Multiple Vortices Research Articles

Coalescence dynamic response of an aqueous droplet at an oil-water interface under a steady electric field

The electrocoalescence of an aqueous droplet at the oil-water interface in the presence of externally direct current electric fields was numerically analyzed with the finite element method by solving the Navier-Stokes and charge conservation equations. The proprietary software Comsol Multiphysics was used for this purpose, and the interface motion was captured by the Level-Set method. Good agreement was obtained between numerical and experimental results in the literature. The numerical description of droplet-interface coalescence transition from the viewpoint of flow field evolution and bridge dynamics was systematically examined, analyzed, and discussed. In the early droplet-interface merging process of CC (complete coalescence) modes, the droplet vortex pair was more strongly developed than the interface vortex pair, which gave rise to the enlargement of the droplet-interface liquid bridge and the fluid motion from the droplet to the interface. The interfacial velocity at the liquid bridge was much larger than at the other regions of the droplet surface in the upheaval CC mode. The upward velocity of the outflow-natured outer vortex pair was observed in the PC (partial coalescence) mode, leading to the formation of secondary droplets. In the jet-like PC mode, multiple outflow-natured vortex pairs simultaneously existed, forcing the droplet tail to break up into tiny satellite droplets. In the NC (non-coalescence) mode, the outflow-natured outer vortex pair was always directed upward, and with the breakup of bouncing-off droplets in the NC mode, an abnormal flow field with an irregular outflow-natured outer vortex pair was formed. Conductivity played little or no part in determining the CC-PC transition, but influenced the PC-NC transition. With the whole liquid bridge dynamics involving liquid bridge growth and decay dynamics taken into consideration, a good quartic polynomial function trend was obtained between the non-dimensional liquid bridge width W* and the non-dimensional time t*. In addition, the liquid decay dynamics and the coupling effect of the electric field and fluid physical properties (such as interfacial tension and viscosity) determine the partial coalescence process. The outcome of this work is potentially useful for optimizing the design of compact and efficient oil-water separators.

Particle approximation of the two-fluid model for superfluid 4He using smoothed particle hydrodynamics

This paper presents a finite particle approximation of the two-fluid model for liquid 4He using smoothed particle hydrodynamics (SPH). In recent years, several studies have combined the vortex filament model (VFM), which describes quantized vortices in superfluid components, with the Navier–Stokes equations, which describe the motion of normal fluids. These studies led us to assume that coupling both components of the two-fluid model instead of using the VFM to describe the superfluid component enables us to approximate the system. In this study, we formulated a new SPH model that simultaneously solves both equations of motion of the two-fluid model. We then performed a numerical simulation of the rotating liquid 4He using our SPH. The results showed that the two major phenomena, the emergence of multiple independent vortices parallel to the circular axis and that of the so-called rigid-body rotation, can be reproduced by solving the two-fluid model using SPH. This finding is interesting because it was previously assumed that only a single vortex emerges when addressing similar problems without considering quantum mechanics. Our further analysis found that the emergence of multiple independent vortices can be realized by reformulating the viscosity term of the two-fluid model to conserve the angular momentum of the particles around their axes. Consequently, our model succeeded in reproducing the phenomena observed in quantum cases, even though we solve the phenomenological governing equations of liquid 4He.

Wing-tip vortex dynamics at moderate Reynolds numbers

The flow over a flat-tipped wing at three Reynolds numbers: Re=1×104, Re=4×104, and Re=1×105 is investigated using direct numerical simulation. A set of grid independent results are obtained which allow for the dynamics of the tip flow, trailing vortices, and their interplay with the boundary layer dynamics to be examined in detail. The results show significant changes across the Reynolds number range. At the lowest Reynolds number, a single trailing vortex forms downstream of the trailing edge, whereas multiple vortices form over the tip at higher Reynolds numbers. The tip geometry is shown to be important with regard to the development of different structures and in the transition of the flow from laminar to turbulent. This is due to unstable shear layers, with turbulent flow becoming entrained in the vortex cores at higher Reynolds numbers. These changing vortex dynamics mean that the value of the minimum vortex core pressure and its location change with Reynolds number. This has important consequences for cavitation inception and scaling for hydrodynamic applications. The influence of the tip flow on the boundary layer is further considered by comparing the flow with that of an infinite-span wing. Analysis of the two cases shows that the tip flow reduces the effective angle of attack, which prevents the flow separation at the leading edge that is responsible for the boundary layer transition for the infinite-span case. This, in turn, changes the character of the trailing edge flow which would have significant consequences on the trailing edge noise.

Constraining Martian Regolith and Vortex Parameters From Combined Seismic and Meteorological Measurements

AbstractThe InSight mission landed on Mars in November 2018 and has since observed multiple convective vortices with both the high performance barometer and the low‐noise seismometer SEIS that has unprecedented sensitivity. Here, we present a new method that uses the simultaneous pressure and seismic measurements of convective vortices to place constraints on the elastic properties of the Martian subsurface and the Martian vortex properties, while also allowing a reconstruction of the convective vortex trajectories. From data filtered in the (0.02–0.3 Hz) frequency band, we estimate that the mean value ofη(η = E/[1 − ν2], whereEis the Young's modulus andνis the Poisson's ratio) of the Martian ground in the region around SEIS is 239 ± 140 MPa. In addition, we suggest that the previously reported paucity of vortex seismic observations to the west of InSight may be due to the fact that the ground is harder to the west than to the east, consistent with geomorphological surface interpretations.

A 30 m scale modeling of extreme gusts during Hurricane Irma (2017) landfall on very small mountainous islands in the Lesser Antilles

Abstract. In view of the high vulnerability of the small islands of the Lesser Antilles to cyclonic hazards, realistic very fine scale numerical simulation of hurricane-induced winds is essential to prevent and manage risks. The present innovative modeling aims at combining the most realistically simulated strongest gusts driven by tornado-scale vortices within the eyewall and the most realistic complex terrain effects. The Weather Research and Forecasting (WRF) model with the nonlinear backscatter and anisotropy (NBA) large eddy simulation (LES) configuration was used to reconstruct the devastating landfall of category 5 Hurricane Irma (2017) on Saint Barthélemy and Saint Martin. The results pointed out that the 30 m scale seems necessary to simulate structures of multiple subtornadic-scale vortices leading to extreme peak gusts of 132 m s−1 over the sea. Based on the literature, such extreme gust values have already been observed and are expected for category 5 hurricanes like Irma. Risk areas associated with terrain gust speed-up factors greater than 1 have been identified for the two islands. The comparison between the simulated gusts and the remote sensing building damage highlighted the major role of structure strength linked with the socio-economic development of the territory. The present modeling method could be easily extended to other small mountainous islands to improve the understanding of observed past damage and to develop safer urban management and appropriate building standards.

Development of hybrid thermal management techniques for battery packs

In this study, the thermal management issue of electric vehicle and hybrid electric vehicle battery pack is studied. Passive and hybrid techniques are developed and used in the battery pack. Multiple delta winglet vortex generators are introduced to enhance turbulence before the air flow interacts with the cells’ surface. Multiple jet inlets are introduced that enable the air flow to change its directions and pass through the dead air regions. A hybrid technique is also used in which a liquid jacket is added to each of the cells. The liquid within the jackets is in contact with the cells maximizing the contact surface area to improve heat transfer. Steady state computational fluid dynamic simulations are performed to study the effects of the passive and hybrid techniques added to the battery pack. The results indicate a substantial improvement in the temperature uniformity. The temperature difference of the hybrid battery pack reduces from 4.87 °C to 1.26 °C. Additionally, the temperature variance at the cell level reduces from 3.29 °C to 0.36 °C. This battery pack does not require moving parts and pumping power and it can achieve high levels of temperature uniformity.

Persistence length regulates emergent dynamics in active roller ensembles.

Active colloidal fluids, biological and synthetic, often demonstrate complex self-organization and the emergence of collective behavior. Spontaneous formation of multiple vortices has been recently observed in a variety of active matter systems, however, the generation and tunability of the active vortices not controlled by geometrical confinement remain challenging. Here, we exploit the persistence length of individual particles in ensembles of active rollers to tune the formation of vortices and to orchestrate their characteristic sizes. We use two systems and employ two different approaches exploiting shape anisotropy or polarization memory of individual units for control of the persistence length. We characterize the dynamics of emergent multi-vortex states and reveal a direct link between the behavior of the persistence length and properties of the emergent vortices. We further demonstrate common features between the two systems including anti-ferromagnetic ordering of the neighboring vortices and active turbulent behavior with a characteristic energy cascade in the particles velocity field energy spectra. Our findings provide insights into the onset of spatiotemporal coherence in active roller systems and suggest a control knob for manipulation of dynamic self-assembly in active colloidal ensembles.

Assinatura de tornado em imagens de radar em ocorrência de 2015 em Marechal Cândido Rondon e Quatro Pontes, PR

Tornadoes are columns of air in very high rotation, which have high destructive power. The phenomenon happens in Brazil, but its occurrence is little recognized. In this work, we intend to characterize the multiple vortex tornado that occurred in Marechal Cândido Rondon and Quatro Pontes in 2015, to find out if there was the possibility of identifying the hook echo in the radar image. For that, the images made available by the Meteorology System of Paraná were compared with the course of the phenomenon. The analyzes performed allowed the glimpse of a hook in the area of occurrence, demonstrating that the event had a signature. However, the subscription took place very quickly, with only 7 minutes in advance.

Generation of optical vortex beams via metasurfaces (Invited)

Optical vortex beams, carrying orbital angular momentum, possess tremendous advanced applications ranging from optical communication, micromanipulation and nonlinear optics to quantum information. Various methods have been proposed to generate optical vortices, such as spiral phase plate (SPP), mode converter and spatial light modulator (SLM). However, changing phase by accumulating propagation distance restrains the applications in integrated optics. Owing to the salient properties that metasurface is small-sized and easy to be integrated, it is expected to be an ideal optical vortices generator with excellent ability of regulating light field. The basic principles of generating vortex beams and recent progress in the use of metasurfaces were introduced in this article. First, methods of using dynamic phase, Pancharatnam-Berry (P-B) phase and hybrid phase to generate optical vortices were introduced. Subsequently, holography and encoding metasurfaces and multiplexing metasurfaces were reviewed to generate multiple vortices. Finally, based on the generation of optical vortices via metasurfaces, some potential applications and problems were briefly summarized and discussed.

Generalized Adler--Moser Polynomials and Multiple Vortex Rings for the Gross--Pitaevskii Equation

Related DatabasesWeb of Science You must be logged in with an active subscription to view this.Article DataHistorySubmitted: 26 January 2021Accepted: 24 September 2021Published online: 14 December 2021KeywordsGP equation, Adler--Moser polynomials, vortex ringAMS Subject Headings35B08, 35Q40, 37K35Publication DataISSN (print): 0036-1410ISSN (online): 1095-7154Publisher: Society for Industrial and Applied MathematicsCODEN: sjmaah

Existence of steady multiple vortex patches to the vortex-wave system

In this paper we prove the existence of steady multiple vortex patch solutions to the vortex-wave system in a planar bounded domain. The construction is performed by solving a certain variational problem for the vorticity and studying its asymptotic behavior as the vorticity strength goes to infinity.

Generation of Arbitrary Longitudinal Polarization Vortices by Pupil Function Manipulation

The properties of optical vortex provide new insights into a wide range of optical and physical phenomena, giving rise to numerous applications in multiple disciplines. Notably, as much as the associated technologies have become increasingly flexible, it is still challenging to simultaneously generate multiple longitudinal polarization optical vortices with random topological charges (l) and tunable intensities at arbitrary positions. Herein, a novel approach that, by manipulating phase and amplitude at the back pupil of a high numerical‐aperture (NA) objective, realizes arbitrary longitudinal polarization vortices within the tightly focused light field is developed. Building upon the same model, the impacts of polarization on the optical vortex field and its potential of tuning the ratio of the longitudinal polarization component are further investigated.

Vortex structures in a rotating Rydberg-dressed Bose-Einstein condensate with the Lee-Huang-Yang correction

We numerically investigate the vortex structures in a fast rotating two-dimensional Rydberg-dressed Bose-Einstein condensate (BEC) taking into account the Lee-Huang-Yang (LHY) quantum correction. In a rotating BEC of reduced dimensionality, it is shown that there is room to tune the LHY coupling against the short- and long-range couplings. In the absence of the LHY effect, hexagonal, square, striped, and honeycomb lattices can exhibit upon increasing the long-range interaction, which can be realized in the context of superfluid (SF)-supersolid (SS) transition. In the presence of the LHY effect, competition between LHY and long-range terms results in rich lattice structures. In particular, clustering of multiple vortices can occur due to the trapping effect of the SS triangles or grids. Estimates of number of vortices in the clustering are provided.

Numerical study on turbulent natural convection and radiation heat transfer of nanofluids in a differentially heated square enclosure

Due to the low performance observed during natural convection with fluids such as air and water, nanofluid research was carried out to analyse them for convective heat transfer applications. Heat transfer comparison between water and different water-based nanofluids comprising of MWCNT, alumina and silver has been established for Rayleigh Number 1.5 × 109. Numerical analysis of 2-D differentially heated square cavity has been performed under turbulent natural convection. The top and bottom walls are considered to be at constant temperatures, while the side walls are adiabatic in nature. Based on previous research, nanofluid volume concentration of 0.1 vol% has been considered for this study, and the nature of flow physics and natural convection heat transfer has been explored. It is observed that multiple vortices (almost similar size) exist and evenly speared within the computational domain for air. The viscosity of the fluid was observed to be a deciding factor for the degree of turbulence, thickness and velocity variations within the boundary layer. The average fluid velocity and vortex circulation strength are highest for alumina nanofluid and least for water. The other two nanofluids lie in between with the velocity and vorticity variations of 12.8 and 16.5%, respectively. In terms of heat transfer, alumina nanofluid performs admirably well, followed by MWCNT nanofluid with a variation in radiation heat transfer of 60.8 and 53.19% when compared to air, while for convective heat transfer the variation observed was 98.4 and 97.8%, respectively. Due to the high densities of these nanofluids as compared to air, achieving thermal stratification is difficult. Alumina nanofluid performs admirably well in enhancing convection and radiation heat transfer.

Jumping archer fish exhibit multiple modes of fin–fin interaction

Aquatic organisms jumping for aerial prey require high-performance propulsion, accurate aim, and trajectory control to succeed. Archer fish, capable of jumping up to twice their body length out of the water, address these considerations through multifaceted fin and body kinematics. In this study, we utilized 3D synthetic aperture particle image velocimetry to visualize the wakes of archer fish throughout the jumping process. We found that multiple modes of interaction between the anal and caudal fins occur during jump behaviors. Time-resolved volumetric measurements presented herein illustrate the hydrodynamics of each interaction mode in detail. Additionally, regardless of which fin uses and interactions were exhibited during a jump, we found similar relationships between the cumulative impulse of multiple propulsive vortices in the wake and the instantaneous ballistic momentum of the fish. Our results suggests that fin use may compensate for variations in individual kinematic events and in the aiming posture assumed prior to jumping and highlight how interactions between tailbeats and other fins help the archer fish reach necessary prey heights in a spatially- and visually-constrained environment. In the broader context of bioinspired propulsion, the archer fish exemplifies that multiple beneficial hydrodynamic interactions can be generated in a high-performance scenario using a single set of actuators.

Image-based flow decomposition using empirical wavelet transform

Abstract

A new Majorana platform in an Fe-As bilayer superconductor

Iron-chalcogenide superconductors have emerged as a promising Majorana platform for topological quantum computation. By combining topological band and superconductivity in a single material, they provide significant advantage to realize isolated Majorana zero modes. However, iron-chalcogenide superconductors, especially Fe(Te,Se), suffer from strong inhomogeneity which may hamper their practical application. In addition, some iron-pnictide superconductors have been demonstrated to have topological surface states, yet no Majorana zero mode has been observed inside their vortices, raising a question of universality about this new Majorana platform. In this work, through angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy measurement, we identify Dirac surface states and Majorana zero modes, respectively, for the first time in an iron-pnictide superconductor, CaKFe4As4. More strikingly, the multiple vortex bound states with integer-quantization sequences can be accurately reproduced by our model calculation, firmly establishing Majorana nature of the zero mode.

Geometric metasurface for multiplexing terahertz plasmonic vortices

Surface plasmon polaritons carrying orbital angular momentum (OAM), namely, as plasmonic vortices, have attracted considerable attention in optical trapping, quantum information processing, and communications. The previous studies of near-field OAM are limited to generate only one single plasmonic vortex, which inevitably degrades further on-chip applications. Geometric metasurfaces, two-dimensional counterpart of metamaterials, enable the unprecedented capability in manipulating the phase, polarization, and amplitude of electromagnetic waves, providing a flexible platform in controlling plasmonic vortices. Here, we propose and experimentally demonstrate an approach to realize the multiplexing of terahertz (THz) plasmonic vortices based on geometric metasurfaces. Under the illumination of circularly polarized THz waves, multiple plasmonic vortices with identical topological charges are generated at the metal/air interface. Furthermore, the conversion from spin angular momentum to multiple plasmonic OAM, i.e., multiple plasmonic vortices with different topological charges, is also demonstrated. Geometric metasurfaces consisting of paired air-slits with different in-plane orientations are designed to demonstrate these characteristics. Our proposed approach may open an avenue for on-chip applications with increasing information capacity.

The influence of electric current application configuration on the electro-vortex flow structure of conductive medium in cylindrical cell

A numerical study of the liquid metal electro-vortex flows (EVF) in a closed cylindrical cell, the radius of which is equal to its height, is performed. A direct current of 1000 A is applied through the electrodes at the bottom cylinder face, and is collected at the entire surface of the cylinder top end face. Various configurations of electrode location are considered. Namely, from one to five electrodes are placed on the cylinder bottom end face. The three-dimensional fields of the conducting medium flow velocity in the cell are obtained as a result of numerical simulations. The EVF is non-stationary in all considered regimes. In the one-electrode case, the flow is poloidal and is represented by one large-scale vortex. In the multielectrode case, the flow consists of multiple small-scale vortices, the size and quantity of which depend on the configuration of the electric current application. At the same electric current value of 1000 A, the mean flow velocity and characteristic frequency of the process are higher for the localized current application — 6.4 and 2.5 times respectively.

Throughput Performance of Wireless Multiple-Input Multiple-Output Systems Using OAM Antennas

This letter experimentally demonstrated the performance improvement of orbital-angular-momentum (OAM) based 2 $\times $ 2 MIMO communication by using the diversity of different OAM modes. The OAM antenna we used is an eight-arm Archimedean spiral antenna (ASA) capable of generating multiple high-quality OAM vortex waves individually or two types of two-mode mixed vortex waves simultaneously. Both of the two cases are investigated for MIMO communication by evaluating the throughput performance. For MIMO with two OAM modes (generated by two ASAs separately), the throughput improves upon traditional MIMO by up to 30.50%, while for MIMO with two-mode mixed vortex waves (generated by one ASA), 6.59% throughput improvement is obtained.