric vortex is the circulation of electron space charge about a magnetic field line that is transported by ion momentum. In cold, or low β flow the vortex diameter is the minimum length scale of charge neutrality. The distinctive feature of the vortex is its radial electric field which manifests the interplay of electrostatics, magnetism, and motion

Non-coaxial superposition of vector vortex beams.

Science.gov (United States)

Aadhi, A; Vaity, Pravin; Chithrabhanu, P; Reddy, Salla Gangi; Prabakar, Shashi; Singh, R P

2016-02-10

Vector vortex beams are classified into four types depending upon spatial variation in their polarization vector. We have generated all four of these types of vector vortex beams by using a modified polarization Sagnac interferometer with a vortex lens. Further, we have studied the non-coaxial superposition of two vector vortex beams. It is observed that the superposition of two vector vortex beams with same polarization singularity leads to a beam with another kind of polarization singularity in their interaction region. The results may be of importance in ultrahigh security of the polarization-encrypted data that utilizes vector vortex beams and multiple optical trapping with non-coaxial superposition of vector vortex beams. We verified our experimental results with theory.

Some observations of tip-vortex cavitation

Science.gov (United States)

Arndt, R. E. A.; Arakeri, V. H.; Higuchi, H.

1991-08-01

Cavitation has been observed in the trailing vortex system of an elliptic platform hydrofoil. A complex dependence on Reynolds number and gas content is noted at inception. Some of the observations can be related to tension effects associated with the lack of sufficiently large-sized nuclei. Inception measurements are compared with estimates of pressure in the vortex obtained from LDV measurements of velocity within the vortex. It is concluded that a complete correlation is not possible without knowledge of the fluctuating levels of pressure in tip-vortex flows. When cavitation is fully developed, the observed tip-vortex trajectory flows. When cavitation is fully developed, the observed tip-vortex trajectory shows a surprising lack of dependence on any of the physical parameters varied, such as angle of attack, Reynolds number, cavitation number, and dissolved gas content.

Vortex trapping by tilted columnar defects

International Nuclear Information System (INIS)

Baladie, I.; Buzdin, A.

2000-01-01

The irradiation of high-T c superconductors by inclined heavy-ion beam can create columnar defects (CD's) practically at any angle towards the crystal c axis. We calculate the energy of a tilted vortex trapped on an inclined columnar defect within the framework of an electromagnetic model. Under a weak perpendicular magnetic field, and if the CD radius is larger than the superconducting coherence length, vortices always prefer to be on a tilted CD than to be aligned along the external field. We calculate also the interaction energy between two tilted vortices and find that large attractive regions appear. In particular, in the plane defined by c axis and the CD axis, tilted vortices attract each other at long distances, leading to the formation of vortex chains. The equilibrium distance between vortices in a chain is of the order of the magnitude of the in-plane London penetration depth. The existence of the inclined trapped vortices could be revealed by torque measurements, and could also lead to the anisotropy of the in-plane resistivity and the critical current

Regimes of flow past a vortex generator

DEFF Research Database (Denmark)

Velte, Clara Marika; Okulov, V.L.; Naumov, I.V.

2012-01-01

A complete parametric investigation of the development of multi-vortex regimes in a wake past simple vortex generator has been carried out. It is established that the vortex structure in the wake is much more complicated than a simple monopole tip vortex. The vortices were studied by stereoscopic...... particle image velocimetry (SPIV). Based on the obtained SPIV data, a map of the regimes of flow past the vortex generator has been constructed. One region with a developed stable multivortex system on this map reaches the vicinity of the optimum angle of attack of the vortex generator....

Spectral analysis of point-vortex dynamics: first application to vortex polygons in a circular domain

International Nuclear Information System (INIS)

Speetjens, M F M; Meleshko, V V; Van Heijst, G J F

2014-01-01

The present study addresses the classical problem of the dynamics and stability of a cluster of N-point vortices of equal strength arranged in a polygonal configuration (‘N-vortex polygons’). In unbounded domains, such N-vortex polygons are unconditionally stable for N⩽7. Confinement in a circular domain tightens the stability conditions to N⩽6 and a maximum polygon size relative to the domain radius. This work expands on existing studies on stability and integrability by a first giving an exploratory spectral analysis of the dynamics of N vortex polygons in circular domains. Key to this is that the spectral signature of the time evolution of vortex positions reflects their qualitative behaviour. Expressing vortex motion by a generic evolution operator (the so-called Koopman operator) provides a rigorous framework for such spectral analyses. This paves the way to further differentiation and classification of point-vortex behaviour beyond stability and integrability. The concept of Koopman-based spectral analysis is demonstrated for N-vortex polygons. This reveals that conditional stability can be seen as a local form of integrability and confirms an important generic link between spectrum and dynamics: discrete spectra imply regular (quasi-periodic) motion; continuous (sub-)spectra imply chaotic motion. Moreover, this exposes rich nonlinear dynamics as intermittency between regular and chaotic motion and quasi-coherent structures formed by chaotic vortices. (ss 1)

Vortex diode jet

Science.gov (United States)

Houck, Edward D.

1994-01-01

A fluid transfer system that combines a vortex diode with a jet ejector to transfer liquid from one tank to a second tank by a gas pressurization method having no moving mechanical parts in the fluid system. The vortex diode is a device that has a high resistance to flow in one direction and a low resistance to flow in the other.

Decreasing vortex flux in channels

International Nuclear Information System (INIS)

Migaj, V.K.; Nosova, I.S.

1979-01-01

A new method for reducing vortex flow losses in power plant channels is suggested. The method is based on vortex splitting in vortex flow areas with transverse barriers placed on the channel walls. The upper barrier ends are at the level of the upper boundary of the vortex area and don't protrude to the active flow beyond this boundary. The effectiveness of the method suggested is illustrated taking as an example the investigation of square and flat channels with abrupt widening in one plane, diffusers with widening in one plane, or a rectangualr bend. It is shown that splitting the vortex areas with transverse barriers in the channels results in reduction of hydraulic losses by 10-25%. The above method is characteristic of an extreme simplicity, its application doesn't require changes in the channel shape nor installation of any devices in the flow

Backreaction of excitations on a vortex

OpenAIRE

Arodz, Henryk; Hadasz, Leszek

1996-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their backreaction on the vortex. In the present paper we investigate backreaction of Proca type excitations on a straightlinear vortex in the Abelian Higgs model. We propose exact Ansatz for fields of the excited vortex. From initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the backreaction corrections. Their approximate solutions are found ...

An investigation of the vortex method

Energy Technology Data Exchange (ETDEWEB)

Pryor, Jr., Duaine Wright [Univ. of California, Berkeley, CA (United States)

1994-05-01

The vortex method is a numerical scheme for solving the vorticity transport equation. Chorin introduced modern vortex methods. The vortex method is a Lagrangian, grid free method which has less intrinsic diffusion than many grid schemes. It is adaptive in the sense that elements are needed only where the vorticity is non-zero. Our description of vortex methods begins with the point vortex method of Rosenhead for two dimensional inviscid flow, and builds upon it to eventually cover the case of three dimensional slightly viscous flow with boundaries. This section gives an introduction to the fundamentals of the vortex method. This is done in order to give a basic impression of the previous work and its line of development, as well as develop some notation and concepts which will be used later. The purpose here is not to give a full review of vortex methods or the contributions made by all the researchers in the field. Please refer to the excellent review papers in Sethian and Gustafson, chapters 1 Sethian, 2 Hald, 3 Sethian, 8 Chorin provide a solid introduction to vortex methods, including convergence theory, application in two dimensions and connection to statistical mechanics and polymers. Much of the information in this review is taken from those chapters, Chorin and Marsden and Batchelor, the chapters are also useful for their extensive bibliographies.

Instability of vortex pair leapfrogging

DEFF Research Database (Denmark)

Tophøj, Laust; Aref, Hassan

2013-01-01

Leapfrogging is a periodic solution of the four-vortex problem with two positive and two negative point vortices all of the same absolute circulation arranged as co-axial vortex pairs. The set of co-axial motions can be parameterized by the ratio 0 vortex pair sizes at the time when one...... pair passes through the other. Leapfrogging occurs for α > σ2, where is the silver ratio. The motion is known in full analytical detail since the 1877 thesis of Gröbli and a well known 1894 paper by Love. Acheson ["Instability of vortex leapfrogging," Eur. J. Phys.21, 269-273 (2000...... pairs fly off to infinity, and a "walkabout" mode, where the vortices depart from leapfrogging but still remain within a finite distance of one another. We show numerically that this transition is more gradual, a result that we relate to earlier investigations of chaotic scattering of vortex pairs [L...

Topological fluid mechanics of the formation of the Kármán-vortex street

DEFF Research Database (Denmark)

Heil, Matthias; Rosso, Jordan; Hazel, Andrew L.

2017-01-01

consider to be feature points for vortices. The basic vortex creation mechanism is shown to be a topological cusp bifurcation in the vorticity field, where a saddle and an extremum of the vorticity are created simultaneously. We demonstrate that vortices are first created approximately 100 diameters...

Soliton on thin vortex filament

International Nuclear Information System (INIS)

Konno, Kimiaki; Mituhashi, Masahiko; Ichikawa, Y.H.

1990-12-01

Showing that one of the equations found by Wadati, Konno and Ichikawa is equivalent to the equation of motion of a thin vortex filament, we investigate solitons on the vortex filament. N vortex soliton solution is given in terms of the inverse scattering method. We examine two soliton collision processes on the filament. Our analysis provides the theoretical foundation of two soliton collision processes observed numerically by Aref and Flinchem. (author)

ASRS Reports on Wake Vortex Encounters

Science.gov (United States)

Connell, Linda J.; Taube, Elisa Ann; Drew, Charles Robert; Barclay, Tommy Earl

2010-01-01

ASRS is conducting a structured callback research project of wake vortex incidents reported to the ASRS at all US airports, as well as wake encounters in the enroute environment. This study has three objectives: (1) Utilize the established ASRS supplemental data collection methodology and provide ongoing analysis of wake vortex encounter reports; (2) Document event dynamics and contributing factors underlying wake vortex encounter events; and (3) Support ongoing FAA efforts to address pre-emptive wake vortex risk reduction by utilizing ASRS reporting contributions.

New scanning technique for the optical vortex microscope.

Science.gov (United States)

Augustyniak, Ireneusz; Popiołek-Masajada, Agnieszka; Masajada, Jan; Drobczyński, Sławomir

2012-04-01

In the optical vortex microscopy the focused Gaussian beam with optical vortex scans a sample. An optical vortex can be introduced into a laser beam with the use of a special optical element--a vortex lens. When moving the vortex lens, the optical vortex changes its position inside the spot formed by a focused laser beam. This effect can be used as a new precise scanning technique. In this paper, we study the optical vortex behavior at the sample plane. We also estimate if the new scanning technique results in observable effects that could be used for a phase object detection.

Fabrication and Operation of Microfluidic Hanging-Drop Networks.

Science.gov (United States)

Misun, Patrick M; Birchler, Axel K; Lang, Moritz; Hierlemann, Andreas; Frey, Olivier

2018-01-01

The hanging-drop network (HDN) is a technology platform based on a completely open microfluidic network at the bottom of an inverted, surface-patterned substrate. The platform is predominantly used for the formation, culturing, and interaction of self-assembled spherical microtissues (spheroids) under precisely controlled flow conditions. Here, we describe design, fabrication, and operation of microfluidic hanging-drop networks.

Moving vortex matter with coexisting vortices and anti-vortices

International Nuclear Information System (INIS)

Carneiro, Gilson

2009-01-01

Moving vortex matter, driven by transport currents independent of time, in which vortices and anti-vortices coexist is investigated theoretically in thin superconducting films with nanostructured defects. A simple London model is proposed for the vortex dynamics in films with periodic arrays of nanomagnets or cylindrical holes (antidots). Common to these films is that vortex anti-vortex pairs may be created in the vicinity of the defects by relatively small transport currents, because it adds to the current generated by the defects - the nanomagnets screening current, or the antidots backflow current - and may exceed locally the critical value for vortex anti-vortex pair creation. The model assumes that vortex matter dynamics is governed by Langevin equations, modified to account for creation and annihilation of vortex anti-vortex pairs. For pair creation, it is assumed that whenever the total current at some location exceeds a critical value, equal to that needed to separate a vortex from an anti-vortex by a vortex core diameter, a pair is created instantaneously around this location. Pair annihilation occurs by vortex anti-vortex collisions. The model is applied to films at zero external magnetic field and low temperatures. It is found that several moving vortex matter steady-states with equal numbers of vortices and anti-vortices are possible.

Review of Idealized Aircraft Wake Vortex Models

Science.gov (United States)

Ahmad, Nashat N.; Proctor, Fred H.; Duparcmeur, Fanny M. Limon; Jacob, Don

2014-01-01

Properties of three aircraft wake vortex models, Lamb-Oseen, Burnham-Hallock, and Proctor are reviewed. These idealized models are often used to initialize the aircraft wake vortex pair in large eddy simulations and in wake encounter hazard models, as well as to define matched filters for processing lidar observations of aircraft wake vortices. Basic parameters for each vortex model, such as peak tangential velocity and circulation strength as a function of vortex core radius size, are examined. The models are also compared using different vortex characterizations, such as the vorticity magnitude. Results of Euler and large eddy simulations are presented. The application of vortex models in the postprocessing of lidar observations is discussed.

Cutting a drop of water pinned by wire loops using a superhydrophobic surface and knife.

Directory of Open Access Journals (Sweden)

Ryan Yanashima

Full Text Available A water drop on a superhydrophobic surface that is pinned by wire loops can be reproducibly cut without formation of satellite droplets. Drops placed on low-density polyethylene surfaces and Teflon-coated glass slides were cut with superhydrophobic knives of low-density polyethylene and treated copper or zinc sheets, respectively. Distortion of drop shape by the superhydrophobic knife enables a clean break. The driving force for droplet formation arises from the lower surface free energy for two separate drops, and it is modeled as a 2-D system. An estimate of the free energy change serves to guide when droplets will form based on the variation of drop volume, loop spacing and knife depth. Combining the cutting process with an electrofocusing driving force could enable a reproducible biomolecular separation without troubling satellite drop formation.

Characterisation of the Interaction between Toroidal Vortex Structures and Flame Front Propagation

International Nuclear Information System (INIS)

Long, E J; Hargrave, G K; Jarvis, S; Justham, T; Halliwell, N

2006-01-01

Experimental laser diagnostic data is presented for flame characterisation during interactions with toroidal vortices generated in the wake of an annular obstacle. A novel twin section combustion chamber has been utilised to allow the controlled formation of stable eddy structures into which a flame front can propagate. High speed laser sheet visualisation was employed to record the flow field and flame front temporal development and high-speed digital particle image velocimetry was used to quantify the velocity field of the unburnt mixture ahead of the flame front. Results provide characterisation of the toroidal vortex/flame front interaction for a range of vortex scales of and recirculation strengths

Characterisation of the Interaction between Toroidal Vortex Structures and Flame Front Propagation

Energy Technology Data Exchange (ETDEWEB)

Long, E J; Hargrave, G K; Jarvis, S; Justham, T; Halliwell, N [Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, Leicestershire, LE11 3TU (United Kingdom)

2006-07-15

Experimental laser diagnostic data is presented for flame characterisation during interactions with toroidal vortices generated in the wake of an annular obstacle. A novel twin section combustion chamber has been utilised to allow the controlled formation of stable eddy structures into which a flame front can propagate. High speed laser sheet visualisation was employed to record the flow field and flame front temporal development and high-speed digital particle image velocimetry was used to quantify the velocity field of the unburnt mixture ahead of the flame front. Results provide characterisation of the toroidal vortex/flame front interaction for a range of vortex scales of and recirculation strengths.

Characterisation of the Interaction between Toroidal Vortex Structures and Flame Front Propagation

Science.gov (United States)

Long, E. J.; Hargrave, G. K.; Jarvis, S.; Justham, T.; Halliwell, N.

2006-07-01

Experimental laser diagnostic data is presented for flame characterisation during interactions with toroidal vortices generated in the wake of an annular obstacle. A novel twin section combustion chamber has been utilised to allow the controlled formation of stable eddy structures into which a flame front can propagate. High speed laser sheet visualisation was employed to record the flow field and flame front temporal development and high-speed digital particle image velocimetry was used to quantify the velocity field of the unburnt mixture ahead of the flame front. Results provide characterisation of the toroidal vortex/flame front interaction for a range of vortex scales of and recirculation strengths.

Meissner effects, vortex core states, and the vortex glass phase transition

International Nuclear Information System (INIS)

Huang, Ming.

1991-01-01

This thesis covers three topics involving Meissner effects and the resulting defect structures. The first is a study of Meissner effects in superconductivity and in systems with broken translational symmetry. The Meissner effect in the superconductors is a rigidity against external magnetic field caused by the breaking of the gauge symmetry. Other condensed matter systems also exhibit rigidities like this: The breaking of the translational symmetry in a cubic-liquid-crystal causes the system to expel twist deformations and the breaking of the translational symmetry in a nematic liquid crystal gives it a tendency to expel twist and bend deformations. In this thesis, the author studies these generalized Meissner effects in detail. The second is a study of the quasiparticle states bound to the vortex defect in superconductors. Scanning-tunneling-microscope measurements by Harald Hess et al. of the local density of states in a vortex core show a pronounced peak at small bias. These measurements contradict with previous theoretical calculations. Here, he solves the Bogoliubov equations to obtain the local density of states in the core and satisfactorily explain the experimental observations. He also predicted additional structure in the local density of states which were later observed in experiments. The third is a study of vortex dynamics in the presence of disorder. A mean field theory is developed for the recently proposed normal to superconducting vortex glass transition. Using techniques developed to study the critical dynamics of spin glasses, he calculates the mean field vortex glass phase boundary and the critical exponents

Leapfrogging of multiple coaxial viscous vortex rings

International Nuclear Information System (INIS)

Cheng, M.; Lou, J.; Lim, T. T.

2015-01-01

A recent theoretical study [Borisov, Kilin, and Mamaev, “The dynamics of vortex rings: Leapfrogging, choreographies and the stability problem,” Regular Chaotic Dyn. 18, 33 (2013); Borisov et al., “The dynamics of vortex rings: Leapfrogging in an ideal and viscous fluid,” Fluid Dyn. Res. 46, 031415 (2014)] shows that when three coaxial vortex rings travel in the same direction in an incompressible ideal fluid, each of the vortex rings alternately slips through (or leapfrogs) the other two ahead. Here, we use a lattice Boltzmann method to simulate viscous vortex rings with an identical initial circulation, radius, and separation distance with the aim of studying how viscous effect influences the outcomes of the leapfrogging process. For the case of two identical vortex rings, our computation shows that leapfrogging can be achieved only under certain favorable conditions, which depend on Reynolds number, vortex core size, and initial separation distance between the two rings. For the case of three coaxial vortex rings, the result differs from the inviscid model and shows that the second vortex ring always slips through the leading ring first, followed by the third ring slipping through the other two ahead. A simple physical model is proposed to explain the observed behavior

Anisotropic Formation of Quantum Turbulence Generated by a Vibrating Wire in Superfluid {}4{He}

Science.gov (United States)

Yano, H.; Ogawa, K.; Chiba, Y.; Obara, K.; Ishikawa, O.

2017-06-01

To investigate the formation of quantum turbulence in superfluid {}4{He}, we have studied the emission of vortex rings with a ring size of larger than 38 μm in diameter from turbulence generated by a vibrating wire. The emission rate of vortex rings from a turbulent region remains low until the beginning of high-rate emissions, suggesting that some of the vortex lines produced by the wire combine to form a vortex tangle, until an equilibrium is established between the rate of vortex line combination with the tangle and dissociation. The formation times of equilibrium turbulence are proportional to ɛ ^{-1.2} and ɛ ^{-0.6} in the directions perpendicular and parallel to the vibrating direction of the generator, respectively, indicating the anisotropic formation of turbulence. Here, ɛ is the generation power of the turbulence. This power dependence may be associated with the characteristics of quantum turbulence with a constant energy flux.

Aerodynamically shaped vortex generators

DEFF Research Database (Denmark)

Hansen, Martin Otto Laver; Velte, Clara Marika; Øye, Stig

2016-01-01

An aerodynamically shaped vortex generator has been proposed, manufactured and tested in a wind tunnel. The effect on the overall performance when applied on a thick airfoil is an increased lift to drag ratio compared with standard vortex generators. Copyright © 2015 John Wiley & Sons, Ltd....

Experiments concerning the theories of vortex breakdown

Science.gov (United States)

Panton, Ronald L.; Stifle, Kirk E.

1991-01-01

An experimental project was undertaken to investigate the character of vortex breakdown with particular regard to the stagnation and wave guide theories of vortex breakdown. Three different wings were used to produce a trailing vortex which convected downstream without undergoing breakdown. Disturbances were then introduced onto the vortex using a moving wire to 'cut' the vortex. The development of upstream and downstream propagating disturbance waves was observed and the propagation velocities measured. A downstream traveling wave was observed to produce a structure similar in appearance to a vortex breakdown. An upstream traveling wave produced a moving turbulent region. The upstream disturbance moved into an axial velocity profile that had a wake-like defect while the downstream moving vortex breakdown moved against a jet-like overshoot. The longitudinal and swirl velocity profiles were documented by LDV measurement. Wave velocities, swirl angles, and swirl parameters are reported.

Topology breaking of the vortex in multiferroic Y0.67Lu0.33MnO3

International Nuclear Information System (INIS)

Zhang, Qing-Hua; Gu, Lin; Yao, Yuan; Jin, Chang-Qing; Wang, Yan-Guo; Duan, Xiao-Feng; Yu, Ri-Cheng; Tan, Guo-Tai

2014-01-01

Although topological defects, such as domain walls (DWs) or vortices, are naturally protected by topological invariance, yet, we discover an exception that the six-state topology of the vortex with Z2 × Z3 symmetry is broken by a partial edge dislocation (PED) in hexagonal Y 0.67 Lu 0.33 MnO 3 , where the topologies of the four-state vortex or closed DWs emerges. Using aberration-corrected scanning transmission electron microscopy, we found that the PED plays an important role in changing the phase of translation domain. The PED at the vortex core leads to the formation of the four-state vortex, while the ones at closed DWs connect different types of DWs, both corresponding to continuous phase changes. These results indicate that PEDs can change the topology of translation-related domain vortices and more vortices with even domains can be expected.

Magnetic vortex racetrack memory

Energy Technology Data Exchange (ETDEWEB)

Geng, Liwei D.; Jin, Yongmei M., E-mail: ymjin@mtu.edu

2017-02-01

We report a new type of racetrack memory based on current-controlled movement of magnetic vortices in magnetic nanowires with rectangular cross-section and weak perpendicular anisotropy. Data are stored through the core polarity of vortices and each vortex carries a data bit. Besides high density, non-volatility, fast data access, and low power as offered by domain wall racetrack memory, magnetic vortex racetrack memory has additional advantages of no need for constrictions to define data bits, changeable information density, adjustable current magnitude for data propagation, and versatile means of ultrafast vortex core switching. By using micromagnetic simulations, current-controlled motion of magnetic vortices in cobalt nanowire is demonstrated for racetrack memory applications. - Highlights: • Advance fundamental knowledge of current-driven magnetic vortex phenomena. • Report appealing new magnetic racetrack memory based on current-controlled magnetic vortices in nanowires. • Provide a novel approach to adjust current magnitude for data propagation. • Overcome the limitations of domain wall racetrack memory.

Propeller and inflow vortex interaction : vortex response and impact on the propeller performance

NARCIS (Netherlands)

Yang, Y.; Zhou, T; Sciacchitano, A.; Veldhuis, L.L.M.; Eitelberg, G.

2016-01-01

The aerodynamic operating conditions of a propeller can include complex situations where vorticity from sources upstream can enter the propeller plane. In general, when the vorticity enters in a concentrated form of a vortex, the interaction between the vortex and blade is referred to as

Vortex Thermometry for Turbulent Two-Dimensional Fluids.

Science.gov (United States)

Groszek, Andrew J; Davis, Matthew J; Paganin, David M; Helmerson, Kristian; Simula, Tapio P

2018-01-19

We introduce a new method of statistical analysis to characterize the dynamics of turbulent fluids in two dimensions. We establish that, in equilibrium, the vortex distributions can be uniquely connected to the temperature of the vortex gas, and we apply this vortex thermometry to characterize simulations of decaying superfluid turbulence. We confirm the hypothesis of vortex evaporative heating leading to Onsager vortices proposed in Phys. Rev. Lett. 113, 165302 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.165302, and we find previously unidentified vortex power-law distributions that emerge from the dynamics.

Criterion for vortex breakdown on shock wave and streamwise vortex interactions.

Science.gov (United States)

Hiejima, Toshihiko

2014-05-01

The interactions between supersonic streamwise vortices and oblique shock waves are theoretically and numerically investigated by three-dimensional (3D) Navier-Stokes equations. Based on the two inequalities, a criterion for shock-induced breakdown of the streamwise vortex is proposed. The simple breakdown condition depends on the Mach number, the swirl number, the velocity deficit, and the shock angle. According to the proposed criterion, the breakdown region expands as the Mach number increases. In numerical simulations, vortex breakdown appeared under conditions of multiple pressure increases and the helicity disappeared behind the oblique shock wave along the line of the vortex center. The numerical results are consistent with the predicted breakdown condition at Mach numbers 2.0 and 3.0. This study also found that the axial velocity deficit is important for classifying the breakdown configuration.

Numerical studies of the integration of a trapped vortex combustor into traditional combustion chambers

Energy Technology Data Exchange (ETDEWEB)

Patrignani, L.; Losurdo, M.; Bruno, C. [Sapienza Univ. de Roma, Rome (Italy)

2010-09-15

Exhaust emissions from furnace burners can be reduced by premixing reactants with combustion products. This paper discussed the use of a trapped vortex combustor (TVC) as a very promising technology for gas turbines. The TVC can reduce emissions and ensure that the temperature is uniform in the exhaust products, which is a key aspect for certain types of heat treatments, such as in steel rolling mills. The TVC for gas turbines is configured to mix air, fuel and hot products at turbulent scales fine enough to render the combustion mode flameless, or close to flameless. The vortex ensures a high recirculation factor between hot combustion products and reactants, and ultimately flame stability. In this study, the TVC configuration for an existing gas turbine was numerically investigated by means of RANS and LES. According to preliminary results of the fast-flameless combustion (FFC) strategy, the proposed TVC is a suitable candidate to reduce nitrogen oxide (NOx) emissions while keeping the pressure drop below 1 per cent. Both RANS and LES show that too much fuel burns along the main duct. Better fuel splitting or a different position for the injectors may enhance combustion inside the recirculation zone. Behaviour of the main vortices showed that a more accurate design of the internal shape of the combustor is needed to prevent excessive velocity fluctuation or vortex instabilities and therefore emissions. 13 refs., 9 figs.

Analytical model of the optical vortex microscope.

Science.gov (United States)

Płocinniczak, Łukasz; Popiołek-Masajada, Agnieszka; Masajada, Jan; Szatkowski, Mateusz

2016-04-20

This paper presents an analytical model of the optical vortex scanning microscope. In this microscope the Gaussian beam with an embedded optical vortex is focused into the sample plane. Additionally, the optical vortex can be moved inside the beam, which allows fine scanning of the sample. We provide an analytical solution of the whole path of the beam in the system (within paraxial approximation)-from the vortex lens to the observation plane situated on the CCD camera. The calculations are performed step by step from one optical element to the next. We show that at each step, the expression for light complex amplitude has the same form with only four coefficients modified. We also derive a simple expression for the vortex trajectory of small vortex displacements.

Microscale vortex laser with controlled topological charge

Science.gov (United States)

Wang, Xing-Yuan; Chen, Hua-Zhou; Li, Ying; Li, Bo; Ma, Ren-Min

2016-12-01

A microscale vortex laser is a new type of coherent light source with small footprint that can directly generate vector vortex beams. However, a microscale laser with controlled topological charge, which is crucial for virtually any of its application, is still unrevealed. Here we present a microscale vortex laser with controlled topological charge. The vortex laser eigenmode was synthesized in a metamaterial engineered non-Hermitian micro-ring cavity system at exceptional point. We also show that the vortex laser cavity can operate at exceptional point stably to lase under optical pumping. The microscale vortex laser with controlled topological charge can serve as a unique and general building block for next-generation photonic integrated circuits and coherent vortex beam sources. The method we used here can be employed to generate lasing eigenmode with other complex functionalities. Project supported by the “Youth 1000 Talent Plan” Fund, Ministry of Education of China (Grant No. 201421) and the National Natural Science Foundation of China (Grant Nos. 11574012 and 61521004).

A note on integral vortex strength

Czech Academy of Sciences Publication Activity Database

Kolář, Václav

2010-01-01

Roč. 58, č. 1 (2010), s. 23-28 ISSN 0042-790X R&D Projects: GA AV ČR IAA200600801 Institutional research plan: CEZ:AV0Z20600510 Keywords : circulation * unsteady Taylor vortex * vortex intensity * vortex strength * vorticity * vorticity decomposition Subject RIV: BK - Fluid Dynamics Impact factor: 0.553, year: 2010

Obstacle-induced spiral vortex breakdown

OpenAIRE

Pasche, Simon; Gallaire, François; Dreyer, Matthieu; Farhat, Mohamed

2014-01-01

An experimental investigation on vortex breakdown dynamics is performed. An adverse pressure gradient is created along the axis of a wing-tip vortex by introducing a sphere downstream of an elliptical hydrofoil. The instrumentation involves high-speed visualizations with air bubbles used as tracers and 2D Laser Doppler Velocimeter (LDV). Two key parameters are identified and varied to control the onset of vortex breakdown: the swirl number, defined as the maximum azimuthal velocity divided by...

Vortex and source rings

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre

2017-01-01

The velocity field, vector potential and velocity gradient of a vortex ring is derived in this chapter. The Biot-Savart law for the vector potential and velocity is expressed in a first section. Then, the flow is derived at specific locations: on the axis, near the axis and in the far field where...... the analogy to a doublet field is made. The following section derive the value of the vector potential and velocity field in the full domain. The expression for the velocity gradient is also provided since it may be relevant in a simulation with vortex particles and vortex rings. Most of this chapter...

Development of vortex model with realistic axial velocity distribution

International Nuclear Information System (INIS)

Ito, Kei; Ezure, Toshiki; Ohshima, Hiroyuki

2014-01-01

A vortex is considered as one of significant phenomena which may cause gas entrainment (GE) and/or vortex cavitation in sodium-cooled fast reactors. In our past studies, the vortex is assumed to be approximated by the well-known Burgers vortex model. However, the Burgers vortex model has a simple but unreal assumption that the axial velocity component is horizontally constant, while in real the free surface vortex has the axial velocity distribution which shows large gradient in radial direction near the vortex center. In this study, a new vortex model with realistic axial velocity distribution is proposed. This model is derived from the steady axisymmetric Navier-Stokes equation as well as the Burgers vortex model, but the realistic axial velocity distribution in radial direction is considered, which is defined to be zero at the vortex center and to approach asymptotically to zero at infinity. As the verification, the new vortex model is applied to the evaluation of a simple vortex experiment, and shows good agreements with the experimental data in terms of the circumferential velocity distribution and the free surface shape. In addition, it is confirmed that the Burgers vortex model fails to calculate accurate velocity distribution with the assumption of uniform axial velocity. However, the calculation accuracy of the Burgers vortex model can be enhanced close to that of the new vortex model in consideration of the effective axial velocity which is calculated as the average value only in the vicinity of the vortex center. (author)

Passive scalar transport mediated by laminar vortex rings

Energy Technology Data Exchange (ETDEWEB)

Hernández, R H; Rodríguez, G, E-mail: rohernan@ing.uchile.cl [LEAF-NL, Depto. Ingeniería Civil Mecánica, Universidad de Chile, Casilla 2777, Santiago (Chile)

2017-04-15

Numerical simulations were used to study the dynamics of a passive conserved scalar quantity entrained by a self-propelling viscous vortex ring. The transport and mixing process of the passive scalar variable were studied considering two initial scalar distributions: (i) The scalar substance was introduced into the ring during its formation, further focusing in the shedding into the wake of the ring; (ii) A disk-like scalar layer was placed in the ring’s path where the entrainment of the scalar substance into the ring bubble was studied as a function of the ring strength. In both cases, the scalar concentration inside the vortex bubble exhibits a steady decay with time. In the second case, it was shown that the entrained scalar mass grows with both the Reynolds number of the ring and the thickness of the scalar layer in the propagation direction. The ring can be viewed as a mechanism for scalar transportation along important distances. (paper)

Self-excited hydrothermal waves in evaporating sessile drops

Science.gov (United States)

Sefiane, K.; Moffat, J. R.; Matar, O. K.; Craster, R. V.

2008-08-01

Pattern formation driven by the spontaneous evaporation of sessile drops of methanol, ethanol, and FC-72 using infrared thermography is observed and, in certain cases, interpreted in terms of hydrothermal waves. Both methanol and ethanol drops exhibit thermal wave trains, whose wave number depends strongly on the liquid volatililty and substrate thermal conductivity. The FC-72 drops develop cellular structures whose size is proportional to the local thickness. Prior to this work, hydrothermal waves have been observed in the absence of evaporation in shallow liquid layers subjected to an imposed temperature gradient. In contrast, here both the temperature gradients and the drop thickness vary spatially and temporally and are a natural consequence of the evaporation process.

Nanostructure of vortex during explosion welding.

Science.gov (United States)

Rybin, V V; Greenberg, B A; Ivanov, M A; Patselov, A M; Antonova, O V; Elkina, O A; Inozemtsev, A V; Salishchev, G A

2011-10-01

The microstructure of a bimetallic joint made by explosion welding of orthorhombic titanium aluminide (Ti-30Al-16Nb-1Zr-1Mo) with commercially pure titanium is studied. It is found that the welded joint has a multilayered structure including a severely deformed zone observed in both materials, a recrystallized zone of titanium, and a transition zone near the interface. Typical elements of the transition zone-a wavy interface, macrorotations of the lattice, vortices and tracks of fragments of the initial materials-are determined. It is shown that the observed vortices are formed most probably due to local melting of the material near the contact surface. Evidence for this assumption is deduced from the presence of dipoles, which consist of two vortices of different helicity and an ultrafine duplex structure of the vortex. Also, high mixing of the material near the vortex is only possible by the turbulent transport whose coefficient is several orders of magnitude larger than the coefficient of atomic diffusion in liquids. The role played by fragmentation in both the formation of lattice macrorotations and the passage of coarse particles of one material through the bulk of the other is determined.

Measurement of vortex velocities over a wide range of vortex age, downstream distance and free stream velocity

Science.gov (United States)

Rorke, J. B.; Moffett, R. C.

1977-01-01

A wind tunnel test was conducted to obtain vortex velocity signatures over a wide parameter range encompassing the data conditions of several previous researchers while maintaining a common instrumentation and test facility. The generating wing panel was configured with both a revolved airfoil tip shape and a square tip shape and had a semispan aspect of 4.05/1.0 with a 121.9 cm span. Free stream velocity was varied from 6.1 m/sec to 76.2 m/sec and the vortex core velocities were measured at locations 3, 6, 12, 24 and 48 chordlengths downstream of the wing trailing edge, yielding vortex ages up to 2.0 seconds. Wing pitch angles of 6, 8, 9 and 12 deg were investigated. Detailed surface pressure distributions and wing force measurements were obtained for each wing tip configuration. Correlation with vortex velocity data taken in previous experiments is good. During the rollup process, vortex core parameters appear to be dependent primarily on vortex age. Trending in the plateau and decay regions is more complex and the machanisms appear to be more unstable.

Shock/vortex interaction and vortex-breakdown modes

Science.gov (United States)

Kandil, Osama A.; Kandil, H. A.; Liu, C. H.

1992-01-01

Computational simulation and study of shock/vortex interaction and vortex-breakdown modes are considered for bound (internal) and unbound (external) flow domains. The problem is formulated using the unsteady, compressible, full Navier-Stokes (NS) equations which are solved using an implicit, flux-difference splitting, finite-volume scheme. For the bound flow domain, a supersonic swirling flow is considered in a configured circular duct and the problem is solved for quasi-axisymmetric and three-dimensional flows. For the unbound domain, a supersonic swirling flow issued from a nozzle into a uniform supersonic flow of lower Mach number is considered for quasi-axisymmetric and three-dimensional flows. The results show several modes of breakdown; e.g., no-breakdown, transient single-bubble breakdown, transient multi-bubble breakdown, periodic multi-bubble multi-frequency breakdown and helical breakdown.

Air Entrapment and Drop Formation in Piezo Inkjet Printing

NARCIS (Netherlands)

van der Bos, J.A.

2011-01-01

Piezo drop-on-demand (DOD) inkjet printers are used in an increasing number of applications for their reliable deposition of droplets onto a substrate. Droplets of a few picoliters are ejected from an ink jet nozzle at a frequency of up to 50 kHz. However, entrapment of an air microbubble into the

Three-vortex configurations in trapped Bose-Einstein condensates

International Nuclear Information System (INIS)

Seman, J. A.; Henn, E. A. L.; Shiozaki, R. F.; Ramos, E. R. F.; Caracanhas, M.; Castilho, P.; Castelo Branco, C.; Tavares, P. E. S.; Poveda-Cuevas, F. J.; Magalhaes, K. M. F.; Bagnato, V. S.; Haque, M.; Roati, G.

2010-01-01

We report on the creation of three-vortex clusters in a 87 Rb Bose-Einstein condensate by oscillatory excitation of the condensate. This procedure can create vortices of both circulations, so that we are able to create several types of vortex clusters using the same mechanism. The three-vortex configurations are dominated by two types, namely, an equilateral-triangle arrangement and a linear arrangement. We interpret these most stable configurations respectively as three vortices with the same circulation and as a vortex-antivortex-vortex cluster. The linear configurations are very likely experimental signatures of predicted stationary vortex clusters.

Formation of plasma and gaseous toroidal vortices in air

International Nuclear Information System (INIS)

Yusupaliev, U.; Yusupaliev, P. U.; Shuteev, S. A.

2007-01-01

The mechanism for the formation of high-temperature (plasma) vortices and low-temperature vortex rings produced by ejecting pulsed subsonic plasma/gas jets into air was investigated experimentally. A toroidal vortex forms due to the interaction between a pulsed jet with the flow induced by this jet in the ambient medium. By analyzing the experimental data and conservation laws, an equation is derived that allows one to determine the initial propagation velocity of the vortex as a function of the characteristics of the vortex generator and the ambient medium. The results obtained by solving this equation agree well with the experimental data

Magnetic vortex racetrack memory

Science.gov (United States)

Geng, Liwei D.; Jin, Yongmei M.

2017-02-01

We report a new type of racetrack memory based on current-controlled movement of magnetic vortices in magnetic nanowires with rectangular cross-section and weak perpendicular anisotropy. Data are stored through the core polarity of vortices and each vortex carries a data bit. Besides high density, non-volatility, fast data access, and low power as offered by domain wall racetrack memory, magnetic vortex racetrack memory has additional advantages of no need for constrictions to define data bits, changeable information density, adjustable current magnitude for data propagation, and versatile means of ultrafast vortex core switching. By using micromagnetic simulations, current-controlled motion of magnetic vortices in cobalt nanowire is demonstrated for racetrack memory applications.

Phase diagram of a lattice of pancake vortex molecules

International Nuclear Information System (INIS)

Tanaka, Y.; Crisan, A.; Shivagan, D.D.; Iyo, A.; Shirage, P.M.; Tokiwa, K.; Watanabe, T.; Terada, N.

2009-01-01

On a superconducting bi-layer with thickness much smaller than the penetration depth, λ, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom.

Phenomenological Model of Vortex Generators

DEFF Research Database (Denmark)

Hansen, Martin Otto Laver; Westergaard, C.

1995-01-01

For some time attempts have been made to improve the power curve of stall regulated wind turbines by using devices like vortex generators VG and Gurney flaps. The vortex produces an additional mixing of the boundary layer and the free stream and thereby increasing the momentum close to the wall......, which again delays separation in adverse pressure gradient regions. A model is needed to include the effect of vortex generators in numerical computations of the viscous flow past rotors. In this paper a simple model is proposed....

Three-dimensional parallel vortex rings in Bose-Einstein condensates

International Nuclear Information System (INIS)

Crasovan, Lucian-Cornel; Perez-Garcia, Victor M.; Danaila, Ionut; Mihalache, Dumitru; Torner, Lluis

2004-01-01

We construct three-dimensional structures of topological defects hosted in trapped wave fields, in the form of vortex stars, vortex cages, parallel vortex lines, perpendicular vortex rings, and parallel vortex rings, and we show that the latter exist as robust stationary, collective states of nonrotating Bose-Einstein condensates. We discuss the stability properties of excited states containing several parallel vortex rings hosted by the condensate, including their dynamical and structural stability

Experimental and numerical studies in a vortex tube

International Nuclear Information System (INIS)

Sohn, Chang Hyun; Kim, Chang Soo; Gowda, B. H. L Lakshmana; Jung, Ui Hyun

2006-01-01

The present investigation deals with the study of the internal flow phenomena of the counter-flow type vortex tube using experimental testing and numerical simulation. Visualization was carried out using the surface tracing method, injecting dye on the vortex tube wall using a needle. Vortex tube is made of acrylic to visualize the surface particle tracing and the input air pressure was varied from 0.1 MPa to 0.3 MPa. The experimentally visualized results on the tube show that there is an apparent sudden changing of the trajectory on the vortex tube wall which was observed in every experimental test case. This may indicate the stagnation position of the vortex flow. The visualized stagnation position moves towards the vortex generator with increase in cold flow ratio and input pressure. Three-dimensional computational study is also conducted to obtain more detailed flow information in the vortex tube. Calculated total pressure, static pressure and total temperature distributions in the vortex tube were in good agreement with the experimental data. The computational particle trace on the vortex tube wall is very similar to that observed in experiments

Vortex phase diagram and vortex dynamics at low temperature in a thick a-MgxB1-x film

International Nuclear Information System (INIS)

Okuma, S.; Kohara, M.

2007-01-01

We report on the equilibrium vortex phase diagram and vortex dynamics at low temperature T in a thick amorphous (a-)Mg x B 1-x film based on the measurements of the dc resistivity ρ and time (t)-dependent component of the flux-flow voltage, δV(t), respectively. Both ρ(T) in perpendicular fields and the vortex phase diagram are qualitatively similar to those for the a-Mo x Si 1-x films, in which evidence for the quantum-vortex-liquid (QVL) phase has been obtained. In either material system we observe anomalous vortex flow with the asymmetric distribution of δV(t) in the QVL phase, suggesting that the anomalous flow is a universal phenomenon commonly observed for disordered amorphous films, independent of material

The influence of airfoil kinematics on the formation of leading-edge vortices in bio-inspired flight

Energy Technology Data Exchange (ETDEWEB)

Rival, David; Prangemeier, Tim; Tropea, Cameron [Technische Universitaet Darmstadt (Germany). Institute of Fluid Mechanics and Aerodynamics

2009-05-15

The formation process of leading-edge vortices has been investigated experimentally using Particle Image Velocimetry. Various airfoil kinematics have been tested, including asymmetric and peak-shifted plunging motions, and are evaluated for Re = 30,000 and a reduced frequency range of 0.2{<=}k{<=}0.33. By measuring the growth in the leading-edge vortex during the dynamic-stall process, the vortex pinch-off process is examined based on the concept of an optimal vortex formation time. The various kinematics are then evaluated with respect to their associated vortex strength, timing and convection into the wake. (orig.)

Green functions of vortex operators

International Nuclear Information System (INIS)

Polchinski, J.; California Univ., Berkeley

1981-01-01

We study the euclidean Green functions of the 't Hooft vortex operator, primarly for abelian gauge theories. The operator is written in terms of elementary fields, with emphasis on a form in which it appears as the exponential of a surface integral. We explore the requirement that the Green functions depend only on the boundary of this surface. The Dirac veto problem appears in a new guise. We present a two-dimensional solvable model of a Dirac string, which suggests a new solution of the veto problem. The renormalization of the Green functions of the abelian Wilson loop and abelian vortex operator is studied with the aid of the operator product expansion. In each case, an overall multiplication of the operator makes all Green functions finite; a surprising cancellation of divergences occurs with the vortex operator. We present a brief discussion of the relation between the nature of the vacuum and the cluster properties of the Green functions of the Wilson and vortex operators, for a general gauge theory. The surface-like cluster property of the vortex operator in an abelian Higgs theory is explored in more detail. (orig.)

A new role for reduction in pressure drop in cyclones using computational fluid dynamics techniques

Directory of Open Access Journals (Sweden)

D. Noriler

2004-01-01

Full Text Available In this work a new mechanical device to improve the gas flow in cyclones by pressure drop reduction is presented and discussed. This behavior occurs due to the effects of introducing swirling breakdown phenomenon at the inlet of the vortex finder tube. The device consists of a tube with two gas inlets in an appositive spiral flux that produces a sudden reduction in the tangential velocity peak responsible for practically 80 % of the pressure drop in cyclones. In turn, peak reduction causes a decrease in pressure drop by a breakdown of the swirling, and because of this the solid particles tend to move faster toward the wall , increasing collection efficiency. As a result of this phenomenon the overall performance of cyclones is improved. Numerical simulations with 3-D, transient, asymmetric and anisotropic turbulence closure by differential Reynolds stress for Lapple and Stairmand standard geometries of 0.3 m in diameter, show a reduction in pressure drop of 20 % and a shift of the tangential velocity peak toward the wall. All numerical experiments were carried out with a commercial CFD code showing numerical stability and good convergence rates with high-order interpolation schemes, SIMPLEC pressure-velocity coupling and other numerical features.

Single vortex states in a confined Bose-Einstein condensate

International Nuclear Information System (INIS)

Komineas, S.; Cooper, N. R.; Papanicolaou, N.

2005-01-01

It has been demonstrated experimentally that non-axisymmetric vortices precess around the center of a Bose-Einstein condensate. Two types of single vortex states have been observed, usually referred to as the S vortex and the U vortex. We study theoretically the single vortex excitations in spherical and elongated condensates as a function of the interaction strength. We solve numerically the Gross-Pitaevskii equation and calculate the angular momentum as a function of precession frequency. The existence of two types of vortices means that we have two different precession frequencies for each angular momentum value. As the interaction strength increases the vortex lines bend and the precession frequencies shift to lower values. We establish that for given angular momentum the S vortex has higher energy than the U vortex in a rotating elongated condensate. We show that the S vortex is related to the solitonic vortex, which is a nonlinear excitation in the nonrotating system. For small interaction strengths the S vortex is related to the dark soliton. In the dilute limit a lowest Landau level calculation provides an analytic description of these vortex modes in terms of the harmonic oscillator states

Vortex dynamics in the wake of a pivoted cylinder undergoing vortex-induced vibrations with elliptic trajectories

Science.gov (United States)

Marble, Erik; Morton, Christopher; Yarusevych, Serhiy

2018-05-01

Vortex-induced vibrations of a pivoted cylinder are investigated experimentally at a fixed Reynolds number of 3100, a mass ratio of 10.8, and a range of reduced velocities, 4.42 ≤ U^* ≤ 9.05. For these conditions, the cylinder traces elliptic trajectories, with the experimental conditions producing three out of four possible combinations of orbiting direction and primary axis alignment relative to the incoming flow. The study focuses on the quantitative analysis of wake topology and its relation to this type of structural response. Velocity fields were measured using time-resolved, two-component particle image velocimetry (TR-PIV). These results show that phase-averaged wake topology generally agrees with the Morse and Williamson (J Fluids Struct 25(4):697-712, 2009) shedding map for one-degree-of-freedom vortex-induced vibrations, with 2S, 2{P}o, and 2P shedding patterns observed within the range of reduced velocities studied here. Vortex tracking and vortex strength quantification are used to analyze the vortex shedding process and how it relates to cylinder response. In the case of 2S vortex shedding, vortices are shed when the cylinder is approaching the maximum transverse displacement and reaches the streamwise equilibrium. 2P vortices are shed approximately half a period earlier in the cylinder's elliptic trajectory. Leading vortices shed immediately after the peak in transverse oscillation and trailing vortices shed near the equilibrium of transverse oscillation. The orientation and direction of the cylinder's elliptic trajectory are shown to influence the timing of vortex shedding, inducing changes in the 2P wake topology.

Effect of coolant velocity on the fragmentation of single melt drops in water

International Nuclear Information System (INIS)

Cunningham, M.H.; Frost, D.L.

1997-01-01

Flash X-ray radiography and high-speed photography are used to investigate the effect of the coolant velocity on the fine fragmentation of molten tin drops in water. A water cannot is used to accelerate the water to a constant speed of up to 30 m/s. The water is accelerated with a double piston arrangement including a foam shock absorber to eliminate the formation of a shock wave. In this way, the effect of coolant velocity on drop breakup is investigated in the absence of the strong shock wave that is present in most earlier studies. The results show that there is a transition from thermal to hydrodynamic fragmentation through an intermediate stage in which the drops initially undergo hydrodynamic fragmentation followed by the formation of a vapour bubble. For low velocities (9 m/s) this bubble collapses, fragmenting the remainder of the drop while at greater velocities (15 m/s) the drop breaks up within the bubble before it condenses. At 22 and 28 m/s there is no vapour formation and the drop fragments due to hydrodynamic effects. Quantitative analysis of the radiographs is used to determine the mass distribution of the melt during the drop fragmentation. Comparison with earlier work in which the ambient flow is preceded by a strong shock wave indicates that the transition from thermal to hydrodynamic breakup is strongly dependent on the characteristics of the pressure field experienced by the drop. (author)

Back reaction of excitations on a vortex

Science.gov (United States)

Arodź, Henryk; Hadasz, Leszek

1997-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their back reaction on the vortex. In the present paper we investigate back reaction of Proca-type excitations on a straight linear vortex in the Abelian Higgs model. We propose an exact ansatz for fields of the excited vortex. From an initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the back reaction corrections. Their approximate solutions are found in the cases of plane wave and wave-packet-type excitations. We find that the excited vortex radiates the vector field and that the Higgs field has a very broad oscillating component.

Generalized Kutta–Joukowski theorem for multi-vortex and multi-airfoil flow (a lumped vortex model

Directory of Open Access Journals (Sweden)

Bai Chenyuan

2014-02-01

Full Text Available For purpose of easy identification of the role of free vortices on the lift and drag and for purpose of fast or engineering evaluation of forces for each individual body, we will extend in this paper the Kutta–Joukowski (KJ theorem to the case of inviscid flow with multiple free vortices and multiple airfoils. The major simplification used in this paper is that each airfoil is represented by a lumped vortex, which may hold true when the distances between vortices and bodies are large enough. It is found that the Kutta–Joukowski theorem still holds provided that the local freestream velocity and the circulation of the bound vortex are modified by the induced velocity due to the outside vortices and airfoils. We will demonstrate how to use the present result to identify the role of vortices on the forces according to their position, strength and rotation direction. Moreover, we will apply the present results to a two-cylinder example of Crowdy and the Wagner example to demonstrate how to perform fast force approximation for multi-body and multi-vortex problems. The lumped vortex assumption has the advantage of giving such kinds of approximate results which are very easy to use. The lack of accuracy for such a fast evaluation will be compensated by a rigorous extension, with the lumped vortex assumption removed and with vortex production included, in a forthcoming paper.

Numerical study of the vortex tube reconnection using vortex particle method on many graphics cards

Science.gov (United States)

Kudela, Henryk; Kosior, Andrzej

2014-08-01

Vortex Particle Methods are one of the most convenient ways of tracking the vorticity evolution. In the article we presented numerical recreation of the real life experiment concerning head-on collision of two vortex rings. In the experiment the evolution and reconnection of the vortex structures is tracked with passive markers (paint particles) which in viscous fluid does not follow the evolution of vorticity field. In numerical computations we showed the difference between vorticity evolution and movement of passive markers. The agreement with the experiment was very good. Due to problems with very long time of computations on a single processor the Vortex-in-Cell method was implemented on the multicore architecture of the graphics cards (GPUs). Vortex Particle Methods are very well suited for parallel computations. As there are myriads of particles in the flow and for each of them the same equations of motion have to be solved the SIMD architecture used in GPUs seems to be perfect. The main disadvantage in this case is the small amount of the RAM memory. To overcome this problem we created a multiGPU implementation of the VIC method. Some remarks on parallel computing are given in the article.

Numerical study of the vortex tube reconnection using vortex particle method on many graphics cards

International Nuclear Information System (INIS)

Kudela, Henryk; Kosior, Andrzej

2014-01-01

Vortex Particle Methods are one of the most convenient ways of tracking the vorticity evolution. In the article we presented numerical recreation of the real life experiment concerning head-on collision of two vortex rings. In the experiment the evolution and reconnection of the vortex structures is tracked with passive markers (paint particles) which in viscous fluid does not follow the evolution of vorticity field. In numerical computations we showed the difference between vorticity evolution and movement of passive markers. The agreement with the experiment was very good. Due to problems with very long time of computations on a single processor the Vortex-in-Cell method was implemented on the multicore architecture of the graphics cards (GPUs). Vortex Particle Methods are very well suited for parallel computations. As there are myriads of particles in the flow and for each of them the same equations of motion have to be solved the SIMD architecture used in GPUs seems to be perfect. The main disadvantage in this case is the small amount of the RAM memory. To overcome this problem we created a multiGPU implementation of the VIC method. Some remarks on parallel computing are given in the article.

Ozone and water vapour in the austral polar stratospheric vortex and sub-vortex

Directory of Open Access Journals (Sweden)

E. Peet

2004-12-01

Full Text Available In-situ measurements of ozone and water vapour, in the Antarctic lower stratosphere, were made as part of the APE-GAIA mission in September and October 1999. The measurements show a distinct difference above and below the 415K isentrope. Above 415K, the chemically perturbed region of low ozone and water vapour is clearly evident. Below 415K, but still above the tropopause, no sharp meridional gradients in ozone and water vapour were observed. The observations are consistent with analyses of potential vorticity from the European Centre for Medium Range Weather Forecasting, which show smaller radial gradients at 380K than at 450K potential temperature. Ozone loss in the chemically perturbed region above 415K averages 5ppbv per day for mid-September to mid-October. Apparent ozone loss rates in the sub-vortex region are greater, at 7ppbv per day. The data support, therefore, the existence of a sub-vortex region in which meridional transport is more efficient than in the vortex above. The low ozone mixing ratios in the sub-vortex region may be due to in-situ chemical destruction of ozone or transport of ozone-poor air out of the bottom of the vortex. The aircraft data we use cannot distinguish between these two processes. Key words. Meteorology and atmospheric dynamics polar meteorology – Atmospheric composition and structure (middle atmosphere–composition and chemistry

Vortex Ring Interaction with a Heated Screen

Science.gov (United States)

Smith, Jason; Krueger, Paul S.

2008-11-01

Previous examinations of vortex rings impinging on porous screens has shown the reformation of the vortex ring with a lower velocity after passing through the screen, the creation of secondary vortices, and mixing. A heated screen could, in principle, alter the vortex-screen interaction by changing the local liquid viscosity and density. In the present investigation, a mechanical piston-cylinder vortex ring generator was used to create vortex rings in an aqueous sucrose solution. The rings impinged on a screen of horizontal wires that were heated using electrical current. The flow was visualized with food color and video imaging. Tests with and without heat were conducted at a piston stroke-to-jet diameter ratio of 4 and a jet Reynolds number (Re) of 1000. The vortex rings slowed after passing through the screen, but in tests with heat, they maintained a higher fraction of their before-screen velocity due to reduction in fluid viscosity near the wires. In addition, small ``fingers'' that developed on the front of the vortex rings as they passed through the screen exhibited positive buoyancy effects in the heated case.

Effect of the Mitral Valve's Anterior Leaflet on Axisymmetry of Transmitral Vortex Ring.

Science.gov (United States)

Falahatpisheh, Ahmad; Pahlevan, Niema M; Kheradvar, Arash

2015-10-01

The shape and formation of transmitral vortex ring are shown to be associated with diastolic function of the left ventricle (LV). Transmitral vortex ring is a flow feature that is observed to be non-axisymmetric in a healthy heart and its inherent asymmetry in the LV assists in efficient ejection of the blood during systole. This study is a first step towards understanding the effects of the mitral valve's anterior leaflet on transmitral flow. We experimentally study a single-leaflet model of the mitral valve to investigate the effect of the anterior leaflet on the axisymmetry of the generated vortex ring based on the three-dimensional data acquired using defocusing digital particle image velocimetry. Vortex rings form downstream of a D-shaped orifice in presence or absence of the anterior leaflet in various physiological stroke ratios. The results of the statistical analysis indicate that the formed vortex ring downstream of a D-shaped orifice is markedly non-axisymmetric, and presence of the anterior leaflet improves the ring's axisymmetry. This study suggests that the improvement of axisymmetry in presence of the anterior leaflet might be due to coupled dynamic interaction between rolling-up of the shear layer at the edges of the D-shaped orifice and the borders of the anterior leaflet. This interaction can reduce the non-uniformity in vorticity generation, which results in more axisymmetric behavior compared to the D-shaped orifice without the anterior leaflet.

Vortex dynamics in superconducting Corbino disk at zero field

International Nuclear Information System (INIS)

Enomoto, Y.; Ohta, M.

2007-01-01

We study the radial current driven vortex dynamics in the Corbino disk sample at zero field, by using a logarithmically interacting point vortex model involving effect of temperature, random pinning centers, and disk wall confinement force. We also take into account both the current induced vortex pair nucleation and the vortex pair annihilation processes in the model. Simulation results demonstrate that the vortex motion induced voltage exhibits almost periodic pulse behavior in time, observed experimentally, for a certain range of the model parameters. Such an anomalous behavior is thought to originate from large fluctuations of the vortex number due to the collective dynamics of this vortex system

Square vortex lattice in p-wave superconductors

International Nuclear Information System (INIS)

Shiraishi, J.

1999-01-01

Making use of the Ginzburg Landau equation for isotropic p-wave superconductors, we construct the single vortex solution in part analytically. The fourfold symmetry breaking term arising from the tetragonal symmetry distortion of the Fermi surface is crucial, since this term indicates a fourfold distortion of the vortex core somewhat similar to the one found in d-wave superconductors. This fourfold distortion of the vortex core in turn favors the square vortex lattice as observed recently by small angle neutron scattering (SANS) experiment from Sr 2 RuO 4 . We find that the hexagonal vortex lattice at H = H c1 transforms into the square one for H = H cr = 0.26 H c2 . On the other hand the SANS data does not reveal such transition. The square vortex covers everywhere studied by the SANS implying H cr is very close to H c1 . Therefore some improvement in the present model is certainly desirable. (orig.)

Guiding-center dynamics of vortex dipoles in Bose-Einstein condensates

International Nuclear Information System (INIS)

Middelkamp, S.; Schmelcher, P.; Torres, P. J.; Kevrekidis, P. G.; Frantzeskakis, D. J.; Carretero-Gonzalez, R.; Freilich, D. V.; Hall, D. S.

2011-01-01

A quantized vortex dipole is the simplest vortex molecule, comprising two countercirculating vortex lines in a superfluid. Although vortex dipoles are endemic in two-dimensional superfluids, the precise details of their dynamics have remained largely unexplored. We present here several striking observations of vortex dipoles in dilute-gas Bose-Einstein condensates, and develop a vortex-particle model that generates vortex line trajectories that are in good agreement with the experimental data. Interestingly, these diverse trajectories exhibit essentially identical quasiperiodic behavior, in which the vortex lines undergo stable epicyclic orbits.

Vortex sorter for Bose-Einstein condensates

International Nuclear Information System (INIS)

Whyte, Graeme; Veitch, John; Courtial, Johannes; Oehberg, Patrik

2004-01-01

We have designed interferometers that sort Bose-Einstein condensates into their vortex components. The Bose-Einstein condensates in the two arms of the interferometer are rotated with respect to each other through fixed angles; different vortex components then exit the interferometer in different directions. The method we use to rotate the Bose-Einstein condensates involves asymmetric phase imprinting and is itself new. We have modeled rotation through fixed angles and sorting into vortex components with even and odd values of the topological charge of two-dimensional Bose-Einstein condensates in a number of states (pure or superposition vortex states for different values of the scattering length). Our scheme may have applications for quantum information processing

A Computational Fluid Dynamics Study of Swirling Flow Reduction by Using Anti-Vortex Baffle

Science.gov (United States)

Yang, H. Q.; Peugeot, John W.; West, Jeff S.

2017-01-01

An anti-vortex baffle is a liquid propellant management device placed adjacent to an outlet of the propellant tank. Its purpose is to substantially reduce or eliminate the formation of free surface dip and vortex, as well as prevent vapor ingestion into the outlet, as the liquid drains out through the flight. To design an effective anti-vortex baffle, Computational Fluid Dynamic (CFD) simulations were undertaken for the NASA Ares I vehicle LOX tank subjected to the simulated flight loads with and without the anti-vortex baffle. The Six Degree-Of-Freedom (6-DOF) dynamics experienced by the Crew Launch Vehicle (CLV) during ascent were modeled by modifying the momentum equations in a CFD code to accommodate the extra body forces from the maneuvering in a non-inertial frame. The present analysis found that due to large moments, the CLV maneuvering has a significant impact on the vortical flow generation inside the tank. Roll maneuvering and side loading due to pitch and yaw are shown to induce swirling flow. The vortical flow due to roll is symmetrical with respect to the tank centerline, while those induced by pitch and yaw maneuverings showed two vortices side by side. The study found that without the anti-vortex baffle, the swirling flow caused surface dip during the late stage of drainage and hence early vapor ingestion. The flow can also be non-uniform in the drainage pipe as the secondary swirling flow velocity component can be as high as 10% of the draining velocity. An analysis of the vortex dynamics shows that the swirling flow in the drainage pipe during the Upper Stage burn is mainly the result of residual vortices inside the tank due to the conservation of angular momentum. The study demonstrated that the swirling flow in the drainage pipe can be effectively suppressed by employing the anti-vortex baffle.

Vortex 'puddles' and magic vortex numbers in mesoscopic superconducting disks

Energy Technology Data Exchange (ETDEWEB)

Connolly, M R; Milosevic, M V; Bending, S J [Department of Physics, University of Bath - Claverton Down, Bath, BA2 7AY (United Kingdom); Clem, J R [Ames Laboratory Department of Physics and Astronomy - Iowa State University, Ames, IA 50011-3160 (United States); Tamegai, T, E-mail: mrc61@cam.ac.u [Department of Applied Physics, University of Tokyo - Hongo, Bunkyo-ku, Tokyo 113-8627 (Japan)

2009-03-01

The magnetic properties of a superconducting disk change dramatically when its dimensions become mesoscopic. Unlike large disks, where the screening currents induced by an applied magnetic field are strong enough to force vortices to accumulate in a 'puddle' at the centre, in a mesoscopic disk the interaction between one of these vortices and the edge currents can be comparable to the intervortex repulsion, resulting in a destruction of the ordered triangular vortex lattice structure at the centre. Vortices instead form clusters which adopt polygonal and shell-like structures which exhibit magic number states similar to those of charged particles in a confining potential, and electrons in artificial atoms. We have fabricated mesoscopic high temperature superconducting Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+delta} disks and investigated their magnetic properties using magneto-optical imaging (MOI) and high resolution scanning Hall probe microscopy (SHPM). The temperature dependence of the vortex penetration field measured using MOI is in excellent agreement with models of the thermal excitation of pancake vortices over edge barriers. The growth of the central vortex puddle has been directly imaged using SHPM and magic vortex numbers showing higher stability have been correlated with abrupt jumps in the measured local magnetisation curves.

Interaction of a strong vortex with decaying turbulence

International Nuclear Information System (INIS)

Terry, P.W.

1988-01-01

The evolution of a localized, axially symmetric vortex under the action of shear stresses associated with decaying two-dimensional turbulent vorticity which is inhomogeneous in the presence of the vortex is studied analytically. For a vortex which is sufficiently strong relative to the coefficient of turbulent eddy viscosity, it is shown that turbulent fluctuations in the vortex interior and diffusion of coherent vorticity by the turbulence localize to the vortex periphery. It is also found that the coefficient of diffusion is small compared to the coefficient of eddy viscosity. 8 refs

Back reaction of excitations on a vortex

International Nuclear Information System (INIS)

Arodz, H.; Hadasz, L.

1997-01-01

Excitations of a vortex are usually considered in a linear approximation neglecting their back reaction on the vortex. In the present paper we investigate back reaction of Proca-type excitations on a straight linear vortex in the Abelian Higgs model. We propose an exact ansatz for fields of the excited vortex. From an initial set of six nonlinear field equations we obtain (in a limit of weak excitations) two linear wave equations for the back reaction corrections. Their approximate solutions are found in the cases of plane wave and wave-packet-type excitations. We find that the excited vortex radiates the vector field and that the Higgs field has a very broad oscillating component. copyright 1997 The American Physical Society

Spectral analysis of point-vortex dynamics : first application to vortex polygons in a circular domain

NARCIS (Netherlands)

Speetjens, M.F.M.; Meleshko, V.V.; Heijst, van G.J.F.

2014-01-01

The present study addresses the classical problem of the dynamics and stability of a cluster of N point vortices of equal strength arranged in a polygonal configuration ("N-vortex polygons"). In unbounded domains, such N-vortex polygons are unconditionally stable for N

Dynamically controlled energy dissipation for fast magnetic vortex switching

Science.gov (United States)

Badea, R.; Berezovsky, J.

2017-09-01

Manipulation of vortex states in magnetic media provides new routes towards information storage and processing technology. The typical slow relaxation times (˜100 ns) of magnetic vortex dynamics may present an obstacle to the realization of these applications. Here, we investigate how a vortex state in a ferromagnetic microdisk can be manipulated in a way that translates the vortex core while enhancing energy dissipation to rapidly damp the vortex dynamics. We use time-resolved differential magneto-optical Kerr effect microscopy to measure the motion of the vortex core in response to applied magnetic fields. We first map out how the vortex core becomes sequentially trapped by pinning sites as it translates across the disk. After applying a fast magnetic field step to translate the vortex from one pinning site to another, we observe long-lived dynamics of the vortex as it settles to the new equilibrium. We then demonstrate how the addition of a short (<10 ns) magnetic field pulse can induce additional energy dissipation, strongly damping the long-lived dynamics. A model of the vortex dynamics using the Thiele equation of motion explains the mechanism behind this effect.

Vortex Filaments in Grids for Scalable, Fine Smoke Simulation.

Science.gov (United States)

Meng, Zhang; Weixin, Si; Yinling, Qian; Hanqiu, Sun; Jing, Qin; Heng, Pheng-Ann

2015-01-01

Vortex modeling can produce attractive visual effects of dynamic fluids, which are widely applicable for dynamic media, computer games, special effects, and virtual reality systems. However, it is challenging to effectively simulate intensive and fine detailed fluids such as smoke with fast increasing vortex filaments and smoke particles. The authors propose a novel vortex filaments in grids scheme in which the uniform grids dynamically bridge the vortex filaments and smoke particles for scalable, fine smoke simulation with macroscopic vortex structures. Using the vortex model, their approach supports the trade-off between simulation speed and scale of details. After computing the whole velocity, external control can be easily exerted on the embedded grid to guide the vortex-based smoke motion. The experimental results demonstrate the efficiency of using the proposed scheme for a visually plausible smoke simulation with macroscopic vortex structures.

Giant moving vortex mass in thick magnetic nanodots.

Science.gov (United States)

Guslienko, K Y; Kakazei, G N; Ding, J; Liu, X M; Adeyeye, A O

2015-09-10

Magnetic vortex is one of the simplest topologically non-trivial textures in condensed matter physics. It is the ground state of submicron magnetic elements (dots) of different shapes: cylindrical, square etc. So far, the vast majority of the vortex dynamics studies were focused on thin dots with thickness 5-50 nm and only uniform across the thickness vortex excitation modes were observed. Here we explore the fundamental vortex mode in relatively thick (50-100 nm) dots using broadband ferromagnetic resonance and show that dimensionality increase leads to qualitatively new excitation spectra. We demonstrate that the fundamental mode frequency cannot be explained without introducing a giant vortex mass, which is a result of the vortex distortion due to interaction with spin waves. The vortex mass depends on the system geometry and is non-local because of important role of the dipolar interaction. The mass is rather small for thin dots. However, its importance increases drastically with the dot thickness increasing.

Dynamic vortex dust structures in a nuclear-track plasma

International Nuclear Information System (INIS)

Rykov, V A; Khudyakov, A V; Filinov, V S; Vladimirov, V I; Deputatova, L V; Krutov, D V; Fortov, V E

2003-01-01

Results are presented from Monte Carlo calculations of the electric charge on dust grains in a plasma produced during the slowing down of radioactive decay products of californium nuclei in neon. The dust grain charging is explained as being due to the drift of electrons and ions in an external electric field. It is shown that the charges of the grains depend on their coordinates and strongly fluctuate with time. The time-averaged grain charges agree with the experimental data obtained on ordered liquid-like dust structures in a nuclear-track plasma. The time-averaged dust grain charges are used to carry out computer modelling of the formation of dynamic vortex structures observed in experiments. Evidence is obtained for the fact that the electrostatic forces experienced by the dust grains are potential in character. The paper is supplemented by a video clip showing the typical dynamics of the simulated vortex dust structure

Modeling Vortex Generators in a Navier-Stokes Code

Science.gov (United States)

Dudek, Julianne C.

2011-01-01

A source-term model that simulates the effects of vortex generators was implemented into the Wind-US Navier-Stokes code. The source term added to the Navier-Stokes equations simulates the lift force that would result from a vane-type vortex generator in the flowfield. The implementation is user-friendly, requiring the user to specify only three quantities for each desired vortex generator: the range of grid points over which the force is to be applied and the planform area and angle of incidence of the physical vane. The model behavior was evaluated for subsonic flow in a rectangular duct with a single vane vortex generator, subsonic flow in an S-duct with 22 corotating vortex generators, and supersonic flow in a rectangular duct with a counter-rotating vortex-generator pair. The model was also used to successfully simulate microramps in supersonic flow by treating each microramp as a pair of vanes with opposite angles of incidence. The validation results indicate that the source-term vortex-generator model provides a useful tool for screening vortex-generator configurations and gives comparable results to solutions computed using gridded vanes.

Experimental investigations on the vortex instability and time effects of YBa2Cu3O7−x coated conductors

International Nuclear Information System (INIS)

Zhang, Xingyi; Zhou, Jun; Yue, Donghua; Liu, Wei; Zhou, Youhe

2014-01-01

Highlights: •Influences of the current sweep rate on the I–V and V–t curves are investigated. •Significant voltages jumps including increase and drop are observed. •With an increase of magnetic field, the maximum voltage increases. -- Abstract: We have investigated the effect of the current sweep rate (CSR) on the vortex dynamic in the YBa 2 Cu 3 O 7–x coated conductors (YBCO CCs). It is found that the CSR has several effects on vortex motion in that it gives rise to enhancement of dissipation as the CSR decreases, significant time effects and instabilities are observed in current–voltage (I–V) and voltage–time (V–t) curves. Thus, the CSR on practical applications of the YBCO CCs can be optimized, and relevant CSR which is designing superconducting devices made by the YBCO CCs should be considered in future

Three-dimensional supersonic vortex breakdown

Science.gov (United States)

Kandil, Osama A.; Kandil, Hamdy A.; Liu, C. H.

1993-01-01

Three-dimensional supersonic vortex-breakdown problems in bound and unbound domains are solved. The solutions are obtained using the time-accurate integration of the unsteady, compressible, full Navier-Stokes (NS) equations. The computational scheme is an implicit, upwind, flux-difference splitting, finite-volume scheme. Two vortex-breakdown applications are considered in the present paper. The first is for a supersonic swirling jet which is issued from a nozzle into a supersonic uniform flow at a lower Mach number than that of the swirling jet. The second is for a supersonic swirling flow in a configured circular duct. In the first application, an extensive study of the effects of grid fineness, shape and grid-point distribution on the vortex breakdown is presented. Four grids are used in this study and they show a substantial dependence of the breakdown bubble and shock wave on the grid used. In the second application, the bubble-type and helix-type vortex breakdown have been captured.

Experiments on the breakup of drop-impact crowns by Marangoni holes

KAUST Repository

Aljedaani, Abdulrahman Barakat

2018-04-04

We investigate experimentally the breakup of the Edgerton crown due to Marangoni instability when a highly viscous drop impacts on a thin film of lower-viscosity liquid, which also has different surface tension than the drop liquid. The presence of this low-viscosity film modifies the boundary condition, giving effective slip to the drop along the solid substrate. This allows the high-viscosity drop to form a regular bowl-shaped crown, which rises vertically away from the solid and subsequently breaks up through the formation of a multitude of Marangoni holes. Previous experiments have proposed that the breakup of the crown results from a spray of fine droplets ejected from the thin low-viscosity film on the solid, e.g. Thoroddsen et al. (J. Fluid Mech., vol. 557, 2006, pp. 63–72). These droplets can hit the inner side of the crown forming spots with lower surface tension, which drives a thinning patch leading to the hole formation. We test the validity of this assumption with close-up imaging to identify individual spray droplets, to show how they hit the crown and their lower surface tension drive the hole formation. The experiments indicate that every Marangoni-driven patch/hole is promoted by the impact of such a microdroplet. Surprisingly, in experiments with pools of higher surface tension, we also see hole formation. Here the Marangoni stress changes direction and the hole formation looks qualitatively different, with holes and ruptures forming in a repeatable fashion at the centre of each spray droplet impact. Impacts onto films of the same liquid, or onto an immiscible liquid, do not in general form holes. We furthermore characterize the effects of drop viscosity and substrate-film thickness on the overall evolution of the crown. We also measure the three characteristic velocities associated with the hole formation: i.e. the Marangoni-driven growth of the thinning patches, the rupture speed of the resulting thin films inside these patches and finally the

Diagnostics of BubbleMode Vortex Breakdown in Swirling Flow in a Large-Aspect-Ratio Cylinder

DEFF Research Database (Denmark)

Kulikov, D. V.; Mikkelsen, Robert Flemming; Naumov, Igor

2014-01-01

We report for the first time on the possible formation of regions with counterflow (bubble-mode vortex breakdown or explosion) at the center of strongly swirling flow generated by a rotating endwall in a large-aspect-ratio cylindrical cavity filled with a liquid medium. Previously, the possibility...... of bubble-mode breakdown was studied in detail for cylindrical cavities of moderate aspect ratio (length to radius ratios up to H/R ∼ 3.5), while flows in large-aspect-ratio cylinders were only associated with regimes of self-organized helical vortex multiplets. In the present study, a regime...

High Magnetic Field Vortex Microscopy by NMR

Science.gov (United States)

Mitrović, V. F.; Sigmund, E. E.; Bachman, H. N.; Halperin, W. P.; Reyes, A. P.; Kuhns, P.; Moulton, W. G.

2001-03-01

At low temperatures the ^17O NMR spectrum of HTS exhibits a characteristic vortex lattice line shape. Measurements of spin-lattice relaxation rate, T_1-1, across the vortex spectrum represent a probe of low-energy quasiparticle excitations as a function of distance from the vortex core. We report ^17O(2,3) T_1-1 measurements of YBa_2Cu_3O7 at low temperatures in magnetic fields up to 37 T. We find that the rate increases on approaching the vortex core. In the vortex core region at 37 T we observe an additional increase in the relaxation rate. The temperature dependence of the rate will also be discussed. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity.

Vortex molecule in a nanoscopic square superconducting plate

International Nuclear Information System (INIS)

Suematsu, Hisataka; Kato, Masaru; Ishida, Takekazu; Koyama, Tomio; Machida, Masahiko

2010-01-01

Using the finite element method and solving the Bogoliubov-de Gennes equation, we have investigated magnetic field dependence of the stable vortex structures in a mesoscopic superconducting plate at low temperature (T = 0.1T c ). Because of the compactness of vortex configuration, there is interference between bound states around vortices and such quasi-particle structure affects the vortex configuration. Especially in two-vortices state, vortices form a molecule-like state, where bound states of each vortex form molecular orbital like bonding and anti-bonding states. The vortex configuration is different from that, which is expected from the repulsive interaction between vortices. (author)

Tunable magnetic vortex resonance in a potential well

Science.gov (United States)

Warnicke, P.; Wohlhüter, P.; Suszka, A. K.; Stevenson, S. E.; Heyderman, L. J.; Raabe, J.

2017-11-01

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

Dynamic Control of Collapse in a Vortex Airy Beam

Science.gov (United States)

Chen, Rui-Pin; Chew, Khian-Hooi; He, Sailing

2013-01-01

Here we study systematically the self-focusing dynamics and collapse of vortex Airy optical beams in a Kerr medium. The collapse is suppressed compared to a non-vortex Airy beam in a Kerr medium due to the existence of vortex fields. The locations of collapse depend sensitively on the initial power, vortex order, and modulation parameters. The collapse may occur in a position where the initial field is nearly zero, while no collapse appears in the region where the initial field is mainly distributed. Compared with a non-vortex Airy beam, the collapse of a vortex Airy beam can occur at a position away from the area of the initial field distribution. Our study shows the possibility of controlling and manipulating the collapse, especially the precise position of collapse, by purposely choosing appropriate initial power, vortex order or modulation parameters of a vortex Airy beam. PMID:23518858

Vortex-line fluctuations in model high-temperature superconductors

International Nuclear Information System (INIS)

Li, Y.; Teitel, S.

1993-01-01

We carry out Monte Carlo simulations of the uniformly frustrated three-dimensional XY model, as a model for vortex-line fluctuations in a high-T c superconductor in an external magnetic field. A density of vortex lines of f=1/25 is considered. We find two sharp phase transitions. The low-T superconducting phase is an ordered vortex-line lattice. The high-T normal phase is a vortex-line liquid, with much entangling, cutting, and loop excitations. An intermediate phase is found, which is characterized as a vortex-line liquid of disentangled, approximately straight, lines. In this phase, the system displays superconducting properties in the direction parallel to the magnetic field, but normal behavior in planes perpendicular to the field. A detailed analysis of the vortex structure function is carried out

Aperiodicity Correction for Rotor Tip Vortex Measurements

Science.gov (United States)

Ramasamy, Manikandan; Paetzel, Ryan; Bhagwat, Mahendra J.

2011-01-01

The initial roll-up of a tip vortex trailing from a model-scale, hovering rotor was measured using particle image velocimetry. The unique feature of the measurements was that a microscope was attached to the camera to allow much higher spatial resolution than hitherto possible. This also posed some unique challenges. In particular, the existing methodologies to correct for aperiodicity in the tip vortex locations could not be easily extended to the present measurements. The difficulty stemmed from the inability to accurately determine the vortex center, which is a prerequisite for the correction procedure. A new method is proposed for determining the vortex center, as well as the vortex core properties, using a least-squares fit approach. This approach has the obvious advantage that the properties are derived from not just a few points near the vortex core, but from a much larger area of flow measurements. Results clearly demonstrate the advantage in the form of reduced variation in the estimated core properties, and also the self-consistent results obtained using three different aperiodicity correction methods.

Superconductivity and vortex properties in various multilayers

International Nuclear Information System (INIS)

Koorevaar, P.

1994-01-01

In this thesis three qualitatively different type of superconducting multilayers are studied. We discuss the vortex lattice structure in Nb/NbZr multilayers, a system where both type of constituting layers are superconducting. At certain temperatures and for parallel fields close to H c2parallel , the Nb/NbZr system has a strongly modulated order parameter, and in this aspect resembles the high-Tc materials. By lowering the field the modulation decreases, having important consequences for the vortex lattice structure. By studying the transport critical currents we show that in the case of strong modulation the vortex lattice has a kinked structure, but at weaker modulations the vortices are straight, and the change in modulation actually results in a vortex lattice transition. Our study confirms the picture of the existence of kinked vortex lattices, but it is rather surprising that these kinked structures can exist in a system which in itself is not at all that anisotropic. It indicates the relevance of other parameters governing the vortex lattice structure. (orig.)

Computational investigation of the temperature separation in vortex chamber

International Nuclear Information System (INIS)

Anish, S.; Setoguchi, T.; Kim, H. D.

2014-01-01

The vortex chamber is a mechanical device, without any moving parts that separates compressed gas into a high temperature region and a low temperature region. Functionally vortex chamber is similar to a Ranque-Hilsch vortex tube (RVHT), but it is a simpler and compact structure. The objective of the present study is to investigate computationally the physical reasoning behind the energy separation mechanism inside a vortex chamber. A computational analysis has been performed using three-dimensional compressible Navier Stokes equations. A fully implicit finite volume scheme was used to solve the governing equations. A commercial software ANSYS CFX is used for this purpose. The computational predictions were validated with existing experimental data. The results obtained show that the vortex chamber contains a large free vortex zone and a comparatively smaller forced vortex region. The physical mechanism that causes the heating towards periphery of the vortex chamber is identified as the work done by the viscous force. The cooling at the center may be due to expansion of the flow. The extent of temperature separation greatly depends on the outer diameter of the vortex chamber. A small amount of compression is observed towards the periphery of the vortex chamber when the outer diameter is reduced.

Topological Vortex and Knotted Dissipative Optical 3D Solitons Generated by 2D Vortex Solitons.

Science.gov (United States)

Veretenov, N A; Fedorov, S V; Rosanov, N N

2017-12-29

We predict a new class of three-dimensional (3D) topological dissipative optical one-component solitons in homogeneous laser media with fast saturable absorption. Their skeletons formed by vortex lines where the field vanishes are tangles, i.e., N_{c} knotted or unknotted, linked or unlinked closed lines and M unclosed lines that thread all the closed lines and end at the infinitely far soliton periphery. They are generated by embedding two-dimensional laser solitons or their complexes in 3D space after their rotation around an unclosed, infinite vortex line with topological charge M_{0} (N_{c}, M, and M_{0} are integers). With such structure propagation, the "hula-hoop" solitons form; their stability is confirmed numerically. For the solitons found, all vortex lines have unit topological charge: the number of closed lines N_{c}=1 and 2 (unknots, trefoils, and Solomon knots links); unclosed vortex lines are unknotted and unlinked, their number M=1, 2, and 3.

The formation of intestinal organoids in a hanging drop culture.

Science.gov (United States)

Panek, Malgorzata; Grabacka, Maja; Pierzchalska, Malgorzata

2018-01-25

Recently organoids have become widely used in vitro models of many tissue and organs. These type of structures, originated from embryonic or adult mammalian intestines, are called "mini guts". They organize spontaneously when intestinal crypts or stem cells are embedded in the extracellular matrix proteins preparation scaffold (Matrigel). This approach has some disadvantages, as Matrigel is undefined (the concentrations of growth factors and other biologically active components in it may vary from batch to batch), difficult to handle and expensive. Here we show that the organoids derived from chicken embryo intestine are formed in a hanging drop without embedding, providing an attractive alternative for currently used protocols. Using this technique we obtained compact structures composed of contiguous organoids, which were generally similar to chicken organoids cultured in Matrigel in terms of morphology and expression of intestinal epithelial markers. Due to the simplicity, high reproducibility and throughput capacity of hanging drop technique our model may be applied in various studies concerning the gut biology.

The bathtub vortex in a rotating container

DEFF Research Database (Denmark)

Andersen, Anders Peter; Bohr, Tomas; Stenum, B.

2006-01-01

We study the time-independent free-surface flow which forms when a fluid drains out of a container, a so-called bathtub vortex. We focus on the bathtub vortex in a rotating container and describe the free-surface shape and the complex flow structure using photographs of the free surface, flow...... expansion approximation of the central vortex core and reduce the model to a single first-order equation. We solve the equation numerically and find that the axial velocity depends linearly on height whereas the azimuthal velocity is almost independent of height. We discuss the model of the bathtub vortex...

A counter-rotating vortex pair in inviscid fluid

Science.gov (United States)

Habibah, Ummu; Fukumoto, Yasuhide

2017-12-01

We study the motion of a counter-rotating vortex pair with the circulations ±Γ move in incompressible fluid. The assumption is made that the core is very thin, that is the core radius σ is much smaller than the vortex radius d such that ɛ = σ/d ≪ 1. With this condition, the method of matched asymptotic expansion is employed. The solutions of the Navier-Stokes equations and the Biot-Savart law, regarding the inner and outer solutions respectively, are constructed in the form of a small parameter. An asymptotic expansion of the Biot-Savart law near the vortex core provides with the matching condition for an asymptotic expansion for limiting the Navier-Stokes equations for large radius r. The general formula of an anti-parallel vortex pair is established. At leading order O(ɛ0), we apply the special case in inviscid fluid, the Rankine vortex, a circular vortex of uniform vorticity. Furthermore at leading order O(ɛ5) we show the traveling speed of a vortex pair.

Quantum Kinematics of Bosonic Vortex Loops

International Nuclear Information System (INIS)

Goldin, G.A.; Owczarek, R.; Sharp, D.H.

1999-01-01

Poisson structure for vortex filaments (loops and arcs) in 2D ideal incompressible fluid is analyzed in detail. Canonical coordinates and momenta on coadjoint orbits of the area-preserving diffeomorphism group, associated with such vortices, are found. The quantum space of states in the simplest case of ''bosonic'' vortex loops is built within a geometric quantization approach to the description of a quantum fluid. Fock-like structure and non-local creation and annihilation operators of quantum vortex filaments are introduced

Bifurcation and instability problems in vortex wakes

DEFF Research Database (Denmark)

Aref, Hassan; Brøns, Morten; Stremler, Mark A.

2007-01-01

A number of instability and bifurcation problems related to the dynamics of vortex wake flows are addressed using various analytical tools and approaches. We discuss the bifurcations of the streamline pattern behind a bluff body as a vortex wake is produced, a theory of the universal Strouhal......-Reynolds number relation for vortex wakes, the bifurcation diagram for "exotic" wake patterns behind an oscillating cylinder first determined experimentally by Williamson & Roshko, and the bifurcations in topology of the streamlines pattern in point vortex streets. The Hamiltonian dynamics of point vortices...... in a periodic strip is considered. The classical results of von Kármán concerning the structure of the vortex street follow from the two-vortices-in-a-strip problem, while the stability results follow largely from a four-vortices-in-a-strip analysis. The three-vortices-in-a-strip problem is argued...

On the self-induced motion of a helical vortex

NARCIS (Netherlands)

Boersma, J.; Wood, D.H.

1999-01-01

The velocity field in the immediate vicinity of a curved vortex comprises a circulation around the vortex, a component due to the vortex curvature, and a ‘remainder’ due to the more distant parts of the vortex. The first two components are relatively well understood but the remainder is known only

Melting of heterogeneous vortex matter: The vortex 'nanoliquid'

Indian Academy of Sciences (India)

E ZELDOV2, A SOIBEL3, F de la CRUZ4,CJ van der BEEK5,. M KONCZYKOWSKI5, T ... 2Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot. 76100, Israel ..... heterogeneous nature of the vortex nanoliquid.

Motion of a single quantized vortex in an orifice

International Nuclear Information System (INIS)

Schwarz, K.W.

1993-01-01

Discrete phase-slip events are observed when superfluid 4 He moves through a microscopic orifice. In order to understand such behavior, one must know (a) how a quantized vortex is introduced into the orifice, and (b) how such a vortex evolves fluid dynamically so as to absorb energy from the applied flow field. To begin the study of the latter question, the authors present calculations done with an idealized orifice geometry. It is found that vortex loops larger than a critical size are carried out of the orifice and stretched by the diverging flow. As it stretches, such a vortex will cross the orifice, the energy required to stretch the vortex being absorbed from the flow field. Both a vortex loop introduced directly into the orifice and a remanent vortex extending to infinity will be discussed

Theory of vortex flows in partially ionized magnetoplasmas

Energy Technology Data Exchange (ETDEWEB)

Jovanovic, D.; Shukla, P.K

2004-06-07

A complete theory for vortex flows in partially ionized magnetoplasmas is presented. Accurate analytical and numerical results are obtained concerning the structure of a Burger's vortex and a tripolar vortex. A novel type of rotating tripolar vortices with elliptic cores are found in the systems dominated by the convection in incompressible flows, but whose generation is triggered by the diffusive and compressible effects. Our vortex flow models successfully explain recent observations from laboratory magnetoplasmas and geophysical flows.

Vortex Lattices in the Bose-Fermi Superfluid Mixture.

Science.gov (United States)

Jiang, Yuzhu; Qi, Ran; Shi, Zhe-Yu; Zhai, Hui

2017-02-24

In this Letter we show that the vortex lattice structure in the Bose-Fermi superfluid mixture can undergo a sequence of structure transitions when the Fermi superfluid is tuned from the BCS regime to the BEC regime. This is due to the difference in the vortex core structure of a Fermi superfluid in the BCS regime and in the BEC regime. In the BCS regime the vortex core is nearly filled, while the density at the vortex core gradually decreases until it empties out in the BEC regime. Therefore, with the density-density interaction between the Bose and the Fermi superfluids, interaction between the two sets of vortex lattices gets stronger in the BEC regime, which yields the structure transition of vortex lattices. In view of the recent realization of this superfluid mixture and vortices therein, our theoretical predication can be verified experimentally in the near future.

Generalized Kutta–Joukowski theorem for multi-vortex and multi-airfoil flow with vortex production — A general model

Directory of Open Access Journals (Sweden)

Bai Chenyuan

2014-10-01

Full Text Available By using a special momentum approach and with the help of interchange between singularity velocity and induced flow velocity, we derive in a physical way explicit force formulas for two-dimensional inviscid flow involving multiple bound and free vortices, multiple airfoils, and vortex production. These force formulas hold individually for each airfoil thus allowing for force decomposition, and the contributions to forces from singularities (such as bound and image vortices, sources, and doublets and bodies out of an airfoil are related to their induced velocities at the locations of singularities inside this airfoil. The force contribution due to vortex production is related to the vortex production rate and the distance between each pair of vortices in production, thus frame-independent. The formulas are validated against a number of standard problems. These force formulas, which generalize the classic Kutta–Joukowski theorem (for a single bound vortex and the recent generalized Lagally theorem (for problems without a bound vortex and vortex production to more general cases, can be used to identify or understand the roles of outside vortices and bodies on the forces of the actual body, optimize arrangement of outside vortices and bodies for force enhancement or reduction, and derive analytical force formulas once the flow field is given or known.

Modeling of aerodynamics in vortex furnace

Energy Technology Data Exchange (ETDEWEB)

Anufriev, I.; Krasinsky, D. [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. of Thermophysics; Salomatov, V.; Anikin, Y.; Sharypov, O. [Russian Academy of Sciences, Novosibirsk (Russian Federation). Inst. of Thermophysics; Novosibirsk State Univ. (Russian Federation); Enkhjargal, Kh. [Mongol Univ. of Science and Technology, Ulan Bator (Mongolia)

2013-07-01

At present, the torch burning technology of pulverized-coal fuel in vortex flow is one of the most prospective and environmentally-friendly combustion technologies of low-grade coals. Appropriate organization of aerodynamics may influence stability of temperature and heat flux distributions, increase slag catching, and reduce toxic emissions. Therefore, from scientific point of view it is interesting to investigate aerodynamics in the devices aiming at justification of design and operating parameters for new steam generators with vortex furnace, and upgrade of existing boiler equipment. The present work is devoted to physical and mathematical modeling of interior aerodynamics of vortex furnace of steam generator of thermal power plants. Research was carried out on the air isothermal model which geometry was similar to one section of the experimental- industrial boiler TPE-427 of Novosibirsk TPS-3. Main elements of vortex furnace structure are combustion chamber, diffuser, and cooling chamber. The model is made from organic glass; on the front wall two rectangular nozzles (through which compressed air is injected) are placed symmetrically at 15 to the horizon. The Laser Doppler Velocimeter LAD-05 was used for non-contact measurement of vortex flow characteristics. Two velocity components in the XY-plane (in different cross- sections of the model) were measured in these experiments. Reynolds number was 3.10{sup 5}. Numerical simulation of 3-D turbulent isothermal flow was performed with the use of CFD package FLUENT. Detailed structure of the flow in vortex furnace model has been obtained in predictions. The distributions of main flow characteristics (pressure, velocity and vorticity fields, turbulent kinetic energy) are presented. The obtained results may be used at designing boilers with vortex furnace. Computations were performed using the supercomputer NKS-160.

Vortex operators in gauge field theories

International Nuclear Information System (INIS)

Polchinski, J.

1980-07-01

Several related aspects of the 't Hooft vortex operator are studied. The current picture of the vacuum of quantum chromodynamics, the idea of dual field theories, and the idea of the vortex operator are reviewed first. The Abelian vortex operator written in terms of elementary fields and the calculation of its Green's functions are considered. A two-dimensional solvable model of a Dirac string is presented. The expression of the Green's functions more neatly in terms of Wu and Yang's geometrical idea of sections is addressed. The renormalization of the Green's functions of two kinds of Abelian looplike operators, the Wilson loop and the vortex operator, is studied; for both operators only an overall multiplicative renormalization is needed. In the case of the vortex this involves a surprising cancellation. Next, the dependence of the Green's functions of the Wilson and 't Hooft operators on the nature of the vacuum is discussed. The cluster properties of the Green's functions are emphasized. It is seen that the vortex operator in a massive Abelian theory always has surface-like clustering. The form of Green's functions in terms of Feynman graphs is the same in Higgs and symmetric phases; the difference appears in the sum over all tadpole trees. Finally, systems having fields in the fundamental representation are considered. When these fields enter only weakly into the dynamics, a vortex-like operator is anticipated. Any such operator can no longer be local looplike, but must have commutators at long range. A U(1) lattice gauge theory with two matter fields, one singly charged (fundamental) and one doubly charged (adjoint), is examined. When the fundamental field is weakly coupled, the expected phase transitions are found. When it is strongly coupled, the operator still appears to be a good order parameter, a discontinuous change in its behavior leads to a new phase transition. 18 figures

Vorticity budget of a tornado-like vortex

Energy Technology Data Exchange (ETDEWEB)

Sassa, Koji; Takemura, Saki, E-mail: sassa@kochi-u.ac.jp [Department of Applied Science, Kochi University (Japan)

2011-12-22

We evaluated the vorticity budget of a tornado-like vortex by measuring vertical and horizontal circulations of it. Though spiral horizontal vortices are clearly observed to converge and tilted into the tornado-like vortex, their circulation is quite small. The conversion of the vertical vorticity concentrated at the side of the spiral horizontal vortices was found to mainly contribute to the maintenance of the tornado-like vortex.

Distributed amplifier using Josephson vortex flow transistors

International Nuclear Information System (INIS)

McGinnis, D.P.; Beyer, J.B.; Nordman, J.E.

1986-01-01

A wide-band traveling wave amplifier using vortex flow transistors is proposed. A vortex flow transistor is a long Josephson junction used as a current controlled voltage source. The dual nature of this device to the field effect transistor is exploited. A circuit model of this device is proposed and a distributed amplifier utilizing 50 vortex flow transistors is predicted to have useful gain to 100 GHz

Nonlinear Binormal Flow of Vortex Filaments

Science.gov (United States)

Strong, Scott; Carr, Lincoln

2015-11-01

With the current advances in vortex imaging of Bose-Einstein condensates occurring at the Universities of Arizona, São Paulo and Cambridge, interest in vortex filament dynamics is experiencing a resurgence. Recent simulations, Salman (2013), depict dissipative mechanisms resulting from vortex ring emissions and Kelvin wave generation associated with vortex self-intersections. As the local induction approximation fails to capture reconnection events, it lacks a similar dissipative mechanism. On the other hand, Strong&Carr (2012) showed that the exact representation of the velocity field induced by a curved segment of vortex contains higher-order corrections expressed in powers of curvature. This nonlinear binormal flow can be transformed, Hasimoto (1972), into a fully nonlinear equation of Schrödinger type. Continued transformation, Madelung (1926), reveals that the filament's square curvature obeys a quasilinear scalar conservation law with source term. This implies a broader range of filament dynamics than is possible with the integrable linear binormal flow. In this talk we show the affect higher-order corrections have on filament dynamics and discuss physical scales for which they may be witnessed in future experiments. Partially supported by NSF.

The Acoustically Driven Vortex Cannon

Science.gov (United States)

Perry, Spencer B.; Gee, Kent L.

2014-01-01

Vortex cannons have been used by physics teachers for years, mostly to teach the continuity principle. In its simplest form, a vortex cannon is an empty coffee can with a hole cut in the bottom and the lid replaced. More elaborate models can be purchased through various scientific suppliers under names such as "Air Cannon" and…

Vortex lattices in layered superconductors

International Nuclear Information System (INIS)

Prokic, V.; Davidovic, D.; Dobrosavljevic-Grujic, L.

1995-01-01

We study vortex lattices in a superconductor--normal-metal superlattice in a parallel magnetic field. Distorted lattices, resulting from the shear deformations along the layers, are found to be unstable. Under field variation, nonequilibrium configurations undergo an infinite sequence of continuous transitions, typical for soft lattices. The equilibrium vortex arrangement is always a lattice of isocell triangles, without shear

Magnetic vortex state and multi-domain pattern in electrodeposited hemispherical nanogranular nickel films

International Nuclear Information System (INIS)

Samardak, Alexander; Sukovatitsina, Ekaterina; Ognev, Alexey; Stebliy, Maksim; Davydenko, Alexander; Chebotkevich, Ludmila; Keun Kim, Young; Nasirpouri, Forough; Janjan, Seyed-Mehdi; Nasirpouri, Farzad

2014-01-01

Magnetic states of nickel nanogranular films were studied in two distinct structures of individual and agglomerated granules electrodeposited on n-type Si(1 1 1) surface from a modified Watts bath at a low pH of 2. Magnetic force microscopy and micromagnetic simulations revealed three-dimensional out-of-plane magnetic vortex states in stand-alone hemispherical granules and their arrays, and multi-domain patterns in large agglomerates and integrated films. Once the granules coalesce into small chains or clusters, the coercivity values increased due to the reduction of inter-granular spacing and strengthening of the magnetostatic interaction. Further growth leads to the formation of a continuous granulated film which strongly affected the coercivity and remanence. This was characterized by the domain wall nucleation and propagation leading to a stripe domain pattern. Magnetoresistance measurements as a function of external magnetic field are indicative of anisotropic magnetoresistance (AMR) for the continuous films electrodeposited on Si substrate. - Highlights: • Magnetic states of electrodeposited nickel in isolated spherical and agglomerated nanogranules, and a continuous film. • Preferential magnetization reversal mechanism in isolated granules is vortex state. • Micromagnetic simulations confirm the three-dimensional vortex. • Transition between the vortex state and multi-domain magnetic pattern causes a significant decrease in the coercive force. • Continuous nickel films electrodeposited on silicon substrate exhibit AMR whose magnitude increases with the film thickness

Vortex particle method in parallel computations on graphical processing units used in study of the evolution of vortex structures

International Nuclear Information System (INIS)

Kudela, Henryk; Kosior, Andrzej

2014-01-01

Understanding the dynamics and the mutual interaction among various types of vortical motions is a key ingredient in clarifying and controlling fluid motion. In the paper several different cases related to vortex tube interactions are presented. Due to problems with very long computation times on the single processor, the vortex-in-cell (VIC) method is implemented on the multicore architecture of a graphics processing unit (GPU). Numerical results of leapfrogging of two vortex rings for inviscid and viscous fluid are presented as test cases for the new multi-GPU implementation of the VIC method. Influence of the Reynolds number on the reconnection process is shown for two examples: antiparallel vortex tubes and orthogonally offset vortex tubes. Our aim is to show the great potential of the VIC method for solutions of three-dimensional flow problems and that the VIC method is very well suited for parallel computation. (paper)

A Model for the Onset of Vortex Breakdown

Science.gov (United States)

Mahesh, K.

1996-01-01

A large body of information exists on the breakdown of incompressible streamwise vortices. Less is known about vortex breakdown at high speeds. An interesting example of supersonic vortex breakdown is the breakdown induced by the interaction of vortices with shock waves. The flow in supersonic engine inlets and over high-speed delta wings constitute technologically important examples of this phenomenon, which is termed 'shock-induced vortex breakdown'. In this report, we propose a model to predict the onset of shock-induced vortex breakdown. The proposed model has no adjustable constants, and is compared to both experiment and computation. The model is then extended to consider two other problems: the breakdown of a free compressible vortex, and free incompressible vortex breakdown. The same breakdown criterion is used in all three problems to predict the onset of breakdown. Finally, a new breakdown map is proposed that allows the simultaneous comparison of data from flows ranging from incompressible breakdown to breakdown induced by a shock wave.

Examples of Applications of Vortex Methods to Wind Energy

DEFF Research Database (Denmark)

Branlard, Emmanuel Simon Pierre

2017-01-01

The current chapter presents wind-energy simulations obtained with the vortex code OmniVor (described in Chap. 44 ) and compared to BEM, CFD and measurements. The chapter begins by comparing rotor loads obtained with vortex methods, BEM and actuator-line simulations of wind turbines under uniform...... and yawed inflows. The second section compares wakes and flow fields obtained by actuator-disk simulations and a free-wake vortex code that uses vortex segments and vortex particles. The third section compares different implementations of viscous diffusion models and investigate their effects...

Controlling abruptly autofocusing vortex beams to mitigate crosstalk and vortex splitting in free-space optical communication.

Science.gov (United States)

Yan, Xu; Guo, Lixin; Cheng, Mingjian; Li, Jiangting

2018-05-14

Orbital angular momentum (OAM) mode crosstalk induced by atmospheric turbulence is a challenging phenomenon commonly occurring in OAM-based free-space optical (FSO) communication. Recent advances have facilitated new practicable methods using abruptly autofocusing light beams for weakening the turbulence effect on the FSO link. In this work, we show that a circular phase-locked Airy vortex beam array (AVBA) with sufficient elements has the inherent ability to form an abruptly autofocusing light beam carrying OAM, and its focusing properties can be controlled on demand by adjusting the topological charge values and locations of these vortices embedded in the array elements. The performance of a tailored Airy vortex beam array (TAVBA) through atmospheric turbulence is numerically studied. In a comparison with the ring Airy vortex beam (RAVB), the results indicate that TAVBA can be a superior light source for effectively reducing the intermodal crosstalk and vortex splitting, thus leading to improvement in the FSO system performance.

Vortex Shedding Inside a Baffled Air Duct

Science.gov (United States)

Davis, Philip; Kenny, R. Jeremy

2010-01-01

Common in the operation of both segmented and un-segmented large solid rocket motors is the occurrence of vortex shedding within the motor chamber. A portion of the energy within a shed vortex is converted to acoustic energy, potentially driving the longitudinal acoustic modes of the motor in a quasi-discrete fashion. This vortex shedding-acoustic mode excitation event occurs for every Reusable Solid Rocket Motor (RSRM) operation, giving rise to subsequent axial thrust oscillations. In order to better understand this vortex shedding/acoustic mode excitation phenomena, unsteady CFD simulations were run for both a test geometry and the full scale RSRM geometry. This paper covers the results from the subscale geometry runs, which were based on work focusing on the RSRM hydrodynamics. Unsteady CFD simulation parameters, including boundary conditions and post-processing returns, are reviewed. The results were further post-processed to identify active acoustic modes and vortex shedding characteristics. Probable locations for acoustic energy generation, and subsequent acoustic mode excitation, are discussed.

Vortex dynamics in nonrelativistic version of Abelian Higgs model: Effects of the medium on the vortex motion

Directory of Open Access Journals (Sweden)

Kozhevnikov Arkadii

2016-01-01

Full Text Available The closed vortex dynamics is considered in the nonrelativistic version of the Abelian Higgs Model. The effect of the exchange of excitations propagating in the medium on the vortex string motion is taken into account. The obtained are the effective action and the equation of motion both including the exchange of the propagating excitations between the distant segments of the vortex and the possibility of its interaction with the static fermion asymmetric background. They are applied to the derivation of the time dependence of the basic geometrical contour characteristics.

Flow in a circular expansion pipe flow: effect of a vortex perturbation on localised turbulence

Energy Technology Data Exchange (ETDEWEB)

Selvam, Kamal; Peixinho, Jorge [Laboratoire Ondes Milieux Complexes, CNRS and Université du Havre, F-76600 Le Havre (France); Willis, Ashley P, E-mail: jorge.peixinho@univ-lehavre.fr [School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH (United Kingdom)

2016-12-15

We report the results of three-dimensional direct numerical simulations for incompressible viscous fluid in a circular pipe flow with a sudden expansion. At the inlet, a parabolic velocity profile is applied together with a finite amplitude perturbation in the form of a vortex with its axis parallel to the axis of the pipe. At sufficiently high Reynolds numbers the recirculation region breaks into a turbulent patch that changes position axially, depending on the strength of the perturbation. This vortex perturbation is believed to produce a less abrupt transition than in previous studies, which applied a tilt perturbation, as the localised turbulence is observed via the formation of a wavy structure at a low order azimuthal mode, which resembles an optimally amplified perturbation. For large vortex amplitude, the localised turbulence remains at a constant axial position. It is further investigated using proper orthogonal decomposition, which indicates that the centre region close to the expansion is highly energetic. (paper)

Nano-structuring of multi-layer material by single x-ray vortex pulse with femtosecond duration

Science.gov (United States)

Kohmura, Yoshiki; Zhakhovsky, Vasily; Takei, Dai; Suzuki, Yoshio; Takeuchi, Akihisa; Inoue, Ichiro; Inubushi, Yuichi; Inogamov, Nail; Ishikawa, Tetsuya; Yabashi, Makina

2018-03-01

A narrow zero-intensity spot arising from an x-ray vortex has huge potential for future applications such as nanoscopy and nanofabrication. We here present an X-ray Free Electron Laser (XFEL) experiment with a focused vortex wavefront which generated high aspect ratio nanoneedles on a Cr/Au multi-layer (ML) specimen. A sharp needle with a typical width and height of 310 and 600 nm was formed with a high occurrence rate at the center of a 7.71 keV x-ray vortex on this ML specimen, respectively. The observed width exceeds the diffraction limit, and the smallest structures ever reported using an intense-XFEL ablation were fabricated. We found that the elemental composition of the nanoneedles shows a significant difference from that of the unaffected area of Cr/Au ML. All these results are well explained by the molecular dynamics simulations, leading to the elucidation of the needle formation mechanism on an ultra-fast timescale.

Application of Proteomics to the Study of Pollination Drops

Directory of Open Access Journals (Sweden)

Natalie Prior

2013-04-01

Full Text Available Premise of the study: Pollination drops are a formative component in gymnosperm pollen-ovule interactions. Proteomics offers a direct method for the discovery of proteins associated with this early stage of sexual reproduction. Methods: Pollination drops were sampled from eight gymnosperm species: Chamaecyparis lawsoniana (Port Orford cedar, Ephedra monosperma, Ginkgo biloba, Juniperus oxycedrus (prickly juniper, Larix ×marschlinsii, Pseudotsuga menziesii (Douglas-fir, Taxus ×media, and Welwitschia mirabilis. Drops were collected by micropipette using techniques focused on preventing sample contamination. Drop proteins were separated using both gel and gel-free methods. Tandem mass spectrometric methods were used including a triple quadrupole and an Orbitrap. Results: Proteins are present in all pollination drops. Consistency in the protein complement over time was shown in L. ×marschlinsii. Representative mass spectra from W. mirabilis chitinase peptide and E. monosperma serine carboxypeptidase peptide demonstrated high quality results. We provide a summary of gymnosperm pollination drop proteins that have been discovered to date via proteomics. Discussion: Using proteomic methods, a dozen classes of proteins have been identified to date. Proteomics presents a way forward in deepening our understanding of the biological function of pollination drops.

Excitation of high density surface plasmon polariton vortex array

Science.gov (United States)

Kuo, Chun-Fu; Chu, Shu-Chun

2018-06-01

This study proposes a method to excite surface plasmon polariton (SPP) vortex array of high spatial density on metal/air interface. A doughnut vector beam was incident at four rectangularly arranged slits to excite SPP vortex array. The doughnut vector beam used in this study has the same field intensity distribution as the regular doughnut laser mode, TEM01* mode, but a different polarization distribution. The SPP vortex array is achieved through the matching of both polarization state and phase state of the incident doughnut vector beam with the four slits. The SPP field distribution excited in this study contains stable array-distributed time-varying optical vortices. Theoretical derivation, analytical calculation and numerical simulation were used to discuss the characteristics of the induced SPP vortex array. The period of the SPP vortex array induced by the proposed method had only half SPPs wavelength. In addition, the vortex number in an excited SPP vortex array can be increased by enlarging the structure.

Vortex flows in the solar chromosphere. I. Automatic detection method

Science.gov (United States)

Kato, Y.; Wedemeyer, S.

2017-05-01

Solar "magnetic tornadoes" are produced by rotating magnetic field structures that extend from the upper convection zone and the photosphere to the corona of the Sun. Recent studies show that these kinds of rotating features are an integral part of atmospheric dynamics and occur on a large range of spatial scales. A systematic statistical study of magnetic tornadoes is a necessary next step towards understanding their formation and their role in mass and energy transport in the solar atmosphere. For this purpose, we develop a new automatic detection method for chromospheric swirls, meaning the observable signature of solar tornadoes or, more generally, chromospheric vortex flows and rotating motions. Unlike existing studies that rely on visual inspections, our new method combines a line integral convolution (LIC) imaging technique and a scalar quantity that represents a vortex flow on a two-dimensional plane. We have tested two detection algorithms, based on the enhanced vorticity and vorticity strength quantities, by applying them to three-dimensional numerical simulations of the solar atmosphere with CO5BOLD. We conclude that the vorticity strength method is superior compared to the enhanced vorticity method in all aspects. Applying the method to a numerical simulation of the solar atmosphere reveals very abundant small-scale, short-lived chromospheric vortex flows that have not been found previously by visual inspection.

Vortex Analysis of Intra-Aneurismal Flow in Cerebral Aneurysms.

Science.gov (United States)

Sunderland, Kevin; Haferman, Christopher; Chintalapani, Gouthami; Jiang, Jingfeng

2016-01-01

This study aims to develop an alternative vortex analysis method by measuring structure ofIntracranial aneurysm (IA) flow vortexes across the cardiac cycle, to quantify temporal stability of aneurismal flow. Hemodynamics were modeled in "patient-specific" geometries, using computational fluid dynamics (CFD) simulations. Modified versions of known λ 2 and Q -criterion methods identified vortex regions; then regions were segmented out using the classical marching cube algorithm. Temporal stability was measured by the degree of vortex overlap (DVO) at each step of a cardiac cycle against a cycle-averaged vortex and by the change in number of cores over the cycle. No statistical differences exist in DVO or number of vortex cores between 5 terminal IAs and 5 sidewall IAs. No strong correlation exists between vortex core characteristics and geometric or hemodynamic characteristics of IAs. Statistical independence suggests this proposed method may provide novel IA information. However, threshold values used to determine the vortex core regions and resolution of velocity data influenced analysis outcomes and have to be addressed in future studies. In conclusions, preliminary results show that the proposed methodology may help give novel insight toward aneurismal flow characteristic and help in future risk assessment given more developments.

Vortex deformation and reduction of the Lorentz force

International Nuclear Information System (INIS)

Vuorio, M.

1977-01-01

A vortex of an extreme II-type superconductor is considered in the presence of a transport current. The equivalence of Magnus and Lorentz forces in a static vortex is discussed and the effect of vortex deformation is included in calculating corrections to the conventional expression of the Lorentz force. (author)

Fundamental vortices, wall-crossing, and particle-vortex duality

Energy Technology Data Exchange (ETDEWEB)

Hwang, Chiung; Yi, Piljin [School of Physics, Korea Institute for Advanced Study,Seoul 02455 (Korea, Republic of); Yoshida, Yutaka [Research Institute for Mathematical Sciences, Kyoto University,Kyoto 606-8502 (Japan)

2017-05-18

We explore 1d vortex dynamics of 3d supersymmetric Yang-Mills theories, as inferred from factorization of exact partition functions. Under Seiberg-like dualities, the 3d partition function must remain invariant, yet it is not a priori clear what should happen to the vortex dynamics. We observe that the 1d quivers for the vortices remain the same, and the net effect of the 3d duality map manifests as 1d Wall-Crossing phenomenon; although the vortex number can shift along such duality maps, the ranks of the 1d quiver theory are unaffected, leading to a notion of fundamental vortices as basic building blocks for topological sectors. For Aharony-type duality, in particular, where one must supply extra chiral fields to couple with monopole operators on the dual side, 1d wall-crossings of an infinite number of vortex quiver theories are neatly and collectively encoded by 3d determinant of such extra chiral fields. As such, 1d wall-crossing of the vortex theory encodes the particle-vortex duality embedded in the 3d Seiberg-like duality. For N=4, the D-brane picture is used to motivate this 3d/1d connection, while, for N=2, this 3d/1d connection is used to fine-tune otherwise ambiguous vortex dynamics. We also prove some identities of 3d supersymmetric partition functions for the Aharony duality using this vortex wall-crossing interpretation.

Stability of barotropic vortex strip on a rotating sphere.

Science.gov (United States)

Sohn, Sung-Ik; Sakajo, Takashi; Kim, Sun-Chul

2018-02-01

We study the stability of a barotropic vortex strip on a rotating sphere, as a simple model of jet streams. The flow is approximated by a piecewise-continuous vorticity distribution by zonal bands of uniform vorticity. The linear stability analysis shows that the vortex strip becomes stable as the strip widens or the rotation speed increases. When the vorticity constants in the upper and the lower regions of the vortex strip have the same positive value, the inner flow region of the vortex strip becomes the most unstable. However, when the upper and the lower vorticity constants in the polar regions have different signs, a complex pattern of instability is found, depending on the wavenumber of perturbations, and interestingly, a boundary far away from the vortex strip can be unstable. We also compute the nonlinear evolution of the vortex strip on the rotating sphere and compare with the linear stability analysis. When the width of the vortex strip is small, we observe a good agreement in the growth rate of perturbation at an early time, and the eigenvector corresponding to the unstable eigenvalue coincides with the most unstable part of the flow. We demonstrate that a large structure of rolling-up vortex cores appears in the vortex strip after a long-time evolution. Furthermore, the geophysical relevance of the model to jet streams of Jupiter, Saturn and Earth is examined.

Stability of barotropic vortex strip on a rotating sphere

Science.gov (United States)

Sohn, Sung-Ik; Sakajo, Takashi; Kim, Sun-Chul

2018-02-01

We study the stability of a barotropic vortex strip on a rotating sphere, as a simple model of jet streams. The flow is approximated by a piecewise-continuous vorticity distribution by zonal bands of uniform vorticity. The linear stability analysis shows that the vortex strip becomes stable as the strip widens or the rotation speed increases. When the vorticity constants in the upper and the lower regions of the vortex strip have the same positive value, the inner flow region of the vortex strip becomes the most unstable. However, when the upper and the lower vorticity constants in the polar regions have different signs, a complex pattern of instability is found, depending on the wavenumber of perturbations, and interestingly, a boundary far away from the vortex strip can be unstable. We also compute the nonlinear evolution of the vortex strip on the rotating sphere and compare with the linear stability analysis. When the width of the vortex strip is small, we observe a good agreement in the growth rate of perturbation at an early time, and the eigenvector corresponding to the unstable eigenvalue coincides with the most unstable part of the flow. We demonstrate that a large structure of rolling-up vortex cores appears in the vortex strip after a long-time evolution. Furthermore, the geophysical relevance of the model to jet streams of Jupiter, Saturn and Earth is examined.

Vortex dynamics in Josephson junctions arrays

International Nuclear Information System (INIS)

Shalom, Diego Edgar

2005-01-01

In this work we study the dynamics of vortices in two-dimensional overdamped Josephson Junctions Arrays (JJA) driven by dc current in a wide range of conditions varying magnetic field and temperature using experiments, numerical simulations and analytic studies.We develop the Fixed Phase method, a variation of numeric relaxation techniques in which we fix and control the phase of some islands, adjacent to the vortex center, while allowing all other phases in the system to relax.In this way we are able to pull and push the vortex uphill, as we are forcing the center of rotation of the vortex currents to be in a defined location, allowing us to calculate the potential energy of a vortex located in any arbitrary position.We use this method to study the potential energy of a vortex in a variety of situations in homogeneous and non-homogeneous JJA, such as arrays with defects, channel arrays and ratchets.We study the finite size effects in JJA by means of analytic and numerical tools.We implement the rings model, in which we replace the two-dimensional square array by a series of square, concentric, uncoupled rings. This is equivalent to disregarding the radial junctions that couple consecutive rings.In spite of its extreme simplicity, this model holds the main ingredients of the magnetic dependence of the energy.We combine this model with other terms that take into account the dependence in the position of the vortex to obtain a general expression for the potential energy of a vortex in a finite JJA with applied magnetic field.We also present an expression for the first critical field, corresponding to the value of the magnetic field in which the entrance of the first vortex becomes energetically favorable.We build and study JJA modulated to form periodic and asymmetrical potentials for the vortices, named ratchet potentials.The experimental results clearly show the existence of a rectification in the motion of vortices in these potentials.Under certain conditions we

Review of Vortex Methods for Simulation of Vortex Breakdown

National Research Council Canada - National Science Library

Levinski, Oleg

2001-01-01

The aim of this work is to identify current developments in the field of vortex breakdown modelling in order to initiate the development of a numerical model for the simulation of F/A-18 empennage buffet...

Rotation of a single vortex in dusty plasma

International Nuclear Information System (INIS)

Yan Jia; Feng Fan; Liu Fu-Cheng; He Ya-Feng

2017-01-01

A single vortex is obtained in radio-frequency capacitive discharge in argon gas. The dust subsystem is confined in the horizontal plane with an asymmetrical saw structure placed on the lower electrode. The vortex rotates as a whole along the long side of the saw-teeth. Asymmetry of the saw structure plays an important role in the rotation of the vortex. Nonzero curl of the total force resulting from the local ion flow and the electric field in the plasma sheath could be attributed to the persistent rotation of vortex. (paper)

Proposed thermodynamic method to determine the vortex mass in layered superconductors

International Nuclear Information System (INIS)

Moler, K.A.; Fetter, A.L.; Kapitulnik, A.

1995-01-01

The authors describe a simple method to study vortex dynamics that can determine or set an upper limit on the vortex mass. The specific heat of the vortex lattice in layered superconductors has a classical limit of 1 k B per pancake vortex if the vortex mass is zero. If the vortex mass m v is finite, a new Einstein branch of normal modes will appear with a crossover temperature Θ E ∝ m v -1 , and the specific heat will saturate at a new classical limit of 2 k B per pancake vortex

Transverse force on a moving vortex with the acoustic geometry

International Nuclear Information System (INIS)

Zhang Pengming; Cao Liming; Duan Yishi; Zhong Chengkui

2004-01-01

We consider the transverse force on a moving vortex with the acoustic metric using the phi-mapping topological current theory. In the frame of effective space-time geometry the vortex appear naturally by virtue of the vortex tensor in the Lorentz space-time and we show that it is just the vortex derived with the order parameter in the condensed matter. With the usual Lagrangian we obtain the equation of motion for the vortex. At last, we show that the transverse force on the moving vortex in our equation is just the usual Magnus force in a simple model

RANS computations of tip vortex cavitation

Science.gov (United States)

Decaix, Jean; Balarac, Guillaume; Dreyer, Matthieu; Farhat, Mohamed; Münch, Cécile

2015-12-01

The present study is related to the development of the tip vortex cavitation in Kaplan turbines. The investigation is carried out on a simplified test case consisting of a NACA0009 blade with a gap between the blade tip and the side wall. Computations with and without cavitation are performed using a R ANS modelling and a transport equation for the liquid volume fraction. Compared with experimental data, the R ANS computations turn out to be able to capture accurately the development of the tip vortex. The simulations have also highlighted the influence of cavitation on the tip vortex trajectory.

Vortex breakdown in a supersonic jet

Science.gov (United States)

Cutler, Andrew D.; Levey, Brian S.

1991-01-01

This paper reports a study of a vortex breakdown in a supersonic jet. A supersonic vortical jets were created by tangential injection and acceleration through a convergent-divergent nozzle. Vortex circulation was varied, and the nature of the flow in vortical jets was investigated using several types of flow visualization, including focusing schlieren and imaging of Rayleigh scattering from a laser light sheet. Results show that the vortical jet mixed much more rapidly with the ambient air than a comparable straight jet. When overexpanded, the vortical jet exhibited considerable unsteadiness and showed signs of vortex breakdown.

Theory of pairing symmetry in the vortex states

NARCIS (Netherlands)

Yokoyama, Takehito; Ichioka, Yukio; Yanaka, Yukio; Golubov, Alexandre Avraamovitch

2010-01-01

We investigate pairing symmetry in an Abrikosov vortex and vortex lattice. It is shown that the Cooper pair wave function at the center of an Abrikosov vortex with vorticity m has a different parity with respect to frequency from that in the bulk if m is an odd number, while it has the same parity

The Vortex and the Line: Performative Gestures in Allen Ginsberg's ‘Wichita Vortex Sutra’

DEFF Research Database (Denmark)

Sørensen, Bent

and their identity politics… Queering the straight lines of Modernism, Allen Ginsberg suggests in his long poem about America and the Vietnam War, ‘Wichita Vortex Sutra’, that lying media discourses and corrupt political and military statements about the necessity of participation in the war may be cancelled out...... by a poet performing the simple, yet impossible speech act of declaring the end of the war, and in doing so queering the original declaratory speech act of the executive power. The poet must enter intrepidly the vortex of lies told by the voices disseminated by the media on behalf of politicians, authority...... to provide the reader of the Sutra with the possibility of Enlightenment. While the poet may be forced to travel along straight lines to penetrate the vortex, he should at any given opportunity queer these lines as much as possible....

Vectorial diffraction properties of THz vortex Bessel beams.

Science.gov (United States)

Wu, Zhen; Wang, Xinke; Sun, Wenfeng; Feng, Shengfei; Han, Peng; Ye, Jiasheng; Yu, Yue; Zhang, Yan

2018-01-22

A vortex Bessel beam combines the merits of an optical vortex and a Bessel beam, including a spiral wave front and a non-diffractive feature, which has immense application potentials in optical trapping, optical fabrication, optical communications, and so on. Here, linearly and circularly polarized vortex Bessel beams in the terahertz (THz) frequency range are generated by utilizing a THz quarter wave plate, a spiral phase plate, and Teflon axicons with different opening angles. Taking advantage of a THz focal-plane imaging system, vectorial diffraction properties of the THz vortex Bessel beams are comprehensively characterized and discussed, including the transverse (Ex, Ey) and longitudinal (Ez) polarization components. The experimental phenomena are accurately simulated by adopting the vectorial Rayleigh diffraction integral. By varying the opening angle of the axicon, the characteristic parameters of these THz vortex Bessel beams are exhibited and compared, including the light spot size, the diffraction-free range, and the phase evolution process. This work provides the precise experimental and theoretical bases for the comprehension and application of a THz vortex Bessel beam.

Superconducting coherence in a vortex line liquid

International Nuclear Information System (INIS)

Chen, T.; Teitel, S.

1995-01-01

We carry out simulations of the anisotropic uniformly frustrated 3d XY model, as a model for vortex line fluctuations in high T c superconductors. We compute the phase diagram as a function of temperature and anisotropy, for a fixed applied magnetic field B. We find two distinct phase transitions. Upon heating, there is first a lower T c perpendicular where the vortex line lattice melts and super-conducting coherence perpendicular to the applied magnetic field vanishes. At a higher T cz , within the vortex line liquid, superconducting coherence parallel to the applied magnetic field vanishes. For finite anisotropy, both T c perpendicular and T cz lie well below the crossover from the vortex line liquid to the normal state

Longitudinal vortex control - Techniques and applications (The 32nd Lanchester Lecture)

Science.gov (United States)

Bushnell, D. M.

1992-01-01

A summary is presented of vortex control applications and current techniques for the control of longitudinal vortices produced by bodies, leading edges, tips and intersections. Vortex control has up till now been performed by many approaches in an empirical fashion, assisted by the essentially inviscid nature of much of longitudinal vortex behavior. Attention is given to Reynolds number sensitivities, vortex breakdown and interactions, vortex control on highly swept wings, and vortex control in juncture flows.

The observation of a triangular vortex in a rotating fluid

NARCIS (Netherlands)

Beckers, M.; Heijst, van G.J.F.

1998-01-01

A dye visualization study of a triangular vortex in a rotating fluid is presented. The emergence and subsequent break-up of the vortex structure are described. Soon after the generation of the triangular vortex it becomes unstable: two satellite vortices merge and pair with the core vortex into an

Vortex phase diagram and vortex dynamics at low temperature in a thick a-Mg{sub x}B{sub 1-x} film

Energy Technology Data Exchange (ETDEWEB)

Okuma, S. [Research Center for Low Temperature Physics, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8551 (Japan)], E-mail: sokuma@o.cc.titech.ac.jp; Kohara, M. [Research Center for Low Temperature Physics, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro-ku, Tokyo 152-8551 (Japan)

2007-09-01

We report on the equilibrium vortex phase diagram and vortex dynamics at low temperature T in a thick amorphous (a-)Mg{sub x}B{sub 1-x} film based on the measurements of the dc resistivity {rho} and time (t)-dependent component of the flux-flow voltage, {delta}V(t), respectively. Both {rho}(T) in perpendicular fields and the vortex phase diagram are qualitatively similar to those for the a-Mo{sub x}Si{sub 1-x} films, in which evidence for the quantum-vortex-liquid (QVL) phase has been obtained. In either material system we observe anomalous vortex flow with the asymmetric distribution of {delta}V(t) in the QVL phase, suggesting that the anomalous flow is a universal phenomenon commonly observed for disordered amorphous films, independent of material.

Coalescence of liquid drops: Different models versus experiment

KAUST Repository

Sprittles, J. E.

2012-01-01

The process of coalescence of two identical liquid drops is simulated numerically in the framework of two essentially different mathematical models, and the results are compared with experimental data on the very early stages of the coalescence process reported recently. The first model tested is the "conventional" one, where it is assumed that coalescence as the formation of a single body of fluid occurs by an instant appearance of a liquid bridge smoothly connecting the two drops, and the subsequent process is the evolution of this single body of fluid driven by capillary forces. The second model under investigation considers coalescence as a process where a section of the free surface becomes trapped between the bulk phases as the drops are pressed against each other, and it is the gradual disappearance of this "internal interface" that leads to the formation of a single body of fluid and the conventional model taking over. Using the full numerical solution of the problem in the framework of each of the two models, we show that the recently reported electrical measurements probing the very early stages of the process are better described by the interface formation/disappearance model. New theory-guided experiments are suggested that would help to further elucidate the details of the coalescence phenomenon. As a by-product of our research, the range of validity of different "scaling laws" advanced as approximate solutions to the problem formulated using the conventional model is established. © 2012 American Institute of Physics.

Inclined Jet in Crossflow Interacting with a Vortex Generator

Science.gov (United States)

Zaman, K. B. M. Q.; Rigby, D .L.; Heidmann, J. D.

2011-01-01

An experiment is conducted on the effectiveness of a vortex generator in preventing liftoff of a jet in crossflow, with possible relevance to film-cooling applications. The jet issues into the boundary layer at an angle of 20 degreees to the freestream. The effect of a triangular ramp-shaped vortex generator is studied while varying its geometry and location. Detailed flowfield properties are obtained for a case in which the height of the vortex generator and the diameter of the orifice are comparable with the approach boundary-layer thickness. The vortex generator produces a streamwise vortex pair with a vorticity magnitude 3 times larger (and of opposite sense) than that found in the jet in crossflow alone. Such a vortex generator appears to be most effective in keeping the jet attached to the wall. The effect of parametric variation is studied mostly from surveys 10 diameters downstream from the orifice. Results over a range of jet-to-freestream momentum flux ratio (1 vortex generator has a significant effect even at the highest J covered in the experiment. When the vortex generator height is halved, there is a liftoff of the jet. On the other hand, when the height is doubled, the jet core is dissipated due to larger turbulence intensity. Varying the location of the vortex generator, over a distance of three diameters from the orifice, is found to have little impact. Rounding off the edges of the vortex generator with the increasing radius of curvature progressively diminishes its effect. However, allowing for a small radius of curvature may be quite tolerable in practice.

A new approach on anti-vortex devices at water intakes including a submerged water jet

Science.gov (United States)

Tahershamsi, Ahmad; Rahimzadeh, Hassan; Monshizadeh, Morteza; Sarkardeh, Hamed

2018-04-01

A new approach on anti-vortex methods as hydraulic-based anti-vortex was investigated experimentally in the present study. In the investigated method, a submerged water jet is used as the anti-vortex mechanism. The added jet acts as a source of external momentum. This leads to change the intake-induced hydrodynamic pattern in the near-field of the intake structure, which can prevent formation of undesirable intake vortices. The experiments were carried out on a horizontal pipe intake. By performing 570 test cases in two different categories, including the inclined jet with respect to the axis of the intake, and the inclined jet with respect to the water surface, the effects of the jet inclination angle on the anti-vortex performance were investigated. It was found that the inclined jet with respect to the water surface is the best alternative to consider as the water jet injection pattern. Results showed that using the inclined jet with respect to the water surface can simply reduce the amounts of the expected water jet momentum more than 50% compared to that of the similar condition of the horizontal injection pattern. Moreover, it was concluded that the intake critical submergence can easily be minimized using the inclined jet with respect to the water surface.

Drop jumping. II. The influence of dropping height on the biomechanics of drop jumping

NARCIS (Netherlands)

Bobbert, M F; Huijing, P A; van Ingen Schenau, G J

In the literature, athletes preparing for explosive activities are recommended to include drop jumping in their training programs. For the execution of drop jumps, different techniques and different dropping heights can be used. This study was designed to investigate for the performance of bounce

Investigation of the viscous reconnection phenomenon of two vortex tubes through spectral simulations

Science.gov (United States)

Beardsell, Guillaume; Dufresne, Louis; Dumas, Guy

2016-09-01

This paper aims to shed further light on the viscous reconnection phenomenon. To this end, we propose a robust and efficient method in order to quantify the degree of reconnection of two vortex tubes. This method is used to compare the evolutions of two simple initial vortex configurations: orthogonal and antiparallel. For the antiparallel configuration, the proposed method is compared with alternative estimators and it is found to improve accuracy since it can account properly for the formation of looping structures inside the domain. This observation being new, the physical mechanism for the formation of those looping structures is discussed. For the orthogonal configuration, we report results from simulations that were performed at a much higher vortex Reynolds number (ReΓ ≡ circulation/viscosity = 104) and finer resolution (N3 = 10243) than previously presented in the literature. The incompressible Navier-stokes equations are solved directly (Direct Numerical Simulation or DNS) using a Fourier pseudospectral algorithm with triply periodic boundary conditions. The associated zero-circulation constraint is circumvented by solving the governing equations in a proper rotating frame of reference. Using ideas similar to those behind our method to compute the degree of reconnection, we split the vorticity field into its reconnected and non-reconnected parts, which allows to create insightful visualizations of the evolving vortex topology. It also allows to detect regions in the vorticity field that are neither reconnected nor non-reconnected and thus must be associated to internal looping structures. Finally, the Reynolds number dependence of the reconnection time scale Trec is investigated in the range 500 ≤ ReΓ ≤ 10 000. For both initial configurations, the scaling is generally found to vary continuously as ReΓ is increased from T rec ˜ R eΓ - 1 to T rec ˜ R eΓ - 1 / 2 , thus providing quantitative support for previous claims that the reconnection

The Interaction Between Dynamics and Chemistry of Ozone in the Set-up Phase of the Northern Hemisphere Polar Vortex

Science.gov (United States)

Kawa, S. R.; Bevilacqua, R.; Margitan, J. J.; Douglass, A. R.; Schoeberl, M. R.; Hoppel, K.; Sen, B.; Bhartia, P. K. (Technical Monitor)

2001-01-01

The morphology and evolution of the stratospheric ozone (O3) distribution at high latitudes in the Northern Hemisphere (NH) are examined for the late summer and fall seasons of 1999. This time period sets the O3 initial condition for the SOLVE/THESEO field mission performed during winter 1999-2000. In situ and satellite data are used along with a three-dimensional model of chemistry and transport (CTM) to determine the key processes that control the distribution of O3 in the lower-to-middle stratosphere. O3 in the vortex at the beginning of the winter season is found to be nearly constant from 500 to above 800 K with a value at 3 ppmv +/- approx. 10%. Values outside the vortex are up to a factor of 2 higher and increase significantly with potential temperature. The seasonal time series of data from POAM shows that relatively low O3 mixing ratios, which characterize the vortex in late fall, are already present at high latitudes at the end of summer before the vortex circulation sets up. Analysis of the CTM output shows that the minimum O3 and increase in variance in late summer are the result of: 1) stirring of polar concentric O3 gradients by nascent wave-driven transport, and 2) an acceleration of net photochemical loss with decreasing solar illumination. The segregation of low O3 mixing ratios into the vortex as the circulation strengthens through the fall suggests a possible feedback role between O3 chemistry and the vortex formation dynamics. Trajectory calculations from O3 sample points early in the fall, however, show only a weak correlation between initial O3 mixing ratio and potential vorticity later in the season consistent with order-of-magnitude calculations for the relative importance of O3 in the fall radiative balance at high latitudes. The possible connection between O3 chemistry and the dynamics of vortex formation does suggest that these feedbacks and sensitivities need to be better understood in order to make confident predictions of the recovery

Helicity conservation under quantum reconnection of vortex rings.

Science.gov (United States)

Zuccher, Simone; Ricca, Renzo L

2015-12-01

Here we show that under quantum reconnection, simulated by using the three-dimensional Gross-Pitaevskii equation, self-helicity of a system of two interacting vortex rings remains conserved. By resolving the fine structure of the vortex cores, we demonstrate that the total length of the vortex system reaches a maximum at the reconnection time, while both writhe helicity and twist helicity remain separately unchanged throughout the process. Self-helicity is computed by two independent methods, and topological information is based on the extraction and analysis of geometric quantities such as writhe, total torsion, and intrinsic twist of the reconnecting vortex rings.

Three-wave electron vortex lattices for measuring nanofields.

Science.gov (United States)

Dwyer, C; Boothroyd, C B; Chang, S L Y; Dunin-Borkowski, R E

2015-01-01

It is demonstrated how an electron-optical arrangement consisting of two electron biprisms can be used to generate three-wave vortex lattices with effective lattice spacings between 0.1 and 1 nm. The presence of vortices in these lattices was verified by using a third biprism to perform direct phase measurements via off-axis electron holography. The use of three-wave lattices for nanoscale electromagnetic field measurements via vortex interferometry is discussed, including the accuracy of vortex position measurements and the interpretation of three-wave vortex lattices in the presence of partial spatial coherence. Copyright © 2014 Elsevier B.V. All rights reserved.

First drop dissimilarity in drop-on-demand inkjet devices

International Nuclear Information System (INIS)

Famili, Amin; Palkar, Saurabh A.; Baldy, William J. Jr.

2011-01-01

As inkjet printing technology is increasingly applied in a broader array of applications, careful characterization of its method of use is critical due to its inherent sensitivity. A common operational mode in inkjet technology known as drop-on-demand ejection is used as a way to deliver a controlled quantity of material to a precise location on a target. This method of operation allows ejection of individual or a sequence (burst) of drops based on a timed trigger event. This work presents an examination of sequences of drops as they are ejected, indicating a number of phenomena that must be considered when designing a drop-on-demand inkjet system. These phenomena appear to be driven by differences between the first ejected drop in a burst and those that follow it and result in a break-down of the linear relationship expected between driving amplitude and drop mass. This first drop, as quantified by high-speed videography and subsequent image analysis, can be different in morphology, trajectory, velocity, and volume from subsequent drops within a burst. These findings were confirmed orthogonally by both volume and mass measurement techniques which allowed quantitation down to single drops.

Vortex operators in gauge field theories

International Nuclear Information System (INIS)

Polchinski, J.G.

1980-01-01

We study several related aspects of the t Hooft vortex operator. The first chapter reviews the current picture of the vacuum of quantum chromodynamics, the idea of dual field theories, and the idea of the vortex operator. The second chapter deals with the Abelian vortex operator written in terms of elementary fields and with the calculation of its Green's functions. The Dirac veto problem appears in a new guise. We present a two dimensional solvable model of a Dirac string. This leads us to a new solution of the veto problem; we discuss its extension to four dimensions. We then show how the Green's functions can be expressed more neatly in terms of Wu and Yang's geometrical idea of sections. In the third chapter we discuss the dependence of the Green's functions of the Wilson and t Hooft operators on the nature of the vacuum. In the fourth chapter we consider systems which have fields in the fundamental representation, so that there are no vortex operators. When these fields enter only weakly into the dynamics, as is the case in QCD and in real superconductors, we would expect to be able to define a vortex-like operator. We show that any such operator can no longer be local looplike, but must have commutators at long range. We can still find an operator with useful properties, its cluster property, though more complicated than that of the usual vortex operator, still appears to distinguish Higgs, confining and perturbative phases. To test this, we consider a U(1) lattice gauge theory with two matter fields, one singly charged (fundamental) and one doubly charged (adjoint)

A new look at sound generation by blade/vortex interaction

Science.gov (United States)

Hardin, J. C.; Mason, J. P.

1985-01-01

As a preliminary attempt to understand the dynamics of blade/vortex interaction, the two-dimensional problem of a rectilinear vortex filament interacting with a Joukowski airfoil is analyzed in both the lifting and nonlifting cases. The vortex velocity components could be obtained analytically and integrated to determine the vortex trajectory. With this information, the aeroacoustic low-frequency Green's function approach could then be employed to calculate the sound produced during the encounter. The results indicate that the vortex path deviates considerably from simple convection due to the presence of the airfoil and that a reasonably sharp sound pulse is radiated during the interaction whose fundamental frequency is critically dependent upon whether the vortex passes above or below the airfoil. Determination of this gross parameter of the interaction is shown to be highly nonlinearly dependent upon airfoil circulation, vortex circulation, and initial position.

Vortex dynamics in ferromagnetic/superconducting bilayers

Energy Technology Data Exchange (ETDEWEB)

Cieplak, M.Z.; Adamus, Z. [Polish Acad Sci, Inst Phys, PL-02668 Warsaw, (Poland); Konczykowski, M. [CEA, DSM, DRECAM, Lab Solides Irradies, Ecole Polytechnique, CNRS-UMR 7642, F-91128 Palaiseau (France); Zhu, L.Y.; Chien, C.L. [Johns Hopkins Univ, Dept Phys and Astron, Baltimore, MD 21218 (United States)

2008-07-01

The dependence of vortex dynamics on the geometry of magnetic domain pattern is studied in the superconducting/ferromagnetic bilayers, in which niobium is a superconductor, and Co/Pt multilayer with perpendicular magnetic anisotropy serves as a ferromagnetic layer. Magnetic domain patterns with different density of domains per surface area and different domain size, w, are obtained for Co/Pt with different thickness of Pt. The dense patterns of domains with the size comparable to the magnetic penetration depth (w {>=} {lambda}) produce large vortex pinning and smooth vortex penetration, while less dense patterns with larger domains (w {>=}{>=} {lambda}) enhance pinning less effectively and result in flux jumps during flux motion. (authors)

The major stratospheric final warming in 2016: dispersal of vortex air and termination of Arctic chemical ozone loss

Directory of Open Access Journals (Sweden)

G. L. Manney

2016-12-01

Full Text Available The 2015/16 Northern Hemisphere winter stratosphere appeared to have the greatest potential yet seen for record Arctic ozone loss. Temperatures in the Arctic lower stratosphere were at record lows from December 2015 through early February 2016, with an unprecedented period of temperatures below ice polar stratospheric cloud thresholds. Trace gas measurements from the Aura Microwave Limb Sounder (MLS show that exceptional denitrification and dehydration, as well as extensive chlorine activation, occurred throughout the polar vortex. Ozone decreases in 2015/16 began earlier and proceeded more rapidly than those in 2010/11, a winter that saw unprecedented Arctic ozone loss. However, on 5–6 March 2016 a major final sudden stratospheric warming ("major final warming", MFW began. By mid-March, the mid-stratospheric vortex split after being displaced far off the pole. The resulting offspring vortices decayed rapidly preceding the full breakdown of the vortex by early April. In the lower stratosphere, the period of temperatures low enough for chlorine activation ended nearly a month earlier than that in 2011 because of the MFW. Ozone loss rates were thus kept in check because there was less sunlight during the cold period. Although the winter mean volume of air in which chemical ozone loss could occur was as large as that in 2010/11, observed ozone values did not drop to the persistently low values reached in 2011.We use MLS trace gas measurements, as well as mixing and polar vortex diagnostics based on meteorological fields, to show how the timing and intensity of the MFW and its impact on transport and mixing halted chemical ozone loss. Our detailed characterization of the polar vortex breakdown includes investigations of individual offspring vortices and the origins and fate of air within them. Comparisons of mixing diagnostics with lower-stratospheric N2O and middle-stratospheric CO from MLS (long-lived tracers show rapid vortex erosion and

Kinetics of contrail particles formation and heterogeneous reactions on such particles

Energy Technology Data Exchange (ETDEWEB)

Kogan, M.N.; Butkovsky, A.V.; Erofeev, A.I.; Freedlender, O.G.; Makashev, N.K. [Central Aerohydrodynamic Inst., Zhukovsky (Russian Federation)

1997-12-31

The research of impact of aircraft emissions upon the atmosphere is very complex and difficult problem. More than two decades of intensive investigations of the problem of ozone decay do not permit to make definite conclusions. Many important problems still remain unsolved in the aircraft/atmosphere interaction: engine, nozzle, jet, jet/vortex system interaction, vortex breakdown, contrail formation, meso-scale and global processes, their effects on climate. The particles formation and heterogeneous reactions play an important role in some of these processes. These problems are discussed. (author) 11 refs.

Kinetics of contrail particles formation and heterogeneous reactions on such particles

Energy Technology Data Exchange (ETDEWEB)

Kogan, M N; Butkovsky, A V; Erofeev, A I; Freedlender, O G; Makashev, N K [Central Aerohydrodynamic Inst., Zhukovsky (Russian Federation)

1998-12-31

The research of impact of aircraft emissions upon the atmosphere is very complex and difficult problem. More than two decades of intensive investigations of the problem of ozone decay do not permit to make definite conclusions. Many important problems still remain unsolved in the aircraft/atmosphere interaction: engine, nozzle, jet, jet/vortex system interaction, vortex breakdown, contrail formation, meso-scale and global processes, their effects on climate. The particles formation and heterogeneous reactions play an important role in some of these processes. These problems are discussed. (author) 11 refs.

Studies on a burner used biomass pellets as fuel. Performance of a spiral vortex pellet burner

Energy Technology Data Exchange (ETDEWEB)

Iwao, Toshio

1987-12-21

In order to develop a small size burner with high performance using biomass pellets fuel substitute for fuel oil, the burning performance of a spiral vortex pallet burner has been studied. An experimental equipment for the pellet burning is made up of a fuel supply unit, combustion chamber and a furnace. The used woody pellet is made of mixed sawdust and bark; with water content of 10.29%, particle diameter of 5.5-9mm, length of 5-50mm, and, apparent and real specific gravities are 0.59 and 1.334 respectively. The pellets are sent to bottom of the combustion chamber, spiral vortex combustion are carried out with blown air, the ashes and unburnt residues are discharged to out of combustion chamber with spiral vortex hot gases. As the result, it was clarified that the formation of the burning layers in a burner is required to be in order of the layers of ash, oxidation, reduction and carbonization up to the upper layer for high burning performance, and the formation of the layer is influenced by the condition of sedimentation of pellets in the combustion chamber. In the meanwhile the burning performance of the burner is influenced by the quantity of blast, the rate of feeding, and by the time of pre-heating in the combustion chamber. (23 figs, 5 refs)

Magnetization reversal in circular vortex dots of small radius.

Science.gov (United States)

Goiriena-Goikoetxea, M; Guslienko, K Y; Rouco, M; Orue, I; Berganza, E; Jaafar, M; Asenjo, A; Fernández-Gubieda, M L; Fernández Barquín, L; García-Arribas, A

2017-08-10

We present a detailed study of the magnetic behavior of Permalloy (Ni 80 Fe 20 alloy) circular nanodots with small radii (30 nm and 70 nm) and different thicknesses (30 nm or 50 nm). Despite the small size of the dots, the measured hysteresis loops manifestly display the features of classical vortex behavior with zero remanence and lobes at high magnetic fields. This is remarkable because the size of the magnetic vortex core is comparable to the dot diameter, as revealed by magnetic force microscopy and micromagnetic simulations. The dot ground states are close to the border of the vortex stability and, depending on the dot size, the magnetization distribution combines attributes of the typical vortex, single domain states or even presents features resembling magnetic skyrmions. An analytical model of the dot magnetization reversal, accounting for the large vortex core size, is developed to explain the observed behavior, providing a rather good agreement with the experimental results. The study extends the understanding of magnetic nanodots beyond the classical vortex concept (where the vortex core spins have a negligible influence on the magnetic behavior) and can therefore be useful for improving emerging spintronic applications, such as spin-torque nano-oscillators. It also delimits the feasibility of producing a well-defined vortex configuration in sub-100 nm dots, enabling the intracellular magneto-mechanical actuation for biomedical applications.

On the electron vortex beam wavefunction within a crystal

International Nuclear Information System (INIS)

Mendis, B.G.

2015-01-01

Electron vortex beams are distorted by scattering within a crystal, so that the wavefunction can effectively be decomposed into many vortex components. Using a Bloch wave approach equations are derived for vortex beam decomposition at any given depth and with respect to any frame of reference. In the kinematic limit (small specimen thickness) scattering largely takes place at the neighbouring atom columns with a local phase change of π/2 rad. When viewed along the beam propagation direction only one vortex component is present at the specimen entrance surface (i.e. the ‘free space’ vortex in vacuum), but at larger depths the probe is in a mixed state due to Bragg scattering. Simulations show that there is no direct correlation between vortex components and the pendellösung, i.e. at a given depth probes with relatively constant can be in a more mixed state compared to those with more rapidly varying . This suggests that minimising oscillations in the pendellösung by probe channelling is not the only criterion for generating a strong electron energy loss magnetic circular dichroism (EMCD) signal. - Highlights: • Equations are derived for vortex decomposition due to scattering within a crystal. • There is no direct correlation between vortex decomposition and pendellösung. • Results are also discussed in the context of EMCD measurements

Characterisation of vortex flow inside an entrained cavity

Energy Technology Data Exchange (ETDEWEB)

Rambert, A.; Elcafsi, A.; Gougat, P. [Centre National de la Recherche Scientifique, 91 - Orsay (France). Lab. d' Informatique pour la Mecanique et les Sciences de l' Ingenieur

2000-07-01

A number of studies have referred to the existence of a vortex cell within an urban street canyon when ambient winds aloft are perpendicular to the street. The understanding of vortex dynamics or vorticity distribution in a such configuration is of great interest. Vortex structures play an important role in the dynamics of pollutant dispersion. This configuration was simulated by the interaction between a boundary layer and a cavity. Experimental characterisation of the vortex structures evolution was developed by flow velocity measurements inside and out of the cavity. Classical methods like hot wire and laser Doppler velocimetry (LDV) display only local measurements. Particle image velocimetry (PIV) method based on the optical flow technique permitted global velocity measurements. This technique emphasis the vortex structures inside the cavity which present small scales as well as large scales related to the cavity geometry. These vortices are usually non-stationary. (orig.)

Vortex Tube Modeling Using the System Identification Method

Energy Technology Data Exchange (ETDEWEB)

Han, Jaeyoung; Jeong, Jiwoong; Yu, Sangseok [Chungnam Nat’l Univ., Daejeon (Korea, Republic of); Im, Seokyeon [Tongmyong Univ., Busan (Korea, Republic of)

2017-05-15

In this study, vortex tube system model is developed to predict the temperature of the hot and the cold sides. The vortex tube model is developed based on the system identification method, and the model utilized in this work to design the vortex tube is ARX type (Auto-Regressive with eXtra inputs). The derived polynomial model is validated against experimental data to verify the overall model accuracy. It is also shown that the derived model passes the stability test. It is confirmed that the derived model closely mimics the physical behavior of the vortex tube from both the static and dynamic numerical experiments by changing the angles of the low-temperature side throttle valve, clearly showing temperature separation. These results imply that the system identification based modeling can be a promising approach for the prediction of complex physical systems, including the vortex tube.

Anomalous Josephson effect controlled by an Abrikosov vortex

Science.gov (United States)

Mironov, S.; Goldobin, E.; Koelle, D.; Kleiner, R.; Tamarat, Ph.; Lounis, B.; Buzdin, A.

2017-12-01

The possibility of a fast and precise Abrikosov vortex manipulation by a focused laser beam opens the way to create laser-driven Josephson junctions. We theoretically demonstrate that a vortex pinned in the vicinity of the Josephson junction generates an arbitrary ground state phase which can be equal not only to 0 or π but to any desired φ0 value in between. Such φ0 junctions have many peculiar properties and may be effectively controlled by the optically driven Abrikosov vortex. Also we theoretically show that the Josephson junction with the embedded vortex can serve as an ultrafast memory cell operating at sub THz frequencies.

Reactive Flow Control of Delta Wing Vortex (Postprint)

Science.gov (United States)

2006-08-01

wing aircraft. A substantial amount of research has been dedicated to the control of aerodynamic flows using both passive and active control mechanisms...Passive vortex control devices such as vortex generators and winglets attach to the wing and require no energy input. Passive vortex control...leading edges is also effective for changing the aerodynamic characteristics of delta wings [2] [3]. Gutmark and Guillot [5] proposed controlling

Roles of pinning strength and density in vortex melting

International Nuclear Information System (INIS)

Obaidat, I M; Khawaja, U Al; Benkraouda, M

2008-01-01

We have investigated the role of pinning strength and density on the equilibrium vortex-lattice to vortex-liquid phase transition under several applied magnetic fields. This study was conducted using a series of molecular dynamic simulations on several samples with different strengths and densities of pinning sites which are arranged in periodic square arrays. We have found a single solid-liquid vortex transition when the vortex filling factor n>1. We have found that, for fixed pinning densities and strengths, the melting temperature, T m , decreases almost linearly with increasing magnetic field. Our results provide direct numerical evidence for the significant role of both the strength and density of pinning centers on the position of the melting line. We have found that the vortex-lattice to vortex-liquid melting line shifts up as the pinning strength or the pinning density was increased. The effect on the melting line was found to be more pronounced at small values of strength and density of pinning sites

Stable dissipative optical vortex clusters by inhomogeneous effective diffusion.

Science.gov (United States)

Li, Huishan; Lai, Shiquan; Qui, Yunli; Zhu, Xing; Xie, Jianing; Mihalache, Dumitru; He, Yingji

2017-10-30

We numerically show the generation of robust vortex clusters embedded in a two-dimensional beam propagating in a dissipative medium described by the generic cubic-quintic complex Ginzburg-Landau equation with an inhomogeneous effective diffusion term, which is asymmetrical in the two transverse directions and periodically modulated in the longitudinal direction. We show the generation of stable optical vortex clusters for different values of the winding number (topological charge) of the input optical beam. We have found that the number of individual vortex solitons that form the robust vortex cluster is equal to the winding number of the input beam. We have obtained the relationships between the amplitudes and oscillation periods of the inhomogeneous effective diffusion and the cubic gain and diffusion (viscosity) parameters, which depict the regions of existence and stability of vortex clusters. The obtained results offer a method to form robust vortex clusters embedded in two-dimensional optical beams, and we envisage potential applications in the area of structured light.

Optical vortex beams: Generation, propagation and applications

Science.gov (United States)

Cheng, Wen

An optical vortex (also known as a screw dislocation or phase singularity) is one type of optical singularity that has a spiral phase wave front around a singularity point where the phase is undefined. Optical vortex beams have a lot of applications in areas such as optical communications, LADAR (laser detection and ranging) system, optical tweezers, optical trapping and laser beam shaping. The concepts of optical vortex beams and methods of generation are briefly discussed. The properties of optical vortex beams propagating through atmospheric turbulence have been studied. A numerical modeling is developed and validated which has been applied to study the high order properties of optical vortex beams propagating though a turbulent atmosphere. The simulation results demonstrate the advantage that vectorial vortex beams may be more stable and maintain beam integrity better when they propagate through turbulent atmosphere. As one important application of optical vortex beams, the laser beam shaping is introduced and studied. We propose and demonstrate a method to generate a 2D flat-top beam profile using the second order full Poincare beams. Its applications in two-dimensional flat-top beam shaping with spatially variant polarization under low numerical aperture focusing have been studied both theoretically and experimentally. A novel compact flat-top beam shaper based on the proposed method has been designed, fabricated and tested. Experimental results show that high quality flat-top profile can be obtained with steep edge roll-off. The tolerance to different input beam sizes of the beam shaper is also verified in the experimental demonstration. The proposed and experimentally verified LC beam shaper has the potential to become a promising candidate for compact and low-cost flat-top beam shaping in areas such as laser processing/machining, lithography and medical treatment.

Application of multiphase modelling for vortex occurrence in vertical pump intake - a review

International Nuclear Information System (INIS)

Samsudin, M L; Munisamy, K M; Thangaraju, S K

2015-01-01

Vortex formation within pump intake is one of common problems faced for power plant cooling water system. This phenomenon, categorised as surface and sub-surface vortices, can lead to several operational problems and increased maintenance costs. Physical model study was recommended from published guidelines but proved to be time and resource consuming. Hence, the use of Computational Fluid Dynamics (CFD) is an attractive alternative in managing the problem. At the early stage, flow analysis was conducted using single phase simulation and found to find good agreement with the observation from physical model study. With the development of computers, multiphase simulation found further enhancement in obtaining accurate results for representing air entrainment and sub-surface vortices which were earlier not well predicted from the single phase simulation.The purpose of this paper is to describe the application of multiphase modelling with CFD analysis for investigating vortex formation for a vertically inverted pump intake. In applying multiphase modelling, there ought to be a balance between the acceptable usage for computational time and resources and the degree of accuracy and realism in the results as expected from the analysis. (paper)

The Energy Budget of a Southwest Vortex With Heavy Rainfall over South China

Institute of Scientific and Technical Information of China (English)

无

2011-01-01

Energy budgets were analyzed to study the development of an eastward propagating southwest vortex （SWV） associated with heavy rainfall over southern China（11-13 June 2008）.The results show that kinetic energy（KE） generation and advection were the most important KE sources,while friction and sub-grid processes were the main KE sinks.There was downward conversion from divergent to rotational wind KE consistent with the downward stretching of SWVs.The Coriolis force was important for the formation and maintenance of the SWV.Convergence was also an important factor for maintenance,as was vertical motion during the mature stage of the SWV and the formation stage of a newly formed vortex（vortex B）.The conversion from available potential energy（APE） to KE of divergent wind can lead to strong convection.Vertical motion influenced APE by dynamical and thermal processes which had opposite effects. The variation of APE was related to the heavy rainfall and convection;in this case,vertical motion with direct thermal circulation was the most important way in which APE was released,while latent heat release and vertical temperature advection were important for APE generation.

Application of multiphase modelling for vortex occurrence in vertical pump intake - a review

Science.gov (United States)

Samsudin, M. L.; Munisamy, K. M.; Thangaraju, S. K.

2015-09-01

Vortex formation within pump intake is one of common problems faced for power plant cooling water system. This phenomenon, categorised as surface and sub-surface vortices, can lead to several operational problems and increased maintenance costs. Physical model study was recommended from published guidelines but proved to be time and resource consuming. Hence, the use of Computational Fluid Dynamics (CFD) is an attractive alternative in managing the problem. At the early stage, flow analysis was conducted using single phase simulation and found to find good agreement with the observation from physical model study. With the development of computers, multiphase simulation found further enhancement in obtaining accurate results for representing air entrainment and sub-surface vortices which were earlier not well predicted from the single phase simulation. The purpose of this paper is to describe the application of multiphase modelling with CFD analysis for investigating vortex formation for a vertically inverted pump intake. In applying multiphase modelling, there ought to be a balance between the acceptable usage for computational time and resources and the degree of accuracy and realism in the results as expected from the analysis.

Generation of intense high-order vortex harmonics.

Science.gov (United States)

Zhang, Xiaomei; Shen, Baifei; Shi, Yin; Wang, Xiaofeng; Zhang, Lingang; Wang, Wenpeng; Xu, Jiancai; Yi, Longqiong; Xu, Zhizhan

2015-05-01

This Letter presents for the first time a scheme to generate intense high-order optical vortices that carry orbital angular momentum in the extreme ultraviolet region based on relativistic harmonics from the surface of a solid target. In the three-dimensional particle-in-cell simulation, the high-order harmonics of the high-order vortex mode is generated in both reflected and transmitted light beams when a linearly polarized Laguerre-Gaussian laser pulse impinges on a solid foil. The azimuthal mode of the harmonics scales with its order. The intensity of the high-order vortex harmonics is close to the relativistic region, with the pulse duration down to attosecond scale. The obtained intense vortex beam possesses the combined properties of fine transversal structure due to the high-order mode and the fine longitudinal structure due to the short wavelength of the high-order harmonics. In addition to the application in high-resolution detection in both spatial and temporal scales, it also presents new opportunities in the intense vortex required fields, such as the inner shell ionization process and high energy twisted photons generation by Thomson scattering of such an intense vortex beam off relativistic electrons.

Vortex structure and characterization of quasiperiodic functions

International Nuclear Information System (INIS)

Dana, Itzhack; Chernov, Vladislav E

2002-01-01

Quasiperiodic functions (QPFs) are characterized by their full vortex structure in one unit cell. This characterization is much finer and more sensitive than the topological one given by the total vorticity per unit cell (the 'Chern index'). It is shown that QPFs with an arbitrarily prescribed vortex structure exist by constructing explicitly such a 'standard' QPF. Two QPFs with the same vortex structure are equivalent, in the sense that their ratio is a function which is strictly periodic, nonvanishing and at least continuous. A general QPF can then be approximately reconstructed from its vortex structure on the basis of the standard QPF and the equivalence concept. As another application of this concept, a simple method is proposed for calculating the quasiperiodic eigenvectors of periodic matrices. Possible applications to the quantum-chaos problem on a phase-space torus are briefly discussed

Formation of a vortex flow at the laser cutting of sheet metal with low pressure of assisting gas

Energy Technology Data Exchange (ETDEWEB)

Kovalev, O B; Yudin, P V; Zaitsev, A V [Khristianovich' s Institute of Theoretical and Applied Mechanics, Russian Academy of Sciences, Siberian Branch, Novosibirsk (Russian Federation)], E-mail: kovalev@itam.nsc.ru

2008-08-07

Specific features of subsonic jet gas flows in narrow channels geometrically similar to the laser cut are studied experimentally and theoretically. Such flows are visualized by a technique based on prior application of a viscous liquid film onto the side walls of the channel made of transparent glass. The gas flow inside the channel induces a liquid flow on the glass wall in the form of extremely small filaments, which coincide with the streamlines of the gas flow. Filming of these filaments by a CCD camera allows one to capture the specific features of these gas-dynamic flows. Mathematical modelling of the dynamics of a viscous compressible heat-conducting gas was performed by solving full three-dimensional Navier-Stokes equations. Numerical calculations and experiments reveal vortex structures in the flow at the entrance and exit of the channel, which may directly affect the surface quality in real gas-laser cutting of metals. The largest vortex, which arises at the channel exit, collects and accumulates the liquid flowing down the channel walls. Jet flows are generated by sonic nozzles with conical or cylindrical exit sections or by a double coaxial nozzle. The double nozzle includes the central conical nozzle and the side concentric nozzle, which allows additional side injection of the gas to be organized. The study with the double nozzle shows that the vortices disappear as the pressure in the external nozzle is increased, and a stable vortex-free attached gas flow is formed.

Fermions and vortex solutions in Abelian and non-Abelian gauge theories

International Nuclear Information System (INIS)

de Vega, H.J.

1978-01-01

The interaction of fermions with an extended vortex solution of the Higgs model is investigated. It is found that this interaction has long-range inverse-square tail. It is caused by the coupling of the fermion angular momentum with the vortex gauge field itself. The fermion-vortex bound states present at the threshold and the fermion-vortex scattering are studied. The scattering phase shifts and the Jost functions are obtained for large and small fermion momenta as well as the low-energy cross section which diverges at zero momentum. The quantum field theory in the one-vortex sectors is developed. It is found that, in the presence of fermions, a vortex with an even (odd) number of flux quanta has a half-integer (integer) fermionic number. It follows that a two-quantum vortex is stable. Finally, the stable vortex solution of an SU(2) Higgs model is investigated. The appropriate ansatz for the field is given and radial equations are discussed. It is shown that the interaction of a vortex with any nonsinglet particle has a long-range inverse-square tail

Investigation of propagation dynamics of truncated vector vortex beams.

Science.gov (United States)

Srinivas, P; Perumangatt, C; Lal, Nijil; Singh, R P; Srinivasan, B

2018-06-01

In this Letter, we experimentally investigate the propagation dynamics of truncated vector vortex beams generated using a Sagnac interferometer. Upon focusing, the truncated vector vortex beam is found to regain its original intensity structure within the Rayleigh range. In order to explain such behavior, the propagation dynamics of a truncated vector vortex beam is simulated by decomposing it into the sum of integral charge beams with associated complex weights. We also show that the polarization of the truncated composite vector vortex beam is preserved all along the propagation axis. The experimental observations are consistent with theoretical predictions based on previous literature and are in good agreement with our simulation results. The results hold importance as vector vortex modes are eigenmodes of the optical fiber.

Intracavity vortex beam generation

Science.gov (United States)

Naidoo, Darryl; Aït-Ameur, Kamel; Forbes, Andrew

2011-10-01

In this paper we explore vortex beams and in particular the generation of single LG0l modes and superpositions thereof. Vortex beams carry orbital angular momentum (OAM) and this intrinsic property makes them prevalent in transferring this OAM to matter and to be used in quantum information processing. We explore an extra-cavity and intra-cavity approach in LG0l mode generation respectively. The outputs of a Porro-prism resonator are represented by "petals" and we show that through a full modal decomposition, the "petal" fields are a superposition of two LG0l modes.

Kaplan turbine tip vortex cavitation - analysis and prevention

Science.gov (United States)

Motycak, L.; Skotak, A.; Kupcik, R.

2012-11-01

The work is focused on one type of Kaplan turbine runner cavitation - a tip vortex cavitation. For detailed description of the tip vortex, the CFD analysis is used. On the basis of this analysis it is possible to estimate the intensity of cavitating vortex core, danger of possible blade surface and runner chamber cavitation pitting. In the paper, the ways how to avoid the pitting effect of the tip vortex are described. In order to prevent the blade surface against pitting, the following possibilities as the change of geometry of the runner blade, dimension of tip clearance and finally the installation of the anti-cavitation lips are discussed. The knowledge of the shape and intensity of the tip vortex helps to design the anti-cavitation lips more sophistically. After all, the results of the model tests of the Kaplan runner with or without anti-cavitation lips and the results of the CFD analysis are compared.

Vortex capturing vertical axis wind turbine

International Nuclear Information System (INIS)

Zannetti, L; Gallizio, F; Ottino, G

2007-01-01

An analytical-numerical study is presented for an innovative lift vertical axis turbine whose blades are designed with vortex trapping cavities that act as passive flow control devices. The unsteady flow field past one-bladed and two-bladed turbines is described by a combined analytical and numerical method based on conformal mapping and on a blob vortex method

Revealing the radial modes in vortex beams

CSIR Research Space (South Africa)

Sephton, Bereneice C

2016-10-01

Full Text Available Light beams that carry orbital angular momentum are often approximated by modulating an initial beam, usually Gaussian, with an azimuthal phase variation to create a vortex beam. Such vortex beams are well defined azimuthally, but the radial profile...

Rotation and oscillation of nonlinear dipole vortex in the drift-unstable plasma

International Nuclear Information System (INIS)

Orito, Kohtaro; Hatori, Tadatsugu.

1997-10-01

The behaviors of the nonlinear dipole vortex in the drift unstable plasma are studied by numerical approaches. Model equations used in numerical simulation are derived from two-fluid model and are composed of two equations with respect to the electrostatic potential and the density perturbation. When the initial dipole vortex is inclined at some angle with respect to the direction of the drift velocity, the dipole vortex oscillates or rotates in the first stage. These phenomenon also happen in the stable system. In the second stage, one part of the dipole vortex grows and another decays because of the destabilization. The shrunk vortex rotates around the enlarged vortex. Consequently, a monopole vortex appears out of the dipole vortex. (author)

Numerical study of the properties of optical vortex array laser tweezers.

Science.gov (United States)

Kuo, Chun-Fu; Chu, Shu-Chun

2013-11-04

Chu et al. constructed a kind of Ince-Gaussian modes (IGM)-based vortex array laser beams consisting of p x p embedded optical vortexes from Ince-Gaussian modes, IG(e)(p,p) modes [Opt. Express 16, 19934 (2008)]. Such an IGM-based vortex array laser beams maintains its vortex array profile during both propagation and focusing, and is applicable to optical tweezers. This study uses the discrete dipole approximation (DDA) method to study the properties of the IGM-based vortex array laser tweezers while it traps dielectric particles. This study calculates the resultant force exerted on the spherical dielectric particles of different sizes situated at the IGM-based vortex array laser beam waist. Numerical results show that the number of trapping spots of a structure light (i.e. IGM-based vortex laser beam), is depended on the relation between the trapped particle size and the structure light beam size. While the trapped particle is small comparing to the beam size of the IGM-based vortex array laser beams, the IGM-based vortex array laser beams tweezers are suitable for multiple traps. Conversely, the tweezers is suitable for single traps. The results of this study is useful to the future development of the vortex array laser tweezers applications.

Integrable Abelian vortex-like solitons

Energy Technology Data Exchange (ETDEWEB)

Contatto, Felipe, E-mail: felipe.contatto@damtp.cam.ac.uk [Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); CAPES Foundation, Ministry of Education of Brazil, Brasília, DF 70040-020 (Brazil)

2017-05-10

We propose a modified version of the Ginzburg–Landau energy functional admitting static solitons and determine all the Painlevé-integrable cases of its Bogomolny equations of a given class of models. Explicit solutions are determined in terms of the third Painlevé transcendents, allowing us to calculate physical quantities such as the vortex number and the vortex strength. These solutions can be interpreted as the usual Abelian-Higgs vortices on surfaces of non-constant curvature with conical singularity.

Magnetic Vortex Based Transistor Operations

Science.gov (United States)

Kumar, D.; Barman, S.; Barman, A.

2014-01-01

Transistors constitute the backbone of modern day electronics. Since their advent, researchers have been seeking ways to make smaller and more efficient transistors. Here, we demonstrate a sustained amplification of magnetic vortex core gyration in coupled two and three vortices by controlling their relative core polarities. This amplification is mediated by a cascade of antivortex solitons travelling through the dynamic stray field. We further demonstrated that the amplification can be controlled by switching the polarity of the middle vortex in a three vortex sequence and the gain can be controlled by the input signal amplitude. An attempt to show fan–out operation yielded gain for one of the symmetrically placed branches which can be reversed by switching the core polarity of all the vortices in the network. The above observations promote the magnetic vortices as suitable candidates to work as stable bipolar junction transistors (BJT). PMID:24531235

Vortex breakdown incipience: Theoretical considerations

Science.gov (United States)

Berger, Stanley A.; Erlebacher, Gordon

1992-01-01

The sensitivity of the onset and the location of vortex breakdowns in concentrated vortex cores, and the pronounced tendency of the breakdowns to migrate upstream have been characteristic observations of experimental investigations; they have also been features of numerical simulations and led to questions about the validity of these simulations. This behavior seems to be inconsistent with the strong time-like axial evolution of the flow, as expressed explicitly, for example, by the quasi-cylindrical approximate equations for this flow. An order-of-magnitude analysis of the equations of motion near breakdown leads to a modified set of governing equations, analysis of which demonstrates that the interplay between radial inertial, pressure, and viscous forces gives an elliptic character to these concentrated swirling flows. Analytical, asymptotic, and numerical solutions of a simplified non-linear equation are presented; these qualitatively exhibit the features of vortex onset and location noted above.

Vortex dynamics and correlated disorder in high-{Tc} superconductors

Energy Technology Data Exchange (ETDEWEB)

Vinokur, V.M.

1993-08-01

We develop a theory for the vortex motion in the presence of correlated disorder in the form of the twin boundaries and columnar defects. Mapping vortex trajectories onto boson world lines enables us to establish the duality of the vortex transport in the systems with correlated disorder and hopping conductivity of charged particles in 2D systems. A glassy-like dynamics of the vortex lines with zero linear-resistivity and strongly nonlinear current-voltage behavior as V {proportional_to} exp[{minus} const/J{sup {mu}}] in a Bose glass state is predicted.

Mathematical aspects of vortex dynamics; Proceedings of the Workshop, Leesburg, VA, Apr. 25-27, 1988

International Nuclear Information System (INIS)

Caflisch, R.E.

1989-01-01

Various papers on the mathematical aspects of vortex dynamics are presented. Individual topics addressed include: mathematical analysis of vortex dynamics, improved vortex methods for three-dimensional flows, the relation between thin vortex layer and vortex sheets, computations of broadband instabilities in a class of closed-streamline flows, vortex-sheet dynamics and hyperfunction theory, free surface vortex method with weak viscous effects, iterative method for computing steady vortex flow systems, invariant measures for the two-dimensional Euler flow, similarity flows containing two-branched vortex sheets, strain-induced vortex stripping, convergence of the vortex method for vortex sheets, boundary conditions and deterministic vortex methods for the Navier-Stokes equations, vorticity creation boundary conditions, vortex dynamics of stratified flows, vortex breakdown, numerical studies of vortex reconnection, vortex lattices in theory and practice, dynamics of vortex structures in the wall region of a turbulent boundary layer, and energy of a vortex lattice configuration

Design Parameters of Vortex Pumps: A Meta-Analysis of Experimental Studies

Directory of Open Access Journals (Sweden)

Angela Gerlach

2017-01-01

Full Text Available Vortex pumps can impel solid-containing fluids and are therefore widely applied, from wastewater transport to the food industry. Despite constant efforts to improve vortex pumps, however, they have remained relatively inefficient compared to conventional centrifugal pumps. To find an optimized design of vortex pumps, this paper provides a systematic analysis on experimental studies that investigated how variations in geometric parameters influence vortex pump characteristics, in particular the pump head, the pressure coefficient and the efficiency for best point operation. To this end, an extensive literature search was conducted, and eighteen articles with 53 primary investigations were identified and meta-integrated. This showed that it is not yet clarified how vortex pumps operate. Two different assumptions of the underlying operating principle of a vortex pump lead to diverging design principles. From the results of this meta-analysis, we deduce recommendations for a more efficient design of a vortex pump and emphasize further aspects on the underlying operating principle of a vortex pump.

Experimental Analysis of a Bubble Wake Influenced by a Vortex Street

Directory of Open Access Journals (Sweden)

Sophie Rüttinger

2018-01-01

Full Text Available Bubble column reactors are ubiquitous in engineering processes. They are used in waste water treatment, as well as in the chemical, pharmaceutical, biological and food industry. Mass transfer and mixing, as well as biochemical or chemical reactions in such reactors are determined by the hydrodynamics of the bubbly flow. The hydrodynamics of bubbly flows is dominated by bubble wake interactions. Despite the fact that bubble wakes have been investigated intensively in the past, there is still a lack of knowledge about how mass transfer from bubbles is influenced by bubble wake interactions in detail. The scientific scope of this work is to answer the question how bubble wakes are influenced by external flow structures like a vortex street behind a cylinder. For this purpose, the flow field in the vicinity of a single bubble is investigated systematically with high spatial and temporal resolution. High-speed Particle Image Velocimetry (PIV measurements are conducted monitoring the flow structure in the equatorial plane of the single bubble. It is shown that the root mean square (RMS velocity profiles downstream the bubble are influenced significantly by the interaction of vortices. In the presence of a vortex street, the deceleration of the fluid behind the bubble is compensated earlier than in the absence of a vortex street. This happens due to momentum transfer by cross-mixing. Both effects indicate that the interaction of vortices enhances the cross-mixing close to the bubble. Time series of instantaneous velocity fields show the formation of an inner shear layer and coupled vortices. In conclusion, this study shows in detail how the bubble wake is influenced by a vortex street and gives deep insights into possible effects on mixing and mass transfer in bubbly flows.

Quantum oscillations in vortex-liquids

Science.gov (United States)

Banerjee, Sumilan; Zhang, Shizhong; Randeria, Mohit

2012-02-01

Motivated by observations of quantum oscillations in underdoped cuprates [1], we examine the electronic density of states (DOS) in a vortex-liquid state, where long-range phase coherence is destroyed by an external magnetic field H but the local pairing amplitude survives. We note that this regime is distinct from that studied in most of the recent theories, which have focused on either a Fermi liquid with a competing order parameter or on a d-wave vortex lattice. The cuprate experiments are very likely in a resistive vortex-liquid state. We generalize the s-wave analysis of Maki and Stephen [2] to d-wave pairing and examine various regimes of the chemical potential, gap and field. We find that the (1/H) oscillations of the DOS at the chemical potential in a d-wave vortex-liquid are much more robust, i.e., have a reduced damping, compared to the s-wave case. We critically investigate the conventional wisdom relating the observed frequency to the area of an underlying Fermi surface. We also show that the oscillations in the DOS cross over to a √H behavior in the low field limit, in agreement with the recent specific heat measurements. [1] L. Taillefer, J. Phys. Cond. Mat. 21, 164212 (2009). [2] M. J. Stephen, Phys. Rev. B 45, 5481 (1992).

Numerical Study of a Southwest Vortex Rainstorm Process Influenced by the Eastward Movement of Tibetan Plateau Vortex

Directory of Open Access Journals (Sweden)

Xiaoli Liu

2018-01-01

Full Text Available A number of studies revealed the possible eastward movement of the Tibetan Plateau low-pressure system in summer and indicated the enhancement effect of this process on the southwest vortex in the Sichuan Basin, which can induce strong convective precipitation and flood events in China. In this study, a numerical simulation of a southwest vortex rainstorm process was performed. The results show that the low-pressure system originated from the Tibetan Plateau affects the southwest vortex mainly at the middle level, causing the strength increase of southwest vortex (SWV, and acts as a connection between the positive vorticity centers at the upper and lower layers. For the microscopic cloud structure, the vertical updraft of the cloud cluster embedded in the SWV increases as the low-pressure system from the plateau arrives at the Sichuan Basin. Vapor and liquid cloud water at the lower level are transported upward, based on which the ice cloud at the upper level and the warm cloud at the lower level are joined to create favorable conditions for the growth of ice crystals. As the ice crystals grow up, snow and graupel particles form, which substantially elevates the precipitation. This effect leads to the rapid development of SWV rainstorm clouds and the occurrence of precipitation. In addition to the effect of the plateau vortex, the subsequent merging of the convective clouds is another important factor for heavy rainfall because it also leads to development of convective clouds, causing heavy rainfall.

Spontaneous symmetry breaking in vortex systems with two repulsive lengthscales.

Science.gov (United States)

Curran, P J; Desoky, W M; Milosević, M V; Chaves, A; Laloë, J-B; Moodera, J S; Bending, S J

2015-10-23

Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications.

Vortex solitons at the interface separating square and hexagonal lattices

Energy Technology Data Exchange (ETDEWEB)

Jović Savić, Dragana, E-mail: jovic@ipb.ac.rs; Piper, Aleksandra; Žikić, Radomir; Timotijević, Dejan

2015-06-19

Vortex solitons at the interface separating two different photonic lattices – square and hexagonal – are demonstrated numerically. We consider the conditions for the existence of discrete vortex states at such interfaces and develop a concise picture of different scenarios of the vortex solutions behavior. Various vortices with different size and topological charges are considered, as well as various lattice interfaces. A novel type of discrete vortex surface solitons in a form of five-lobe solution is observed. Besides stable three-lobe and six-lobe discrete surface modes propagating for long distances, we observe various oscillatory vortex surface solitons, as well as dynamical instabilities of different kinds of solutions and study their angular momentum. Dynamical instabilities occur for higher values of the propagation constant, or at higher beam powers. - Highlights: • We demonstrate vortex solitons at the square–hexagonal photonic lattice interface. • A novel type of five-lobe surface vortex solitons is observed. • Different phase structures of surface solutions are studied. • Orbital angular momentum transfer of such solutions is investigated.

Coherence of the vortex Bessel-Gaussian beam in turbulent atmosphere

Science.gov (United States)

Lukin, Igor P.

2017-11-01

In this paper the theoretical research of coherent properties of the vortex Bessel-Gaussian optical beams propagating in turbulent atmosphere are developed. The approach to the analysis of this problem is based on the analytical solution of the equation for the transverse second-order mutual coherence function of a field of optical radiation. The behavior of integral scale of coherence degree of vortex Bessel-Gaussian optical beams depending on parameters of an optical beam and characteristics of turbulent atmosphere is particularly considered. It is shown that the integral scale of coherence degree of a vortex Bessel-Gaussian optical beam essentially depends on value of a topological charge of a vortex optical beam. With increase in a topological charge of a vortex Bessel-Gaussian optical beam the value of integral scale of coherence degree of a vortex Bessel-Gaussian optical beam are decreased.

Integrable Abelian vortex-like solitons

Directory of Open Access Journals (Sweden)

Felipe Contatto

2017-05-01

Full Text Available We propose a modified version of the Ginzburg–Landau energy functional admitting static solitons and determine all the Painlevé-integrable cases of its Bogomolny equations of a given class of models. Explicit solutions are determined in terms of the third Painlevé transcendents, allowing us to calculate physical quantities such as the vortex number and the vortex strength. These solutions can be interpreted as the usual Abelian-Higgs vortices on surfaces of non-constant curvature with conical singularity.

Intra-cavity vortex beam generation

CSIR Research Space (South Africa)

Naidoo, Darryl

2011-08-01

Full Text Available at exploring the methods of generating optical vortex beams. We will discuss a typical extra-cavity approach that harnesses digital holography through the use of a SLM. We consider vortex beam generation as the fundamental mode of a monolithic microchip laser...-cavity phase diffractive elements can result in the desired mode as the fundamental mode of the cavity with pure modal quality. This approach, although very attractive is insufficient for the generation of these modes in monolithic microchip lasers. A...

Hybrid Vortex Method for the Aerodynamic Analysis of Wind Turbine

Directory of Open Access Journals (Sweden)

Hao Hu

2015-01-01

Full Text Available The hybrid vortex method, in which vortex panel method is combined with the viscous-vortex particle method (HPVP, was established to model the wind turbine aerodynamic and relevant numerical procedure program was developed to solve flow equations. The panel method was used to calculate the blade surface vortex sheets and the vortex particle method was employed to simulate the blade wake vortices. As a result of numerical calculations on the flow over a wind turbine, the HPVP method shows significant advantages in accuracy and less computation resource consuming. The validation of the aerodynamic parameters against Phase VI wind turbine experimental data is performed, which shows reasonable agreement.

A computational study of soot formation in opposed-flow diffusion flame interacting with vortices

KAUST Repository

Selvaraj, Prabhu

2017-01-05

The flame-vortex interaction enables the study of basic phenomena that control the coupling between combustion and turbulence. Employing a gas phase reaction mechanism considering polycyclic aromatic hydrocarbons (PAH), a two dimensional counterflow ethylene-air flame is simulated. A reduced mechanism with PAH pathways that includes until coronene and method of moments with interpolative closure (MOMIC) has been employed to calculate the soot characteristics. Interaction of sooting flame with a prescribed decaying random velocity field is being investigated. Counterflow nonpremixed flames at low strain rate sooting conditions are considered. Effects of vortices are studied on the flame structures and its sensitivity on the soot formation characteristics. As the vortex rolls up the flame, integrated soot volume fraction is found to be larger for the air-side vortex. A detailed analysis on the flame structure and its influence on the formation of soot were carried out. The results indicate that the larger PAH species contributes to the soot formation in the airside perturbation regimes, whereas the soot formation is dominated by the soot transport in fuel-side perturbation.

The challenges of simulating wake vortex encounters and assessing separation criteria

Science.gov (United States)

Dunham, R. E.; Stuever, Robert A.; Vicroy, Dan D.

1993-01-01

During landings and take-offs, the longitudinal spacing between airplanes is in part determined by the safe separation required to avoid the trailing vortex wake of the preceding aircraft. Safe exploration of the feasibility of reducing longitudinal separation standards will require use of aircraft simulators. This paper discusses the approaches to vortex modeling, methods for modeling the aircraft/vortex interaction, some of the previous attempts of defining vortex hazard criteria, and current understanding of the development of vortex hazard criteria.

Topological dynamics of vortex-line networks in hexagonal manganites

Science.gov (United States)

Xue, Fei; Wang, Nan; Wang, Xueyun; Ji, Yanzhou; Cheong, Sang-Wook; Chen, Long-Qing

2018-01-01

The two-dimensional X Y model is the first well-studied system with topological point defects. On the other hand, although topological line defects are common in three-dimensional systems, the evolution mechanism of line defects is not fully understood. The six domains in hexagonal manganites converge to vortex lines in three dimensions. Using phase-field simulations, we predicted that during the domain coarsening process, the vortex-line network undergoes three types of basic topological changes, i.e., vortex-line loop shrinking, coalescence, and splitting. It is shown that the vortex-antivortex annihilation controls the scaling dynamics.

Vortex properties of mesoscopic superconducting samples

Energy Technology Data Exchange (ETDEWEB)

Cabral, Leonardo R.E. [Laboratorio de Supercondutividade e Materiais Avancados, Departamento de Fisica, Universidade Federal de Pernambuco, Recife 50670-901 (Brazil); Barba-Ortega, J. [Grupo de Fi' sica de Nuevos Materiales, Departamento de Fisica, Universidad Nacional de Colombia, Bogota (Colombia); Souza Silva, C.C. de [Laboratorio de Supercondutividade e Materiais Avancados, Departamento de Fisica, Universidade Federal de Pernambuco, Recife 50670-901 (Brazil); Albino Aguiar, J., E-mail: albino@df.ufpe.b [Laboratorio de Supercondutividade e Materiais Avancados, Departamento de Fisica, Universidade Federal de Pernambuco, Recife 50670-901 (Brazil)

2010-10-01

In this work we investigated theoretically the vortex properties of mesoscopic samples of different geometries, submitted to an external magnetic field. We use both London and Ginzburg-Landau theories and also solve the non-linear Time Dependent Ginzburg-Landau equations to obtain vortex configurations, equilibrium states and the spatial distribution of the superconducting electron density in a mesoscopic superconducting triangle and long prisms with square cross-section. For a mesoscopic triangle with the magnetic field applied perpendicularly to sample plane the vortex configurations were obtained by using Langevin dynamics simulations. In most of the configurations the vortices sit close to the corners, presenting twofold or three-fold symmetry. A study of different meta-stable configurations with same number of vortices is also presented. Next, by taking into account de Gennes boundary conditions via the extrapolation length, b, we study the properties of a mesoscopic superconducting square surrounded by different metallic materials and in the presence of an external magnetic field applied perpendicularly to the square surface. It is determined the b-limit for the occurrence of a single vortex in a mesoscopic square of area d{sup 2}, for 4{xi}(0){<=}d{<=}10{xi}(0).

Vortex dynamics in magnetized plasmas

International Nuclear Information System (INIS)

Kono, M.; Krane, B.; Pecseli, H.L.; Trulsen, J.

1998-01-01

Low frequency dynamics of electrostatic fluctuations in strongly magnetized plasmas have been studied. It was found that perturbations in density and potential can be very localized, indicating the applicability of an approximate description based on a finite number of vortices. A model based on a few isolated vortical structures is discussed, with particular attention to vortex collapse, where three vortices merge together within a finite time, or to the converse process, i.e. a vortex explosion. Details of these particular types of vortex dynamics depend on the actual model used for describing the electrons, the presence of a Debye shielding in particular. A ''boomerang''-type of evolution was found, where three shielded vortices expand initially, just as their unshielded counterparts, but eventually the expansion is arrested, and they start converging to collapse ultimately. The study is extended by a numerical simulation where the point model is relaxed to a continuous, but localized, vorticity distribution with finite size vortices. (orig.)

An Improved Wake Vortex Tracking Algorithm for Multiple Aircraft

Science.gov (United States)

Switzer, George F.; Proctor, Fred H.; Ahmad, Nashat N.; LimonDuparcmeur, Fanny M.

2010-01-01

The accurate tracking of vortex evolution from Large Eddy Simulation (LES) data is a complex and computationally intensive problem. The vortex tracking requires the analysis of very large three-dimensional and time-varying datasets. The complexity of the problem is further compounded by the fact that these vortices are embedded in a background turbulence field, and they may interact with the ground surface. Another level of complication can arise, if vortices from multiple aircrafts are simulated. This paper presents a new technique for post-processing LES data to obtain wake vortex tracks and wake intensities. The new approach isolates vortices by defining "regions of interest" (ROI) around each vortex and has the ability to identify vortex pairs from multiple aircraft. The paper describes the new methodology for tracking wake vortices and presents application of the technique for single and multiple aircraft.