Creation Of Vortices Research Articles

Controlled creation and annihilation of isolated robust emergent magnetic monopole like charged vertices in square artificial spin ice

Magnetic analogue of an isolated free electric charge, i.e., a magnet with a single north or south pole, is a long sought-after particle which remains elusive so far. In magnetically frustrated pyrochlore solids, a classical analogue of monopole was observed as a result of excitation of spin ice vertices. Direct visualization of such excitations were proposed and later confirmed in analogous artificial spin ice (ASI) systems of square as well as Kagome geometries. However, such magnetically charged vertices are randomly created as they are thermally driven and are always associated with corresponding equal and opposite emergent charges, often termed as monopole–antimonopole pairs, connected by observable strings. Here, we demonstrate a controlled stabilisation of a robust isolated emergent monopole-like magnetically charged vertices in individual square ASI systems by application of an external magnetic field. The excitation conserves the magnetic charge without the involvement of a corresponding excitation of opposite charge. Well supported by Monte Carlo simulations our experimental results enable, in absence of a true elemental magnetic monopole, creation of electron vortices and studying electrodynamics in presence of a monopole-like field in a solid state environment.

Design of A Micro Hydro Power Plant Based on The Vortex Flow of Water

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

STABILITY OF SKYRMIONS IN THE FRUSTRATED ANTIFERROMAGNETIC/FERROELECTRIC BILAYERS WITH THE TRIANGULAR LATTICE

The formation and conditions of stability of a skyrmions at the interface between a ferroelectric layer and antiferromagnetic layer with triangilar lattice and its phase transition are studied. All interactions between spins and polarizations are limited to nearest neighbors (NN). The antiferromagnetic exchange interaction among the spins inside antiferromagnetic layer will compete with the perpendicular interface interaction between adjacent layers. The ground state spin configuration at zero temperature is calculated by using the numerical high performance steepest descent method. The resulting configuration is non-collinear. Small values of external field yields small values of angles between spins in the plane so that the ground state configurations have antiferromagnetic and non collinear domains. We observe the creation of single spin vortices. We noted that for zero applied magnetic field the skyrmions in the antiferromagnetic/ferroelectric bilayers with triangular lattice can be created in the region of interface magnetoelectric interaction value between 0.85 and 1.95. The strong external magnetic field applied perpendicular to the interface with non-collinear Dzyaloshinskiy-Morya-like magnetoelectric interaction at the interface leads to remove the skyrmion phase and magnetic phase transitions. With increasing the interface magnetoelectric coupling, the skyrmion lattice disappear. We found the formation perfect skyrmion structure at non-zero external magnetic field and moderate values of magnetoelectric interaction. The skyrmions structure is stable in a large region of the interface magnetoelectric interaction between antiferromagnetic and ferroelectric films. The results of Monte Carlo simulations that we carried out confirm that observed skyrmions are stable up to a finite temperature.

Controlled creation and decay of singly-quantized vortices in a polar magnetic phase

Quantized vortices appear in physical systems from superfluids and superconductors to liquid crystals and high energy physics. Unlike their scalar cousins, superfluids with complex internal structure can exhibit rich dynamics of decay and even fractional vorticity. Here, we experimentally and theoretically explore the creation and time evolution of vortex lines in the polar magnetic phase of a trapped spin-1 87Rb Bose–Einstein condensate. A process of phase-imprinting a nonsingular vortex, its decay into a pair of singular spinor vortices, and a rapid exchange of magnetic phases creates a pair of three-dimensional, singular singly-quantized vortex lines with core regions that are filled with atoms in the ferromagnetic phase. Atomic interactions guide the subsequent vortex dynamics, leading to core structures that suggest the decay of the singly-quantized vortices into half-quantum vortices.

Numerical analysis on heat transfer of a pyramid-shaped photovoltaic panel

In the present study, a pyramid-shaped solar panel as a novel design of a photovoltaic (PV) panel is simulated. The simulation process was performed by means of an open source CFD software (Open foam, Version 2.3.1). Also, the Bouyant Boussinesq Pimple Foam solver was used in this study. In this study, four PVs were fabricated in the form of pyramid-shaped construction with trapdoors at the bottom and topsides which were assumed as the inlet and outlet of the coolant air, respectively. The flow was considered to be steady. The inlet velocity is chosen as a governor parameter on heat and fluid flow. Three inlet velocities of 0.01 ms−1, 0.1 ms−1, and 1 ms−1 with constant inlet temperature of 293 K were considered to check the effect of inlet velocity on the cooling of the PVs. For each air velocity, three different heat flux values of 250, 500, and 750 Wm−2 were considered to simulate the effect of different time periods of the day. The results presented that by the increment of air mass flow rate, the flow patterns of air flow change from buoyancy induced flow to forced flow causing to creation of small vortices at the corners of the pyramid which result in augmentation of heat transfer coefficients in this regions. The increment of the inlet air velocity increases the heat transfer coefficient up to 1.9 times which leads in reduction of backside temperature of the PVs. It was found that the increment of air velocity could lead in up to 29% reduction in the backside temperature difference. When the inlet velocity of air stream was equal to 1 ms−1, the backside temperature of the panel faced 42 K lower temperature than that associated with the inlet velocity of 0.01 ms−1.

Twist effects on quantum vortex defects

We demonstrate that on a quantum vortex in Bose-Einstein condensates can form a new, central phase singularity. We define the twist phase for isophase surfaces and show that if the injection of a twist phase is global this phenomenon is given by an analog of the Aharonov-Bohm effect. We show analytically that the injection of a twist phase makes the filament unstable, that is the GP equation is modified by a new term that makes the Hamiltonian non-Hermitian. Using Kleinert’s theory for multi-valued fields we show that this instability is compensated by the creation of the second vortex, possibly linked with the first one.

The numerical simulation of the rope vortex creation and the possibilities of its control

The rope vortex is a phenomena which can be observed in many hydraulic machines, especially turbines and pump–turbines. Its creation is based on a non uniform velocity profile characterized by high value of the circumferential component. This phenomena limits the range of operating conditions, which results in reduction of the energy production. The article presents the flow analysis of the hydraulic Francis turbine, where the rope vortex was observed. The structure of the vortex was identify and some solutions were analysed to prevent or reduce the size of multiphase flow.

Role of Atwood number on flow morphology of a planar shock-accelerated square bubble: A numerical study

The Atwood number plays a critical role in describing the physics of fluids behind the hydrodynamic instabilities in gas dynamics. In order to investigate the impacts of the Atwood number (At), the evolution of a shock-accelerated square bubble containing either SF6, Kr, Ar, Ne, or He and surrounded by N2 is investigated numerically. For this purpose, the unsteady compressible Navier–Stokes–Fourier equations are solved using an explicit modal discontinuous Galerkin method. For validation, the numerical results are compared with available experimental results and are found to be in good agreement. The results demonstrate that the Atwood number has a significant influence on flow morphology with wave patterns, vortex creation, vorticity generation, and bubble deformation. For At > 0, the speed of the shock wave traveling along with the bubble inner surface is often less than that of the incident shock wave and greater than that of the transmitted shock wave. Moreover, vortex pairs from the upstream and downstream corners are generated, and the former vortex pair ultimately dominates the flow morphology. For At ≈ 0, the incident and transmitted shock waves move at the same speeds, whereas for At < 0, the transmitted shock wave travels faster than the incident shock wave. Moreover, only one vortex pair at the upstream corners is generated, which dominates the flow morphology. Furthermore, a detailed study of Atwood number impacts is investigated through the vorticity generation at interfaces. A quantitative analysis based on the shock trajectories, the interface features, and the integral diagnostics is also studied in detail to investigate the impacts of the Atwood number on the flow structure. Finally, a comparative study of the flow physics between the shock-accelerated square and cylindrical bubbles is conducted to examine their natural differences.

Asymmetric crossing of the attractive and repulsive magnetic potential by Abrikosov vortices

We present studies of Abrikosov vortex motion across the magnetically charged edges of long thin ferromagnetic stripes placed above or under a thin superconducting film. The magnetic charges at the stripe edges form attractive or repulsive potential wells for vortices. Using a relatively small in-plane magnetic field to polarize the stripe edges and normal-to-plane magnetic field to induce up or down polarized vortices, we tune the attractive or repulsive stripe-vortex interactions. Imaging of the vortex dynamics reveals that the repulsive magnetic potential ${{U}_{m}}^{+}$ acts as a robust vortex pinning barrier, while the attractive ${{U}_{m}}^{\ensuremath{-}}$ has practically no effect on the vortex motion irrespective of the position of the stripes located above or underneath the superconducting film. We analyze the observed asymmetry using equations of the overdamped vortex motion. The formal analytical solution yields an asymmetry, but the numerical modeling with and without noise terms does not confirm it. Instead, we find that the asymmetry is caused by the creation of spontaneous vortices at the maxima of ${U}_{m}$, which depends on the edge polarity and suppress ${{U}_{m}}^{\ensuremath{-}}$. Furthermore, our experiment and time-dependent Ginzburg-Landau simulations demonstrate that magnetic pinning dominates over vortex pinning due to corrugations of the superconducting layer deposited on top of the ferromagnetic stripes.

Topological transitions in an oscillatory driven liquid crystal cell

Matter under different equilibrium conditions of pressure and temperature exhibits different states such as solid, liquid, gas, and plasma. Exotic states of matter, such as Bose–Einstein condensates, superfluidity, chiral magnets, superconductivity, and liquid crystalline blue phases are observed in thermodynamic equilibrium. Rather than being a result of an aggregation of matter, their emergence is due to a change of a topological state of the system. These topological states can persist out of thermodynamics equilibrium. Here we investigate topological states of matter in a system with injection and dissipation of energy by means of oscillatory forcing. In an experiment involving a liquid crystal cell under the influence of a low-frequency oscillatory electric field, we observe a transition from a non-vortex state to a state in which vortices persist, topological transition. Depending on the period and the type of the forcing, the vortices self-organise, forming square lattices, glassy states, and disordered vortex structures. The bifurcation diagram is characterised experimentally. A continuous topological transition is observed for the sawtooth and square forcings. The scenario changes dramatically for sinusoidal forcing where the topological transition is discontinuous, which is accompanied by serial transitions between square and glassy vortex lattices. Based on a stochastic amplitude equation, we recognise the origin of the transition as the balance between stochastic creation and deterministic annihilation of vortices. Numerical simulations show topological transitions and the emergence of square vortex lattice. Our results show that the matter maintained out of equilibrium by means of the temporal modulation of parameters can exhibit exotic states.

Passive Reduction of Leakage by Transverse Jet

Abstract This article presents investigations of mass flow reduction in a gap above a fin by the air curtain technique. The proposed method uses slots in the fin to generate a bypass flow and to create a fluidic barrier in the gap above the fin. Both numerical and experimental researches were conducted and the air curtain proved to be effective, showing the mass flow reduction up to about 20%. The comparison of numerical simulations and experimental data showed good agreement, and the flow structure details were analyzed based on the numerical results. The analysis shows that the blown air in the gap leads to creation of streamwise vortices. They enforce crosswise nonuniformity of the flow velocity in the gap and downstream, what finally influences on higher dissipation effects and mass flow reduction in the gap.

Temporal shaping and time-varying orbital angular momentum of displaced vortices

The fundamental mode of rotation in quantum fluids is given by a vortex whose quantized value yields the orbital angular momentum (OAM) per particle. If the vortex is displaced (off-centered) from the reference point for rotation, the angular momentum is reduced and becomes fractional. Such displaced vortices can further exhibit a peculiar dynamics in the presence of confining potentials or couplings to other fields. We study analytically a number of 2D systems where displaced vortices exhibit a noteworthy dynamics, including time-varying self-sustained oscillation of the OAM, complex reshaping of their morphology with possible creation of vortex–antivortex pairs, and peculiar trajectories for the vortex core with sequences of strong accelerations and decelerations that can even send the core to infinity and bring it back. Interestingly, these do not have to occur conjointly, with complex time dynamics of the vortex core and/or their wavepacket morphology possibly taking place without affecting the total OAM. Our results generalize to simple and fundamental systems a phenomenology recently reported with Rabi-coupled bosonic fields, showing their wider relevance and opening prospects for new types of control and structuring of the angular momentum of light and/or quantum fluids.

Experimental investigation of hydrothermal characteristics for flow within a circular tube equipped with twisted conical strip inserts under different alignments

This study attempts to experimentally investigate the thermohydraulic characteristics inside a tube fitted with the staggered and non-staggered twisted conical strip inserts. The inserts are built via stereolithography 3D printer. The influences of geometrical attributes such as alignment type (i.e., staggered or non-staggered) and the pitch ratio as well as the Reynolds number (Re) on the Nusselt number (Nu) and friction factor (f) are examined. Because of flow mixing and vortex creation in the flow path, the tube fitted with the conical inserts has greater Nu and f in comparison with the smooth tube. The Nu and f have larger amounts in the tube having the non-staggered inserts in comparison with that with the staggered ones. With the pitch ratio elevation, the Nu and f diminish, while the elevation in the Re decreases the f and enhances the Nu. Thus, the highest Nusselt number and pressure drop belong to the non-staggered insert with pitch ratio of 2.5 and Reynolds number of 2250 with amounts of 15.15 and 795 Pa, respectively. The highest improvement of the Nusselt number in comparison with the plain tube occurs at Reynolds number of 350 for the non-staggered insert with pitch ratio of 2.5, which is recorded about 133.8%. Besides, the performance evaluation criterion (PEC) is higher than 1 at Re numbers of 820 and less than 820, which shows the proper merit of applying both the staggered and non-staggered inserts in this Re span. For small Re, the non-staggered inserts lead to larger PEC than the staggered ones, while an opposite outcome is observed for the high Reynolds numbers. The highest PEC is about 1.56, which belongs to the non-staggered alignment with pitch ratio of 5 and Reynolds number of 350.

Langmuir-type vortices in wall-bounded flows driven by a criss-cross wavy wall topography

Abstract

On-Demand Optical Generation of Single Flux Quanta.

Superconductors can host quantized magnetic flux tubes surrounded by supercurrents, called Abrikosov vortices. Vortex penetration into a superconducting film is usually limited to its edges and triggered by external magnetic fields or local electrical currents. With a view to novel research directions in quantum computation, the possibility to generate and control single flux quanta in situ is thus challenging. We introduce a far-field optical method to sculpt the magnetic flux or generate permanent single vortices at any desired position in a superconductor. It is based on a fast quench following the absorption of a tightly focused laser pulse that locally heats the superconductor above its critical temperature. We achieve ex-nihilo creation of a single vortex pinned at the center of the hotspot, while its counterpart opposite flux is trapped tens of micrometers away at its boundaries. Our method paves the way to optical operation of Josephson transport with single flux quanta.

A fan-shaped plasma reactor for mixing enhancement in a closed chamber

This paper introduces a novel fan-shaped plasma reactor, which employs vortex-induced airflow by atmospheric dielectric barrier discharge to enhance mixing and the resulting distribution of the neighboring species of generated ozone. Through stereoscopic PIV and smoke flow visualizations it was demonstrated that mechanisms of suction, vortex creation and ejection of the fluid combine to form a vertical turbulent flow that yields a more controlled and uniform ozone distribution. The performance of the fan reactor was compared to that of a conventional comb reactor for three cross-sectional planes of a space volume simulating the decontamination environment. Results show that with the fan reactor, ozone starts spreading from the center of the plane, which makes the reactor itself responsible for most of the mixing and ozone’s distribution pattern; whereas in the case of the comb reactor, mixing seems to be mostly dependent on the interaction between the reactor’s characteristic flow and the boundaries of the space volume.

Assessment of the efficiency of non-metallic inclusions removal through the use of centrifugal force at different stages of steel production

Methods for the removal of non-metallic inclusions from steel at various stages of its production are considered: in a teeming ladle, a tundish and a CCM mold. It is proposed to classify methods of non-metallic inclusions removal into two groups: mechanical (inert gas blowing, application of electromagnetic stirrers, etc.) and physical and chemical (modification of non-metallic inclusions, slag treatment, rational deoxidation modes). Particular attention is paid to methods aimed at creating a vortex in the metal, inside which non-metallic inclusions are transported to its axis. The aim of the work is to determine the efficiency of use centrifugal forces to remove non-metallic inclusions at different stages of steel production. To assess the centrifugal force effectiveness, it has been analyzed the transfer time of non-metallic inclusions of various sizes to the vortex axis in the teeming ladle of 50 tons capacity, a rotary chamber of tundish (chamber capacity is 2.0 tons) and the CCM mold of 160 mm in diameter. For typical angular velocities being observed during electromagnetic stirring, the values of the metal inertia moment and the kinetic energy of its rotational motion have been calculated. According to the calculations, the smallest transfer time of inclusions is achieved in the teeming ladle. However, vortex creation in it requires a significant energy. The use of centrifugal force in the mold, although it does not require such a high energy, is also not efficient enough due to the low angular velocity of the vortex, limited by a risk of violating the crust formation in the mold. The possibility of using the kinetic energy of the jet flowing from the teeming ladle to the rotary chamber of the tundish has been assessed.

Natural Convection of Nanofluid in a Triangle Cavity with Different Angular Positions

The effects of the angular position on the flow and heat transfer of the nanofluid in a triangular cavity is investigated numerically. A triangular cavity is chosen with the same boundary conditions as the published results are available. The comparison between the current numerical results with the available data is made to show the accuracy of the numerical simulation. The current structure of triangular cavity is rotated to investigate the effects of various angular positions on the flow and heat transfer characteristics of nanofluid. For this purpose, the equations of continuity, momentum and energy are solved numerically. The results show that the hot fluid is more freely penetrated into the domain by increasing of the angular position. The velocity of fluid in the flow field becomes maximum for the angle of 120 . Also, the creation of vortices in the flow field depends on the value of angular position.

Creation of topological vortices using Pancharatnam-Berry phase liquid crystal holographic plates**Project supported by the National Natural Science Foundation of China (Grant Nos. 11634010, 91850118, 11774289, 61675168, and 11804277), the National Key Research and Development Program of China (Grant No. 2017YFA0303800), the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (Grant No.

Recently, physical fields with topological configurations are evoking increasing attention due to their fascinating structures both in fundamental researches and practical applications. Therein, topological light fields, because of their unique opportunity of combining experimental and analytical studies, are attracting more interest. Here, based on the Pancharatnam–Berry (PB) phase, we report the creation of Hopf linked and Trefoil knotted optical vortices by using phase-only encoded liquid crystal (LC) holographic plates. Utilizing scanning measurement and the digital holographic interference method, we accurately locate the vortex singularities and map these topological nodal lines in three-dimensions. Compared with the common methods realized by the spatial light modulator (SLM), the phase-only LC plate is more efficient. Meanwhile, the smaller pixel size of the LC element reduces the imperfection induced by optical misalignment and pixellation. Moreover, we analyze the influence of the incident beam size on the topological configuration.

Voltage-driven annihilation and creation of magnetic vortices in Ni discs.

Using photoemission electron microscopy (PEEM) to image ferromagnetism in polycrystalline Ni disks, and ferroelectricity in their single-crystal BaTiO3 substrates, we find that voltage-driven 90° ferroelectric domain switching serves to reversibly annihilate each magnetic vortex via uniaxial compressive strain, and that the orientation of the resulting bi-domain reveals the chirality of the annihilated vortex. Micromagnetic simulations reveal that only 60% of this strain is required for annihilation. Voltage control of magnetic vortices is novel, and should be energetically favourable with respect to the use of a magnetic field or an electrical current. In future, stray field from bi-domains could be exploited to read vortex chirality. Given that core polarity can already be read via stray field, our work represents a step towards four-state low-power memory applications.