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The use of the complex velocity potential and the complex velocity is widely disseminated in the study of two-dimensional incompressible potential flows. The advantages of working with complex analytical functions made this representation of the flow ubiquitous in the field of theoretical aerodynamics. However, this representation is not usually employed in linear stability studies, where the representation of the velocity as real vectors is preferred by most authors, in order to allow the representation of the perturbation as the complex exponential function. Some of the classical attempts to use the complex velocity potential in stability studies suffer from formal errors. In this work, we present a framework that reconciles these two complex representations using bicomplex numbers. This framework is applied to the stability of the von Kármán vortex street and a generalized formula is found. It is shown that the classical results of the symmetric and staggered von Kármán vortex streets are just particular cases of the generalized dynamical system in bicomplex formulation. [ABSTRACT FROM AUTHOR]

To effectively analyses the flame propagation of premixed hydrogen-air explosion, this paper carries out a numerical study on the dynamics of flame propagation during hydrogen explosions in a closed duct under different blocking rates. The study shows that flame structure is roughly the same when the flame passes through an obstacle under different blocking rates. The difference in blocking rates only shows a slight difference in the degree of flame deformation. When the flame passes through the obstacle, Rayleigh -Taylor (R-T) instability accompanies the entire flame propagation process and corresponds to each stage flame acceleration. Kelvin-Helmholtz(K-H) instability has a more prominent influence on the tip flame propagation. When the explosion flame propagates, instabilities lead to difference in density gradient and pressure gradient in the duct. Interaction between density gradient and pressure gradient leads to formation of baroclinic torque, which is the main cause of the vorticity. During the flame propagation, the vorticity at the front of the flame is roughly zero, whereas the vorticity formed at the obstacle or in the burned gases is more apparent. The larger the blocking rate, the more prominent the turbulence intensity during the flame propagation. • Flame structure is roughly same under the different blocking rates obstacles. • Rayleigh -Taylor (R-T) instability accompanies the entire flame propagation. • Kelvin-Helmholtz(K-H) instability influence on the tip flame propagation. • Baroclinic torque is the main cause of the vorticity. [ABSTRACT FROM AUTHOR]

In order to study the proppant migration law of fractures in continental shale gas reservoirs, a visual fracture simulation system was used to carry out proppant migration and settlement experiments, which simulated the process of proppants migration and settlement under the conditions of different fracturing fluid viscosities, displacements, sand ratios, proppant particle sizes and proppant densities. At the same time, the PIV particle velocimetry technology was used to draw the velocity fields at the entrance and the front edge of the sand bank, aiming to further analyze the particles movement characteristics during the migration process. And the following research results were obtained. The migration process of proppants in artificial fractures is divided into four stages: the early stage, the middle-early stage, the middle-late stage and the equilibrium state. At the entrance of the fracture: the velocity of suspended particles is approximately horizontal, and the velocity of particles on the surface of the sand bank is upward along the slope. The propulsion of proppants mainly depends on the carrying effect of liquid viscous force; As the displacement increases, there will be obvious disturbances in the flow field. When the displacement is greater, the degree of disturbance is stronger. At the front edge of the sand bank: There is an obvious vortex phenomenon in the flow field at the top of the slope; The viscosity of the liquid increases, the strength of the vortex is weakened, and the viscous force increases. Under the impact and carrying effect of the liquid, the particles lay farther away; As the displacement increases, a larger vortex appears in the entire front edge area, and the vortex action becomes stronger. At this time, the impact of the liquid makes the proppants placement better; When the sand ratio increases, the number of vortices increases, the strength of vortices intensifies, the spread range enlarges, and the proppants migrate to the farther end of the fracture. When the proppants particle size in slippery water is smaller and the density is higher, the sand bank becomes more uniform, but to achieve the required effect, the sand-carrying liquid is needed. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental and numerical investigations on synthetic jet actuators with various arrangements. First, an actuator with one membrane in the cavity is a standard, reference arrangement; and second, one novel modified arrangement has two membranes in the cavity. Authors use constant temperature-anemometry measurements to identify the characteristic frequencies in which the output jet velocity reaches a maximal value, namely, the resonant frequency of the actuator (Helmholtz frequency) and of the membrane (structural resonance). A numerical model of a synthetic jet actuator has been validated using experimental data for the case with one membrane in a cavity. The simulation results confirm the existence of a toroidal vortex at the actuator exit for the frequencies determined in the experiment. Numerical results of a modified actuator with two membranes in the cavity give promising results in the context of separation control by synthetic jet devices, i.e., increase of output velocity and vorticity from the same occupied space is obtained. Numerical simulations show that in the modified actuator with two membranes in the cavity, the jet output velocity and vorticity of a created toroidal vortex at the actuator outlet can be increased by 80%, compared to the case with one membrane. The new geometry of a synthetic jet actuator with perpendicular membranes is to be implemented into the wind tunnel measurements to prove the use of a modified synthetic jet actuator as a device applicable for active flow control. [ABSTRACT FROM AUTHOR]

In this paper, we study the vortex formation of spin-orbit coupled (SOC) spin-1 dipolar Bose–Einstein condensates by numerically solving the Gross–Pitaevskii equation. We focus the effects of dipole–dipole interaction (DDI) on vortex structures and dynamics behavior. We find that the symmetry of density profiles in vortex lattice formation process and time evolution of the angular momentum is broken in the presence of DDI. This is due to the symmetry breaking of anisotropy DDI. Also, the total angular momentum decreases with increasing the relative dipole strength. However, it is shown that increasing SOC strength can improve the rotation efficiency. This result reflects the SOC dominates the DDI. [ABSTRACT FROM AUTHOR]

A novel friction welding technique based on a vortex material flow is developed to obtain linear welds. In this technique, a stir bar that has the identical material with the workpiece together with a holder is used to produce a vortex material flow within the workpiece via rotationally rubbing the workpiece's top surface. In this study, the process characteristics of this technique were exposed by employing 6061-T6 aluminum alloy as experimental material. Through changing the rotation and welding speeds, the effect of welding parameters on weld quality was investigated. The experimental results show that defect-free joints can be obtained at moderate rotation speeds and lower welding speeds. Too high rotation speed results in the interface slip between the workpiece and the stir bar. Too high welding speed or too low rotation speed leads to a lack of penetration defect occurring in welds. Equiaxed grains are observed in the weld center. They are evolved through continuous dynamic recrystallization and dynamic recovery. The average grain size gradually increases with the tool rotation speed increasing. The microhardness distribution on the joint transverse cross-section presents a "W" shape. The lowest hardness value together with the fracture location occurs in the heat affected zone. However, for the joints with lack of penetration, the fractures occur in the weld nugget zone. [ABSTRACT FROM AUTHOR]

Flows in river habitats are characterized by unsteady turbulence due to the existence of woody debris, boulders and vegetation. As a representative aquatic species, fish is important for the riverine ecosystems, with its complex behavioural responses to turbulent flows. Previous studies investigated the fish–vortices interaction with vortex streets by placing objects with simplified geometries centred at the flow. Nonetheless, complex river morphology in natural rivers results in much more spatially heterogeneous flows due to randomly distributed obstructions. Thus, a semi‐circular cylinder patch located on one side of the flume is used to mimic a vegetation patch at the riverbank. The patch varies in diameter (D0 = 16, 20 and 24 cm) and density (φ = 0.04 and 0.1), whereas the flow velocity is fixed at 25 cm s−1. Fish are observed to swim in three typical patterns, which are "swim around" (pattern 1), "spill" (pattern 2) and "swim through" (pattern 3). For flow with a dense patch, all three patterns are recorded, but only patterns 1 and 2 are observed in sparse patches. It is noticed that in patterns 1 and 2, fish prefer to hold place in zones of low velocity and low turbulence. Moreover, variations in patch diameter have little influence on pattern selection. Results showed that tail beat amplitude (TBA*) in each zone displayed more variations compared with tail beat frequency (TBF). In addition, Spearman's rank tests revealed that TBA* is affected by none of the four hydrodynamic variables (U,ustd,τxy,Ωz), whereas flow velocity imposes the most influence on TBF. Both diameter and density of the patch displayed no significant influence on TBA* and TBF. [ABSTRACT FROM AUTHOR]

Multi-hole probes can simultaneously measure the velocity and direction of a flow field, obtain the distribution of the flow field in a three-dimensional space, and obtain the vortex information in the flow field. Moreover, a multi-hole probe needs to be calibrated while in use; therefore, a three-coordinate, multi-directional rotatable testing system, which can measure the flow field at any position and at any angle, was designed herein. A hemispherical seven-hole probe was calibrated with this test system, and the flow field around cylinders of different diameters was measured to obtain the pressure distribution and vortex shedding frequency. Furthermore, the designed test system's ability to perform a multi-angle and multi-azimuth testing during the calibration of a multi-hole probe was verified. Simultaneously, through data mining of the multi-hole probe, vortices were measured, and periodic vortices were detected. [ABSTRACT FROM AUTHOR]

In view of the complicated distribution of fluctuating pressure on the stilling basin slab with sudden enlargement and bottom drop, based on FLOW-3 D software, large eddy model and tru VOF method were used to simulate the time-averaged pressure, root-mean-square of fluctuating pressure and power spectral density. The comparison between the simulation results and the experimental results shows that the large eddy model can simulate the water flow fluctuating pressure in stilling basin with sudden lateral enlargement and bottom drop suitably. The maximum value of root-mean-square fluctuating pressure appears in the vicinity of the front of the stilling basin and the extension line of the venting side wall. The distribution of fluctuating pressure at the bottom of underflow swirling zone and the wall-attached jet zone are affected by the vortex and fluctuating velocity, respectively, and the impact zone is caused by both. [ABSTRACT FROM AUTHOR]

Reconnection electromagnetic launcher is a kind of electromagnetic launcher, which has excellent performance of launching. The change of projectile width has a great influence on the launching efficiency of reconnection electromagnetic launcher. The influence of the reverse vortex generated on both sides of the projectile on the launch efficiency when the projectile width increases is studied in this article. First, the model and basic principles of the reconnection electromagnetic launcher are introduced, and then the electromagnetic finite-element software is used to carry out a large number of simulations to study the launch model. The results show that when the projectile weight is kept constant by digging out a part of the projectile, and the projectile width increases within a certain range, the launch efficiency will increase as the width of the projectile increases, the increasing trend is smaller and smaller, and finally it will gradually decrease. When the mass of the projectile is determined, there is an optimal width. Finally, the eddy current distribution in the projectile is analyzed, and it is found that when the projectile has a wide width, the eddy current opposite to the eddy current in the middle of the projectile will appear on both sides of the projectile. Through the analysis of electromagnetic force, it can be concluded that the reverse eddy current is beneficial to the launch. Therefore, when keeping the weight of the projectile constant and only increasing the width, the efficiency will gradually increase. When the width of the projectile is highly wide, the excavated part of the projectile is very large, which starts to affect the vortex distribution and reduce the efficiency. This research provides a reference for the design of the projectile of the reconnection electromagnetic launcher. [ABSTRACT FROM AUTHOR]

BACKGROUND: Almost 95% of the venous valves are micron scale found in veins smaller than 300μm diameter. The fluid dynamics of blood flow and transport through these micro venous valves and their contribution to thrombosis is not yet well understood or characterized due to difficulty in making direct measurements in murine models. OBJECTIVE: The unique flow patterns that may arise in physiological and pathological non-actuating micro venous valves are predicted. METHODS: Computational fluid and transport simulations are used to model blood flow and oxygen gradients in a microfluidic vein. RESULTS: The model successfully recreates the typical non-Newtonian vortical flow within the valve cusps seen in preclinical experimental models and in clinic. The analysis further reveals variation in the vortex strengths due to temporal changes in blood flow. The cusp oxygen is typically low from the main lumen, and it is regulated by systemic venous flow. CONCLUSIONS: The analysis leads to a clinically-relevant hypothesis that micro venous valves may not create a hypoxic environment needed for endothelial inflammation, which is one of the main causes of thrombosis. However, incompetent micro venous valves are still locations for complex fluid dynamics of blood leading to low shear regions that may contribute to thrombosis through other pathways. [ABSTRACT FROM AUTHOR]

In this article, we introduce new field equations for incompressible non-viscous fluids, which can be treated similarly to Maxwell's electromagnetic equations based on artificial intelligence algorithms. Lagrangian and Hamiltonian formulations are used to arrive at field equations that are solved using convolutional neural networks. Four linear differential equations, which describe the two fields, namely, the dynamic pressure and the vortex fields, are derived, and these can be used in place of Euler's equation. The only assumption while deriving this equation is that the dynamic pressure and vortex fields obey the superposition principle. The important finding to be noted is that Euler's fluid equations can be converted into field equations analogous to Maxwell's electromagnetic equations. We solve the flow problem for laminar flow past a cylinder, sphere, and cone in two dimensions similar to the conduction in a uniform electric field and arrive at closed-form expressions. These closed-form expressions, which are obtained for the potentials of fluid flow, are similar to the streamline potential functions in the case of fluid dynamics. [ABSTRACT FROM AUTHOR]

Gusts of moderate and large magnitude induce flow separation and other complexities when they interact with the lifting surfaces of air vehicles. The presence of these nonlinear gusts are becoming ubiquitous in twenty-first-century air vehicles, where the classic potential flow–based methodologies applied in the past may no longer be valid. In this review, we define the parameter space for the presence of large-amplitude gusts and describe where and when these gusts may primarily be found. Recent research using modern experimental and computational techniques to define the limits of classical unsteady and indicial aerodynamic theories is summarized, with a focus on discrete transverse, streamwise (longitudinal), and vortex gust encounters. We propose areas where future research is needed to transition these studies of large-amplitude gust physics to real-time prediction and mitigation during flight. [ABSTRACT FROM AUTHOR]

Taylor-Couette flows in a horizontal annular gap between finite coaxial cylinders in rotor-stator configuration are numerically investigated. The inner cylinder (rotor) rotates at a constant angular velocity while the outer cylinder (stator) is at rest. They are limited at their extremities by two fixed walls that prevent axial fluid-flow. In addition, a heat transfer is generated by an imposed temperature difference, with the rotor hotter than the stator while the end-walls are adiabatic. The fluid physical properties are temperature dependent. This non-linear physics problem, with a strong coupling of the conservation equations and boundary conditions, is solved by a finite volume method with numerical schemes of second order space and time accuracies. The radius and aspect ratios and the Taylor, Grashof and Prandtl numbers are the control parameters. The developed numerical code has been tested for different meshes and perfectly validated. Extensive calculations have been made in large ranges of the Taylor and Grashof numbers to analyze the Taylor-Couette flow in convection modes. The results highlight the dynamic and thermal instabilities generated in the Taylor-Couette flow from the appearance of Ekman cells to the Taylor vortex propagation in the entire annulus. The combined effect of these vortices with the secondary flow improves the heat transfer. Furthermore, the influence of the physical properties in the radial direction is more marked in the vicinity of the walls. Finally, we propose an empirical correlation of the Nusselt number in the studied parameter ranges. [ABSTRACT FROM AUTHOR]

[Display omitted] • Global performance of windowless vortex-based solar particle receiver measured. • Aerodynamic active control implemented to allow open aperture operations. • Total heat transfer rate enhanced by the presence of solid phase. • Heat absorbed by the fluid higher than that of solid phase. We present an experimental investigation of the thermal performance of a 1-kW directly irradiated suspension-flow solar particle receiver with an open (windowless) aperture under simulated solar conditions. Silicon carbide and air were used as the particulate and fluid media, respectively. A 5 kW el xenon-arc solar simulator was used as the energy source. An outlet-suction strategy was employed to induce a net inflow through the aperture as means to mitigate particle and hot fluid egress from the device. The influence of various operating parameters, namely particle loading, air inlet mass flow rate and net air ingress through the aperture on the global thermal performance (thermal efficiency, exergy disruption, specific heat losses and wall temperature distribution) of the device was investigated systematically. It was found that the ratio of the solar input to total heat capacity of the two-phase flow and the level of suction have controlling influence on the global performance of the device. For the operating conditions investigated here, the heat absorbed by the air through the receiver was found to be 3–15 times higher than that of the solid phase, depending primarily on the mass loading and total inlet fluid flow rate. The presence of the solid phase was found to enhance the total heat absorbed by the two-phase flow albeit at the expense of lowering the value of the maximum outlet air temperature. [ABSTRACT FROM AUTHOR]

In this paper, we study the generation of quantized vortices in multilayered Bose-Einstein condensates confined in a harmonic potential combined with a longitudinal optical lattice. Numerical results are obtained by solving the imaginary time Gross-Pitaevskii equation. We explore the effects of lattice distance and lattice height on vortex formation process. It is demonstrated that the creation of vortex is stratified. The critical rotational frequency has different values in diverse layers. When the rotational frequency is gradually increased, distinct number of vortices are created in these layers. We reveal the reason for this is that the confinement of the trap potential. In addition, we find that the increase of the contact interaction gives rise to the increase in the vortex number and the size of the condensates. [ABSTRACT FROM AUTHOR]

• Supercritical CO 2 heat transfer in lattice structure channel is numerically studied. • Effects of key parameters of lattice on flow and heat transfer are evaluated. • Buoyancy effect and flow acceleration affected by lattice structure is analyzed. • Vortices induced by lattice structure can suppress the heat transfer deterioration. This study numerically explores the fluid flow and heat transfer features of supercritical carbon dioxide (CO 2) in lattice structure array channel. The mitigation mechanism of the miniature cylindrical lattice structure array on heat transfer deterioration (HTD) of supercritical CO 2 in vertically upward heated channel is studied. This paper evaluates the effect of several key influential parameters (length, diameter, pitch and number) of cylindrical lattice structure array on fluid flow field involving vortex structures, heat transfer coefficient, buoyancy effect and accelerated effect. The results indicate that the lattice structure can effectively suppress the HTD by generating the vortex structure which promoting the turbulent mixing effect and enhancing the turbulent kinetic energy (TKE) of the fluid. Compared with the smooth channel, the peak wall temperature of the lattice structure channel is reduced by about 50 °C, with a corresponding increase in the heat transfer coefficient of about 140 %. The average heat transfer coefficient of the channel is increased by more than 1/3. Furthermore, by increasing lattice length can reduce flow layer stratification and by increasing lattice diameter can creating a composite vortex, which enhance flow mixing strength. The larger the lattice pitch, the worse the overall suppression effect. A denser lattice arrangement produces more temperature valleys, thereby increasing the heat transfer coefficient. The conclusions in this study could provide the main theory support for security and stability of supercritical CO 2 heat exchangers in power system. [ABSTRACT FROM AUTHOR]

We explore the topological generation of skyrmions and half-vortices in a uniform spinor exciton-polariton condensate featuring TE-TM splitting and exposed to an external magnetic field. The manipulation of pump intensity and magnetic field enables precise control over the spin texture and integrated winding number. Specifically, under an excitation condition where the power applied to the vortex state surpasses that on the non-vortex state by an amount dictated by the magnetic field, skyrmions emerge. These skyrmions exhibit a distinctive spin texture characterized by a circular polarization inversion extending from the center to the periphery. Conversely, reversing the excitation condition, where the power on the vortex state is diminished with the reversal of the magnetic field direction, leads to the creation of half-vortices across the entire condensate, devoid of any circular polarization inversion. In additional to the skyrmions and half-vortices, half-skyrmions can be also generated in the same configuration without magnetic field. • The skyrmions and half-vortices can be generated in an exciton-polariton condensate subject to an external magnetic field. • They are created separately when the pump powers over the two components has a difference related to magnetic field. • The spin texture of skyrmion is characterized by an inversion of circular polarization from the center towards the edge. • The spin texture of half-vortex is characterized with no inversion of circular polarization across the whole condensate. [ABSTRACT FROM AUTHOR]

In high-altitude areas, suppressing the flicker of methane laminar diffusion flame and reducing carbon emissions simultaneously is a challenge. This paper proposes a combustion strategy involving sub-atmospheric pressure and ammonia mixing. Through high-speed imaging and schlieren techniques, the study explores the flame flicker patterns under mixing ratios of 0–60% ammonia at 0.5–1.0 atm, as well as the structural and dynamic characteristics of shear layers and vortices. The stable combustion mechanism of sub-atmospheric pressure and ammonia mixing is also analyzed. It was found that reducing the pressure reduced the flame Richardson number, eased the formation of vortices and weakened the interaction with the flame. The heat release rate of the flame decreases after mixing ammonia, which leads to a decrease in the density gradient of the shear layer and also slows down the formation of vortices. The characteristic values of flicker were quantified. Decreasing the pressure, the flicker frequency decreases. Increasing the ammonia mixing ratio, the flicker frequency increases and the oscillation amplitude shows a highly nonlinear decreasing trend. It is verified that the flicker frequency still satisfies the function form of the Strouhal-Froude number under sub-atmospheric pressure and ammonia mixed combustion. • Established a combustion chamber capable of simulating plateau areas' pressure. • Provided vortex characteristic information through high-speed Schlieren imaging. • Complete suppression of flame flicker observed at 0.5 atm/50% ammonia mixture. • Ammonia mixture can both reduce carbon emissions and suppress flame flicker. • Pressure reduction and ammonia mixture alter density gradients in the shear layer. [ABSTRACT FROM AUTHOR]

• The effect of lower pressure on flame height and pulsation of convection-controlled diffusion flames is investigated. • Flames change from turbulent to laminar at lower pressure as does a decrease in burner diameter. • Vertical velocity of vortex structures increases at sub-atmospheric conditions. • A new dimensionless correlation is proposed to model the oscillatory frequency of diffusion flames. The oscillatory behaviour of buoyant diffusion flames plays a vital role in determining how flames evolve. Although previous studies have established an inverse square root relationship between oscillatory frequency and pool diameter, f ∼ D -1/2, few have explored the synergistic effect of diameter and reduced pressure on the pulsation phenomenon. This study mainly investigates the characteristics of convection-controlled pool fires (D < 20 cm) at varying sub-atmospheric pressures, with a particular focus on the influence of eddy effects. Four burner sizes (7 cm, 10 cm, 13 cm, and 16 cm) are selected, and pressure levels are set at 95 kPa, 80 kPa, 60 kPa, and 40 kPa, respectively. A pressure chamber, maintaining a nearly constant pressure during combustion, is employed. The morphology of diffusion flames is recorded and subsequently analysed at different pressures. The study finds that flame shapes change from turbulent to laminar as pressure decreases, which is attributed to the smaller vortex size and corresponds to the varicose and sinuous models. Flame height and oscillatory frequency show a slight increase with decreasing pressure. A new correlation based on the dimensionless Richardson number and Strouhal number is proposed to correlate the oscillation and diameter at different pressures, St = 0.58 (1 / R i) 0.54 . This study provides interesting insights into the behaviour of buoyant diffusion flames under sub-atmospheric conditions, highlighting the transition from turbulent to laminar flame shapes, changes in flame height, and pulsation frequency trends. This research could potentially contribute to the comprehension of buoyant diffusion flames at sub-atmospheric conditions in future. [ABSTRACT FROM AUTHOR]

In the present paper, we study the effect of the boundary conditions (deGennes-parameter b) on the magnetization (M), critical fields (H 1 , H 2) , and Cooper pair density ( | ψ | 2) in a three-dimensional superconducting meso-wedge, solving the time-dependent Ginzburg–Landau equations TDGL. These equations are solved by taking into account the demagnetization effects. We show that the slope of the superconducting meso-wedge can be used to control the vortex (fluxoids Φ) configurations, such as the side through which the magnetic flux enters the sample. • Mesoscopic Wedge. • There is a dependence of the slop with the first critical field. • Vortices in different layers [ABSTRACT FROM AUTHOR]

Based on National Oceanic and Atmospheric Administration (NOAA) Coral Reef Conservation Program, climate change causes coral bleaching. In response to the high roughness of coral colonies and reduced current velocity, coral reefs in near-shore regions are susceptible to accumulation of pollutants or sediments. This threatens coral reef ecosystems and causes several challenges. Controlling the wave velocity, Turbulent Kinetic Energy (TKE), and vortical structures help enhance advection/diffusion of particles from coral reef zones. In the current study, a device inspired by a marine sponge (synthetic sponge), was designed. A suction/pumping function was devised through two concentric perforated cylinders to simulate this mechanism in the synthetic sponge. Several physical and numerical experiments (using OpenFOAM software considering RANS modeling) were carried out to investigate the effects of geometrical characteristics (i.e., cylinder and perforation diameters) of synthetic sponge on wave hydrodynamics. Accordingly, wave attenuation, mean horizontal and orbital velocities, turbulent kinetic energy, and vortex structures were evaluated. In summary, the results indicated that the pumping flow can act as an energy recovery downstream of the sponge, and the horizontal velocity and TKE growing in the water column due to generation of special vortices. Therefore, the current synthetic sponge can improve momentum transfer. • Perforation diameter has 60% contribution to the mean velocity in the mid-depth. • The small annular space traps water through the two concentric cylinders. • The secondary flow generation annihilates the spiral and turbulence of flow. • The pumping flow acts as a wave energy recovery in the downstream. [ABSTRACT FROM AUTHOR]

One of the critical problems restricting the development of boundary layer ingestion (BLI) propulsion systems is the strong distortion and swirling flow in the inlet, which will threaten the stable operation of the fan. In this study, the effects of the Exit Mach number (M AIP), the ingested boundary layer thickness (δ) on the internal flow and flow distortion at the aerodynamic interface plane (AIP), are investigated under a freestream Mach number of 0.75. The experimental results indicate that a low total pressure region persistently located at the lower part of the AIP accompanied by a pair of vortices with a maximum swirl angle of 23° With the decrease of exit Mach number, these vortices move toward the center of the AIP, which decreases the total pressure distortion while increases the swirl intensity. However, as the ratio of the ingested boundary layer thickness to the inlet height (δ / h) increases from 18.6 % to 83.8 %, the length-scale of these vortices at AIP increases, leading to a descending trend of the total-pressure recovery coefficient from 0.942 to 0.871. The total pressure distortion gets intensified from 0.34 to 0.42, with the mean swirl intensity (SI mean) dropping from 8° to 6.7° The influence of the δ / h on SI mean could be attributed to the enhancement of SI in the outer ring of AIP. Meanwhile, the validated numerical results of δ / h = 83.8 % and δ / h = 43.3 % show that the vortices at AIP are originated from the coalescence of two vortices. M AIP has a substantial influence on the origin of the vortex, separation positions, and pressure distributions of the inlet. The flow separation position is associated with total pressure distortion at AIP. Further optimization design can be considered by controlling the flow separation position. [ABSTRACT FROM AUTHOR]

• Bridge piers group induced flow by three square-blocks has been investigated in this study. • A comprehensive turbulent structures analysis has been provided for the bridge-piers group induced vortices, in particular in the gap between each pier. • A full map of velocity in 3D (including in streamwise, lateral and vertical directions) and Reynolds shear stress have been provided and fully analysed. • This bridge-piers group study will fill the research gap and lead to detailed understanding on this complicated study. This paper aims to investigate the mean velocities and turbulence characteristics, which include Reynolds shear stresses (RSS) and turbulent intensities, in order to study temporal and spatial flow patterns around a complex three square-piers group. Measurements have been performed by acoustic Doppler velocimeter (ADV) to identify turbulence flow structures alteration and vortices formation in longitudinal, transverse, and vertical directions. In total, 164 locations around the bridge piers have been measured, while each location consists of no lesser than 15 vertical depth ADV data point measurements. To investigate the flow turbulence, critical locations have been observed from high vortex-influenced regions. The impacted mean velocity profiles have been compared to that at the unaffected region to study the flow alteration caused by piers group. The result reveals that the log-law layer near wall has been enhanced by the installation of pier. Furthermore, as identified from the most critical locations of turbulent structures across different measurement rows, the accelerated flow will result in lower observed turbulent structures. Although flow after each pier has been influenced by strong reversal velocities, vortices have managed to form at near wake. Analysis has been divided into inner and outer flow regions (IFR and OFR) based on flow depth to enhance the understanding of how bridge piers contribute to the development of flow turbulence. [ABSTRACT FROM AUTHOR]

• The thermodynamic effects were considered in modified Z-G-B cavitation model. • The thermodynamic effects on the evolution of cavitation structure and the propagation of cavitation noise were analyzed. • Thermodynamic effects inhibit the cavitation noise induced by baroclinic torque. Cavitation-induced vibration and noise in industrial systems have received increasing attention in recent years. In high-temperature fluid cavitation process, the influence of thermodynamic effects becomes a significant factor that cannot be neglected. Based on existing research on cavitation noise experiments conducted on orifice plates, the current study utilized large eddy simulations and the Ffowcs Williams-Hawkings formulation to simulate the cavitation characteristics and noise propagation of a single-hole orifice plate. The thermodynamic effects on the evolution of cavitation structure and the propagation of cavitation noise were analyzed. The increase in fluid temperature causes thermodynamic effects to begin to have a discernible impact and the maximum temperature difference reaches 4.208 K, influencing the growth rate of vapor volume. The vortex stretching term accounts for over 60 % of the relative energy, signifying its prominent role as the primary mechanism driving vorticity changes within the orifice. The thermodynamic effects also lead to shift in cavitation inception, with more small vortexes materializing in the cavitation zone. Cavitation noise manifests at high frequencies and exhibits monopole noise. Thermodynamic effects inhibit the cavitation noise induced by the baroclinic torque. As the relative variation rate of the baroclinic torque term rapidly decreases, the sound pressure level of cavitation noise is reduced. With the increase of fluid temperature, the sound pressure level at the orifice plate position decreased by 12 %, while downstream of the orifice plate the sound pressure level dropped by 8 %. The research presented herein significantly furthers the understanding of cavitation dynamics and the relationship between cavitation and noise. Moreover, it provides important guidance for predicting and controlling cavitation and noise propagation. [ABSTRACT FROM AUTHOR]

Vortex-induced Vibration (VIV) responses of the three-dimensional cylinders inspired by Terebridae are numerically investigated at the Reynolds number ranges of 0.8 × 104 ≤ Re ≤ 8.0 × 104. By Terebridae, we mean that inspired by its slender structural shape, and whether it can be used to improve the VIV suppression performance of the traditional structures. Three different cylinders are considered, including the smooth cylinder (T 0), the Terebridae-inspired cylinder with four-start helical ribs (T 1), and the Terebridae-inspired cylinder with six-start helical ribs (T 2). The VIV responses of T 1 and T 2 is effectively suppressed, and T 1 shows better suppression performance. The results show that the maximum cross-flow amplitude ratio of T 1 is reduced by 70.7 % compared with that of T 0 , and the maximum in-line amplitude ratio of T 1 is reduced by 85.7 % compared with that of T 0. Compared with the maximum mean-drag coefficient of T 0 , it is reduced by 44.0 % for T 1. In the high Reynolds number ranges, the galloping phenomenon does not occur for T 1 and T 2 , and the relationship between the mean-drag coefficients of T 0 , T 1 and T 2 is C d ‾ (T 2) > C d ‾ (T 1) > C d ‾ (T 0). It is found that the changes of Q-criterion vortex structure and wake flow play an important role in the VIV response. The Q-criterion vortex of T 0 is a slightly curved linear shaped, and the Q-criterion vortices of T 1 and T 2 are break up. The three-dimensional geometry of the Terebridae-inspired cylinder undermines the correlation of vortex-shedding along the span. The wake flow of T 0 can develop normally. The wake flow of T 1 quickly rolls up after passing through the top separation point, and the reattachment of the wake vortex destroys the development of the original wake flow. The continuous development of the boundary layer is destroyed by multiple Terebridae-inspired ribs of T 2 , resulting in the broken wake. Through the comparison of vortex force, it can be seen that the vortex force of T1 is significantly weakened compared to that of T 0 , and this also indicates that the three-dimensional geometry of T 1 can effectively reduce the intensity of the wake flow. • Vortex-induced Vibration (VIV) responses of the three-dimensional cylinders inspired by Terebridae are numerically investigated. • The maximum cross-flow amplitude ratio of T 1 is reduced by 70.7% compared with that of T 0. • The wake vortex of T 1 quickly rolls up after passing through the top separation point, and the reattachment of the wake vortex destroys the development of the original wake flow. • The continuous development of the boundary layer is destroyed by multiple Terebridae-inspired ribs of T 2 , resulting in the broken wake. [ABSTRACT FROM AUTHOR]

• The transient jet characteristics of gaseous ammonia fuel was investigated with LES simulation. • Sonic structures of under-expansion and instantaneous vortices was analyzed qualitatively and quantitively. • The transient propagation features of ammonia jets were compared with hydrogen jets. • Numerical results by LES and RANS were compared to exhibit jet characteristics. This study investigates the characteristics of gaseous ammonia jets under an injection pressure of 0.8 MPa and an ambient pressure of 0.1 MPa, using LES and RANS simulation approaches to inform applications of ammonia in internal combustion engines. A three-dimensional constant volume chamber model was established, and the Dynamic Structure model was applied in LES modeling with AMR techniques. The near-nozzle transient structures were successfully captured. Furthermore, a direct comparison between LES and RANS simulation was made, and main jet characteristics were investigated. LES outperforms RANS in predicting the instantaneous structures of ammonia jets and provides a more distinct visualization of oblique shock waves and diamond-like shock cells. RANS excels at displaying averaged features with a smoother distribution curve that represents self-similar characteristics. Additionally, the transient characteristics of ammonia and hydrogen jets were compared. The vortex formation and mixing process in ammonia jets occur at a much slower rate compared to hydrogen jets. Meanwhile, transient vortex ring behaviors were analyzed in detail, including their development tendencies regarding initial, secondary, and broken vortex formation. It is revealed that petal-like swirling movements are strongly correlated with the air–fuel mixing process. [ABSTRACT FROM AUTHOR]

• We propose a novel methodology to design polarized multiplexing multifunctional metasurfaces. • This approach integrates multiple vortex modes into a single-layer metasurface. • The generated vortex beams have the characteristics of longitudinal evolution in three polarization channels. • This approach provides a new option for the research of integrated optics. Vector vortex beams with special irregular spatial polarized distribution have attracted considerable research attention. Here, we demonstrate a new methodology to design multifunctional metasurfaces with capabilities of generating different vector vortex beams in orthogonally polarized channels. The metasurfaces are designed by using polarization and spatial multiplexing. We craft three metasurfaces that generating vector vortex beams with properties of evolving longitudinally under left circularly polarized incidence. When right circularly polarized incidence, the metasurfaces generate the switches of multiple vortex modes with special evolution laws. The proposed design methodology provides convenience and versatility to polarization multiplexing functional metasurfaces, which offers a robust foundation for advancing research in optical metasurfaces and vector vortex beams. [ABSTRACT FROM AUTHOR]

Unbaffled U-shaped mesoscale oscillatory flow reactors (meso-OFRs) were developed to prevent solid deposition and prepare uniform barium sulfate (BaSO 4) nanoparticles with environmental protection function. The results showed that the oscillation significantly reduced granular deposition; the greater the intensity of the oscillation, the faster it reached uniformity, and the less likely the granules were to be deposited. These results can be explained by the formation of a larger vortex size, which can strengthen the turbulent mixing of fluid in the reactor, promote the interaction and forced mixing between the liquid phase and solid particles, enhance the internal shear stress of the fluid, and contribute to the secondary suspension of solid particles and the disintegration of particle agglomeration. The prepared BaSO 4 nanoparticles with oscillation were smaller in size and lower in pressure drop than those produced without oscillation, which conclusively illustrated that oscillation effectively prevented channel deposition and clogging. [Display omitted] • The meso-OFR could prevent solid deposition and prepare uniform nanoparticles. • The formation of vortex contributed to the secondary suspension of solid particles. • The prepared BaSO 4 nanoparticles were smaller in size and lower in pressure drop. [ABSTRACT FROM AUTHOR]

• Microstructures with efficiency enhancing functions have been applied for the first time in gas wave refrigerators. • Clarified the main forms of fluid mass transfer loss caused by vortices during the operation of the air wave machine. • The isentropic expansion efficiency of the gas wave refrigerator can be boosted by up to 19.04 % and temperature drop of 3℃ by the microstructure designed. Wave rotor refrigerator (WRR) is a device that uses compressed flow and pressure wave to produce low-temperature gas. When the high-pressure nozzle gradually approached the wave tube, two vortices are generated in the high-pressure gas incidence stage which caused jet mass transfer loss, which is an important factor that causes the loss of cooling efficiency of the wave rotors. By studying the utility of microstructures in fluid mass transfer field, a method for improving the cooling efficiency of WRR from the mesoscopic aspect has been proposed. The addition of microstructures has the effect of hindering the development of vortices in the tubes. The optimal size parameters of the microstructure were found, and feasible processing conditions were synthesized through numerical simulation. And then, a wave rotor with the microstructure was created, and a comparative test was performed. The results reveal that the rotor with microstructure efficiently undercut the vortices in the tubes and increased the expansion depth of the high-pressure gas, consequently boosting the WRR's cooling performance. With varying pressure ratios and rotational speeds, the approach has a gain impact. When the pressure ratio reaches 2.6 and the relative rotating speed reaches 2900 rpm, the isentropic expansion efficiency of this type of WRR can be boosted by up to 19.04 %, and the temperature drop is increased by a maximum of 3℃, which is significant for reducing jet loss and promoting efficiency for the wave equipment. [ABSTRACT FROM AUTHOR]

Large-scale nondestructive aggregation of micro-particles is essential for cell detection, microplastics removal and micro- and nano pharmaceuticals. To achieve this goal, this work proposes a method by creating a vortex region in the fluid field using low-frequency oscillation of a piezoelectric cantilever beam probe structure. Vibration of the probe agitates the liquid, creating a horseshoe-shaped vortex in the fluid field. This facilitates the movement of micro-particles and traps them. Using polystyrene microspheres with a diameter of 20 µm and pollen (20–40 µm) as aggregated objects, particle agglomeration tests and flow field PIV tests are performed. Experimental results confirm that the designed structure has the best performance with a driving voltage of 100 V and a driving frequency of 72 Hz. The maximum aggregation area of polystyrene and pollen is 106956 µm2 and 234750 µm2. There are symmetrical large vortices regions on both sides of the probe and small vortices zero vorticity near the free end of the probe. It is also confirmed that small vortices are the root cause of microparticle aggregation. The aggregation method proposed in this study has advantages of low cost, non-selectivity of characteristics for controlled samples, large manipulation area and low power consumption (0.42 W). [Display omitted] • The aggregation of microparticles is realized by using the vortex of the flow field. • The edge-based image segmentation is conducted to character the aggregation results of microparticles. • The PIV experiment revealed the distribution of vortex in the flow field when the microparticles are aggregated. [ABSTRACT FROM AUTHOR]

Multiple pipes bundled with a certain distance are used for deep ocean development for such as lifting seafloor massive sulfides (SMS), pumping up a large amount of cooling water for onboard natural gas liquefaction, and production of oil/gas. To understand the vortex-induced phenomenon of fluids and the structural mutual interference among pipes in a steady flow, a towing tank test using a model of two vertical elastic pipes in tandem is performed. The parameters of this test are: the distance between the two pipes, the incident angle of crossflow with the inline direction of the pipes, the flow velocity (towing speed), and the boundary conditions of the tops of the pipes. The two horizontal accelerations of the towing direction and perpendicular direction are measured with synchronization. Then, the motion of the two pipes in each direction was measured, and the influence of the distance between the two pipes on the motion from the amplitude and phase information was analyzed. The results are investigated relatively in detail about the tandem arrangements of the two pipes to the incident flow. It is found that the major motion pattern of the two pipes in the tandem case is a rotational motion around the midpoint of two pipes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A baffled channel with adjustable baffle inclined angle was designed for dedusting. • Coupling CFD-DEM approach was employed for the particle flow around baffles. • The flow in a baffled channel was dominated by complex vortexes. • Vortex flow provided the particles with longer residence time in the channel. One problem in the industrial dedusting process is the removal of fine particles, such as PM 2.5. The gas flow features and subsequent particle behavior in a designed baffled deduster channel were numerically investigated in this study. By means of the coupling of computational fluid dynamics (CFD) and discrete element method (DEM), the key fluid flow patterns, vortex characteristics, and particle behaviors around the baffles were successfully captured. Effects of the baffle inclined angle on the velocity field, pressure drop, and vortex characteristics were analyzed. The results showed that the "dead zone" with low flow velocity was significantly improved with the baffle inclined angle approaching 90°. In addition, small-size particles were found to tend to enter the vortex region while large-size particles were more likely to collide with the walls or baffles. The outcome would provide references and inspirations for the development of novel dedusting technologies. [ABSTRACT FROM AUTHOR]

In this study, the effects of adding trapezoidal ribs to microchannel on functionalized multi-walled nano-tubes/water nanofluid heat transfer are examined. The dimensionless slip coefficient (0–0.1), Reynolds number (50–400) and Hartmann number (0–20) are considered as independent variables and the heat transfer along with the entropy generation are considered as the output parameters. The simulation outcomes confirm that the addition of trapezoidal ribs, on the one hand, increases the heat transfer area and, on the other hand, intensifies the possibility of vortex formation. The presence of a vortex decreases the heat transfer potential and thus reduces the performance of the trapezoidal-wall microchannel compared to the base one. With increasing Reynolds number (Re), the probability of vortex formation intensifies, which in turn diminishes the positive effects of using trapezoidal ribs. However, it is found that, with increasing Hartmann number (Ha) and dimensionless slip coefficient ( β ∗ ) , the vortex strength is weakened, and consequently heat transfer is improved. Based on numerical computations, it is found that at Re = 400, Ha = 0 and β ∗ = 0 and adding trapezoidal ribs to the base microchannel increases heat transfer by 11.12%. [ABSTRACT FROM AUTHOR]

The idea of using the compact device with higher heat transfer potential has encouraged researchers to use microchannels. Creating sinusoidal walls is a technique leading to better effectiveness and smaller size. In this study, the effects of discrete heat sources location on heat transfer and pressure drop are investigated, using graphene nanoplatelets/water inside a sinusoidal microchannel. For this, discrete heat sources are installed in a smooth microchannel (layout A) and compared with two sinusoidal-wall microchannels. In layouts B and C, the heating sources are installed above the convergent/diverging sections, respectively. Since the velocity and temperature gradients are higher in the converging region, the heat exchange and pressure drop for layout B are greater than other ones. In other words, installing heating sources in these regions with high-temperature gradient has a more obvious positive efficacy on heat exchange. For the best layout (B), although the heat exchange compared to the base layout (A) is 37.5% higher, the pressure drop and entropy generation are higher by 79% and 35.2%, respectively. By introducing a new figure of merit (FOM), it is found that layout B is in the desirable zone. [ABSTRACT FROM AUTHOR]

The propeller wake can cause vibrations on the rudder surface, which worsen the noise and reliability. The vibration monitoring of the rudder operating in the propeller wake with fluid-structure interaction (FSI) method is still challenging. In the present study, the structural response during propeller-rudder interaction is investigated using detached eddy simulation. Three-dimensional distributions of loads, stresses, and deformations are discussed. The leading and trailing edges exhibit the strongest deformations in opposite directions, which are S-shaped. The strongest lateral deformation occurs between the tip vortex and hub vortex regions. In the tip vortex region, the dominant lateral vibrations fluctuate at the blade passing frequency (BPF) and shaft frequency (SF). However, the 75 Hz-fluctuation becomes significant at the trailing edge of the rudder. In the hub vortex region, the lateral deformation fluctuates mainly at 75 Hz except the area near the leading edge. There are weak vibrations occurring at the natural frequencies of the rudder when the natural frequencies of the rudder are much higher than the SF and BPF. However, the plate in the propeller suffers intense vibrations at the frequencies near the natural frequencies, where the natural frequencies of the plate are close to SF and BPF. [ABSTRACT FROM AUTHOR]

We propose an experimentally feasible scheme for generating genuinely tripartite entanglement in a hybrid quantum system which consists of topologically protected particle-like excitations (magnetic vortices), cavity microwave photons, and solid-state spins (NV centers in diamond). The magnetic vortices and solid-state spins are simultaneously coupled to the microwave cavity photons via magnetic dipole interaction. By introducing a microwave modulation to the collective spins and under appropriate parameter regimes, we find that the steady state of the system is a genuinely tripartite entangled state where vortices, cavity photons, and spins are entangled with each other. The effect of the introduced modulation on the produced entanglement is analyzed, and we also show that the entanglement is robust against dissipation. This work may offer a promising platform for studying macroscopic quantum effects and quantum information processing with the vortex–photon–spin system. [ABSTRACT FROM AUTHOR]

• Frozen water droplets can serve as vortex generators (VGs) to increase air-side heat transfer. • Hemispherical domes (i.e. model droplets) were simulated numerically to quantify performance. • Ten different configurations were investigated with the staggered VG pattern performing better than the inline pattern. • Changing the longitudinal spacing between VGs led to better performance. • Heat transfer enhancements from 14.0 to 75.9% were observed with pressure drop penalties from 35.7 to 165.6%. In this study, a novel technique for deploying hemispherical vortex generators (VGs) aimed at heat transfer enhancement via the naturally-occurring processes of condensation and freezing was proposed and investigated. By using patterned surface wettability to collect condensate and encourage coalescence in predetermined locations, it was hypothesized that large frozen droplets could be formed in various configurations which could serve as VGs. This approach was simulated numerically in the present communication (Part II) and examined experimentally in a previous study (Part I). For the CFD simulations, ten different configurations in channel flow emulating a fin density of 5 FPI were investigated. Inlet air velocities of 1.0 and 2.0 m s−1 at 20°C were examined for the flow through the channel where the walls and VGs were set to -9°C to match the experimental conditions used in Part I. The air-side heat transfer coefficient, pressure drop, and temperature changes were then calculated after a converged solution was reached. Compared to a baseline configuration without VGs, heat transfer enhancements ranging from 14.0 to 75.9% were observed, with corresponding pressure drop increases (or penalties) ranging from 35.7 to 165.6%. [ABSTRACT FROM AUTHOR]

Objectives: Compare the intraventricular hemodynamics of 60 females with systemic lupus erythematosus (SLE) and 61 healthy female controls, and determine cardiac function changes using vector flow mapping (VFM). Methods: To determine the effect of pulmonary artery pressure changes on left ventricular function, SLE patients were divided into a normal pulmonary artery pressure group (S1, n=24) and an elevated pulmonary artery pressure group (S2, n=36). The energy loss (EL) at each segment of the left ventricular chamber (total, basal, middle, and apical segments) during each period of the cardiac cycle (isovolumic contraction, rapid ejection, rapid filling, reduced filling, atrial contraction) was determined. Results: The S1 group had significantly more vortices than the control group during the rapid ejection, rapid filling, and atrial contraction periods (p<0.01), and the maximum vortex areas in the S1 and S2 groups were smaller than in the control group during rapid filling and atrial contraction periods (p<0.05). Compared with the control group, the S2 group had greater EL during the systole and diastole periods (p<0.01). EL in the S1 group was significantly greater than in the control group during systole (p<0.01). During the rapid filling period, the EL was positively correlated with septal E′ (r=0.784, p<0.01), and during the atrial contraction period, EL was positively correlated with septal E/e′ (r=0.812, p<0.01) and A (r=0.715, p<0.01). Conclusion: VFM of patients with SLE can comprehensively, rapidly, and efficiently evaluate changes of myocardial mechanics and intracardiac hemodynamics and provide quantitative analysis of complex intracardiac blood flow. Key points • Vector flow mapping (VFM) is a new non-invasive ultrasound technique that evaluates changes of myocardial mechanics and intracardiac hemodynamics, and provides quantitative analysis of complex intracardiac blood flow. • This study showed that vortex and energy loss may provide more sensitive detection of cardiac dysfunction than conventional echocardiographic indexes in patients with systemic lupus erythematosus. [ABSTRACT FROM AUTHOR]

We measured the horizontal winds in Jupiter's Great Red Spot (GRS) using data from the WFC3/UVIS instrument on board the Hubble Space Telescope (HST). The data cover 11 epochs from 2009 to 2020. Long‐term monotonic trends in size and shape previously noted from the visible cloud appearance are paralleled by changes in the high‐speed ring around the vortex. The circularization of the GRS cannot be explained by changes in the horizontal wind shear of the surrounding environment. The velocity fields suggest no long‐term trend in the static stability inside or outside the vortex. Instead, the changes are accompanied by a 4%–8% increase in the mean wind speeds of the high‐speed ring from 2009 to 2020. Changes in the wind field coincided with the South Equatorial Belt Outbreak storms of 2016–2017, but not with 2019 "flaking" events involving detachment of red material from the main oval. Plain Language Summary: We measured the horizontal winds in Jupiter's Great Red Spot (GRS) using data from the WFC3/UVIS instrument on board the Hubble Space Telescope (HST). The data cover 11 time periods from 2009 to 2020. Winds blow fastest in a high‐speed ring around the outside of the GRS. Previous pictures of the clouds showed that the GRS was shrinking and becoming more like a circle and less like an oval. We measure similar changes in the high‐speed ring. We rule out some possible causes for the changes: changes in the wind shear of the surrounding atmosphere, or changes in how temperature varies with height. As the GRS shrinks and circularizes, the average wind speed in the high‐speed ring gets faster. Some changes in the GRS wind patterns happened at the same time as a giant nearby storm in 2016/2017, but we did not find changes at the same time as flaking events in 2019. By "flaking" we mean pictures showing that small areas of red, normally kept inside the GRS, detached and blew away from the spot. Key Points: A high‐speed ring marking the edge of the Great Red Spot velocity field has been shrinking and circularizing at a roughly constant rateMean wind speeds within the high‐speed ring have increased by 4%–8% from 2009 to 2020, at a roughly constant rateVelocity field changes coincided with a major 2016 storm, but we found no changes in 2019 when red material flaked away from the main oval [ABSTRACT FROM AUTHOR]

Abrasive flow precision machining technology is an effective technology for precision machining special-shaped curved surface products in the mechanical field. In order to explore the vortex formation mechanism of special inner curved surface machined by abrasive flow precision machining, taking the polygonal spiral curved surface tube as the research object, the large eddy simulation method is used to analyze the precision machining behavior of abrasive flow and the effect of vortex cluster on the wall under different inlet pressure. The motion law of abrasive is expounded, the formation mechanism of the fluid vortex is revealed, and the mechanism of abrasive micro-cutting is discussed. The results show that the inlet pressure of abrasive flow plays an important role in the machining quality of abrasive flow. With the increase of inlet pressure, the precision machining quality of abrasive flow is improved accordingly. Properly increasing the inlet pressure of the abrasive flow can effectively improve the inner surface machining quality of the polygonal spiral curved surface tube, and the abrasive flow precision machining technology can obtain the ideal surface quality and improve the surface accuracy of the machined workpiece. [ABSTRACT FROM AUTHOR]

A novel cooperative injection and suction jet was employed in this work to improve the power extraction characteristics of a semi-active flapping airfoil (S-AFA). The combined Taguchi method and numerical simulations was used to optimize the characteristic parameters of the cooperative injection and suction jet that affect the power extraction characteristics of the S-AFA. Under the Reynolds number of 6 × 104 and the pitching axis location at the center of the ellipse airfoil, the effects of jet position, jet width, jet coefficient as well as phase difference between the cooperative injection and suction jet and the active pitching motion on the power extraction characteristics of the S-AFA are systematically examined. It is concluded that the power extraction characteristics of the S-AFA can be enhanced by employing cooperative injection and suction jet. Compared to the S-AFA without jet, the maximum efficiency is increased 11.06% for the S-AFA with optimized cooperative injection and suction jet. The flow structure behavior analysis shows that the vortex strength, the low pressure range in the suction surface of the airfoil as well as the pressure value in the pressure surface of the airfoil are increased due to the cooperative injection and suction jet, and it is why the power extraction characteristics of S-AFA can be improved. [ABSTRACT FROM AUTHOR]

In order to explore the flow interaction between the oscillating jet of the fluidic oscillator and the crossflow with different crossflow Mach numbers, the transient flow fileds are numerically studied under the nozzle pressure ratio（NPR）of 1.5, 3.0 and the crossflow Mach numbers of 0, 0.2, 0.4, 0.6, 0.8. The effects of crossflow on the internal oscillation features of the fluidic oscillator, as well as the downstream flow interaction characteristics between the oscillating jet and the crossflow, are analyzed. The results show that when NPR=1.5, the Mach number at the secondary throat of the fluidic oscillator is less than 1, the disturbance from the crossflow will affect the internal oscillation frequency of the fluid oscillator; when NPR=3, since the Mach number at the secondary throat of the fluidic oscillator is greater than 1, the disturbance from the crossflow will be effectively isolated. When NPR=3 and the crossflow Ma is 0.2, there are two pairs vortices of downstream flow fields with opposite rotating directions, among which the upper one is the vortex pair induced by the oscillating jet, and the lower one is the horseshoe vortex pair; when the crossflow Mach number exceeds 0.4, there is only a pair of vortices in the downstream space, and the vortex can effectively divert the low-energy flow at the center of the cross-section and make the velocity profile of the boundry layer fuller, shape factor smaller; with the increase of the crossflow Mach number, the momentum ratio of the jet to the crossflow, the penetration depth of the jet and the spanwise influence range of the jet decrease. [ABSTRACT FROM AUTHOR]

Background: The interest in intra‐cardiac blood flow analysis is rapidly growing, and it has encouraged the development of different non‐invasive imaging techniques. Among these, Vector Flow Mapping (VFM), combing Color‐Doppler imaging and speckle tracking data, seems to be a promising approach, feasible in adult and children population. Aim of the review: The aim of this review is to give a historical perspective on the development of VFM method and a summary of the current algorithms and parameters potentially evaluable. Then, we will present the current state‐of‐the‐art of VFM with an overview of clinical studies and applications of this technique. [ABSTRACT FROM AUTHOR]

We study the vortex dynamics of spin-orbit-coupled (SOC) spin-1 Bose-Einstein condensates by numerical simulations of the Gross-Pitaevskii equation. We consider three types of SOC, Rashba, Dresselhaus and an equal mixture of Rashba and Dresselhaus. Different vortex structures and vortex formation process are observed by means of the density distribution, time evolution of the angular momentum per atom and root-mean-square in each component. Our results shows that the type and strength of SOC play a significant role. [ABSTRACT FROM AUTHOR]

The flow pattern around the cylinder body is a very serious problem and this problem may become more serious and sensitive, when we place a vane neighboring to the cylinder. The present paper deals with the vane impact on the flow pattern around the cylinder. To investigate this problem the ANSYS fluent software is employed in order to achieve the two dimensional numerical analysis. Here, Reynolds Average Navier Stokes model is adopted. The investigation comprises the following hydraulic variables, like eddy viscosity, turbulent intensity, turbulent kinetic energy, turbulent dissipation rate, flow velocity profile, static pressure and pressure coefficient. The constant flow velocity, cylinder diameter and vane dimension are adopted in this analysis, while the different certain distance between the vane and the cylinder is considered. The used vane has a rectangular shape. In this analysis, it is clear that the vane plays a sensitive vital role in the hydraulic behavior of the flow pattern around the cylinder. The study has taken up four distances between the vane and the cylinder, these distances is a function of the cylinder diameter, in addition to the direct touch that happens between the vane and the cylinder. The analysis also shows that when the cylinder has direct touch with the vane, the dramatic reduction will occur in hydraulic variables. [ABSTRACT FROM AUTHOR]

In study, flow structures around buildings placed triple-diagonal and 7.5 cm and 10 cm distances between buildings with dimensions of 5cmx5cmx5cm without roof were investigated as experimental by using Particle Image Velocimetry (PIV) technique. Besides, flow analysis vicinity one building without roof as numerical with ANSYS Fluent program having steady, three dimensional, k-ε turbulence model was done and the attained results were matched with these of experimental. In the work, distributions of streamline <ψ> and velocity vectors were drawn and average equivalent velocity curves were researched for different distances between buildings. It was determined that jet flow region fairly enlarged at 10 cm distance according to distance of 7.5 cm and flow separation area around building placed as diagonal shrank. However, it was found that there is at most a 3% differences between experimental and numerical results. [ABSTRACT FROM AUTHOR]

Pursuing topological phases in natural and artificial materials is one of the central topics in modern physical science and engineering. In classical magnetic systems, spin waves (or magnons) and magnetic solitons (such as domain wall, vortex, skyrmion, etc.) represent two important excitations. Recently, the topological insulator and semimetal states in magnon- and soliton-based crystals (or metamaterials) have attracted growing attention owing to their interesting dynamics and promising applications for designing robust spintronic devices. Here, we give an overview of current progress of topological phases in structured classical magnetism. We first provide a brief introduction to spin waves and their band structure in periodic lattices. Then, we elaborate typical topological invariants and pedagogical models that are important to understand the topological nature of magnons, such as the magnon Hall effect, topological magnon insulators, Dirac (Weyl) magnon semimetals, topological magnon polarons (magnon–phonon​ hybrid excitations), and higher-order topological magnons. Appealing proposal of topological magnonic devices is also highlighted. We then review the collective-coordinate approach for describing the dynamics of magnetic soliton lattice. We focus on the topological properties of magnetic solitons, by theoretically analyzing the first-order topological insulating phases in low dimensional systems and higher-order topological states in breathing crystals. Finally, we discuss the experimental realization and detection of the edge states in both magnonic and solitonic crystals. We remark the challenges and future prospects before concluding this article. [ABSTRACT FROM AUTHOR]

Spin‐controlled vortex generation and spin‐Hall effect, two distinct effects discovered in optics, have been extensively studied recently. However, while physical origins of two effects are both due to spin‐orbit interactions, their inherent connections remain obscure which also hinders further explorations on the manipulations of them. Here, in studying the scattering of a spin‐polarized light beam at sharp interfaces, an intriguing phase transition between vortex generation and spin‐Hall shift trigged by varying the incidence angle is revealed. After reflection/refraction, the beam contains two components: normal and abnormal modes acquiring spin‐redirection‐Berry phases and Pancharatnam–Berry phases, respectively. Inside the abnormal beam, two classes of wave components gain Pancharatnam–Berry phases with distinct topological natures, generating intrinsic and extrinsic orbital angular momenta (OAM), respectively. Enlarging incidence angle changes the relative portions of these two contributions, making the abnormal beam undergo a phase transition from vortex generation to spin‐Hall shift. Such intriguing effect is experimentally observed at a purposely designed metamaterial slab, exhibiting efficiency enhanced by several‐thousand times compared to that at a conventional slab. These findings unify two previously discovered effects in a single framework, reinterpret previous results with clearer pictures, and shed light on understanding other physical effects involving the competition between intrinsic and extrinsic OAM. [ABSTRACT FROM AUTHOR]