Vortex Core Research Articles

Microstructure, magnetoresistivity and carrier mobility of HTSC-YBCO tape with pinning centers generated by electron irradiation

Artificial pinning center lattice formed in HTSC both chemically and by irradiation is believed to increase critical current and field although Abrikosov vortex core is in the normal state. The paper presents SEM-EDS, XRD and Hall effect (80-300 K at magnetic field 0.55 Tesla) data in YBCO microfilm on 276-steel tape with metal coating exposed to 5 MeV electrons (1014 cm-2 at 400 nA) in air. No long-living radioisotope was generated. This irradiation resulted in structure modification of microinterfaces YBCO-AgCu, ten times decrease in the magneto-resistance >T c, increase in the 2nd type phase transition steep. The charge carrier mobility μ decreased by a few orders of value, especially at T <100 K and 280 K, where Cooper pairs and magnons condensate, respectively. Within 80-300 K the tape is in mixed magnetic states of YBCO and steel substrate, thereby providing effective flux pinning by highly correlated non-superconducting state.

Vortex core radius in baroclinic turbulence: Implications for scaling predictions

Vortex core radius in baroclinic turbulence: Implications for scaling predictions

Three-dimensional critical points and flow patterns in pulmonary alveoli with rhythmic wall motion

The dynamics of airflow in the pulmonary acini are of broad interest in understanding respiratory diseases and the fate of inhaled particles. This study investigates the three-dimensional (3d) alveolar flows with rhythmic cavity wall motion, using a finite element method based computational fluid dynamics. This study reports the new research findings on the critical points and associated flow patterns. The locations of critical points are found based on the Brouwer degree theory and Broyden’s method. The phase portrait is used to evaluate the flow patterns around the critical points and the stability (repelling/attracting property) of the critical points on the symmetry plane of the alveolus. Based on the Poincare–Bendixson theorem, the closed orbits on the symmetry plane are found which have the capability to alter the spiral direction of the spiral streamlines. In the 3d space, the alveolar flow is symmetric about the geometric symmetry plane of the alveolus. Different types of 3d critical points, including saddle, spiral, and spiral saddle, are revealed. There are only one saddle point and at least one spiral point or spiral saddle in the alveolar flow. Spiral points and spiral saddles are located on the vortex core line and their number is dependent on the Reynolds number and varies with time. The study of critical points and their evolution helps us to understand the mechanism of irreversible transport of particle tracers from a new perspective.

Mechanical properties and abnormal mechanical behaviors of ferroelectric hexagonal manganites

Hexagonal manganites (h-RMnO3, R=Y, Ho-Lu) are emerging as advantageous multiferroic materials with structural ferroelectric topological defects. Strain has been proven as an effective means to control topological vortex cores. To further understand and utilize the mechanical manipulation mechanism, mechanical properties such as the Young’s modulus are important; however, accurate values are still to be obtained for single-crystalline specimens. In this study, by combining contact resonance atomic force microscopy, nanoindentation, and density functional theory calculations, we systematically studied the Young’s moduli of YMnO3, ErMnO3, and LuMnO3 single crystals. The Young's moduli of LuMnO3 obtained by the different methods were consistent, whereas for ErMnO3 and YMnO3, the abnormal mechanical behavior observed in the nanoindentation experiments deviated from the theoretical and experimental calculations. Through in-situ transmission electron microscopy, it was confirmed that lattice distortion plays a key role in resisting deformation, which is the origin of the abnormal mechanical behavior. Our work provides insights into an important mechanical parameter and the origin of the difference in the Young’s modulus of h-RMnO3, which is important for further theoretical investigations and potential applications.

Modal Decomposition Study of the Non-Reactive Flow Field in a Dual-Swirl Combustor

The modal decomposition study of the non-reactive flow field in a dual-swirl combustor is investigated through the large eddy simulation. The formation mechanism and function of various recirculation zones are elaborated by analyzing the time-averaged and instantaneous velocity contours of the center section. The precessing vortex core (PVC) is first visualized by the pressure iso-surface, and the evolution process is presented. Different dimensionality reduction methods are adopted to identify the coherent structures from the flow field. The most energetic spatial structure corresponding to the PVC and its second-order harmonic structure is extracted by the classical proper orthogonal decomposition (POD). The coherent structures with high frequency have relatively low energy content. In addition, a spectral proper orthogonal decomposition (SPOD) method, which can implement spatial-temporal decomposition simultaneously, is introduced to obtain the energy-based spatial structures at all characteristic frequencies. A triple-helix with azimuth wave number m = 3 and a quadruple-helix with azimuth wave number m = 4 are discovered as the third-order and the fourth-order harmonics of single-helix, respectively.

Controllable experimental modulation of high-order Laguerre-Gaussian laser modes.

High-order helical and sinusoidal Laguerre-Gaussian (LG) laser modes have uneven energy distribution among their multiple concentric vortex core rings and lobes, respectively. Here, we explore an experimental method to reshuffle the optical energy among their multiple concentric vortex core rings and lobes of high-order LG modes in a controllable manner. We numerically designed a diffractive optical element displayed over a spatial light modulator to rearrange optical energy among multiple concentric vortex core rings. This changes outer low-intensity concentric vortex core rings into high-intensity vortex core rings of high-order helical LG modes at the Fourier plane. The precise generation of a high-order modulated helical LG laser mode has a maximum number of highly intense concentric vortex core rings compared to known standard helical LG modes. Further, this method is extended to high-order sinusoidal LG modes consisting of both low- and high-intensity lobes to realize modulated sinusoidal LG modes with a maximum number of highly intense lobes in a controllable manner. We envisage that the modulated helical and sinusoidal high-order LG modes may surpass standard LG modes in many applications where highly intense rings and lobes are crucial, as in particle manipulation of micro- and nanoparticles, and optical lithography.

Effects of Precipitation Latent Heating on Structure and Evolution of Northeast China Cold Vortex: A PV Perspective

AbstractBased on potential vorticity (PV) thinking, northeast China cold vortex (NCCV) corresponds to an upper‐level high PV anomaly from stratospheric PV downward intrusion. Within a vortex, latent heating from precipitation would produce a vertical dipole of PV anomalies that would affect structures and evolution of the vortex. In this paper, three‐dimensional structures and evolution of NCCV and, effects of latent heating from precipitation along bent‐back, cold and warm fronts on them are investigated based on convection‐allowing simulations for an intense NCCV case during 8–17 June 2012. Trajectory analysis shows that the negative upper‐level diabatic PV anomaly from bent‐back frontal precipitation, near the vortex center, is the dominant contributor to erosion of high PV in the vortex core region as it is advected in, leading to the weakening of the vortex. The negative PV anomalies along the cold and warm fronts, at the east‐to‐southeast side of the vortex, are mostly advected downstream away from the NCCV. In the middle troposphere, positive PV anomalies are primarily generated along fronts and the accumulated positive PV anomalies filling the vortex region help to reinforce the low‐level cyclonic circulation. The lower‐level PV is affected by surface heating and cooling through their effects on static stability, but such effects are periodic and create mainly diurnal variations. The NCCV eventually decays as the upper‐level vortex weakens due to significant PV erosion.

Anisotropy of turbulence at the core of the tip and hub vortices shed by a marine propeller

Large-eddy simulation on a grid consisting of 5 billion points was utilized to study the properties of turbulence at the core of the tip and hub vortices shed by a marine propeller across working conditions. Turbulence at the core of the tip vortices was found to be initially isotropic, moving towards a ‘cigar-shaped’ axisymmetric state as instability grows, dominated by turbulent fluctuations of the velocity component directed in the radial direction of the cylindrical reference frame centred at the wake axis. The break-up of the coherence of the tip vortices is instead characterized by turbulence recovering an isotropic state. This process is accelerated by growing load conditions of the propeller. In contrast, during instability of the hub vortex, turbulence at its core develops a ‘pancake-shaped’ axisymmetric state, dominated by the fluctuations of the radial and azimuthal velocities. However, at higher propeller loads turbulence at the core of the hub vortex keeps close to isotropy, thanks to a faster instability. Within both tip and hub vortices the deviations from Boussinesq's hypothesis were found very significant, providing evidence of the unsuitability of conventional turbulence modelling. At the core of the tip vortices they become especially large at their break-up and for increasing load conditions of the propeller, equivalent to more intense structures. In contrast, at the core of the hub vortex they were verified to be decreasing functions of the propeller load.

Stencil Lithography‐Assisted Fabrication of Triangular Grid Pb Architecture

AbstractManipulating Majorana zero modes (MZMs) holds significant promise in propelling the field of topological quantum computation. While scanning tunneling microscopy (STM) exhibits remarkable capabilities in characterizing MZMs, additional geometrical constraints are imperative for achieving precise and controllable manipulation of these zero modes. To this end, it is of great help to integrate a micro mask within a molecular beam epitaxy (MBE) system to grow specific patterns containing MZMs. Here, a scenario for manipulating the MZMs in the vortex cores based on a triangular grid architecture is proposed. Additionally, a stencil lithography setup that is compatible with a combined MBE and STM system is introduced and experimentally demonstrated. A fine‐tuning of the Pb patterns, between a hexagonal antidot lattice to a triangular grid array, is achieved by adjusting the spatial gap between the stencil mask and the underlying substrate. This study provides new possibilities for the fabrication and investigation of Majorana devices.

Improving Separation Prediction of Cyclone Separators with a Hybrid URANS-LES Turbulence Model

The CFD simulation of cyclone separators has remarkably evolved over the past decades. Nowadays, computational models are essential for designing, analyzing, and optimizing these devices. Due to the intrinsic anisotropy of the flow inside these separators, the Reynolds stress model (RSM) has been mostly employed. However, RSM models fail to solve most time and space scales, including those relevant to particle behavior. Consequently, the prediction of the grade collection efficiency may be hindered, particularly for low-Stokes-number particles. For example, the precessing vortex core phenomenon (PVC), a well-known phenomenon that is relevant for particle motion, is not usually captured in Reynolds-averaged Navier–Stokes (RANS) simulations. Alternatively, the large-eddy simulation (LES) has been proven to be a superior approach since it captures many time and space scales that would have been otherwise dissipated, allowing for more accurate predictions of particle collection. However, this accuracy comes at a considerable computational cost. To combine the advantages of these two models, the main objective of this research was to evaluate a new hybrid RSM-LES model applied to the cyclone’s flow. The results were compared to experimental data and with RSM model results. It showed that, compared to a RANS model given by the RSM closure model, the grade collection efficiency curve obtained by the hybrid model is closer to the experimental one, even for the coarser mesh. Beyond that, the results showed that while the improvement in results was not proportional to mesh refinement for RANS modeling, the hybrid model showed significant improvement with mesh refinement.

Numerical modeling of body shape effect on the performance of a square cyclone separator

This study aims to determine the effect of a square cyclone body shape on the performance of a square cyclone separator. To achieve this goal, four square cyclone separators with square lengths 0, 1, 2, and 3 times the hydraulic diameter of the cyclone body were considered. The simulation of the gas-solid flow was carried out using the Euler-Lagrange approach, while the gas flow was modeled by Navier–Stokes equations and the Reynolds stress turbulent model (RSTM), and the injected solid particle was solved using the Newton equation. The pressure drop, separation efficiency, and flow pattern were investigated to evaluate the performance of square cyclone separators. The results revealed that the pressure drop and separation efficiency decreased as the relative square length increased. In the case with a lower relative square length, the vortex core penetration is less than that in the other cases, which leads to a decrease in the entrainment phenomena and separation efficiency enhancement. At an inlet velocity of 16 m/s, an increase in the relative square length from 0 to 3 reduced the pressure drop by approximately 35%. At an inlet velocity of 24 m/s and a particle diameter of 8 µm, with an increase in the relative square length from 0 to 3, the efficiency decreased from 88.7 to 77.4%.

The investigation of a likely scenario for natural tornado genesis and evolution from an initial instability profile

A likely mechanism for the little-understood tornado genesis is proposed and its numerical implementation is presented. The Burgers-Rott vortex with its axis in the vertical direction is introduced as an instability mechanism, and the flow field then evolves under the influence of the atmospheric pressure, temperature and density variations with altitude. Buoyancy effects are implemented using the Boussinesq model. Results are presented and discussed for a set of conditions including mesh type and size, different turbulence models, and a few different boundary conditions. Post-processed results of the transient simulations including animations contain a wealth of information to help analyze tornado behavior. Velocity contours, pressure contours, vorticity contours, streamlines, and iso-surfaces show the evolution of a complex flow field possessing many characteristics of a tornado. At longer times from the start, the flow field becomes more asymmetric with the vortex core becoming more twisted, and the eye of the vortex drifting away from the axis of the computational domain. The single initial vortex then transitions into multiple vortices of varying size and orientation. These high Reynolds number (ReΓ ∼109) simulation results show flow fields that resemble highly unsteady, turbulent flows with large regions of flow separation, and large eddy size range.

Analysis of the vortical flow in a cyclone using four vortex identification methods

This paper analyzes the vortex flow field and performance of a solid-gas cyclone separator using computational fluid dynamics (CFD) by employing the Reynolds stress turbulence model (RSM) and Eulerian-Lagrangian particle tracking scheme for particle diameter (d) range of 0.1 to 8 μm. The complex structure of vortices is analyzed using the vorticity method, λ2-criterion, Q-criterion, and Ω-method. The results demonstrate that the presence of helical guide vanes (HGVs) enhances the centrifugal force applied to the solid particles and fluid velocity up to 4.4 times compared to the conventional cyclone. It is revealed that the λ2, Q, and Ω methods provide more details of eddy structure in the inner and outer layers of the isovortex surfaces than the vorticity method. Besides, the vortex core diameter can be estimated by all vortex identification methods.

Vortex dynamics in a spin valve nanopillar having hybrid polarizer and magnetostatic coupling

This study investigates the observation and control of vortex gyration in the free layer by utilizing polarized current. Modifying the current alone proves challenging in adjusting the frequency and amplitude, as the orbit radius of the vortex core remains constant. To address this, a spin valve nanopillar model with hybrid polarizer is introduced and analyzed, enabling support and gyration of the vortex core in the nanodisk under spin polarized current. Manipulating current density and fine-tuning of hybrid polarizer parameters adjusts system frequency and amplitude. However, with hybrid polarizer, while vortex gyration and higher-frequency signal production increase at higher current densities, the amplitude generally decreases. To mitigate this behavior, the study explores the vortex interactions influenced by magnetostatic coupling in the free layers of spin valve nanopillar. The objective of this paper is to advance the understanding of vortex physics for applications that require greater amplitude microwave signals.

Topological vortex mode for flexural waves in pillared plates

Localized topological modes with high robustness to various perturbations are receiving increasing attention. Recently, zero-order topological vortex modes have been designed in phononic structures, in analogy with zero-energy fermionic states modulated by Jackiw-Rossi binding mechanism. Such localized modes may have potential applications for biosensing, bioimaging and on-chip communication. In this work, we propose a pillared phononic plate with a Kekulé distortion of pillars position to bind topological modes at a vortex core via dispersion engineering. The phase winding and amplitude diagrams of the topological vortex mode are observed experimentally. It is found that existence of vibration peaks and corresponding mode patterns are strongly robust against the random perturbation of resonant frequencies of pillars at the vortex core. We further design a topological resonant sensor for mass sensitivity. The frequency of the topological vortex mode is almost linearly sensitive to added small mass at the vortex core in terms of mass values and positions. The proposed pillared plates provide a platform for potential applications such as energy localization and harvesting, remote health monitoring.

Vortex ring formation process in starting jets with uniform background co- and counter-flow

The formation process of the leading vortex ring in starting jets with uniform background co- and counter-flow has been studied numerically for $-0.5\leq R_v\leq 0.5$ , where $R_v$ is the ratio of background velocity to jet velocity. For the cases with background counter-flow, the normal formation process of the leading vortex ring would be destroyed when $R_v&lt;-0.4$ , i.e. the trailing jet would overtake the leading vortex ring through the centre, a phenomenon reminiscent of vortex leapfrogging. As the velocity ratio $R_v$ increases, the formation number $F_{t^*}$ decreases from $9.6$ at $R_v=-0.4$ to $1.92$ at $R_v=0.5$ . An analytical model based on the kinematic criterion has been developed so as to describe the relationship between the formation number $F_{t^*}$ and velocity ratio $R_v$ . A linear relationship between the vortex core parameter and stroke ratio of starting jet ( $\varepsilon \sim k_1L/D$ ) for the Norbury vortex ring has been established and used effectively to close the model. For co-flow with $0&lt; R_v\leq 0.5$ , the results from this model are consistent with the present numerical simulation and the experiments by Krueger et al. (J. Fluid Mech., vol. 556, 2006, pp. 147–166). For counter-flow, two different equations are proposed for $-0.4\leq R_v\leq -0.2$ and $-0.2&lt; R_v&lt;0$ , respectively.

Vortex ring and bubble interaction: Effects of bubble size on vorticity dynamics and bubble dynamics

Bubbly turbulent flows involve complex interactions between bubbles and vortices, in which their size ratio plays a critical role. The present work investigates an idealization, namely, the interaction of a single air bubble with a (water) vortex ring, with the focus being on the effects of the bubble-to-vortex core size ratio (Db/Dc,o) on the bubble and ring dynamics (Db = bubble diameter and Dc,o = initial vortex core diameter). The interaction is studied for size ratio, Db/Dc,o, of 0.6–1.7, over a large Weber number range from 10 to 500 [We=0.87ρ(Γ/πDc,o)2/(σ/Db), Γ = circulation]. On the bubble dynamics side, in the initial stages of the interaction after the bubble's capture by the ring, the bubble's radial equilibrium position, its azimuthal elongation, and breakup pattern are influenced by both Db/Dc,o and We. However, at longer times, the results show that the We alone decides the broken bubbles to Db ratio and scales as We−0.13, which can be contrasted with the scaling of We−0.6 in isotropic turbulence [R. Shinnar, J. Fluid Mech. 10, 259–275 (1961)]. On the ring dynamics side, increasing Db/Dc,o leads to larger deformation of the vortex ring core at low We, and these effects are significant above a critical Db/Dc,o of about 1.2. Under these conditions, the vortex core can fragment, leading to large reductions in the ring's measured convection speed and axial enstrophy, both of which follow a similar scaling, (Db/Dc,o)2/We; the reduction in enstrophy being reminiscent of bubbly turbulent flows. These results and scalings should help us to better understand and model bubble–turbulence interactions.

Coupled quantum vortex kinematics and Berry curvature in real space

The Berry curvature provides a powerful tool to unify several branches of science through their geometrical aspect: topology, energy bands, spin and vector fields. While quantum defects–phase vortices and skyrmions–have been in the spotlight, as rotational entities in condensates, superfluids and optics, their dynamics in multi-component fields remain little explored. Here we use two-component microcavity polaritons to imprint a dynamical pseudospin texture in the form of a double full Bloch beam, a conformal continuous vortex beyond unitary skyrmions. The Berry curvature plays a key role to link various quantum spaces available to describe such textures. It explains for instance the ultrafast spiraling in real space of two singular vortex cores, providing in particular a simple expression–also involving the complex Rabi frequency–for their intricate velocity. Such Berry connections open new perspectives for understanding and controlling highly-structured quantum objects, including strongly asymmetric cases or even higher multi-component fields.

Artificial Pinning Centers and the Quest of High Critical Current Densities in HTS Nanocomposites

After theoretical discovery of quantized magnetic vortices in type II superconductors by Abrikosov, which received 2003 Nobel Prize in Physics, vortex pinning has been an important topic of research for high critical current densities in applied magnetic fields desired for a variety of applications in electric and electronic devices and systems. The small vortex core size in high temperature superconductors (HTSs), of a few nanometers, has prompted an intensive research in development of nanoscale artificial pinning centers (APCs) in so-called HTS nanocomposites. Exciting results of much enhanced in-field critical current densities and pinning force densities have been achieved. This talk intends to highlight the progress made recently in HTS nanocomposites towards controllable generation of APCs with desired morphologies, dimension, concentration, and pinning efficiency for targeted applications. The future research in HTS nanocomposites to meet the need of practical applications will also be discussed.

Numerical simulation and experimental investigation of heat transfer performance of turbine blade with ribbed channel

A combination of numerical simulation and experimental test is carried out, and the vortex core visualization technology is adopted to visualize vortex in the flow field and study the heat transfer mechanism. The heat transfer characteristics of air flow in 45° ribbed straight channel with aspect ratio of 1 and the other 6 new ribbed channels are studied. The results show that the average heat transfer performance of the new ribbed channel with all the fins 3.8 mm cut at the far end of fins along the flow direction is the best by comparing with the original ribbed straight channel under the same conditions. The average Nu, the average Nu/Nu0 and the average heat transfer enhancement factor FT of the ribbed wall is increased respectively by 25.1%, 24.8%, 22.7% on the average by comparing with the original ribbed channel. The experimental results show that the error between the experimental value and the simulated is about 10% for the outer wall temperature of ribbed channel.