Vortex Ring Research Articles

Left ventricle diastolic vortex ring characterization in ischemic cardiomyopathy: insight into atrio-ventricular interplay.

Diastolic vortex ring (VR) plays a key role in the blood-pumping function exerted by the left ventricle (LV), with altered VR structures being associated with LV dysfunction. Herein, we sought to characterize the VR diastolic alterations in ischemic cardiomyopathy (ICM) patients with systo-diastolic LV dysfunction, as compared to healthy controls, in order to provide a more comprehensive understanding of LV diastolic function. 4D Flow MRI data were acquired in ICM patients (n = 15) and healthy controls (n = 15). The λ2 method was used to extract VRs during early and late diastolic filling. Geometrical VR features, e.g., circularity index (CI), orientation (α), and inclination with respect to the LV outflow tract (ß), were extracted. Kinetic energy (KE), rate of viscous energy loss ( ), vorticity (W), and volume (V) were computed for each VR; the ratios with the respective quantities computed for the entire LV were derived. At peak E-wave, the VR was less circular (p = 0.032), formed a smaller α with the LV long-axis (p = 0.003) and a greater ß (p = 0.002) in ICM patients as compared to controls. At peak A-wave, CI was significantly increased (p = 0.034), while α was significantly smaller (p = 0.016) and β was significantly increased (p = 0.036) in ICM as compared to controls. At both peak E-wave and peak A-wave, , WVR/WLV, and VVR/VLV significantly decreased in ICM patients vs. healthy controls. KEVR/VVR showed a significant decrease in ICM patients with respect to controls at peak E-wave, while VVR remained comparable between normal and pathologic conditions. In the analyzed ICM patients, the diastolic VRs showed alterations in terms of geometry and energetics. These derangements might be attributed to both structural and functional alterations affecting the infarcted wall region and the remote myocardium.

Hydrodynamic performance analysis of swimming processes in self-propelled manta rays

To fill the research gap regarding the whole process (steady-state and nonsteady-state phases) of median and/or paired fin (MPF) mode swimming in underwater organisms, a two-degree-of-freedom self-propelled coupling method of motion and hydrodynamics based on user-defined functions of Fluent software was established, and numerical simulations were carried out for the startup, acceleration, and steady-state phases of manta rays. The interaction mechanism among the hydrodynamic characteristics, vortex evolution, and pressure distribution was investigated in the mentioned phases. We concluded that the negative pressure zone generated by the leading edge vortex and the shear layer contributes to thrust generation and changes in swimming velocity dominate the hydrodynamic characteristics by affecting the evolution of the shear layer and the leading edge vortex, with a 17.54% increase in forward average velocity in the fourth cycle compared to the third cycle and a consequent 9.5% increase in average thrust. In the end, the relationship between the formation of trailing edge vortex rings and changes in thrust was revealed. The vortex ring contributes to the increase in thrust, but the formation of the vortex ring comes at the cost of the loss of the leading edge vortex negative pressure zone, which greatly affects thrust, decreasing to 38.3% of its peak. The swimming mechanism revealed in this study provides a reference for the study of MPF-driven biodynamics and a new simulation strategy for the prediction of bionic navigator motions.

Vortical structures and passive scalar transport in starting process of annular purging jet

The evolution of vortical structures and passive scalar transport in the starting process of annular purging jets are numerically investigated by large eddy simulation. Three flow configurations with different nozzle-to-plate distances at a fixed radius ratio of 0.71 and the Reynolds number of 13 750 are simulated. The numerical results are validated against documented experimental data. Three stages during the evolution are proposed based on instantaneous flow visualizations and assessed by calculating the circulation changes of the annular jets and vortex rings. The vortical structures are identified to understand the three-dimensional characteristics. The entrainment process is analyzed focusing on the passive scalar transport in the flow fields and is correlated with the cleaning performance of annular purging jets. The flow structures dominate the process of scalar mixing, especially the inner and outer vortex rings. The large-scale motions of trailing jets cause the intermittent events of scalar transport. During the starting process, the cleaning performance is better with a smaller nozzle-to-plate distance, while the cleaning efficiency may reach the optimum at a moderate distance. The cleaning process is limited by the scalar diffusion and entrainment process. These findings highlight the significance of flow structures for effective cleanness of temperature and contaminations in the purging systems.

Carry of Disperse-Admixture Particles by a Vortex Ring

Carry of Disperse-Admixture Particles by a Vortex Ring

Flow Field Analysis on Critical Feedback Information for UAV Autonomous High Speed Descent in Power Line Scenario

Abstract To improve the UAV efficiency in power line inspection, it must autonomously and rapidly descend to a specific height to complete the charging or landing task. This task requires the UAV to contain a stable control loop to face the specific airflow during autonomous and rapid descent: the vortex ring problem, and this specific airflow will reduce the UAV controllability. To implement the UAV autonomous high-speed descent, a control method must provide feedback information on the affected airflow and output a stable rotational speed. Hence, this paper designs a UAV autonomous high-speed descent control loop and proposes a variable rotor speed method to solve the feedback information in the control loop. This method reveals the relationship between the air movement caused by the rotor rotation and the controllability of the UAV high-speed descent. Therefore, with this method, the UAV control loop can obtain stable feedback on the air movement and achieve autonomous high-speed descent. To solve the UAV feedback information, we built the model to calculate the rotor speed in the autonomous high-speed descent UAV control loop and verified it by the CFD. The verification results showed that the model could reflect the actual fly condition. The proposed method solves the problem of UAV autonomous high-speed descent feedback information, improving the work efficiency of UAVs in power line inspection operations.

Electro-active superposed optical ring vortex beams based on PEDOT: SULF composite metasurface

Electro-active metasurfaces with high efficiency and ultra-small scale active control of integrated components are crucial for developing complex optical devices. Recent attention has focused on vortex beams with ring intensity distribution independent of topological charge, enhancing particle manipulation and fiber optic transmission efficiency. This paper presents a composite metasurface utilizing the conductive polymer PEDOT: SULF, capable of generating and dynamically switching between two types of superposed ring vortex beams. We investigate their characteristics and polarization detection capabilities. Accurate detection of major axis, ellipticity, and handedness of incident polarized light is achieved based on the two superposed ring vortex beams. The metasurface exhibits excellent switching performance, enabling flexible tuning of the ring vortex beams on demand. Additionally, we demonstrate the metasurface's good polarization detection performance for incident polarized light as an application example. The PEDOT: SULF composite metasurface holds great potential in polarization detection, quantum science, and compact photonics-integrated devices.

Study on Aerodynamic Performance and Wake Characteristics of a Floating Offshore Wind Turbine in Wind–Wave Coupling Field

Floating offshore wind turbines (FOWTs) exhibit complex motion with multiple degrees of freedom due to the interaction of wind and waves. The aerodynamic performance and wake characteristics of these turbines are highly intricate and challenging to accurately capture. In this study, dynamic fluid body interaction (DFBI) and overset grid technology are employed to investigate the dynamic motion of a 5 MW FOWT. We use the volume of fluid (VOF) method and improved delayed detached eddy simulation (IDDES) model to investigate the aerodynamic performance and wake evolution mechanism for various wave periods and heights. According to the findings, the magnitude of the pitch motion increases with the period and height of the waves, leading to a decrease in both the power output and thrust; the maximum power was reduced by nearly 6.8% compared to a wind turbine without motion. The value of power and thrust reduction varies for different wave periods and heights, and is influenced by the relative speed and pitch angle, which play a crucial role. Wind–wave coupling has a significant impact on the evolution of both wake and vortex structures for FOWT. The wake shape downstream is also dynamically influenced by the waves. In the presence of wind and wave coupling, the interaction between the wind turbine and the wake is heightened, leading to the merger of two unstable vortex rings into a single, larger vortex ring. The research unveils a comprehensive picture of the offshore wind energy dynamics and wake field, which holds immense significance for the design of floating wind turbines and the optimization of wind farm layout.

Performance enhancement of a vortex ring thruster by adopting the Coanda effect

A vortex ring thruster (VRT) is a propulsion device in which a piston pushes fluid and thrusts it in reaction. As the fluid inside a VRT is moving, the boundary layer near the wall at the edge of the exit surface of a VRT separates and rolls up into a vortex ring. In this paper, we performed performance analysis on a regular VRT and a VRT enhanced by the Coanda effect (hereafter referred to as a CoVoRT) on axisymmetric geometry. A CoVoRT consists of two jets: a primary jet and a Coanda jet. The primary jet has a relatively large volume flow rate compared to the Coanda jet, and the Coanda jet attracts the surrounding fluid by flowing along the curved surface at a relatively small flow rate. The present study evaluates the propulsion performance in two ways using SNUFOAM. This software was developed based on OpenFOAM, which is an open-source computational fluid dynamics (CFD) toolkit and specialized for naval hydrodynamics. The first one quantifies the propulsion performance by calculating the ratio of energy input and energy output generated by two jets during a stroke of the piston motion. The second one is to observe the evolution and pinch-off process of a vortex ring with formation time, which is a non-dimensional time scale. The comparison of propulsion performance was conducted with changes in the curvature of the Coanda jet, changes in the length of the Coanda jet exit, and changes in the Coanda jet velocity and piston stroke ratio. For quantitative evaluation of propulsion performance, the propulsion performance evaluation index (PPEI) was introduced. The results showed that the PPEI of a CoVoRT was improved by about 50% compared to that of a VRT, and it was confirmed that the dynamic characteristics of a CoVoRT’s vortex ring were superior to those of a VRT in terms of propulsion performance.

Plasmonic Toroidal Vortices

AbstractToroidal vortices, or vortex rings, are torus‐shaped vortices observed in various fluid systems. Recently, optical toroidal vortices, novel solutions to Maxwell's equations, have been experimentally observed (Nat. Photonics, 2022, 16, 519). Thus, their nanoplasmonic counterparts, namely plasmonic toroidal vortices, are highly anticipated. This study aims to elucidate the generation and manifestation of plasmonic toroidal vortices. To achieve this, a technique involving the illumination of a gold nanotorus with a radially‐polarized beam is employed. Notably, the plasmonic toroidal vortices exhibit a distinct photon flow trajectory along the minor radius of a nanotorus. This work presents an advancement in toroidal vortices within the plasmonic regime.

Numerical simulation of vortex rings in non-Newtonian fluids

The impulsive viscous flow through an orifice produces vortex rings that self-propagate until total dissipation of the vorticity. This work aims to study numerically such vortex rings for different types of non-Newtonian fluids, including the power-law, Carreau and simplified Phan-Thien-Tanner (PTT) rheological models, with particular focus on the post-formation phase. The simulations were carried out with the finite-volume method, considering small stroke ratios (L/D ≤ 4) and laminar flow conditions (ReG ≤ 103), while parametrically varying shear-thinning, inertia and elasticity. The vortex rings generated in power-law fluids revealed some peculiar features compared to Newtonian fluids, such as a faster decay of the total circulation, a reduction of the axial reach and a faster radial expansion. The behavior in Carreau fluids was found to be bounded between that of power-law and Newtonian fluids, with the dimensionless Carreau number controlling the distance to each of these two limits. The vortex rings in PTT fluids showed the most disruptive behavior compared to Newtonian fluids, which resulted from a combined effect between inertia, elasticity and viscous dissipation. Depending on the Reynolds and Deborah numbers, the dye patterns of the vortex rings can either move continuously forward or unwind and invert their trajectory at some point. Elasticity resists the self-induced motion of the vortex rings, lowering the axial reach and creating disperse patterns of vorticity. Overall, this work shows that the particular non-Newtonian rheology of a fluid can modify the vortex ring behavior typically observed in Newtonian fluids, confirming qualitatively some experimental observations.

The influence of background co-flow on the propulsive characteristics of starting jets

The influence of uniform background co-flow on the propulsive characteristics of starting jets with stroke ratios (length to diameter ratio, L/D) from 1 to 5 and velocity ratios (ratio of co-flow velocity to maximum jet velocity, Rv) from 0 to 0.6 has been investigated numerically. The total impulse generated increases with increasing Rv for L/D<1.5, but increases initially and then decreases for 1.5≤L/D≤3.5. Furthermore, it decreases with increasing Rv for L/D>3.5. The co-flow affects the generation of total impulse mainly by modifying the development of pressure thrust FP(t). The influence on FP(t) can be divided into three stages. During the initial and final stages, FP(t) decreases with increasing Rv, and increases during the middle stage. These three stages are explained by the influence of co-flow on wake vortex ring, leading vortex ring and stopping vortex ring, respectively. Transition between stages can also be related to the instantaneous velocity ratio Rv(t), which is the ratio of co-flow velocity to instantaneous jet velocity. The negative influence of co-flow on the generation of impulse can be mitigated by the velocity program with faster acceleration and shorter deceleration duration, which is equivalent to reducing the average value of Rv(t).

Improving agglomeration efficiency of aerosols with sizes less than 2.5 µm by generation of vortex streams in inhomogeneous ultrasonic field

In this paper a new approach to increase the agglomeration efficiency of finely dispersed aerosols by generating toroidal vortex streams in inhomogeneous ultrasonic field is proposed and studied. From the obtained experimental results (for two types of emitters) it could be established that the toroidal vortex streams generated in an inhomogeneous ultrasonic field provide an increase of the agglomeration efficiency when exposed to a gas-dispersed flow injected into the agglomeration chamber at a speed of up to 0.2 m/s. Further increase of the injected flow velocity leads to disruption of the structure of the generated vortex streams and agglomeration efficiency decreases.In the course of the analysis, it was found that the efficiency of agglomeration by toroidal vortex streams increases in direct proportion to the increase of the sound pressure level up to 165 dB. After that, no further increase in agglomeration efficiency is observed.By analyzing the agglomeration efficiency depending on particle size, it was possible to verify that the efficiency of agglomeration in comparison with agglomeration in a homogeneous ultrasonic field for droplets with a size of 0.2 … 0.6 μm is increased by 25 %, for 1.8 μm droplets by 20 %; and for droplets larger than 2.5 μm, the increase in efficiency is no more than 17 %.

Experimental study on the control of temperature oscillation in power electronics via pulsating jet impingement

Thermal oscillations in power electronics due to transient load conditions present a significant challenge. This experimental study investigates the application of intermittent jet impingement, coupled with transient heat flux boundary conditions of 100 W, 200 W, and 300 W, to a thermal test chip at a frequency of 0.5 Hz (70 % duty cycle), to assess its effectiveness in minimizing junction temperature fluctuations. Temperature oscillations were recorded to compare the advantages of intermittent pulsation over steady jet flow. The results demonstrate reduced hot spot temperature oscillations of 10 %, 12.5 %, and 16.7 % at 100 W, 200 W, and 300 W, respectively, at a Reynolds number of 8850. Remarkably, even during the pulsation off-period, the minimum temperature limit was maintained at the inlet temperature of the jet, attributed to the formation of strong vorticity rings at the end of the jet pulse, inducing a cooling effect and reducing the junction temperature. Pulsating jets exhibit superior control over temperature fluctuation compared to steady jets, with the reduction being more pronounced at Reynolds numbers closer to 2000 and diminishing as Reynolds number increases to 17000. Moreover, the heat transfer coefficient and the Nusselt number enhanced by 18 % due to pulsating jet impingement. An enhancement factor is introduced to quantify the benefits of using pulsating jets, revealing a higher reduction in temperature oscillation compared to steady jets at the same time-averaged Reynolds number, valid within the Reynolds number range of 2000–14000. Additionally, a correlation is proposed to calculate the enhancement factor for pulsating jets. Finally, the pulsating jet impingement proves to reduce the exergy destruction by 30 % compared to steady jet.

Engineering and revealing Dirac strings in spinor condensates

Artificial monopoles have been engineered in various systems, yet there has been no systematic study of the singular vector potentials associated with the monopole field. We show that the Dirac string, the line singularity of the vector potential, can be engineered, manipulated, and made manifest in a spinor atomic condensate. We elucidate the connection among spin, orbital degrees of freedom, and the artificial gauge, and show that there exists a mapping between the vortex filament and the Dirac string. We also devise a proposal where preparing initial spin states with relevant symmetries can result in different vortex patterns, revealing an underlying correspondence between the internal spin states and the spherical vortex structures. Such a mapping also leads to a new way of constructing spherical Landau levels, and monopole harmonics. Our observation provides insights into the behavior of quantum matter possessing internal symmetries in curved spaces. Published by the American Physical Society 2024

The role of axial angular momentum in exact non-linear solutions of multipolar spherical and cylindrical vortices

The time-dependent acceleration of fluid particles in an arbitrary superposition of multipolar spherical and cylindrical vortices in presence of a background rotational rigid flow is the gradient of the difference between their kinetic energy and the product of their total axial angular momentum times the angular velocity of the background flow. If the potential energy is defined as the time-dependent field whose minus gradient equals the acceleration of the flow, then the total energy, defined as the sum of kinetic and potential energies, equals the total axial angular momentum times the angular velocity of the background flow. The total energy of a fluid particle has therefore a linear relationship with the azimuthal velocity field. The role of the axial angular momentum in these oscillating flows is explained also in the classical Lagrangian and Hamiltonian descriptions of motion. The linear relation between total energy and angular momentum makes possible that the free parameters of these flows may be obtained, in a way similar to that developed in the quantum mechanics description of motion, as the eigenvalues of linear operators acting on some components of the spherical modes. Beltrami flow solutions in prolate spheroidal geometry for axisymmetric flows are also discussed.

Investigation on spray combustion modeling for performance analysis of future low- and zero-carbon DI engine

Global warming issues and fossil fuel depletion crisis have forced transportation industry to seek clean engine fuels both liquid and gaseous. Dual-fuel mode with high-pressure direct injection (HPDI) has been recognized as mainstream method in developing flexible-fuel internal combustion engines (ICEs). But flexible-fuels’ physicochemical properties and spray combustion characteristics under HPDI have changed a lot. Unfortunately, there is currently no universal model for predicting spray combustion behaviors and analyzing performance of flexible-fuel ICEs. Therefore, this paper aims to develop a novel spray combustion model and provide optimal injection and combustion strategies for performance improvement of low- and zero-carbon HPDI ICEs. Based on balance of momentum change and vortex ring drag force, the jet spray effective injection velocity is obtained. Then the jet spray penetration under varying injection rate is solved. Finally, the developed model is established and validated experimentally, with the spray combustion characteristics of various fuels investigated. The results show that the developed model has a good accuracy and robustness for flexible-fuels’ characteristic analysis. Meanwhile, multiple-injection could increase the combustion efficiency (CE) over 10.27 % than single-injection, and CE increases with dwell time. Moreover, CE of H2 in nitrogen-oxygen (N2–O2) atmosphere is 10.15 % higher than that in argon-oxygen (Ar–O2) atmosphere.

Time-resolved tomographic particle image velocimetry of flow structures in non-circular orifice impinging jets

In this study, time-resolved tomographic particle image velocimetry (Tomo-PIV) was implemented on two different non-circular orifice impinging jets, i.e., elliptical and square orifices, and the circular one was employed as a reference for comparison, with the same equivalent diameter De=20 mm, impinging distance-to-diameter H/D = 3.0, and the Reynolds number (Re) at 1.6×103. A particular concern was placed on examining the coherent structure dynamics and turbulence dissipation of these impinging jets. The dominant Strouhal number (St) of all three jets has the component of 0.53, representing the large-scale Kelvin–Helmholtz (K–H) vortex ring, particularly for the square orifice, the dominant St is 0.70 at the central axis and 0.18 at the diagonal axis near the impinging surface. In free jet region, the streamwise velocity profile of the square orifice jet always maintains a rhombic development with a 45° difference relative to the outlet shape. In the impingement region, the circular orifice jet has the strongest K–H structure, with two opposite wall jets generated inside and outside, while in elliptical jet impinging, the upturned short axis of the vortex ring after axis-switching invariably contacts the impinging surface first, and then the wall jet vortex ring re-stretches to a circular shape due to the higher velocity of the wall jets generated from the upturned short axis, and the square orifice impinging jet contains no obvious wall K–H vortex rings but undergoes an irregular merging with the vortex ring downstream and stagnation. The time-averaged flow field statistics show that the circular orifice impinging jets have stronger wall jets, while the square orifice is the weakest, due to the strongest turbulent dissipation generated by the more fragmented flow upstream.

Unfolding of shocked hydrodynamic instability at SF[formula omitted] elliptical interface: Physical insights from numerical simulations

The Richtmyer–Meshkov (RM) instability widely exists in variety of industrial and scientific applications, such as in inertial confinement fusion, astrophysics explosions, supersonic combustion, bubble dynamics and cavitation. This study investigates the unfolding physical phenomena of RM instability at SF6 elliptical bubbles using numerical simulations. In contrast to cylindrical bubble, both shocked horizontal/vertical-aligned elliptical bubbles with different aspect ratios are considered, emphasizing the aspect ratio effects on flow morphology, complex wave patterns, interface deformation, vorticity generation, and interface features. For this purpose, a two-dimensional system of compressible Navier–Stokes-Fourier equations for multicomponent flows are solved using by a mixed modal discontinuous Galerkin method. Numerical simulations illustrate that the aspect ratio of elliptical bubbles have a significant influence on the vortex dynamics and the associated RM instability flows in contrast to the cylindrical bubble. In horizontal-aligned elliptical bubbles, some additional complex waves pattern, including inward jet and secondary vortex rings are observed. While, in vertical-aligned elliptical bubbles, the interface between two primary vortex rings is always vertical and has a “hippocampus” appearance due to the enhancement of downstream velocity. The baroclinic vorticity due to misalignment of density and pressure gradients at interface affects the bubble deformation and induces the Kelvin–Helmholtz instability, which leads to turbulent mixing. It is observed that the complexity of the vorticity fields is enhanced with increasing aspect ratios. Further, these aspect ratio effects result in integral diagnostic of important spatially integrated fields, and various interface features.

Wake Modelling Based on the Stokes Stream Function and the Toroidal-Poloidal Decomposition

The Stokes stream function and its generalisation, the Toroidal-Poloidal decomposition, are well-suited for the derivation of axisymmetric engineering wake models, as they are solenoidal and fulfil conservation of mass of an incompressible fluid by construction. The presented model consists of a time-independent contribution based on Laguerre basis functions with a simple parametrisation that is well-suited for the diffusion-dominated far wake. A time-dependent part can be added based on a poloidal component that can model either helical or toroidal vortex structures, and its parametrisation can be closed towards the total thrust force on the rotor. Despite requiring an external solver, the presented model shows potential as a drop-in replacement for the Ainslie wake model that is widely used in the Wind Energy industry as part of the Dynamic Wake Meandering model.

Wake characteristics and vortex structure evolution of floating offshore wind turbine under surge motion

Offshore wind energy is booming and floating offshore wind has been proved to be a promising clean energy. Wake effect is one of the biggest challenges in large-scale floating wind farm which results in power loss and increased fatigue load. In this paper, actuator line model (ALM) coupled with unsteady Reynolds-averaged Navier-Stokes (URANS) is adopted to investigate the wake characteristics and evolution of floating wind turbine under motion. Besides, modal analysis is adopted to extract typical features of turbine wake. Velocity fluctuation is the prominent characteristic of floating turbine wake. The increase of surge frequency results in the decrease of velocity fluctuating region and large surge amplitude leads to bigger velocity deficit fluctuations. In addition, the surge motion brings a faster recovery rate than fixed wind turbine. The induced velocity field generated by vortex ring structure is the key to understanding complex evolution of turbine wake and the vortex ring structure is analyzed in this paper. With the deep understanding of FOWT wake, an innovative vortex ring structure model is proposed in this paper. This work is the basic work of developing the engineering wake model of floating wind turbine, to cope with the wake effect challenge in the large-scale floating wind farm.