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The 122 iron arsenide unconventional superconductors are part of a new class of iron-based superconductors. Co-doped BaFe 2x Co x As 2 (Ba-122) iron superconductors sample have been examine by scanning Hall probe microscopy (SHPM) technique to find out the magnetic properties of Ba-122 . Has been completed the evolution of profiles of vortices which has well isolated and it is as function of temperature, then utilized suitable technique to extract the temperature depending on penetration depth, .So, this allowed to deduce the temperature dependent on density of superfluid and it has been compared with α-model consequences for a (2-band) of superconductor. When the superfluid density for the BaFe 2x CoxAs 2 (Over D x= 0.113) sample. As result, the two gap -model has been fitted to the data with Δ 1 =4.25kT c , Δ 2 =1.92kT c , =0.708, 1 =0.293 then a 2 =1. However, When values of for the BaFe 2-x Co x As 2 (Over D x= 0.075) sample. Result of the superfluid density for BaFe 2-x Co x As 2 with parameters are (Δ 1 =3.9k, Δ 2 =1.6k), =0.615 for Δ 1 , and =0.237, =1. Suitable parameters produce refer into the symmetry of the order parameter at hole pockets with the electron, and then the relative supports of the bands to the density of superfluid in the iron-based crystals

The intensities and phase profiles of the elliptic optics vortex beam both are determined by the topological charge (TC) and ellipticity. This paper presents an efficient and simple method for measuring the TC and ellipticity of elliptic vortex. By observing the diffraction patterns, the TC modulus and ellipticity can be probed with the suitable rectangular aperture, and the TC sign can be detected with the suitable right triangular aperture. The scheme works well even for high-order elliptic vortex with topological charge value as high as ± 18, and ellipticity range from 0.5 to 2 at least. Obviously, the measurement of TC and ellipticity have important research value for promoting the application of elliptical vortex.

In the present study, the effect of conical obstacles on heat transfer and flow characteristics in a circular tube was investigated. In most previous studies, stationary obstacles were used to stim...

The interest in complex plasmas is increasing due to the multiple applications they target (astrophysics, plasma fusion, industry, etc.). A crystal with two vortexes made of spherical microparticles that levitates in an rf plasma interacts with a gas jet. The crystal is displaced in the jet propagation direction due to the neutral pushing force, maintaining its vortex structure. The crystal shift also involves a change of its shape, especially at the level of the two vortexes. One vortex is stretched, and the other one is compressed. During the three phases of modification of the shape of the crystal, its length is approximately constant, about 12.5 mm, this being a consequence of the fact that electric forces and ion drag forces are preserved. The orderly structure of the crystal lasts until the particles begin to fall on the bottom electrode. The changing of the vorticity in the crystal regions can be attributed to the neutral push force.

In granular superconductors, the grain boundaries are closely related to the vortex dynamics and the macroscopic superconducting properties. In our research, Pb films with different grain sizes were prepared by tuning the substrate temperature. With the grain size decreasing, Pb films are prone to feature the anomalous magnetization jumps in the M − T curves, while in the M − H curves flux avalanche happens. Both phenomena appear in the same region of the H − T phase diagram and thus are considered to have the same origin. The further theoretical analysis shows that with grain size decreasing the pinning mechanism evolves from a mixed δTc and δl pinning to the δl pinning mechanism. The results shed light on the study of pinning mechanism for granular superconductors and is beneficial to the potential application of manipulating vortex pinning by regulation of intrinsic defects.

The motion of a domain wall in a magnetic film with an antidot array leads to the formation of a vortex magnetization reversal zone moving along the sample. A description of the magnetization dynamics in the film is obtained by micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation for various film thickness and hole arrangement and size. We show that the magnetization reversal zone either passes through the antidot array or "freezes" on it. Using a special technique for visualizing vortex structures, based on the calculation of topological charges of two types, we establish the relationship between the magnetization dynamics and the types of vortex structures.

The concept of topology has dramatically expanded the landscape of magnetism, leading to the discovery of numerous magnetic textures with intriguing topological properties. A magnetic skyrmion is an emergent topological magnetic texture with a string-like structure in three dimensions and a disk-like structure in one and two dimensions. Skyrmions in zero dimensions have remained elusive owing to challenges from many competing orders. Herein, by integrating electron holography and micromagnetic simulations, we uncover the real-space magnetic configurations of a novel skyrmionic vortex structure confined in a B20-type FeGe tetrahedral nanoparticle. This texture shows excellent robustness against temperature without applying a magnetic field; an isolated skyrmionic vortex forms at the ground state. These findings shed light on zero-dimensional geometrical confinement as a route to engineer and manipulate individual skyrmionic metastructures.

As a fundamental topology-transforming event, reconnection plays a significant role in the dynamics of plasmas, polymers, DNA, and fluids—both (classical) viscous and quantum. Since the 1994 review by Kida & Takaoka, substantial advances have been made on this topic. We review recent studies of vortex reconnection in (classical) viscous flows, including the physical mechanism, its relationship to turbulence cascade, the formation of a finite-time singularity, helicity dynamics, and aeroacoustic noise generation.

A three-dimensional double-sided delta-wing (D-T-W) shape design problem is studied in the present work to estimate the optimal wing-width ratio w/W, height-pitch ratio c/P, and attack angle α of D...

We show that the entropy per quantum vortex per layer in superconductors in external magnetic fields is bounded by the universal value kBln 2, which explains puzzling results of recent experiments on the Nernst effect. The observed plateau of the Nernst signal as a function of the magnetic field is correspondingly attributed to a manifestation of the integer quantum Nernst effect.

Optical vortices with tunable properties in multiple dimensions are highly desirable in modern photonics, particularly for broadly tunable wavelengths and topological charges at the micrometer scale. Compared to solid-state approaches, here we demonstrate tunable optical vortices through the fusion of optofluidics and vortex beams in which the handedness, topological charges, and lasing wavelengths could be fully adjusted and dynamically controlled. Nanogroove structures inscribed in Fabry-Pérot optofluidic microcavities were proposed to generate optical vortices by converting Hermite-Gaussian laser modes. Topological charges could be controlled by tuning the lengths of the nanogroove structures. Vortex laser beams spanning a wide spectral band (430-630 nm) were achieved by alternating different liquid gain materials. Finally, dynamic switching of vortex laser wavelengths in real-time was realized through an optofluidic vortex microlaser device. The findings provide a robust yet flexible approach for generating on-chip vortex sources with multiple dimensions, high tunability, and reconfigurability. Agency for Science, Technology and Research (A*STAR) Ministry of Education (MOE) All the authors would like to thank A*STAR for support. This research is supported by A*STAR under its AME IRG Grant (project no. A20E5c0085). M.K. is also thankful for the support from ACRF Tier 2 (Grant T2EP50120-0003).

The vortex at the Ta/Fe explosively welded interface is featured by the intermediate zone being fully bounded by Ta matrix, which differs from the vortex structures observed in the most bimetallic interfaces. In this work, advanced characterizations and numerical simulations were integrated to establish a detailed evolution model of the special vortex, and the associated governing mechanisms were identified. It was also inferred that the mesoscale cavity and microcracks within the vortex resulted from the geometric hole and extrusion movement that generated during the vortex evolution, respectively. Furthermore, a diversity of metallurgical structure was revealed at the Ta/Fe interface, which did support the deformation path of the interface material observed in the simulations. The insights gathered here benefit an in-depth comprehension of impact welding.

Vortex motion of a cylindrical quantum plasma containing degenerate inertialess electrons and strongly correlated, non-degenerate inertial ions is studied. The electron exchange–correlation and ion–neutral collisional effects are taken into consideration, along with vertical external magnetic field and radial electric field. Considering generalized viscoelastic momentum equation for strongly coupled ions in quasi-crystalline state, variation of different rotational characteristics along radial distance are discussed numerically. Existence of shear rotation is observed near both the core and the periphery of the vortex, which is found to be modified by ion–ion correlation, quantum effects of the degenerate electrons, the ion–neutral collision, as well as by the magnetic field. It is noticed that electron exchange–correlation potential and quantum diffraction play major roles in modifying the rotational characteristics. Vorticity and the rate of increment of enstrophy with respect to radial distance, diminish to zero towards the periphery of the vortex. Also, it is noted that the ion–neutral collision may be responsible for reducing the increment of enstrophy.

Dominating electron-electron scattering enables viscous electron flow exhibiting hydrodynamic current density patterns such as Poiseuille profiles or vortices. The viscous regime has recently been observed in graphene by non-local transport experiments and mapping of the Poiseuille profile. Here, we probe the current-induced surface potential maps of graphene field effect transistors with moderate mobility using scanning probe microscopy at room temperature. We discover micron-sized large areas appearing close to charge neutrality that show current induced electric fields opposing the externally applied field. By estimating the local scattering lengths from the gate dependence of local in-plane electric fields, we find that electron-electron scattering dominates in these areas as expected for viscous flow. Moreover, we suppress the inverted fields by artificially decreasing the electron-disorder scattering length via mild ion bombardment. These results imply that viscous electron flow is omnipresent in graphene devices, even at moderate mobility., Comment: 89 pages, 24 figures, published in Nano Letters

Laboratory experiments were performed to characterize the distinct features of hairpin-like vortical structures induced via pulsed, wall-normal jets in laminar (LBL), and turbulent boundary layers (TBLs). Hotwire anemometry was used to characterize the disturbed flow at multiple streamwise, transverse, and vertical locations. The dominant spatiotemporal structure of the induced motions was reconstructed using Taylor’s hypothesis and time-averaged, phase-locked data. Results support the concept that the meandering of very-long, low-momentum streaks observed in the logarithmic layer and lower part of wake regions of TBLs results from the upwash of hairpin vortices or packets. Comparing the induced hairpin-like vortices in the LBL and TBL reveals the modulation of the mean shear; using the second-order derivative of the mean streamwise velocity, we show a linkage between the mean shear gradient and appearance of low- and high-momentum streaks in the logarithmic layer. Streamwise velocity profiles with a pitot tube by Smith (Effect of Reynolds number on the structure of turbulent boundary layers, 1994) at ten Reynolds numbers from Reθ = 4601 to 13,189 are also inspected to evaluate such linkage in a broader range of Re. As Reynolds number increased, the vertical regions of the negative second derivative of mean streamwise velocity increased. The minimum value of mean shear gradient decreased, indicating that the mean shear stress gradient increased to form more noticeable low- and high-momentum streaks in the logarithmic layer. Besides, the Reynolds tensor’s principal stresses and principal axes angles associated with the hairpin vortex legs stretching are demonstrated by DNS data (Spalart, P. R. 1988) as Reynolds number increased.

Features of the simulation of the thermodynamic and gasdynamic processes occurring in devices for reducing the noise level of a shot from a gun were considered. A simulation of large vortices in the nonstationary turbulent flow of powder gases in a muzzle noise reduction device with a silencer representing a shaped channel with several chambers, whose volumes decrease in the direction to the silencer outlet, has been performed. Results of qualitative and quantitative investigations of the initiation, development, and damping of the shock waves in the flow of powder gases, formed as a result of the firing of a shot made from a signal gun, are presented.

For iron-based superconductors, the phase diagrams under pressure or strain exhibit emergent phenomena between unconventional superconductivity and other electronic orders, varying in different systems. As a stoichiometric superconductor, LiFeAs has no structure phase transitions or entangled electronic states, which manifests an ideal platform to explore the pressure or strain effect on unconventional superconductivity. Here, we observe two types of superconducting states controlled by orientations of local wrinkles on the surface of LiFeAs. Using scanning tunneling microscopy/spectroscopy, we find type-I wrinkles enlarge the superconducting gaps and enhance the transition temperature, whereas type-II wrinkles significantly suppress the superconducting gaps. The vortices on wrinkles show a C2 symmetry, indicating the strain effects on the wrinkles. By statistics, we find that the two types of wrinkles are categorized by their orientations. Our results demonstrate that the local strain effect with different directions can tune the superconducting order parameter of LiFeAs very differently, suggesting that the band shifting induced by directional pressure may play an important role in iron-based superconductivity., The evolution of superconductivity in LiFeAs with respect to pressure or strain remains elusive. Here, the authors observe different response of superconducting states due to different orientations of local wrinkles on the surface of LiFeAs.

Hydrogen fueled rotary engines are potential alternatives to be green engines in vehicles. In this study, a numerical approach is used to investigate and compare the internal flow field characteristics of two types of rotary engines: triangular rotary engine (TRE) and liquid piston engine (LPE) also known as elliptical rotary engine. First, the three-dimensional fluid analysis models are developed for the two engines based on geometric designs of the rotors. The fluid analysis is carried out using the computational fluid dynamics (CFD) tool by assuming two working fluids: air and H 2 , and the dynamic mesh and turbulent flow models are integrated and simulated with ANSYS Fluent solver. For simulation convenience, combustion and thermal effects are neglected. The results show that the flow rate fluctuation coefficient and gas moment fluctuation coefficient are higher in LPE as compared to TRE, indicating LPE has relatively lower stability than TRE. The vortex number is found to be higher in LPE, signifying higher combustion efficiency of LPE as compared to TRE. However, LPE may have more energy dissipations, reduced exhaust and suction efficiency and high risk of leakages. The TRE has more stable flow, larger exhaust, lesser vortex, lower leakages, and simpler flow path as compared to LPE. Comparison of the two fluids i.e. air and H₂ shows that in TRE, air has high magnitude of average gas moment, high mass flow rate, high pressure and low flow velocity as compared to H₂, implying that air is more stable than H₂ in TRE. Conversely, H₂ is more stable than air in the case of LPE. The vortex number is relatively lower in both LPE and TRE using air indicating that air has low leakages than H₂ in both rotary engine types. This study can be used as a reference for a better rotary engine design in the future.

Through the improved delay-detached eddy simulation (IDDES), this paper establishes a 1:1 model for a high-speed train, and simulates the transient state of the train running 600km/h in a vacuum pipeline with the pressure of 1,000Pa. The results show that, following the Ω criteria, a pair of counterrotating vortexes can be captured, which alternatively shed near the tip of the last carriage, and propagate over a long distance along the flow direction. The motion and expansion of the vortexes are clearly three-dimensional (3D). Judging by the physical meaning of vortexes, the high vorticity vortexes mainly concentrate near the tip of the last carriage, while the low vorticity vortexes scatter across the wake zone. The latter vortexes have a low dissipation rate and are dominated by rotation. The turbulent energy and Reynolds stress of the wake field are very obvious near the tip of the last carriage, and attenuate quickly along the flow direction. This means the vortexes near the tip of the last carriage face a strong shear effect, and undergo apparent dissipation. Low turbulent energy and Reynolds stress are distributed in the downstream far from the tip of the last carriage, i.e., the interaction zone between vortexes and the ground / inner pipe wall.

Film-cooling hole-geometry research needs a better understanding in the mechanism of film cooling effectiveness, which was recently shown to depend rather strongly on the counter-rotating vortex pa...

The present paper numerically investigates viscoelastic fluid flow in the developing flow regime through both straight and 90-degree curve ducts. The aim is to investigate the effects of the first and second normal-stress differences (N1 and N2) as well as the curvature ratio ( $$\kappa = D/R$$ , where R and D are the curvature radius and channel side, respectively) and Reynolds number on the secondary flow patterns. Simulations were carried out in developing flow conditions in curved ducts using the finite volume method. The Reynolds numbers were 10, 20, 30, 40, 50, and 100, and the curvature ratios were 0.05, 0.066, 0.1, and 0.2. The Giesekus constitutive equation was utilized to model the non-linear rheological behavior of a 5.0 wt.% solution of polyisobutylene (PIB) in tetradecane (C14H30). The results reveal that a secondary flow with eight corner vortices is generated in a fully developed flow of viscoelastic fluid through a straight duct. This behavior is attributed to the difference in the second normal stress in the flow field. The results of the current study confirm that the second normal stress difference and change in the sign of N2 around the cross section’s corners trigger these corner vortices. Furthermore, the effects of the curvature ratio on the distributions of first and second normal-stress differences in the developing Dean flow were studied for the first time. The vorticity vector method was used for mixing-enhancement assessment. The results show that the intensity of secondary flows was significantly higher in viscoelastic fluid at all curvature ratios and at all considered Reynolds numbers than in Newtonian fluid flow.

Experimental and numerical study of active and passive flow control are notable and highly practical subjects in aircraft and missiles. Fluid jets are invaluable tools for this purpose. Accordingly, the present study delves into the effects of a pair of air microjets on turbulent flow over a plate. For this purpose, numerical model results were verified by experimental data of flow over a plate in the presence of a pair of air jets. Next, vortex formation, merging, and dissipation into the flow were studied at velocity ratio, VR = 4.0, by changing the spacing between the pair of jets and their orientations. The vortex position relative to the floor and other vortices, vortex intensity, flow velocity, Reynolds stresses in different directions, and pressure are discussed. The best vortex-merging results were found in a pair of co-directional jets (d/D = 10) condition. A pair of co-directional jets (d/D = 10) produced better results than opposite ones (d/D = 10—ccr). In the configuration with d/D = 10, the vortex intensity was nearly 80% higher than that of the single jet case. Further, the pair of jets pushed the post-jet pressure rise around 30 cm away.

The buoyancy-driven thermogravitational Rayleigh–Benard convection (RBC) occurs in a 1–3 cm-deep layer of normal He-I in a wide experimental cell heated from above at temperatures below the liquid 4He density maximum T

The Monte Carlo method has been used to calculate the trapped magnetic field in superconducting plates with holes. The mechanism of flux pinning on the holes is implemented with special subprocesses added to the algorithm: vortex capture and emission, both occurring on the hole boundaries. Secondary peaks related to the holes emerge on the calculated profiles of the trapped magnetic field. It has been found that these peaks disappear in plates with sufficiently strong pinning or when the computational mesh is coarse (the case corresponding to a low resolution of probes in experiments). The dependence of the trapped field on the hole radius has been analyzed.

Foam sclerotherapy is a simple and easy minimally invasive treatment for varicose veins, but foam stability is a bottleneck in the treatment. The foam-coalescence pattern can reveal the process of foam decay, whereas the effects of fluid parameters can characterize the decay patterns under various conditions. This study is instructive for clinical and research purposes. Four liquid parameters were considered by the addition of surfactant P-188 to change the liquid properties. A simplified four-foam basic unit model was developed. Two-phase flow calculations were performed in ANSYSA Fluent with grid-independence verification, and post-processing was performed using Tecplot 360. As the concentration of P-188 increased from 0 to 12%, the foam-coalescence time gradually increased from 0.28 to 0.35 ms at a growth rate of approximately 25%. The coalescence of the unit foam group of the four foams finally approached a spherical shape. The first consolidation consumed 0.03 ~ 0.05 ms, and the velocity increased sharply to 1.0 ~ 1.2 m/s in the second consolidation. The greater the concentration of P-188, the later the peak appeared. A simplified spatially stereoscopic coalescence model was developed, and the foam-coalescence time was found to increase linearly with increase in the surfactant concentration. It was revealed that foam coalescences under different conditions mainly included the coalescence proximity effect of the pressure gradient field and the repulsion effect of the vortex on the bubble surface. This paper serves as a basis for the design of more macroscopic foam-stability experiments and paves the way for ideas achieving the stability of sclerosing foam.

Numerical study was carried out in order to investigate thermo-hydraulic performance and flow characteristics of rectangular channel fitted with the novel type conic vortex generator [NTCVG] in the range of Re = 5000–20,000 with an increment of Re = 2500. To evaluate the NTCVG’s effect on heat transfer augmentation, three-dimensional [3D] turbulent flow was analyzed by using the shear-stress transport (SST) k-ω turbulence model. The numerical results revealed that NTCVG was detected to be capable of generating two primary vortices along with four corner vortices for each vortex generator [VG]. NTCVG was compared in terms of TEF with other VGs studied either numerically or experimentally in literature. Due to its curved surface, NTCVG was compared not only with flat surfaced VGs but also with inclined, curved as well as perforated surfaced VGs for the purpose of providing comprehensive comparison. Based on numerical results, NTCVG showed superior performance in comparison to VGs investigated in literature. In terms of heat transfer augmentation, NTCVG manipulates incoming air to the heated surface by its aerodynamically designed shape. The superiority of NTCVG with regard to heat transfer enhancement was exhibited with the use of flow field, temperature and Nu number distribution. DWPC, which performs relatively well in improving heat transfer, was considered for an example of comparison. While both LVGs were determined to be exhibited close f values, an increase in Nu number was attained on the order of 58.75% and 41.05% for NTCVG and DWPC, respectively, in comparison to smooth channel at the lowest Re number. NTCVG showed not only at the rate of 8.42% higher TEF value than DWPC, but also the second highest TEF value [TEFNTCVG = 1.33] was attained among all other VGs compared.

The side-blown vortex smelting reduction reactor proposed in this paper is a new type of metal extraction equipment. The study of fluid dynamics is significant for improving reactor performance. Physical simulation is used to analyze the effects of the angle and number of blown lances, nozzle diameter, gas flow rate, and measuring depths on the reactor’s transfer and mixing characteristics. Dimensional analysis is used to correlate dimensionless numbers (Reynolds number Re, modified Froude number Fr′, capillary number Ca, number of blown lances n, and horizontal angle of the blown lance α) with mixing time and multiphase flow behavior. The results show that when the nozzle diameter and the number of blown lances are constant, Fr′, Ca and α are negatively correlated with the mixing time, and Re is positively correlated with the mixing time. When the angle of the blown lance is constant, Re and Ca are negatively correlated with mixing time, and Fr′ is positively correlated with mixing time. With the increase of Re, Fr′, Ca, the mixing behavior will gradually change from the bubbling regime to the transition regime and then to the steady jetting regime.

In order to study the fluid–solid coupling dynamic characteristics of parachute-payload system during drop process and analyze the unsteady aerodynamic characteristics under finite mass opening conditions, an adaptive moving fluid mesh method is developed on the basis of the existing arbitrary Lagrangian–Eulerian (ALE) fluid–solid coupling method. The calculation results of open force and drop velocity on the C-9 parachute demonstrate the effectiveness of this method. On this basis, the effect of canopies with three different permeability on parachute-payload system motion characteristic including opening property, steady descent property and stability is studied. Comparative analysis is conducted for structures and characteristics of vortex with different canopy materials, and interference mechanism of unsteady flow for parachute-payload system in unsteady oscillation is revealed. The results show that the adaptive moving fluid mesh method can effectively eliminate restrictions of existing simulation methods for parachute-payload system and significantly reduce calculation time. For the lightweight parachute, permeability has significant effect on kinetic characteristic of parachute-payload system. Canopy with large permeability has small opening load and structural stress in opening stage. After opening, there are mainly small vortexes distributed evenly behind the canopy with good stability. However, canopy with small permeability has obvious breath behavior and oscillation in opening stage. The main vortexes periodically shed off after opening. With the change of permeability from small to large, Parachute-payload system eventually presents three steady descent modes: conical descent, gliding descent and stable vertical descent. Graphical abstract

We report the results of micromagnetic simulations of low-frequency resonances associated with gyrotropic motion of exchange-coupled magnetic vortices in a system of two overlapping ferromagnetic disks. The dependences of the resonance frequencies on the method of excitation, the mutual direction of the vortex cores and on the external magnetizing magnetic field are analyzed. The modeling demonstrates that the most effective influence on the change in the resonance frequency is realized when the system is magnetized in the sample plane in the direction perpendicular to the line connecting the disks centers, opposite to the direction of magnetization in the area of disks overlapping. It is shown that for the state with opposite core polarity there are two resonant modes in which the cores and consequently the in-plane dipole moments induced in vortex shells are rotated in the opposite directions. On the contrary, in the resonant mode of the state with the same core polarity, the cores are rotated in the same directions and induced dipole moments are rotated in phase. The possibilities of using the overlapping disks system for the synchronization of vortex nano-oscillators are discussed.

Constructing a fence for potential liquid hydrogen leakage is a common protective measure to prevent the unrestricted spread, and critically evaluating the effects of a fence is essential for the safe use of hydrogen energy. Based on NASA's large-scale experiment of liquid hydrogen release, a 3D numerical model considering the existence of fence is proposed to study the dynamic spread behaviors of hydrogen flammable cloud and liquid hydrogen pool. The results show that the liquid hydrogen pool keeps a downwind radius of about 1.75 m most of the time during the release, and the hydrogen flammable cloud has a limit spread distance. Three cases are set to comparatively evaluate the effect of the fence, which are full fence, downwind half fence and no fence. Under the three cases, liquid hydrogen pools all evaporate completely within 5 s. Full fence scenario has the modest spread scale of hydrogen flammable cloud in the atmosphere but the longest duration for 86 s, and the upwind fence causes an easily overlooked hazardous region due to the vortex here, thus constructing a full fence is not an ideal strategy when the spread direction is constant. Just constructing a downwind half fence leads to the greatest spread distance of the flammable hydrogen cloud, which are 33.6 m and 68 m in vertical and downwind directions. No fence case corresponds to the smallest diffusion scale of flammable hydrogen cloud in atmosphere but the longest near-ground spread distance for 43.35 m. Four stages can be divided to summarize the entire life period of the flammable cloud for the cases with and without a fence, while three stages for the case with a downwind half fence.

Pumped storage units are the main parts in China’s power construction, as a hot issue concerned by the industry. The pump turbine involves the two-way flows and a multiple condition operation, and its operation flow pattern is very complex. The particle image velocimetry (PIV) is a very effective test technique to determine the internal flow field of pump turbines. This paper discusses the key problems of the pump turbine, based on the PIV experiments under typical conditions of the pump turbine, especially for problems such as the S-shape problem, the hump problem, the pressure fluctuation problem and the cavitation problem. In the internal flow fields under typical conditions are determined. The vortices induced and their development are observed in the PIV test. The flow phenomenon is shown at each operating point. The typical problems of the pump turbine are closely related to the vortex distribution in the internal flow field. From the PIV test results under several working conditions and from the comparisons between the optimal condition and the part load condition, it is seen that the vortex distributions are very different. Vortices at the vane-less area between the guide vane and the runner are closely related to the strong pressure pulsation, the first hump and the S-shape curve. From the PIV results of the cavitation working points, it is seen that the flow angle is changed in the vane-less region and the runner leading edge because of the cavitation bubbles and that the flow angle deviates from the optimal setting angle. From the computational fluid dynamics (CFD) result of the second hump working points, it is concluded that the vortex shedding on the runner leading edge is the main cause of the second hump.

We report upon synthesis of stable chains of magnetically aligned zero-valent α-Fe nanoparticles and investigation of their magnetization reversal mechanism. The magnetic hysteresis loops with magnetic field applied at various directions with respect to the nanoparticle chain are measured experimentally and reproduced numerically by precisely mimicking the sample geometry under finite element modeling. The magnetization reversal mechanism is visualized in all three dimensions (3Ds) using 3D simulation and visualization toolkits. The reversal is found to nucleate from the ends of the chains and progressed through curling and fanning modes, vortex nucleation, propagation and annihilation. A better quantitative agreement is observed for increased number of nanoparticles and parallel chains.

Circular section tubular members with smaller wind load shape coefficient and higher stability are widely used in ultra-high-voltage (UHV) transmission towers. However, the tubular members, especially those with a large slenderness ratio, are prone to vortex-induced vibration (VIV) within a specific wind speed range. The sustained vibration of members can easily cause fatigue failure of joints and threaten the operational safety of transmission lines. Consequently, a novel countermeasure for the VIV of tubular towers using a new type of radial spoiler is proposed, whose mechanism is to change the vortex shedding frequency by destroying the large-scale vortexes into small-scale vortexes. Then, the parametric analysis of different variables is carried out based on the orthogonal experiment and numerical simulation, including the height H and length B of the spoiler and the distance S between adjacent spoilers. The results show that the above three parameters all have significant influences on vortex shedding frequency. Additionally, a practical design method of the new radial spoiler is proposed, and the recommended values of H, B, and S are 1D∼2D, 1.5H∼3H, and 5D∼12.5D, respectively, where D is the diameter of the tubular member. Finally, a numerical verification of the suppression effects is carried out, demonstrating that the proposed quick design method is simple and reliable, which can be widely used in the VIV design of tubular towers.

To investigate the nozzle geometry influence on vortex cooling performance in the actual leading edge region, an improved vortex cooling configuration with a coolant chamber is established based on the middle cross section of stage 1 vane blade of GE-E3 high pressure gas turbine. Numerical simulations are conducted to research the effects of nozzle position, nozzle number and nozzle aspect ratio on the flow and heat transfer behavior. Results show that with the introduction of the coolant chamber, the mass flow of nozzles increases gradually from the upstream to the downstream instead of a uniform mass flow distribution. Configurations with nozzles placed at the sides (the vortex cooling) have better cooling performance than with nozzles placed in the middle (the impingement cooling). What’s more, the configuration with nozzles placed along the pressure side has the best comprehensive cooling performance. Due to the irregular blade line, a flow entrainment that is not found in simplified circular configurations is observed on the pressure side weakening the local heat transfer performance. The cooling performance is most sensitive to the nozzle number. As the nozzle number increases, the friction coefficient and heat transfer intensity both decrease. Moreover, as the nozzle aspect ratio increases, the friction coefficient and heat transfer intensity both increases first and then decrease. Results indicate a certain vortex cooling configuration may have the optimal nozzle number and nozzle aspect ratio. For this paper’s configuration, the best nozzle number is 5 and the best nozzle aspect ratio is 4.

Angular momentum plays a central role in a multitude of phenomena in quantum mechanics, recurring in every length scale from the microscopic interactions of light and matter to the macroscopic behavior of superfluids. Vortex beams, carrying intrinsic orbital angular momentum (OAM), are now regularly generated with elementary particles such as photons and electrons, and harnessed for numerous applications including microscopy and communication. Untapped possibilities remain hidden in vortices of non-elementary particles, as their composite structure can lead to coupling of OAM with internal degrees of freedom. However, thus far, the creation of a vortex beam of a non-elementary particle has never been demonstrated experimentally. We present the first vortex beams of atoms and molecules, formed by diffracting supersonic beams of helium atoms and dimers, respectively, off binary masks made from transmission gratings. By achieving large particle coherence lengths and nanometric grating features, we observe a series of vortex rings corresponding to different OAM states in the accumulated images of particles impacting a detector. This method is general and can be applied to most atomic and molecular gases. Our results may open new frontiers in atomic physics, utilizing the additional degree of freedom of OAM to probe collisions and alter fundamental interactions.

Multi-pass friction stir processing (M-FSP) was performed to repair the interface defects of AA5083/T2 copper explosive composite plates. The interface morphology and its bonding mechanism were explored. The results show that higher rotation speed and lower transverse speed produce more heat generated during FSP. The defect-free and good mechanical properties of the AA5083/T2 copper composite plate can be obtained under the condition of the rotation speed of 1200 r/min, the transverse speed of 30 mm/min and the overlap of 2/24. Moreover, M-FSP changes the interface bonding mechanism from metallurgical bonding to vortex connection, improving the bonding strength of composite plate, which can guarantee the repairing quality of composite plates.

We find a novel confinement mechanism in the two-flavor dense quark matter proposed recently, that consists of the 2SC condensates and the $P$-wave diquark condensates of $d$-quarks. This quark matter exhibiting color superconductivity as well as superfluidity is classified into two phases; confined and deconfined phases of vortices. We establish that the criterion of the confinement is color neutrality of Aharonov-Bohm (AB) phases: vortices exhibiting color non-singlet AB phases are confined by the so-called AB defects to form color-singlet bound states. In the deconfined phase, the most stable vortices are non-Abelian Alice strings, which are superfluid vortices with fractional circulation and non-Abelian color magnetic fluxes therein, exhibiting color non-singlet AB phases. On the other hand, in the confined phase, these non-Abelian vortices are confined to either a baryonic or mesonic bound state in which constituent vortices are connected by AB defects. The baryonic bound state consists of three non-Abelian Alice strings with different color magnetic fluxes with the total flux canceled out connected by a domain wall junction, while the mesonic bound state consists of two non-Abelian Alice strings with the same color magnetic fluxes connected by a single domain wall. Interestingly, the latter contains a color magnetic flux in its core, but this can exist because of color neutrality of its AB phase., 35 pages, 3 figures

The authors have performed 3D numerical investigations into the velocity field behind a 3D thin plate by the LES method. The plate was located at a height of 0.002 m in a turbulent boundary layer formed in a water channel. The chord length of the plate and its spanwise size were equal to 0.01 m and 0.024 m respectively. The Reynolds number calculated from the half-width of the channel and the velocity on its axis was equal to 7500. It has been shown that under the impact of the wake of the plate, the longitudinal velocity normalized to the stagnation velocity grew in the logarithmic region at a distance to x/δ = 3.8, and pulsations of all the velocity components decreased in the buffer region to the distance x/δ = 0.8. As the lower shear layer of the wake approached the surface, longitudinal pulsations reached their minima at the wall at x/δ = 1.8, whereas vertical and transverse pulsations became higher than those in an unperturbed boundary layer. The calculated characteristics of the velocity field satisfactorily correlated with the relevant characteristics obtained in experimental investigation with similar initial and boundary conditions. An analysis of the velocity fi eld has revealed the mechanism of impact of the wake on the structural change of wall flow. The involvement of the wall medium in the lower shear layer generated the outflow of the medium from the channel wall, and the involvement in the upper shear layer formed the inflow of a high-speed medium to the buffer region. The medium′soutflow from the wall led to a reduction in the velocity gradient at the surface. Shear stresses decreased at a distance of four thicknesses of the boundary layer, and their local reduction amounted to as much as ~30%. Trailing vortices descending from the plate′s side edges created a nonuniform transverse-velocity distribution. This nonuniformity caused the vorticity to form in the buffer region. The arising system of small-size vortices blocked the feed of the high-speed medium to the wall, retarding the growth in the shear stresses on the surface in the interval 1.4 ≤ x/δ ≤ 2.6. The vortex system degenerated upon the stabilization of the transverse velocity and shear flow on the surface was restored.

In the framework of the classical equations for the magnetization dynamics and the collective variables approximation, the dynamics of magnetic vortices in two-dimensional ferromagnets with the easy-plane anisotropy and spatially inhomogeneous exchange interaction is considered. In the case of a wide straight line of the interface between magnetic media with different but slightly different exchange interaction, the dependence of the magnetic vortex velocity on its distance to the structure defect and position inside the interface domain is obtained.

In this paper, we study the ground state of a binary rotating Bose–Einstein condensate with unequal atomic masses. The results are obtained by numerically solving the Gross–Pitaevskii equation. We conclude that the vortex configuration strongly depends on the strength of spin–orbit coupled, rotational frequency as well as on the ratio of atomic mass. A series changes of vortex structure from a single central, triangular, hexagon to linear vortex string are found. In addition, the vortex necklace, giant vortex and linear hidden vortex are observed. Our results are helpful for understanding the artificial gauge field of the binary rotating ultracold Bose gas under realistic imbalanced condition.

We study the ground-state phases of Rabi-coupled two-component Bose-Einstein condensates with rotation and spatially modulated nonlinear spin-orbit coupling. The spin-orbit coupling and Rabi coupling play important roles on the ground-state phases with the fixed rotation, however, they have the opposite effects on the generation of vortex. When the system without Rabi coupling, spin-orbit coupling can improve the generation of vortex. The vortex chain with regular pattern appears with strong spin-orbit coupling. Considering the Rabi coupling, the number of vortices is inhibited by the Rabi coupling with the fixed spin-orbit coupling and rotation strengths. The ground-state phase diagram spanned by the SOC strength and Rabi coupling with rotation is presented, the non-vortex phase, single-vortex phase and multi-vortex phase are classified. The spin textures of the ground-state phases are also discussed.

Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In the current device, the asymmetric potentials are provided by charged Néel walls located in the vertices of spin ice magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, since they move with trajectories crossing charged Néel walls with different orientations. Moreover, we have found out the asymmetric pair potentials which generate the local ratchet effect. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes., This work was supported by Spanish MICINN grants FIS2016-76058 (AEI/FEDER, UE), EU COST- CA16218. IMDEA Nanociencia acknowledges support from the ‘Severo Ochoa’ Programme for Centres of Excellence in R&D (MICINN, Grant SEV-2016-0686). MCO and AG acknowledges financial support from Spanish MICINN Grant ESP2017-86582-C4-1-R and IJCI-2017-33991; AMN acknowledges financial support from Spanish CAM Grant 2018-T1/IND-10360. MV acknowledges financial support from Spanish MICINN Grant PID2019-104604RB/AEI/10.13039/50110001103.

The fluid-structure interaction (FSI) in case of fish swimming in the vortex street is investigated by numerical simulations. The vortex street is generated by a D-section cylinder. A 2-D fish model is placed on the downstream centerline of the bluff cylinder at a distance of 4 diameters away from the center of the cylinder. To simulate the fish body undulation and movement, the moving mesh is generated by a coupling approach based on the radial basis function and the overset grid technology. The Navier-Stokes equation in the arbitrary Lagrangian-Eulerian form is solved by coupling with the kinematics equation. Three cases are investigated: in a stationary position without deformation, a passive locomotion without deformation, and an active deformation based on the Karman gait model. The results indicate that the fish body is acted by an alternating force and moment when it is located in the centerline of the vortex street. Furthermore, the fish could extract sufficient kinetic energy to overcome the drag under suitable conditions even when it keeps rigid and out of the suction zone. When the fish body undulates based on the Karman gait model, the interaction is evidently shown between the fish body and the vortices. The theoretical analysis demonstrates that the lateral force and the moment acting on the fish body vary in a cosine formula, with the lateral translation and the body rotation as a result. This study focuses on the behavior of the fish body in the bluff cylinder wake and reproduces some phenomena observed in the experiments. Besides, the Karman gait model is also theoretically analyzed, for the further exploration of the FSI mechanism in case of fish swimming.

The vortex-based propulsive systems’ enhanced performance greatly contributes to the vortex added-mass effect, which was initially developed to explain the added drag when a solid body accelerates in fluids. However, the solution of the instantaneous vortex added-mass coefficient is still remaining a question because vortices always do not have a stable geometric shape like solid bodies. In this paper, the formation of a canonical vortex ring is performed to investigate the nature of vortex added-mass and explore a solution for estimating the vortex added-mass coefficient. The vortex ring is generated by a piston-cylinder apparatus, and the time-dependent flow fields are recorded by particle image velocimetry technique. The ridges of finite-time Lyapunov exponent are applied to identify the Lagrangian boundary of the vortex ring. It is found that a part of the ambient fluids is entrained by the vortex ring when it propagates downstream, resulting in the growth of the vortex ring. Besides, a significant drift of the ambient fluid is observed to bypass the Lagrangian boundary of the vortex ring and reveals the nature of the vortex added-mass. Thus, the added-mass coefficient of the vortex is redefined as the ratio of the volume of the Lagrangian drift fluids in finite time interval step to the vortex volume at that instant. By referring to McPhaden’s method to estimate the added-mass of a solid body, a method based on the multiple material lines with relative-timestep is developed to estimate the volume of Lagrangian drift fluids induced by the vortex added-mass. Then, an empirical criterion for determining the material line number and the finite time interval step is suggested for the vortex ring flow, and the eventual vortex added-mass coefficient calculated by the volume of Lagrangian drift fluids is found to well agree with the results of Brennen. Moreover, the method based on multiple material lines for calculating Lagrangian drift fluids’ volume suggests a potential solution for estimating the added-mass coefficient of arbitrary vortex structures.

In this paper, Liutex similarity is extended and revised in channel turbulence. Liutex similarity is free from viscous dissipation, relaxing the very high Reynolds number assumption of K41. Liutex similarity hypothesis in 2-D channel turbulence is first proposed and estimated, which denotes that the statistical properties of Liutex field are uniquely and universally determined by the scale l, Liutex vortex number density n(A) with each area A and mean dissipation rate of square of Liutex magnitude ηL. The Liutex spectrum is EL (k) ∼ C[n(A)1/2ηL]1/3k−5/3 in the inertial range where energy spectrum exhibits double cascades. The scaling behaviors of Liutex spectrum in 2-D are independent of Reynolds number. Liutex structure functions are defined as Liutexp (l) ≡ 〈[δR∥(l)]p〉 which are in dependent of scales. It is found that Liutexp (l) ∼ C′(ηL)p/3l0 by dimensional analysis.

Alternative fuels and stocks like biomass or chemical and refinery waste, may potentially be used in gas turbines and industrial applications after gasification. Thus, understanding the role of hydrogen in these fuels is critical to the broader aim of utilising alternative fuels for power generation. In this work, the interaction between the flame and the flow field was studied in a quarl-stabilised swirl non-premixed flame burning CH4 and H2–enriched CH4. Simultaneous high-speed OH-PLIF/PIV imaging at 5 kHz was carried out on these flames to explore the flame-flow interaction. The instantaneous flow fields in the CH4 or CH4+H2 flames showed a small scale vortical structure near the shear layers, which were not apparent in the time-averaged flow fields. Increasing H2% in the fuel jet was observed to dampen the velocity fluctuations. The fuel composition affected the spatial location of the reaction zone; in the CH4 flames, the axial position of the reaction zone is seen to track the relatively large-magnitude axial velocity fluctuations while remaining in locally low-speed regions of the flow. In contrast, in H2-enriched flames, where the flame is more robust, the reaction zone was able to survive longer, in terms of axial distance, in the vicinity of high swirling jet velocity, with less sensitivity to velocity fluctuations. With increasing the H2%, the reaction zone steadily leaves the IRZ towards the swirling jet flow and localised between its outer and inner vortices. This acts as a stabilisation factor where the internal vortices convect hot product towards the fresh mixture. Moreover, the flame curvatures, the vorticity and compressive strain fields interactions with the reaction zone are presented and discussed. This article outlines results that yield more in-depth insight into hydrogen-enriched hydrocarbon non-premixed swirling flames' combustion, which is essential to accelerate the fuel switching from hydrocarbons to hydrogen.

Flow visualization experiments were conducted in a water channel and a low-speed wind tunnel at Reynolds number of 1.54 $$\times$$ × 104 to 1.2 $$\times$$ × 105 for a leading-edge extension model, which is referred to as a NASA TP-1803 model in this study. In addition, particle image velocimetry velocity measurements were taken in the water channel to obtain the quantitative information about the three-dimensional velocity field over the strake and wing surfaces. The results obtained at low, medium and high angles of attacks represent three distinct cases of interaction between the strake and wing vortices. Namely, at α = 5o and 10° the strake and wing vortices were developed over the wing surface without significant interaction noticed; at α = 20°, the strake vortex strongly interacted with the wing vortex in an intertwining manner, which was sensitive to Reynolds number; at α = 30°, the breakdown of the strake vortex took place close to the junction of the strake and the wing; thus, the interaction of the strake and the wing vortices appeared to be less significant than the case of α = 20°. Graphic abstract