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In this paper, we present a numerical investigation into the influence of electric and magnetic fields on the dynamics of a suspended liquid film that carries an electric current. A nonuniform magnetic field is considered utilizing a disk-shaped magnet located above the two-dimensional fluid. Electric and magnetic forces exerted on the fluid induce a new dynamical features. We perform a numerical study of the dynamics of such two-dimensional fluid system commonly named Liquid Film Motor. The presence of the nonuniform external magnetic field causes changes in the fluid’s behavior. Specifically, the previously symmetric vortex becomes asymmetric under the influence of the magnetic field. In this dynamic behavior, as the external magnetic field increases, the center of the vortex shifts in a direction perpendicular to the electric current passing through the fluid film. The unique combination of electric and magnetic field allows to manipulate the motion of the vortex without resorting to traditional mechanical methods. This finding implies that the motion of the vortex can be directed and controlled by adjusting the strength of the external magnetic field, without the need for direct contact with the fluid or mechanical tools. [ABSTRACT FROM AUTHOR]

Unstable flows in the runner of water turbines, such as reverse flow, vorticity and flow direction transition, are the main factors causing increased losses and decreased efficiency, and changing the geometry structure in the downstream of the runner is an important means of mitigating these instabilities. The different flow fields downstream of runners induced by different locking nut structures are numerically calculated and verified by experimental results. The flow states are evaluated in terms of characteristic quantities such as pressure gradient, swirling flow, reverse flow, and vorticity. The results show a non-negligible effect of the locking nut, which leads to a more uniform pressure distribution, increases the descending speed of the reverse flow rate, and reduces the volume and strength of the vortex. The small locking nut significantly weakens the pressure gradient, reduces the top reverse flow zone, and decreases the vortex volume at the blade flow passage outlet and the size of the downstream disturbance vortex. The extended lock nut reduces the growth rate of the vortex generation rate and the size of the partial vortex, but increases the range of the high-pressure zone, causing the bottom reverse flow and increasing the vortex. [ABSTRACT FROM AUTHOR]

The paper proposes a theory of similarity of quasi-geostrophic vortices against the background of large-scale flows. This information is useful when planning laboratory and numerical experiments to study mesoscale and submesoscale vortex dynamics of vortices interacting with currents. Special attention is paid to studying geometric similarity of phenomena. It is revealed that the complete set of dimensionless similarity numbers of baroclinic vortices includes four dimensionless parameters: the dimensionless intensity of the vortex, the geometric similarity of the background flow (the ratio of the relative vorticity to the deformation coefficient of the background flow), the coefficient of horizontal stretching of the vortex core, and the coefficient of vertical oblateness of the vortex core coinciding with the Burger number. To describe the similarity of barotropic vortices against the background of barotropic flows, the number of necessary dimensionless parameters is reduced by one number: the coefficient of vertical oblateness of the vortex core is eliminated from consideration. When studying axisymmetric vortices or vortex structures close to axisymmetric, another geometric parameter of the vortex is eliminated from consideration—the coefficient of horizontal stretching of the vortex core. As a result, the maximum possible set of similarity parameters includes four dimensionless numbers, and the minimum is two. [ABSTRACT FROM AUTHOR]

The evolution of unforced and weakly damped two-dimensional turbulence over random rough topography presents two extreme states. If the initial kinetic energy E is sufficiently high, then the topography is a weak perturbation, and evolution is determined by the spontaneous formation and mutual interaction of coherent axisymmetric vortices. High-energy vortices roam throughout the domain and mix the background potential vorticity (PV) to homogeneity, i.e., in the region between vortices, which is most of the domain, the relative vorticity largely cancels the topographic PV. If E is low, then vortices still form but they soon become locked to topographic features: Anticyclones sit above topographic depressions and cyclones above elevated regions. In the low-energy case, with topographically locked vortices, the background PV retains some spatial variation. We develop a unified framework of topographic turbulence spanning these two extreme states of low and high energy. A main organizing concept is that PV homogenization demands a particular kinetic energy level E#. E# is the separator between high-energy evolution and low-energy evolution. [ABSTRACT FROM AUTHOR]

Here we consider a model of an isolated vortex to understand the vertical dynamics induced by mesoscale eddies in the ocean. We use the analytical solutions to a balanced model for an ellipsoid of uniform potential vorticity to examine how the vertical motions induced depend on the vortex shape and its orientation, i.e. whether the vortex is vertically upright or tilted with respect to the vertical axis. The motion induced by the vortex can be divided into two kinds: (1) the interior flow which acts on the vortex itself and (2) the exterior flow which acts on its surroundings. For an upright ellipsoid, there are no self-induced vertical motions and the vortex rotates steadily about the vertical axis. However, for a tilted ellipsoid we find solutions exist where the vortex rotates about the vertical axis, while the vertical motions cause the tilt angle of the vortex to oscillate. This effect is stronger as the tilt angle is increased. Considering the exterior flow, there exists an exterior vertical velocity for the upright and tilted ellipsoids. However, the dynamics induced by the exterior vertical velocity is very different for the upright and tilted cases. We find that for an upright ellipsoidal vortex, the vertical motions are largest for vortices with high horizontal eccentricity and a vertical height-to-width aspect ratio near unity, vanishing as the horizontal cross-section of the vortex becomes circular. Instead for the tilted case, the vertical motions are largest when the horizontal cross section is circular, and for strongly prolate vortices, with the largest vertical motions occurring when the tilt angle is 45 ∘ . [ABSTRACT FROM AUTHOR]

The article discusses various aspects of the interaction of vortices with the barotropic flow. Vortex interaction with a flow results in rotation variants, nutational oscillations, and unlimited stretching of its core. The vortex remains in a localized formation, with the semi-axes of the ellipse experiencing fluctuations near an average value in the first two cases. In the third case, the vortex is significantly elongated, and its shape in the horizontal plane changes as follows: one axis of the ellipse increases, and the other decreases. In this case, the vortex, when viewed from above, stretches into a thread, while remaining ellipsoidal. These vortex formations are called filaments. The latter arise from initially almost circular vortices in the horizontal plane and represent structures with non-zero vorticity elongated in one direction. Here, we aim to study the energy transformation of a vortex during its evolution process, mainly due to changes in its shape by stretching. The energy evolution of a mesoscale vortex located in the Norwegian Sea is analyzed using GLORYS12V1 ocean reanalysis data to verify the theoretical conclusions. During the evolution, the vortex is found to transform from a round shape and becomes elongated, and after three weeks its longitudinal scale becomes 4 times larger than the transverse one. During the transformation of a vortex, the kinetic energy and available potential energy decrease respectively by 3 times and 1.7 times. Concurrently, the total energy of the vortex is found to decrease by 2.3 times. We argue that the stretching of vortices results in a loss of energy as well as its redistribution from mesoscale to submesoscale. The lost part of the energy returns to the flow and results in the occurrence of the reverse energy cascade phenomenon. [ABSTRACT FROM AUTHOR]

This paper presents a critical evaluation of the physical aspects of lift generation to prove that no lift can be generated in a steady inviscid flow. Hence, the answer to the recurring question in the paper title is negative. In other words, the fluid viscosity is necessary in lift generation. The relevant topics include D'Alembert's paradox of lift and drag, the Kutta condition, the force expression based on the boundary enstrophy flux (BEF), the vortex lift, and the generation of the vorticity and circulation. The physical meanings of the variational formulations to determine the circulation and lift are discussed. In particular, in the variational formulation based on the continuity equation with the first-order Tikhonov regularization functional, an incompressible flow with the artificial viscosity (the Lagrange multiplier) is simulated, elucidating the role of the artificial viscosity in lift generation. The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics. [ABSTRACT FROM AUTHOR]

The Liutex vector is new quantity introduced to represent the rigid-body rotation part of fluid motion and thus to define and identify vortices in various flows. In this work, the intermittency and power-law similarity of the Liutex vector in homogeneous, isotropic turbulence and a turbulent channel are explored. First, we found that the Liutex vector is more intermittent than the vorticity vector in the considered turbulent flows, which indicates that an iso-surface of a Liutex magnitude with an appropriate threshold could capture the major rotating motions or vortical motions of the flow. Second, the three-dimensional energy spectrums of velocity, vorticity (enstrophy spectrum) and the Liutex vector in homogeneous isotropic turbulence are shown to exhibit power laws of −5/3, 1/3 and 1/3 in the inertial subrange, respectively, whilst the Liutex energy spectrum particularly satisfies an additional −10/3 power law in the viscous subrange. This viscous similarity of the Liutex vector is the only power law that survived from the wall presence and is argued to originate from the fact that the Liutex vector represents the rigid part of fluid motion and is free from any shear contamination. The existence of such a viscous similarity law indicates a certain coherence of the small scales of turbulence and could possibly help understand and model turbulence. [ABSTRACT FROM AUTHOR]

The regular polygons of circumpolar cyclones, discovered by Juno in 2017, are one of the most puzzling features of Jupiter. Here we show new recent global pictures of the North polar cyclones' structure. These are the first simultaneous images of the whole structure since 2017, and we find that it remained almost unperturbed, just like the South one. The observation of these long‐lasting structures poses questions regarding the formation mechanism of cyclones, and on their vertical structure. Data by Juno/JIRAM infrared camera collected over the last 5 years show that cyclones migrate around what may seem like equilibrium positions, with timescales of a few months but, aside from that, the cyclones systems are very stable. Our analysis of the observations shows that the motion of cyclones around their equilibrium position is uncorrelated with their position if a barotropic approximation (β‐drift) is assumed. Thus, a different dynamical explanation than the barotropic β‐drift is needed to explain the stability of the observed features. Each cyclone has a peculiar morphology, which differs from the others and is stable over the observed lapse of time in most cases. Plain Language Summary: In 2017, Juno discovered that the poles of Jupiter are occupied by regular polygons of cyclones. Here we report 5 years of observations of these cyclones by JIRAM, the infrared imaging spectrometer on board Juno. In particular, we show the latest observations of the North Pole cyclones structure. In fact, this structure has only been partially observed since its discovery 5 years ago. One important question is how these structures of cyclones form, and if they are stable. We find that both remained almost unperturbed. Hence, we show that these cyclones may have very long lifetimes. Cyclones migrate around what may appear to be equilibrium positions. The scale time is a few months. We analyzed the movement of cyclones and compared it with a model where winds don't change with depth (a barotropic model). We found that the motion of the cyclones is not related to their position according to this model. We conclude that a different model is needed to explain some of the observed characteristics. Each cyclone has a peculiar morphology, which differs from the others and is stable over the observed time span in most cases. Key Points: For the first time after 5 years, we show a global picture of the North polar cyclones' structure, which has remained almost unperturbedEach cyclone has a peculiar morphology, which differs from the others and it is stable over the observed lapse of timeBeta‐drift is not responsible for the motion of the vortices on timescales of months [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]

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]

To assess unsteady vortex interaction between rim seal purge flow and upstream stator, numerical investigations were conducted under different purge flow rates. The vortex distributions for the stator and cavity were investigated and the interaction processes near the cavity exit, in particular the vorticity change resulting from the ingress and egress, were analyzed. Results show the intensity of hub passage vortex (HPV) and hub trailing shedding vortex (HTSV) at stator exit is decreased as a consequence of enhancing blockage effects caused by the egress flow. However, when the purge flow rate increases, from stator exit to downstream of cavity exit, the reduction in the intensity of two vortices is weakened as the extrusion of egress flow thins their vortex tubes. The vortex inside the cavity is generated as the combined effect of relative rotation of cavity walls and nonuniform circumferential pressure mainly imposed by upstream stator. The ingress leads the positive axial vorticity near the stator hub to ingest into the cavity and eject into the main passage due to the blockage of purge flow. Furthermore, the interaction between the ingress of the mainstream and purge flow produces local negative axial vorticity. The egress flow carries negative axial vorticity mainly originated from the rotational cavity wall, and enters into the main flow passage near the rotating hub, then locations of HPV and HTSV move to the mid-span slightly with the extrusion of egress flow. [ABSTRACT FROM AUTHOR]

A rotating mass of fluid is known as vortex and the motion of the rotating mass of fluid is known as vortex motion. Vorticity is the circulation per unit area. In this research simulation of a vortex chamber is to be carried out in ANSYS CFD taking water as fluid domain for generating a water vortex that is capable enough to move a turbine for electricity generation. The CAD modelling of the setup was set down and simulation was done in fine mesh by taking suitable wall function in the model of a cylindrical chamber along with a rectangular channel with a contraction portion at the end of it where good amount of vortex generation was acquired by observing velocity and pressure by setting different parameters. The results shows the pressure and velocity contours with 3D velocity streamline flow and the curve of the velocity and pressure curve shows the decrease of pressure and increase of velocity from inlet to outlet that leads to a decent vortex generation. [ABSTRACT FROM AUTHOR]

Background: The non-invasive quantitative evaluation of left ventricle (LV) function plays a critical role in clinical cardiology. This study proposes a novel ultrasonic biomechanics method by integrating both LV vortex and wall motion to fully assess and understand the LV structure and function. The purpose of this study was to validate the ultrasonic biomechanics method as a quantifiable approach to evaluate LV function.Methods: Firstly, B-mode ultrasound images were acquired and processed, which were utilized to implement parameters for quantifying the LV vortex and wall motion respectively. Next, the parameters were compared in polyvinyl alcohol cryogen (PVA) phantoms with different degree of stiffness corresponding to different freezing and thawing cycles in vitro. Finally, the parameters were computed in vivo during one cardiac cycle to assess the LV function in normal and abnormal subjects in vivo.Results: In vitro study, the velocity field of PVA phantom differed with stiffness (varied elasticity modulus). The peak of strain for wall motion decreases with the increase of elasticity modulus, and periodically changed values. Statistical analysis for parameters of vortex dynamics (energy dissipation index, DI; kinetic energy fluctuations, KEF; relative strength, RS; and vorticity, W) based on different elasticity (E) of phantom depicted the good viability of this algorithm. In vivo study, the results confirmed that subjects with LV dysfunction had lower vorticity and strain (S) compared to the normal group.Conclusion: Ultrasonic biomechanics method can obtain the vortex and wall motion of left ventricle. The method may have potential clinical value in evaluation of LV dysfunction. [ABSTRACT FROM AUTHOR]

The runaway condition is unsteady and is of significant importance in pump turbines. In this research, the shear-stress transport (SST) k - ω turbulence model is used to simulate the unsteady flow in the vaneless region and the runner of a prototype pump turbine. The characteristics of pressure fluctuations, vortex identification based on Q criterion and local entropy generation rate (LEGR) in the pump turbine under runaway condition are studied, and the relationships of these physical quantities in the vaneless region are determined. Internal flow research reveals the motion and transmission characteristics of vortices in the vaneless region and the runner. The results show that the vortices that move clockwise in the vaneless region are responsible for the flow separation, the increase of LEGR, and the generation of the characteristic frequency 1.4 f n of these physical quantities (pressure fluctuations, Q criterion and LEGR). In runner, it is found that the characteristic frequency of pressure fluctuation is 3.6 f n , which satisfies a linear relationship with the characteristic frequency 1.4 f n in the vaneless region. The vortices, moving in the vaneless and runner region, interact with the blades of runner and mainly contribute to the pressure fluctuation characteristic frequency in the runner. • Unsteady flow and fluctuations of a pump turbine under runaway condition are studied. • Flow separation and vortices cause energy dissipation in vaneless region and runner. • Vortex motion greatly affects pressure fluctuation in vaneless region. • Interaction between blade and vortex causes pressure fluctuation frequency in runner. [ABSTRACT FROM AUTHOR]

The newly developed vortex-identification method, Liutex, has provided a new systematic description of the local fluid rotation, which includes scalar, vector, and tensor forms. However, the advantages of Liutex over the other widely used vortex-identification methods such as Q, ∆, λ2, and λci have not been realized. These traditional methods count on shearing and stretching as a part of vortex strength. But, in the real flow, shearing and stretching do not contribute to fluid rotation. In this paper, the decomposition of the velocity gradient tensor is conducted in the Principal Coordinate for uniqueness. Then the contamination effects of stretching and shearing of the traditional methods are investigated and compared with the Liutex method in terms of mathematical analysis and numerical calculations. The results show that the Liutex method is the only method that is not affected by either stretching or shear, as it represents only the local fluid rigid rotation. These results provide supporting evidence that Liutex is the superior method over others. [ABSTRACT FROM AUTHOR]

Unsteady cavitating turbulent flow around a NACA66 hydrofoil was simulated using a mass transfer cavitation model and a modified filter-based turbulence model in this paper. The modified filter-based turbulence model can accurately predict the pressure coefficient in midplane and shedding frequency of the unsteady cloud cavitation than standard κ – 𝜀 model and filter-based turbulence model. The time evolution of transient cavitation cloud structure predicted by the three-turbulence model was compared. The result which was predicted by the modified filter-based turbulence model is in good agreement with the experimental results. The time evolution of re-entrant jet had been analyzed. The instantaneous wall-pressure evolution on the suction surface (SS) predicted by the modified filter-based turbulence model had been analyzed. The cavitation-vortex interaction had been analyzed in this study. The different effects on the cavitation-vortex interaction of the vortex stretching term, vortex dilatation term and baroclinic torque term in the transport equation of vorticity had been discussed. [ABSTRACT FROM AUTHOR]

Concentration-compactness is used to prove compactness of maximising sequences for a variational problem governing symmetric steady vortex-pairs in a uniform planar ideal fluid flow, where the kinetic energy is to be maximised and the constraint set comprises the set of all equimeasurable rearrangements of a given function (representing vorticity) that have a prescribed impulse (linear momentum). A form of orbital stability is deduced. [ABSTRACT FROM AUTHOR]

In the framework of two-dimensional ideal hydrodynamics, we define a vortex system as a smooth vorticity function with a few local positive maximums and negative minimums separated by curves of zero vorticity. We discuss the invariants of such structures that follow from the vorticity conservation law and the invertibility of Lagrangian motion. Introducing new functional variables diagonalizing the original noncanonical Poisson bracket, we develop a Hamiltonian formalism for vortex systems. [ABSTRACT FROM AUTHOR]

By using the Stereo Particle Image Velocimetry (PIV) technique we observe the secondary flow of second kind in a corner of a channel of square cross-section. The boundary layer thickness is much lower than the channel size. Therefore, the flow is still developing, not filling the entire channel cross-section, which is the case more widely reported in literature studied in a very long channel. The non-linear secondary effects of interacting boundary layers are observed as a single stream-wise vortex close to the channel corner in case of laminar boundary layers. In the case of turbulent boundary layers, the secondary flow takes shape of a symmetric pair of counter-rotating vortices. This pattern is observable only in the average velocity field, while the instantaneous ones display large amount of vortices, whose spatial distribution close to the corner in dependence on their orientation leads to statistically emergent net vorticity. At the same time, this pattern is reproduced by using a numerical simulation. • Secondary flow of second kind in a short channel observed by Stereo PIV • For R e L ≤ 1. 0 ⋅ 1 0 5 , the secondary flow is laminar in shape of single vortex in the corner. • The size of laminar secondary flow vortex decreases with R e L as R ∼ R e L − 1 ∕ 2 . • At R e L ≥ 1. 3 ⋅ 1 0 5 , a pair of counter-rotating vortices appears in the averaged sense. • This pattern develops also in a "steady-state" numerical simulation. [ABSTRACT FROM AUTHOR]

Vortex intensification plays an important role in a wide range of flows of engineering interest. One scenario of interest is when a streamwise vortex passes through the contracting streamtube of an aircraft intake. There is, however, limited experimental data of flows of this type to reveal the dominant flow physics and to guide the development of vortex models. To this end, the evolution of wing-tip vortices inside a range of streamtube contractions has been measured using stereoscopic particle image velocimetry. A semi-empirical model has been applied to provide new insight on the role of vorticity diffusion during the intensification process. The analysis demonstrates that for mild flow contractions, vorticity diffusion has a negligible influence due to the low rates of diffusion in the vortex flow prior to intensification and the short convective times associated with the streamtube contraction. As the contraction levels increase, there is a substantial increase in the rates of diffusion which is driven by the greater levels of vorticity in the vortex core. A new semi-empirical relationship, as a function of the local streamtube contraction levels and vortex Reynolds number, has been developed. The model comprises a simple correction to vortex filament theory and provides a significant improvement in the estimation of vortex characteristics in contracting flows. For the range of contractions investigated, errors in the estimation of vortex core radius, peak tangential velocity and vorticity are reduced by an order of magnitude. The model can be applied to estimate the change in vortex characteristics for a range of flows with intense axial strain, such as contracting intake streamtubes and swirling flows in turbomachinery. [ABSTRACT FROM AUTHOR]

Barotropic geostrophic flows are investigated using rectangular and polar coordinate systems. It is shown that, for the analysis of geostrophic flows with radial symmetry, the use of a polar coordinate system is preferable. Relations between the hydrodynamic characteristics, including the expressions of the fluid particle velocity components and vorticity through pressure, are obtained. It is established that, in the case of stationary barotropic flows, isobaths coincide with current lines. Stationary radially symmetric geostrophic flows are considered. [ABSTRACT FROM AUTHOR]

Taking advantage of alternative expressions for potential vorticity (PV) in divergence forms, we derive balances between volume integral of PV and boundary conditions, that are then applied to practical computations of PV: • We propose a new method for diagnosing the Ertel potential vorticity from model output, that preserves the balances; • We show how the expression of PV can be derived in general coordinate systems. This is here emphasised with isopycnic coordinates by generalising the PV expression to the general Navier-Stokes equations; • We propose a generalised derivation for the Haynes-McIntyre impermeability theorem, which highlights the role of the bottom boundary condition choice (e.g. no-slip vs free-slip) and mixing near the bottom boundary for the volume integral of PV. The implications of balances between volume integral of PV and boundary conditions are then analysed for specific processes at various scales: • At large scale, we show how an integral involving surface observations (derived from satellite observations) is linked to the integral of PV within a layer (between two isopycnals). This surface integral can be calculated for models and observations and can be used for validation; • At mesoscale or sub-mesoscale, we analyse the relationship between net PV anomalies and net surface density anomalies for idealised vortices and 2D fronts. This can help determining vortex or jet structures for idealised studies or empirical methodologies; • We also confirm and integrate previous results on the modification of PV within a bottom boundary layer into a single diagnostic taking into account the effect of density and velocity modifications by diabatic processes along the topography and diapycnal mixing within the boundary layer. • Ertel potential vorticity (PV) expressions in divergence form improve PV diagnostics in models. • Balances are derived between volume integral of PV and boundary conditions. • Practical numerical computations of PV, preserving balances, are proposed. • The implications of balances are examined for selected processes. [ABSTRACT FROM AUTHOR]

Highlights • A new method is proposed to analyze the vortex. • A new iso-vortex surface is done according to Q criterion. • Tendency of vortex structure is intuitive according to the iso-vortex surface. • Vorticity magnitude has a sudden change near the wall. Abstract This study presents a new method to analyze the vortex of cyclone separator by using the vortex identification of Q criterion. The Phase Doppler Particle Analyzer (PDPA) is used to measure the flow, and the numerical simulation is done by using the Reynolds stress model (RSM). In addition, a new conception of iso-vortex surface according to Q criterion is proposed for identifying the vortex structure. Since the model is validated by agreement between the numerical results and experimental data, and then is used to analyze the flow field. The results show that the tendency of the vortex structure is intuitive according to the new iso-vortex surface. Equivalent diameter of the iso-vortex surface is large in the upper region of the cylinder and decreases along the axis downward. The carrier energy of vortex decay gradually. In the process, vortex develops rapidly, even ruptures. Meanwhile, the vorticity magnitude has a sudden change near r /R = 0.93, and then vorticity magnitude rises up sharply. The vortex line of relative stable region is almost circular distribution, while the vortex line is complex at the upper region of cylinder, which has a hierarchical trend. The trend of the vortex center deviating from the geometric center firstly increases, reaches a peak value, and then reduces gradually. The axial position of peak value increases with the increase of velocity. Furthermore, the vortex structure can be appropriately adjusted to improve the flow instability, which is highly significant. [ABSTRACT FROM AUTHOR]

Abstract The rotary-type energy recovery device (RERD) is a promising energy recovery device which can significantly reduce the energy consumption of the Reverse Osmosis system in seawater desalination. A two-dimensional particle image velocimetry (PIV) measurement has been carried out in our previous study to visualize and understand the flow dynamics in the duct of the RERD. Based on the PIV experimental results, a computational fluid dynamics (CFD) method was applied to study flow characteristics and mixing process in the RERD. Three different turbulence modeling approaches (standard k - ε , RNG k - ε , and Realizable k - ε) were compared and validated by PIV experimental data. As a result, the simulation method was able to capture major features of the flow characteristic in the duct, such as the jet flow and the vortex structure. The Realizable k - ε turbulence model, presenting a good agreement with the experimental data, was recommended for analyzing the detailed information of flow characteristics. The simulation results revealed a swirling flow formed in the duct. This three-dimensional flow structure caused high flow turbulence and significant mass transfer in the mixing zone. These results would be beneficial to researchers in better understanding the mixing process in the duct of the RERD. Highlights • Three different k - ε turbulence model results were compared with experimental data. • Numerical results enriched the finding of the "entrance effect" observed by PIV method. • The Realizable k - ε model showed better predictions of vortex structures in the duct center. • A high concentration gradient and a swirling flow were in the duct transverse plane. [ABSTRACT FROM AUTHOR]

Much work has been conducted on the topic of forward osmosis (FO), but only a few studies have focused on mitigating external concentration polarization (ECP). This study introduced a simple structure, the corrugated wall channel, to the design of FO module, to induce vortex, and then mitigate ECP. In this study, the corrugated wall channel module (CWCM) was tested under given conditions, with a traditional flat membrane module (FMM) as control. CWCM could mitigate ECP and then enhance water flux. When deionized water was taken as feed solution (FS) and 2-M NaCl solution as draw solution (DS), the water flux enhancement was 16.49 and 18.51% in FO mode (active layer facing FS) and PRO mode (active layer facing DS), respectively. When 0.5-M NaCl solution was taken as FS, the corresponding values were 15.92 and 17.13%, respectively. Computational fluid dynamics (CFD) analysis showed that the CWCM could induce vortex, promote the mixing of the solution in the module, and further contribute to the increase of water flux. The specific shape of CWCM affected its performance on mitigating ECP. Also, the more tortuous CWCM exhibited higher water flux. In addition, CWCM could lessen membrane fouling. [ABSTRACT FROM AUTHOR]

In the present study, the performance of the vorticity confinement method has been improved by combining it with the vortex feature detection methods. In the conventional vorticity confinement method, the only parameter to apply or not to apply vorticity confinement is the non-zero value of vorticity. On the other hand, the presence of vorticity in some cases, like the boundary layer and the shear layer flows, does not imply the presence of vortices. Applying the vorticity confinement at these points can lead to errors, in addition to loss of solution time. In order to solve this problem, using the combination of vorticity confinement method and four methods of vortex feature detection (non-dimensional Q, non-dimensional λ2, non-dimensional modified Δ, and the S − Ω correlation) the vorticity confinement term is applied only in vortex regions. In order to investigate the effects of this combination, the compressible Euler equation has been investigated for the problem of two-dimensional stationary single vortex at Mach number 0.5. The results indicate significant positive effects in reducing the solving time, decreasing the sensitivity of the solution to the amount of confinement parameter and significant elimination of the oscillation. [ABSTRACT FROM AUTHOR]

The importance of type-II superconductors with strong pinning comes from their ability to carry large transport currents in the presence of a magnetic field. We report on the results of the bulk magnetization measurements in the superconducting state in clean single crystals of NdFeAsO 0.9 F 0.1 at various temperatures. The zero-temperature superconducting critical current density, J c , where the superconducting transition temperature T c reaches a maximum of 45(1) kelvin, displays a remarkable high value. The field dependence of the critical current density was analyzed within the collective pinning model. A remarkably good agreement between the experimental results and theoretical δ1 pinning curve is obtained. This indicates that pinning in NdFeAsO 0.9 F 0.1 crystal originates from spatial variation of the mean free path. Additionally, the normalized pinning force density, F p , curves verses H/H irr (H irr is the irreversibility field) were scaled using the Dew-Hughes model. Our analysis suggests that point pinning alone cannot explain the observed field variation of F p . [ABSTRACT FROM AUTHOR]

We apply the modulation theory to study the vortex and radiation solution in the 2D nonlinear Schrödinger equation. The full modulation equations which describe the dynamics of the vortex and radiation separately are derived. A general algorithm is proposed to efficiently and accurately find vortices with prescribed values of energy and spin index. The modulation equations are solved by accurate numerical method. Numerical tests and simulations of radiation are given. [ABSTRACT FROM AUTHOR]

A new mathematical analysis for the dynamics of laminar spray diffusion flames in the vicinity of a vortex flow field is presented. The governing equations for a spray evaporating in an unsteady vortex are studied. New similarity solutions are found for the dynamics of the spray and the flame it supports. Analytical solutions for the spray flames are derived using Shvab-Zeldovich parameters, through which the radial evolution of the flames is found. The results based on the solution reveal the significant effects vorticity and droplet evaporation have on the flame dynamics. An extinction analysis is carried out which maps the influence of the evaporation coefficient and vortex intensity on flame extinguishment. A number of competing factors such as vortex intensity and heat loss due to evaporation were found to be responsible for flame extinction. Despite the model’s simplicity, its predictions offer new insights into the driving mechanisms of more complex spray-combustion situations in which droplets are evaporating in vortical environments. [ABSTRACT FROM AUTHOR]

Vortexes induced by tsunamis, “tsunami vortexes”, pose a potential danger for ship evacuation, and their prediction is important to determine their role in navigation and safe vessel evacuation. This study simulated tsunami-induced vortexes in Osaka Bay and investigated their spatial and temporal scales using a port-resolved, high-resolution tsunami model based on a scenario for the largest tsunamigenic earthquake expected to occur along the Nankai Trough in the near future. Vortexes induced by tidal currents were also evaluated using a realistic tidal simulation for comparison with the magnitudes of the tsunami vortexes. The tsunami simulation identified the dominant areas of the tsunami vortexes characterized by the magnitude of the vorticity. Unified maps of tsunami speeds and vortexes showed the difficult areas for ship evacuation and indicated that these areas can persist after the approach of the leading wave around the entrances to port areas. The areas of tsunami vortex formation were largely deduced by analyzing the vorticity fields in the tidal simulations, because the magnitude of tsunami-induced vorticities was closely correlated with that of the tide-induced vorticities. The combination of tide and tsunami simulations can identify areas of tsunami vortex formation and provide valuable information to guide measures for safer vessel evacuation. [ABSTRACT FROM AUTHOR]

The vortex motion of a dust cloud was experimentally observed in unmagnetized cogenerated dusty plasma in different experimental parameters. Particle image velocimetry analysis demonstrated that several vortex zones exist in the dust cloud at relatively low pressures (0.06 mbar (or 6 Pa)–0.08 mbar (or 8 Pa)) and low discharge voltages (peak‐to‐peak voltage 540–560 V), whereas in relatively high pressure (0.4 mbar (or 40 Pa)–0.7 mbar (or 70 Pa)) and high discharge voltage (peak‐to‐peak voltage 690–740 V), dust vortices formed in dense dust cloud with background plasma fluctuation. [ABSTRACT FROM AUTHOR]

In this paper, starting from Biot-Savart mechanics for entangled vortex-membranes, a new theory - knot physics - is developed to explore the underlying physics of quantum mechanics. Owning to the conservation conditions of the volume of knots on vortices in incompressible fluid, the shape of knots will never be changed and the corresponding Kelvin waves cannot evolve smoothly. Instead, the knot can only be split. The knot-pieces evolve following the equation of motion of Biot-Savart equation that becomes Schrödinger equation for probability waves of knots. The classical functions for Kelvin waves become wave-functions for knots. The effective theory of perturbative entangled vortex-membranes becomes a traditional model of relativistic quantum field theory - a massive Dirac model. As a result, this work would help researchers to understand the mystery in quantum mechanics. [ABSTRACT FROM AUTHOR]

Mixing is an essential operation in many microfluidic devices. Droplet-based micromixers utilize droplets for mixing enhancement. In the present study, a novel three-dimensional simulation is conducted which has the ability to capture not only the mixing process, but also the chemical reactions inside liquid droplets. This two-phase model is used for simulating the reacting flow inside a serpentine microchannel and explores the effects of droplet size and reaction rate on the production and consumption of species in droplets. It is observed that the chemical reaction in each droplet, begins from its front area. Furthermore, it is shown that the production of species does not depend on water fraction (ratio of water flow rate to total flow rate) and for all droplet sizes, only depends on the reaction rate. Moreover, different transient generated vortices and secondary flows are studied in the presence and absence of droplets and explained in details based on the position of droplets. It is found that during the passage of droplets through a microchannel bend, the number of cross-sectional vortices changes and the velocity magnitude in these secondary flows increases dramatically. [ABSTRACT FROM AUTHOR]

In wind farms, the wake of the upstream turbines becomes the inflow for the downstream machines. Ideally, the turbine wake is a stable vortex system. In reality, because of factors like background turbulence, mean flow shear, and tower-wake interaction, the wake velocity deficit is not symmetric and is displaced away from its mean position. The irregular velocity profile leads to a decreased efficiency and increased blade stress levels for the downstream turbines. The object of this work is the experimental investigation of the effect of the wind turbine tower on the symmetry and displacement of the wake velocity deficit induced by one and two in-line model wind turbines (, D= 0.9 m). The results of the experiments, performed in the closed-loop wind tunnel of the Norwegian University of Science and Technology in Trondheim (Norway), showed that the wake of the single turbine expanded more in the horizontal direction (side-wall normal) than in the vertical (floor normal) direction and that the center of the wake vortex had a tendency to move toward the wind tunnel floor as it was advected downstream from the rotor. The wake of the turbine tandem showed a similar behavior, with a larger degree of non-symmetry. The analysis of the cross-stream velocity profiles revealed that the non-symmetries were caused by a different cross-stream momentum transport in the top-tip and bottom-tip region, induced by the turbine tower wake. In fact, when a second additional turbine tower, mirroring the original one, was installed above the turbine nacelle, the wake recovered its symmetric structure. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The concepts and methods of the visual representation of fluid dynamics computations of vortical flows are studied. Approaches to the visualization of vortical flows based on the use of various definitions of a vortex and various tests for its identification are discussed. Examples of the visual representation of solutions to some fluid dynamics problems related to the computation of vortical flows in jets, channels, and cavities and of the computation of separated flows occurring in flows around bodies of various shapes are discussed. [ABSTRACT FROM AUTHOR]

We did a numerical study of the internal flow field of a vortex pump. Five operating points were considered and validated through a measured characteristic curve. The internal flow pattern of a vortex pump was analyzed and compared to the Hamel-Oseen vortex model. The calculated flow field was assessed with respect to the circumferential velocity, the vorticity and the axial velocity. Whereas the trajectories of the circumferential velocity were largely in line with the Hamel-Oseen vortex model, the opposite was true for vorticity. Only the vorticity at strong part load was in line with the predictions of the Hamel-Oseen vortex model. We therefore compared the circumferential velocity and vorticity for strong part load operation to the analytical predictions of the Hamel-Oseen vortex model. The simulated values were below the analytical values. The study therefore suggests that a vortex similar to the Hamel-Oseen vortex is only present at the strong part load operation. [ABSTRACT FROM AUTHOR]

This paper presents flow-structure interaction between a sphere wake and a free water surface for different submerged elevations in an open water channel for Reynolds numbers in the range of 2.5×103 ⩽Re⩽1×104 based on the diameter of the sphere. [ABSTRACT FROM AUTHOR]

The design of turbine blades is a critical issue in the performance of vertical-axis wind-turbines (VAWTs). In a previous study, it is discovered that a loss of thrust in VAWT blades with a wave-like leading edge can be attributed primarily to vortex distribution. This finding prompted us to apply the wave-like blade design to the trailing edge rather than the leading edge. In this study, computational fluid dynamics was used to observe the flow field on straight and tubercle blades in order to predict the resulting thrust and power performance. Increasing the amplitude and wavelength of the tubercle was shown to increase the maximum thrust by as much as 2.31% and the power coefficient by 16.4%, compared to a straight blade. Furthermore, the overall and maximum thrust performance of blades with a modified trailing edge was shown to exceed those of blades with a wave-like leading edge, due to a shift in the location of the vortices by the induced flow. [ABSTRACT FROM AUTHOR]

Through-silicon via (TSV) technology has been quickly improved, however, there are challenges in reducing electrodeposition time. In this research, new conical TSVs, 3 μm diameter and 27 μm depth (3 × 27 μm), were made. The flow pattern of the electrolyte inside a conical TSV and a cylindrical TSV is simulated with a TSV chip attached on a rotating disk electrode (RDE) rotating at 1000 rpm in the electrolyte. The flow pattern inside conical TSVs confirmed advantages of the conical shape over the cylindrical shape. The conical shape forms deeper vortexes and shows higher velocities at the same depth than the cylindrical shape. A character of electrolyte bases on anodic area charge was used to optimize electrolyte bath composition for the extreme fast filling. Without additives, the anodic area charge at 1000 rpm was larger than that at 10 rpm, however, the reverse obtained in the presence of additives. D-optimal designs for quantitative multilevel of additives were applied to create an experiment plan. The result confirmed a strong effect of Cl − concentration and interactions of Cl − with polyethylene glycol (PEG) and bis-(3-sodiumsulfopropyl)-disulfide (SPS) with sulfonated diallyl dimethyl ammonium chloride copolymer (SDDACC) which bring to anodic area charge at 1000 rpm was smaller than that at 10 rpm. In an optimal concentration of SDDACC, the 3 × 27 μm conical TSV was filled within 3 minutes. A new additive acceleration mechanism was proposed from the accumulation of Cu(I) thiolate inside vortexes. [ABSTRACT FROM AUTHOR]

Surface friction is important to a vortex moving toward Taiwan but was ignored in several previous studies. The change of the potential vorticity comes from friction in the shallow-water equation, hence, it was applied to study the westbound vortex influenced by the central mountain range (CMR) blocking and surface friction, which is defined as friction coefficient multiplied by the square root of topographic elevation. Without surface friction, the movement of vortex is not affected by the CMR due to the conservation of potential vorticity. With small surface friction, the simulated vortex first deflects southward slightly, then rebounds gently north due to the effect of channel flow, as the previous studies. With moderate or large surface friction, when the vortex approaching Taiwan, it deforms and creates two wind maxima; one due to effect of channel flow and the other on the east of the vortex, because the slowdown vortex is pushed by the mean easterly flow behind. Meanwhile, the vortex and two wind maxima rotate cyclonically. Hence, the vortex can deflect north or south, or form a loop, that depends on the strength and location of the wind maxima. If the circulation of the vortex moves around the northern tip of Taiwan, it can induce a significant secondary vortex on the lee side. On the other hand, the secondary vortex, triggered by the flow passing over the CMR, is rather weak. This paper may provide the formation of asymmetric inner flow and the deflection of the vortex, which may be difficult to define in a more complicated atmospheric model. [ABSTRACT FROM AUTHOR]

The static and dynamic properties of vortices in a nanosized superconducting strip with one central weak link (weakly superconducting region or normal metal) are investigated in the presence of external magnetic and electric fields. The time-dependent Ginzburg-Landau equations are used to describe the electronic transport and have been solved numerically by a finite element analysis. Anisotropy is included through the spatially dependent anisotropy coefficient $$\zeta $$ in different layers of the sample. Our results show that the energy barrier for vortices to enter a weak link is smaller than that for vortices to enter the superconducting layers. The magnetization shows periodic oscillations. With the introduction of the weak link, the period of oscillations decreases. [ABSTRACT FROM AUTHOR]

Water vapor in natural gas often leads to the decrease of gas calorific value per unit volume; it also reduces the flow area of pipeline. Moreover, the CO2 and H2S will corrode the pipeline when dissolved in liquid water. According to the containing water problems in high pressure natural gas during development, a roof-mounted type supersonic cyclone flow natural gas dehydration unit was designed in combination with the fluid mechanics and engineering thermodynamics principle. Based on the research status at home and abroad, the supersonic natural gas condensate flow numerical model was built, including multicomponent two-phase expansion flow model and water vapor condensing model. The flow characteristics of each work section of supersonic natural gas dehydration unit were numerical analyzed, and the device internal pressure, temperature, Mach number, vapor nucleation rate, moisture distribution were obtained. According to the results of numerical simulation, optimization design was carried out to improve the efficiency of separation. [ABSTRACT FROM AUTHOR]

We calculate the relaxation of Brinkman-Smith mode via Leggett-Takagi relaxation in the presence of an isolated vortex in superfluid $$^{3}$$ He-B. The calculation is based on an analytical solution of the order parameter far from the vortex axis. We obtain an expression for the dissipated power per vortex length as a function of the tipping angle of the magnetization and the orientation of the static magnetic field with respect to the vortex. [ABSTRACT FROM AUTHOR]

We construct a class of self-similar 2d incompressible Euler solutions that have initial vorticity of mixed sign. The regions of positive and negative vorticity form algebraic spirals. [ABSTRACT FROM AUTHOR]

The vortex motion is a sign of the desire to achieve balance. In the study, vortices described by complex numbers are moved from a sphere into a "squeezed" sphere - where the pair of opposite poles become one - called a pinched sphere or concave disk. Vortices on the pinched sphere reflect what is commonly observed in nature. A family of the pinched spheres very well represents the spatial vortices observed daily in gusts of wind. Stock market zigzags constitute an economic vortex - a spiral on the cone whose equivalent is the pinched sphere. [ABSTRACT FROM AUTHOR]

The coherent secondary flow structures (i.e., swirling motions) in a curved artery model possess a variety of spatio-temporal morphologies and can be encoded over an infinitely-wide range of wavelet scales. Wavelet analysis was applied to the following vorticity fields: (i) a numerically-generated system of Oseen-type vortices for which the theoretical solution is known, used for bench marking and evaluation of the technique; and (ii) experimental two-dimensional, particle image velocimetry data. The mother wavelet, a two-dimensional Ricker wavelet, can be dilated to infinitely large or infinitesimally small scales. We approached the problem of coherent structure detection by means of continuous wavelet transform (CWT) and decomposition (or Shannon) entropy. The main conclusion of this study is that the encoding of coherent secondary flow structures can be achieved by an optimal number of binary digits (or bits) corresponding to an optimal wavelet scale. The optimal wavelet-scale search was driven by a decomposition entropy-based algorithmic approach and led to a threshold-free coherent structure detection method. The method presented in this paper was successfully utilized in the detection of secondary flow structures in three clinically-relevant blood flow scenarios involving the curved artery model under a carotid artery-inspired, pulsatile inflow condition. These scenarios were: (i) a clean curved artery; (ii) stent-implanted curved artery; and (iii) an idealized Type IV stent fracture within the curved artery. [ABSTRACT FROM AUTHOR]