Behavior Of Vortices Research Articles

On the Theory of Individual Atmospheric Vortices: an Example of the Subtropical Anticyclone Evolution

The physics of individual atmospheric vortices is far from clear, despite the fact that modern hydrodynamic models reliably reproduce them. In this paper, we develop the theory of vortices that stably exist for a long time in a certain region. Their structure is characterized by the first (dominant) empirical orthogonal function (EOF, NOF), and the dynamics is determined by the coefficient at a given mode y1(t), for which an ordinary differential equation is obtained based on the vorticity budget equation. The residual between the explicitly resolved terms is compensated by the parameterization, which is based on taking into account the effects of the second and subsequent modes of the EOF expansion. It is shown that it consists of Gaussian noise and a non-random component, which can be approximated using a cubic function of y1(t). To test the developed technique, we used modeling of the vorticity behavior describing the dynamics of the most stable vortex among all existing in the Earth’s atmosphere—the subtropical (Hawaiian) anticyclone. ERA5 reanalysis data were used for the work. The proposed approach to the analysis of integral vortex structures is supposed to be used to evaluate various circulation systems, identify factors affecting their dynamics in different regions, and study extreme hydrometeorological events associated with long-lived vortexes.

Comparison of Flow Topology Between Major Groups of Airfoil with Vortex Shedding

The effect of vortex behavior on airfoil aerodynamic performance has been widely debated for many years, and many research studies have been conducted to examine the relationship. This paper highlights the in-depth study of flow topological processes on major airfoil groups with vortex shedding. It considers various typeof corresponding geometriesincludingsymmetrical, asymmetrical, thick, and thin airfoilsin order to showthe differences in flow topology. The study also emphasized the behavior of separationbubbles, vortex shedding and reattachment points. The use of a commercial CFD softwarefor the studygave reliable resultswithinan adequate length of time. The vortex shedding wassuccessfully highlighted either physically or hypothetically. The separation bubble was relatively easier to be identified in all cases of airfoil of interest. The evolution of separation bubble captured by the topology in the case of Eppler169 was the unique, and involved the break of reattachment point.

Irreversible switching of vortex core in Pac-man nanodisks induced by rotating magnetic fields

Vortex has attracted great attention recently due to its potential applications in information storage, nano-oscillators and logic devices. The control of vortex polarity is key to the devices based on vortex. In this paper, an irreversible vortex core (VC) switching in Pac-man disks has been investigated by micromagnetic simulations. The switching process is closely related to the evolution of energy densities and there is a sharp peak in the local exchange energy density when VC switching occurs. Irreversible switching of VC can be realized due to the weak interaction between reversed vortex and rotating magnetic field. In the process of VC reversal, the positive and negative magnetization regions of the gyrofield are separated. Moreover, the switching time of VC decreases monotonously with frequency under rotating magnetic fields. When one direction of the rotating magnetic field is turned off, the difference in switching time is attributed to the different motion behaviors of vortex. This work benefits the potential storage applications in vortex-based spintronic devices.

Investigating the Pressure Fluctuations of Hydraulic Jump in an Abrupt Expanding Stilling Basin with Roughened Bed

Stilling basins with sudden expansions are one of the energy dissipation structures. In the hydraulic jump, pressure fluctuations cause significant damages in stilling basins by cavity formation, erosion, and vibration. Roughness can also lead to changes of the behavior of stream lines and vortices. Despite the large number of works on the topic, the role of roughness in spatial hydraulic jumps is not yet fully understood. Present research aimed to study the influence of rough bed on pressure fluctuations of S-jump in abrupt expanding stilling basin. Experiments were conducted in a 0.8 m width and 12 m length flume. Channel expansions ratios were 0.33, 0.5, 0.67, and 1 within the range of Froude numbers, 2 to 9.5. The results showed that roughness decreases intensity of pressure fluctuations in an abrupt expansion stilling basin. Additionally, in sudden expanding sections, the energy loss increases, and the intensity of pressure fluctuations decrease due to the formation of lateral vortices. The reduction rate of maximum pressure fluctuation was 27%, 46%, and 58% for expansion ratio of 0.67, 0.5, and 0.33, respectively. The results revealed the clear dependence of these variables on the Froude number and the distance to the hydraulic jump toe. The maximum values of extreme pressure fluctuations occur in the range 0.609 < X < 3.385, where X is dimensionless distance from the toe of the hydraulic jump, which makes it highly advisable to reinforce the bed of stilling basins in this range.

Ultra-fast dynamic deposition of EuBa2Cu3O7−δ-BaHfO3 nanocomposite films: Self-assembly structure modulation and flux pinning behaviors

Structure modulation of rare-earth barium cuperates (REBCO) superconducting films plays an essential role in the flux pinning behaviors. In this paper, nano-composite EuBa2Cu3O7−δ-BaHfO3 (EuBCO/BHO) films were deposited by the ultra-fast pulsed laser deposition technique. All nano-composite films exhibited high-quality orientation under the growth rates up to 100 nm/s. TEM cross-sectional analysis reveals that the EuBCO/BHO films have a distinct lamellar structure, which is related to the periodic change of growth conditions during the multi-turn dynamic deposition. In addition, the morphology of BHO varies with dopant content, which suggests a strong correlation between dopant content and the BHO self-assembly mechanism. Consequently, the vortex behavior shifts from giant-flux creep to vortex-glass formation at the thermally activated flux flow region as the dopant content increases. The primary flux pinning behaviors change from random to correlated pinning with the increase of dopant content at 4.2 K. Due to the larger contribution of the correlated pinning machinimas, the 8% BHO-doped EuBCO film exhibits the highest Jc value at 4.2 K, with moderate fields (below 8 T) among all the three films. At 4.2 K and 14 T, the 6% BHO doped EuBCO film has the highest Fp value attributing to the predominate random pinning mechanism.

Dynamics of dust particles in the glow discharge stratum in crossed E × B field

AbstractIn this work, the dynamic behaviour of micron‐sized dust particles suspended in the glow discharge stratum at low pressure in the crossed magnetic and electric fields was experimentally studied. The observations showed that the dust particles move in the direction opposite to the ExB drift with increasing magnetic field induction. When the magnetic field induction reaches a threshold point (B > 10 mT), the dust particles begin to rotate, forming pair of counter‐rotating vortex in the horizontal plane. It was also found that the shape of the dust structures changes from a disk shape to an ellipsoid shape. The dynamic behaviour of the dust vortices was analysed using the PIV (particle image velocimetry) method. The quantitative explanation of the generation of the co‐vortex rotation observed in the experiment was explained on the basis of the charge gradient of the dust particles, which was orthogonal to the ion drag force.

Causes and Consequences of Ordering and Dynamic Phases of Confined Vortex Rows in Superconducting Nanostripes.

Understanding the behaviour of vortices under nanoscale confinement in superconducting circuits is important for the development of superconducting electronics and quantum technologies. Using numerical simulations based on the Ginzburg-Landau theory for non-homogeneous superconductivity in the presence of magnetic fields, we detail how lateral confinement organises vortices in a long superconducting nanostripe, presenting a phase diagram of vortex configurations as a function of the stripe width and magnetic field. We discuss why the average vortex density is reduced and reveal that confinement influences vortex dynamics in the dissipative regime under sourced electrical current, mapping out transitions between asynchronous and synchronous vortex rows crossing the nanostripe as the current is varied. Synchronous crossings are of particular interest, since they cause single-mode modulations in the voltage drop along the stripe in a high (typically GHz to THz) frequency range.

Görtler vortices behavior and prediction in dual-incident shock-wave/turbulent-boundary-layer interactions

Görtler vortices (GVs) in dual-incident shock-wave/turbulent-boundary-layer interactions (dual-ISWTBLIs) are experimentally investigated in a Mach 2.48 flow. A double-wedge shock generator with two deflection angles of 8° and 5° is used to produce two incident shock waves (ISWs). Flow structures of the experiments with three different shock-wave distances were visualized by the ice-cluster-based planar laser scattering technique at two orthogonal planes (x–y and x–z planes). The images in the x–y plane present three types of flow patterns of dual-ISWTBLIs corresponding to the first type with a triangle-like separation, the second type with a quadrilateral-like separation, and the third type with two isolated interactions induced by the two ISWs. The images in the x–z plane indicate that the GVs exist in the first type of dual-ISWTBLI originating in the vicinity of the apex of the separation region and cover nearly the whole spanwise range of the reattachment region. By comparison, the GVs intermittently occur in the limited spanwise range of the reattachment region in the second type of dual-ISWTBLI. No GVs are observed in the third type of dual-ISWTBLI because no visible separation is induced under the experimental conditions considered in this situation. In addition, based on the wall-pressure distribution in the former two types of dual-ISWTBLIs, this paper proposes a method to estimate the mean-flow streamline curvature in the reattachment region, thereby obtaining the criteria for the existence of GVs, according to which reasonable explanations for the different distributions of GVs in the two types of dual-ISWTBLIs are provided.

Flux pinning evolution in multilayer Pb/Ge/Pb/Ge/Pb superconducting systems

Multicomponent superconductors exhibit nontrivial vortex behaviors due to the various vortex–vortex interactions, including the competing one in the recently proposed type-1.5 superconductor. However, potential candidate that can be used to study the multicomponent superconductivity is rare. Here, we prepared an artificial superconducting multilayer to act as an alternative approach to study multicomponent superconductivity. The additional repulsive length and the coupling strength among superconducting films were regulated by changing the thickness of the insulting layer. The magnetization measurements were performed to clarify the effect of the competition between the repulsive vortex interactions on the macroscopic superconductivity. The vortex phase diagram and the optimum critical current density have been determined. Furthermore, a second magnetization effect is observed, and is attributed to the upper layer, which provides the weak pinning sites to localize the flux lines. The pinning behaviors switches to the mixed type with the increase of the insulting layer thicknesses. Our results open a new perspective to the study and related applications of the multilayer superconducting systems.

Motion of magnetic vortices in type-Ⅱ superconductor with randomly distributed pinning centers

The dynamic behaviors of the magnetic vortices in a two-dimensional square superconductor with randomly distributed pinning centers of normal state were considered using the Ginzburg-Landau (G-L) model. The pinning centers are randomly distributed as various contents in all the area of the superconductor and a distribution function p(r) defined in a MATLAB is used to determinate the size and sites of normal state pinning centers. Using COMSOL and MATLAB, we analyzed the magnetization curves and the density of superconducting electrons as a function of the external magnetic field applied along the z-axis. Simulation results showed that the vortices configurations and magnetization depend on the content of the pinning centers and the maximum magnetization values decrease exponentially as the content increases. The content of pinning centers with the largest mixed state is determined by modeling the number of the magnetic vortices trapped in the pinning centers. This work will provide good results into understanding the dynamics of the magnetic vortices in a superconductor with randomly distributed pinning centers in view of the circumstance that they are randomly distributed in the superconductor during fabricating it.

Numerical analysis of the three-dimensional flow phenomena in a 19-pin wire-wrapped tight lattice bundle

The wire-wrapped tight lattice assembly has the advantages of compact arrangement, small volume, and high power density, and it has been widely used in the design of advanced nuclear reactors. A wire-wrapped tight lattice assembly has been proposed at Shanghai Jiao Tong University, and the mixing characteristics of this assembly have been experimentally investigated in a 19-pin wire-wrapped bundle in the previous work. In the present study, the numerical simulation for this bundle based on the Reynolds-Averaged-Navier-Stokes SST k-ω model has been carried out, and the numerical method was verified by the mixing experiment data. Then the three-dimensional flow phenomena have been discussed for a wide range of Reynolds numbers from 5843 to 100,000. The axial flow split parameters, vortex behaviors in cross-section, and the flow sweeping behaviors in subchannel gaps were analyzed in a typical condition, and the effect of the Reynolds number also has been discussed, which shows little effect on these parameters. This study is a continuation of our previous work, and they both aim to provide a reference for the design of wire-wrapped tight lattice assembly.

Circulation statistics and the mutually excluding behavior of turbulent vortex structures.

The small-scale statistical properties of velocity circulation in classical homogeneous and isotropic turbulent flows are assessed through a modeling framework that brings together the multiplicative cascade and the structural descriptions of turbulence. We find that vortex structures exhibit short-distance repulsive correlations, which is evidenced when they are "tomographically" investigated, by means of planar cuts of the flow, as two-dimensional vortex gases. This phenomenon is suggested from model improvements which allow us to obtain an accurate multiscale description of the intermittent fluctuations of circulation. Its crucial new ingredient, the conjectured hard disk behavior of the effective planar vortices, is then found to be strongly supported from a study of their spatial distributions in direct numerical simulations of the Navier-Stokes equations.

Turbulence Structure and Dynamics Investigation of Turbulent Swirl Flow in Pipe Using High-Speed Stereo PIV Data

Turbulent swirl flow, which exists in numerous turbomachinery systems, is the focus of this paper. It consumes a significant amount of energy, so it is a subject of investigation for many researchers. It is even more present in ventilation systems, as numerous axial fans are still installed without guide vanes. The experimental investigation of the turbulent swirl flow behind an axial fan in a pipe, installed in a test rig with a free inlet and ducted outlet, as defined in the international standard ISO 5801, is presented in this paper. Moreover, in this paper, the axially restricted case is studied. A designed axial fan generates a Rankine vortex with a complex structure, and research on the vortex turbulence structure and dynamics is presented. On the basis of the HSS PIV (high-speed stereo particle image velocimetry), measurement results are calculated using invariant maps. All states of turbulence anisotropy are thoroughly analyzed by applying the invariant theory on HSS PIV results. Vortex dynamics is observed on the basis of the total velocity minima positions and their repetitions. Both methods are correlated, and important conclusions regarding vortex behavior are deduced.

Spatiotemporal dynamics of a vortex induced vibration system in the presence of stochastic inflow fluctuations

In this study, influence of stochastic parametric inflow on the spatiotemporal dynamics of a vortex induced vibration system has been examined. The study has been carried out using an incompressible Navier–Stokes based flow solver at a Reynolds number of 100, and it highlights the role of stochastic fluctuations/noise in triggering complex spatiotemporal dynamics in the laminar vortex shedding regime. Wavelets and space–time plots were used to analyse the spatiotemporal data. Noise has been seen to advance the instability regime and alter the frequency characteristics of the response by exciting additional system frequencies, which in turn affects the phase dynamics as well. The study has also revealed that the time scale of the input is an important factor in deciding the dynamics. A short time-scaled noise can trigger aperiodic dynamics, whereas, a long time-scaled input invokes switch states or intermittent states. Noise affects the separation behaviour of the near-field vortices by delaying or advancing it, depending on the regime of operation. For the long time-scaled case, the flow-field becomes a combination of strong or weak von Kárman streets and transitionally disordered wakes. With the short time-scaled noise, the flow-field is predominantly disordered and characterised by phenomena such as vortex pairing and deflected wakes.

Conv-Wake: A Lightweight Framework for Aircraft Wake Recognition

The recognition of aircraft wake vortex can provide an indicator of early warning for civil aviation transportation safety. In this paper, several wake vortex recognition models based on deep learning and traditional machine learning were presented. Nonetheless, these models are not completely suitable owing to their dependence on the visualization of LiDAR data that yields the information loss of in reconstructing the behavior patterns of wake vortex. To tackle this problem, we proposed a lightweight deep learning framework to recognize aircraft wake vortex in the wind field of Shenzhen Baoan Airport’s arrival and departure routes. The nature of the introduced model is geared towards three aspects. First, the dilation patch embedding module is used as the input representation of the framework, attaining additional rich semantics information over long distances while maintaining parameters. Second, we combined a separable convolution module with a hybrid attention mechanism, increasing the model’s attention to the space position of wake vortex core. Third, environmental factors that affect the vortex behavior of the aircraft’s wake were encoded into the model. Experiments were conducted on a Doppler LiDAR acquisition dataset to validate the effectiveness of the proposed model. The results show that the proposed network has an accuracy of 0.9963 and a recognition speed at 100 frames per second was achieved on an experimental device with 0.51 M parameters.

Motion of a Neutrally Buoyant Circular Particle in a Lid-Driven Square Cavity: A Numerical Study

Understanding, predicting and controlling the motion of the solid particles in a confined cavity is significant. The motion of a neutrally buoyant circular particle in a lid-driven square cavity is studied with the lattice Boltzmann method, where the effects of the initial position, particle size and Reynolds number are investigated. The obvious characteristic of the motion of the circular particle is the existence of the limit cycle, which is the competitive result of the inertia, wall-repulsion force and vortex behavior. The limit cycle is insensitive to the initial position of the circular particle, namely, no matter where the circular particle is placed initially, the limit cycle is the same. With the increase of the particle size, the wall-repulsion force becomes stronger, which is dominant over the centrifugal force, and the limit cycle shrinks toward the center of the square cavity. With the increase of the Reynolds number, a new secondary vortex develops at the top left corner of the square cavity, and the limit cycle is pushed toward the bottom right corner of the square cavity.

Toroidal vortices of light

Toroidal vortices, also known as vortex rings, are whirling, closed-loop disturbances that form a characteristic ring shape in liquids and gases and propagate in a direction that is perpendicular to the plane of the ring. They are well-studied structures and commonly found in various fluid and gas flow scenarios in nature, for example in the human heart, underwater air bubbles and volcanic eruptions1–3. Here we report the experimental observation of a photonic toroidal vortex as a new solution to Maxwell’s equations, generated by the use of conformal mapping4–7. The resulting light field has a helical phase that twists around a closed loop, leading to an azimuthal local orbital angular momentum density. The preparation of such an intriguing state of light may offer insights for exploring the behaviour of toroidal vortices in other disciplines and find important applications in light–matter interactions, optical manipulation, photonic symmetry and topology, and quantum information8–17.

Bistability of turbulent flow in open-channel expansion: Characterization and suppression

Three-dimensional turbulent bistable flow (TBF) in an open-channel expansion is predicted using large eddy simulation. The free surface of TBF is tracked using the volume of fluid method, coupled with the level-set method. This paper aims to reveal the ensemble-average flow characteristics and explore effective ways to control bistability. For a given condition of flow approaching an expansion, either of two stable flow states can possibly occur, depending on the flow history. The predicted pressure field agrees well with experimental data. The velocity field is decomposed into deformation regions and eddy-rotation regions using the Okubo–Weiss parameter. Turbulent eddies initiated by shear instability dominate those associated with sidewall-friction force; this condition is responsible for the occurrence of bistability. Fitting a simple hump at a flat-bottom expansion is an effective way to suppress bistability. The presence of the hump shrinks eddy cores and breaks the interaction between eddies triggered by instabilities and eddies induced by friction forces; the result is an increase in flow uniformity and control of turbulence, flow separation, and vortex behavior.

Evaluation of the spatiotemporal unsteady characteristics of the tip leakage vortex based on a direct numerical simulation database

The spatiotemporal evolution of the tip clearance vortical structures behind a flat hydrofoil immersed in a turbulent boundary layer over a flat plate was investigated by means of direct numerical simulation, with focus on the unsteady behaviors of the tip-leakage vortex (TLV) and their effects on the flow blockage. It is found that the TLV evolutionary processes can be characterized by three typical phases: the formation phase, the vortex wandering phase, and the vortex splitting and breakdown phase. In the second phase, the TLV is subject to the wall-normal low-frequency wandering motion, which is excited by the induced vortex. The abrupt increase in vortex wandering intensity near the trailing edge of the hydrofoil can be attributed to the frequent occurrence of vortex splitting and breakdown events in the third phase. The time-averaged vortex intensity of the TLV increases gradually in the first and second phases. On the other hand, instantaneous vortex intensity shows an initially decreasing and then increasing trend, as a result of the breakdown of the TLV and the formation of the secondary TLV, respectively. In addition, the investigation of flow blockage caused by the TLV indicates that along the streamwise direction, the time-averaged blockage area and blockage coefficient both follow an exponential distribution. The present results provide a qualitative and quantitative characterization for the spatiotemporal evolution of the TLV, which is critical for improving the efficiency loss and mechanical vibration caused by the unsteady behaviors of the TLV.

Hierarchical clustering method of volumetric vortical regions with application to the late stage of laminar-turbulent transition

This paper proposes a hierarchical clustering method which can analyze the behavior of vortices in detail by dividing volumetric vortical regions obtained by a direct numerical simulation into individual groups of vortical points and automatically tracking them. In addition to visualizing and tracking the instantaneous spatial distribution and temporal motion of each point set of vortices linked by a data hierarchy (inclusivity), which is called ``p-clusters'' in a unified manner, it is now possible to mechanically search for common local dynamics among many different vortical structures found in transitional and turbulent flows.