Vortex Center Research Articles

Influence of speed on the internal flow characteristics of a multiphase pump based on a coupled CFD-PBM model

Under the influence of the characteristic behavior of the bubbles, the flow pattern in the multiphase pump suffers a serious deterioration and the pressurization performance is significantly reduced. In order to be more close to the engineering practice, the CFD-PBM (Computational Fluid Dynamics-Population Balance Model) coupling model is established and verified on the basis of considering the bubble coalescence and breakup behavior, revealing the bubble distribution characteristics in the pressurization unit, and studying the influence of speed on the internal flow characteristics of the multiphase pump. The results show that the volume fraction of large bubbles in the pressurization unit of the multiphase pump decreases significantly with increasing speed, and the bubble coalescence zone shrinks parallel to the blade profile along the flow direction. The volume fraction of small bubbles increases sharply with speed, and the bubble breakup zone covers almost the entire fluid domain at high speed conditions. The speed has a significantly greater influence on the distribution of the gas phase and the vortex structure in the diffuser domain than in the impeller domain. In the diffuser domain, a pair of mutually separate vortices are formed, and a large number of gas phases are sucked near the vortex center. With the increase of speed, the velocity slip in impeller domain is weakened, but in diffuser domain is intensified. The results of the study can accurately predict the performance variation of the multiphase pump and are important for their optimal design and engineering application.

Optical bottle beam transmit in polycyclic tornado mode

Light-field shaping technology is of significant importance for applications in particle trapping and optical communication. In this paper, we generate a new class of tunable polycyclic tornado Laguerre-Gaussian beams (TPTLGBs) experimentally and numerically by applying an annular spiral-zone phase (ASZP) with the second order chirped factor to Laguerre-Gaussian beams. By the parameters of the ASZP, we can modulate the focusing and diffraction of TPTLGBs along z-axis, controlling the number and quality of optical bottles (OBs) formed. In addition, it is possible to precisely control the direction of rotation of TPTLGBs during propagation. We further explore the specific effects of the ASZP and the central vortex phase on TPTLGBs. Adjusting the parameters of TPTLGBs, we obtain a high intensity focus. The multi-dimensional tunability and complex phase structure of TPTLGBs also provide new possibilities for further development of optical technology.

Sloshing-induced evolution of self-cleaning performance and flow characteristics within a tank installed on an offshore aquaculture vessel

In this study, a six-degree-of-freedom (6-DOF) motion platform is utilized to simulate the transverse rolling motion of aquaculture tanks aboard deep-sea aquaculture vessels. It examines the effects of different inlet configurations (single and four-pipe inlet), rolling motions (amplitude Θ and period T), and inlet pipe jet angles α (the acute angle between the jet direction of the inlet pipe and the inclined wall to which it is connected) on the self-cleaning capabilities and flow field characteristics of the aquaculture tank. The findings indicate that the waste collection time in the tank is affected by the combined influences of rolling amplitude and period. In the single-pipe inlet configuration, waste collection time increases with the rolling period and initially increases, then decreases with the rolling amplitude. In the four-pipe inlet configuration, waste collection time increases with the rolling period and decreases with the rolling amplitude. Optimal waste collection performance is achieved at α = 45° in both configurations. Regarding flow field characteristics, variations in rolling period and amplitude significantly alter the flow field within the aquaculture tank. In both configurations, as the period decreases and the amplitude increases, the high-velocity regions and the central vortex area within the tank expand, and the average flow velocity of the water also rises. This corresponds to a reduction in waste collection time and an increase in the waste collection rate. In both configurations, the Flow field is most uniform at α = 45°, which corresponds to the highest waste collection capabilities among all jet angles. The results indicate that while decreasing the rolling period and increasing the amplitude can enhance the self-cleaning capabilities, they also lead to excessively rapid water flow velocities. In practical applications, it is important to select appropriate farming areas based on fish suitability and to choose the correct inlet jet angles for different numbers of inlets. The findings can provide theoretical support and a scientific basis for optimizing the flow characteristics and self-cleaning performance of aquaculture vessels under rolling motion and contribute positively to the advancement of deep-sea aquaculture technology.

Characterization of Wind Turbine Blade Deformation and Wake Flow Field with Different Numbers of Lay-Up Layers

The change in the composite lay-up method affects the blade stiffness, which in turn affects the structural dynamic and aerodynamic characteristics, but the influence law is not yet clear. In this paper, two-way fluid–structure coupling is used to study wind turbine blades with different numbers of lay-up layers. The analysis results show the following: (1) With the increase in the number of pavement layers, the maximum deformation of the blade tip decreases, the magnitude of the decrease also decreases gradually, and the growth trend of deformation along the blade spreading direction is gradually flattened. (2) The maximum stress–strain of the root of the blade gradually decreases, the tip of the blade is the opposite of the blade, the unevenness of the distribution of the stress–strain of the surface of the blade is gradually slowed down, and the concentration area is shifted back. (3) The different numbers of pavement layers affect the turbulence intensity of the blade in the flow field space. Herein, the spatial distribution trend of turbulence intensity in the flow field of wind turbine blades with different numbers of layers is basically the same, and the trend of turbulence intensity changes is gentle when the number of layers is increased. (4) The amount of the tip vortex in the wake stream of the wind turbine decreases, and the decay rate of the center vortex increases. A reasonable lay-up scheme can improve the deformation and stress of the blade, extend the service life of the blade, promote airflow mixing, and enhance the energy conversion efficiency.

Effect of rotation on wake vortices in stratified flow

Stratified wakes past an isolated conical seamount are simulated at a Froude number of $Fr = 0.15$ and Rossby numbers of $Ro = 0.15$ , 0.75 and $\infty$ . The wakes exhibit a Kármán vortex street, unlike their unstratified, non-rotating counterpart. Vortex structures are studied in terms of large-scale global modes, as well as spatially localised vortex evolution, with a focus on rotation effects. The global modes are extracted by spectral proper orthogonal decomposition (SPOD). For all three studied $Ro$ ranging from mesoscale, submesoscale and non-rotating cases, the frequency of the SPOD modes at different heights remains coupled as a global constant. However, the shape of the SPOD modes changes from slanted ‘tongues’ at zero rotation ( $Ro=\infty$ ) to tall hill-height columns at strong rotation ( $Ro=0.15$ ). A novel method for vortex centre tracking shows that, in all three cases, the vortices at different heights advect uniformly at approximately $0.9U_{\infty }$ beyond the near wake, consistent with the lack of variability of the global modes. Under system rotation, cyclonic vortices and anticyclonic vortices (AVs) present considerable asymmetry, especially at $Ro = 0.75$ . The vorticity distribution as well as the stability of AVs are tracked downstream using statistics conditioned to the identified vortex centres. At $Ro=0.75$ , intense AVs with relative vorticity up to $\omega _z/f_{c}=-2.4$ (where $\omega_z$ is the vertical vorticity and $f_c$ is the Coriolis frequency) are seen with small regions of instability and they maintain large $\omega _z/f_{c}$ magnitude in the far wake. Recent stability analysis that accounts for stratification and viscosity is found to improve on earlier criteria and show that these intense AVs are stable.

Effect of settling vortex of coal slime flocs with different sizes on the settlement of microfine particles

This article explores the flow field changes and micro vortex formation mechanisms caused by coagulation and sedimentation of coal slurry flocs of different sizes. The collision adhesion rate, motion trajectory and force analysis of fine particles under micro vortex disturbance. Particle image velocimetry (PIV) and high-speed camera were used to capture deposition process of coal slime flocs, the changes of flow field and fine particles were analyzed by numerical simulation. The smaller flocs form a single vortex ane larger flocs show periodic vortex shedding, resulting in increase fluid velocity and larger interference area. The collision adhesion rate of fine particles in the 3.4 mm floc settling disturbance area is the largest, 9.45 %;Particles<0.3 mm are easily sucked into vortices, while particles>0.3 mm are disturbed by vortices and change their motion trajectory towards the vortex center. It is mainly affected by gravity, pressure gradient force, flow field resistance, and centrifugal force.

Lubrication flow law and cooling mechanism considering cavitation in mechanical seals with Rayleigh step pattern

The purpose of this research is to obtain the cavitation cooling characteristics and flow law in mechanical seals with Rayleigh step pattern. A new cooling approach has been proposed, which is of great significance to preventing liquid film vaporization and limiting thermal deformation of sealing face. Based on the previous literatures focused only on cavitation or viscous heat, the thermohydrodynamic lubrication (THD) and hydrodynamic lubrication (HD) numerical models with cavitation in mechanical seals are developed to obtain the cavitation cooling characteristics and flow mechanism by FLUENT software. The results show that the liquid film cavitation occurs severely in the reverse Rayleigh step and generates a remarkable local cooling effect to the fluid film and sealing faces, which leads to a temperature rise reduction of up to 39.2% and a leakage rate reduction of up to 72.7%. Meanwhile, the high-temperature zone at downstream side migrates upstream, especially, forming temperature valley and peak zones at liquid film rupture and reformation boundaries. The cooling level is controlled by the intensity and area of cavitation. Moreover, the vapor phase block of cavitation, the pressure flow and the shear flow collectively generate a vortex flow behind the cavitation zone in the reverse Rayleigh step. The center and intensity of vortices are closely related to the cavitation area, viscous heat, shear flow and pressure flow. Under THD conditions, the vortex is enhanced due to the viscosity loss and the small cavitation area. The cavitation, viscous heat and vortex flow have important effects on the sealing performance.

Unifying Monopole and Center Vortex as the Semiclassical Confinement Mechanism.

Magnetic excitations play a crucial role in understanding the color confinement of 4D Yang-Mills theory, and we have the monopole and the center vortex as plausible candidates to explain its mechanism. Under suitable compactified setups of 4D Yang-Mills theory, we can achieve different weakly coupled descriptions of confinement phenomena: The monopole mechanism takes place on R^{3}×S^{1} with the double-trace deformation, and the center-vortex mechanism is effective on R^{2}×T^{2} with the 't Hooft flux. We unify these two semiclassical descriptions by showing the explicit relation between the monopole and center vortex.

Flow state transition induced by emergence of orbiting satellite eddies in two-dimensional turbulent Rayleigh–Bénard convection

We report a numerical investigation of a previously noticed but less explored flow state transition in two-dimensional turbulent Rayleigh–Bénard convection. The simulations are performed in a square domain over a Rayleigh number range of $10^7 \leq Ra \leq 2 \times 10^{11}$ and a Prandtl number range of $0.25 \leq Pr \leq 20$ . The transition is characterized by the emergence of multiple satellite eddies with increasing $Ra$ , which orbit around and interact with the main vortex roll in the system. Consequently, the main roll is squeezed to a smaller size compared with the domain and wanders around in the bulk region irregularly and extensively. This is in sharp contrast to the flow state before the transition, which is featured by a domain-sized circulatory roll with its vortex centre ‘condensed’ near the domain's centre. Detailed velocity field analysis reveals that there exists an abrupt increase in the energy fluctuations of the Fourier modes during the transition. Based on this phase-transition-like signal, the critical condition for the transition is found to follow a scaling relation as $Ra_t \sim Pr^{1.41}$ where $Ra_t$ is the critical Rayleigh number for the transition. This scaling relation is quantitatively explained by a phenomenological model grounded on the bistability behaviour (i.e. spontaneous and stochastic switching between the two flow states) observed at the edge of the transition. The model can also account for the effects of aspect ratio on the transition reported in the literature (van der Poel et al., Phys. Fluids, vol. 24, 2012).

Application of FFBP neural network to the prediction of swirling flow

Since ancient times, man has been seeking to improve in the field of transportation and energy consumption, as the combination of optimal energy consumption and not polluting the environment in exchange for obtaining a better return made him constantly searching for optimal methods in the field of anxiety and industry based on combustion. The swirl or vortex flow is one of the most important discoveries of the last century seeking to develop combustion, as research is still focused on it in many aspects, whether in terms of the shape of the rotational areas it forms. This study aims to determine the extent to which artificial intelligence can predict the characteristics of the Swirl flow. The model adopted experimental data of the Swirl flow, both descriptive and positional data as inputs and horizontal, vertical, and kinetic energy as outputs for several positions within the combustion chamber. The results indicate that the model can capture the spatial characteristics of the vortex flow field and the combined Learning of the relationship between the input and output parameters. The results of the velocity density distribution and the position of the vortex center of the vortex flow field agree well with the experimental results. The generated prediction model has good prediction accuracy based on previously observed datasets and can reconstruct the vortex flow field. In addition, it can perform inductive prediction on a previously unseen dataset and has some generalization ability. Finally, this study suggests that many potential architectures have applications based on the induction prediction model created here.

Floating particles transport through the free surface vortex technique: A novel numerical study to assess the interaction among different scales of vortex structures

Fat, oil, and grease (FOG) floating particles in the sump of sewage pumping stations will accumulate together to form rigid layers, resulting in failure for pump device. To overcome this, the free surface vortex (FSV) technique has been considered and applied to transport floating particles toward the submerged suction pump inlet. This paper investigates the potential of vortices as a means of downward motion of FOG. The entrainment capacity of FSV is investigated by numerical simulations using a coupled level-set and volume-of-fluid method. Two coherent structures are decomposed by proper orthogonal decomposition: FSV represented by the first two orders with high energy content and spiral vortex bands represented by low energy and high order models. The extracted ridges of the finite-time Lyapunov exponent (FTLE) delineate different regions of the flow field and effectively capture the evolution of Lagrangian coherent structures. The floating particles in the sump are first caught by the dividing line formed by the FTLE ridges, mixed in the entrainment zone, and then merged into the vortex. The enstrophy production term dominates the development of vorticity. Subject to the influence of flow velocity gradients, both radial and tangential vortices undergo a transition into axial vortices. This transformation enhances the vortex's capacity to entrain particles within the vortex core area, leading to their rapid inward spiraling toward the vortex center and eventual expulsion due to the vortex's entrainment effect.

Investigating azimuthal propagation of Pc5 geomagnetic pulsations and their equivalent current vortices from ground-based and satellite data

Using phase delays at spaced stations and satellite observations in the magnetosphere during two events, we have studied azimuthal propagation of resonant bursts of geomagnetic pulsations in the Pc5 range. We have also examined propagation of equivalent current vortices during these events. It has been found that the pulsations, observed in the magnetosphere and ionosphere, and the equivalent current vortices in the ionosphere propagate in the azimuthal direction from the dayside to the nightside. Propagation velocities according to ground-based observations are 5–25 km/s; according to satellite observations, 114–236 km/s. Propagation velocities according to satellite observations do not exceed the Alfvén velocity in the magnetosphere, which is 620–1006 km/s. According to data from various instruments, there are signatures of fast magnetosonic and Alfvén waves at a time in one of the events on the satellite. This clearly reflects the transformation of these waves. The geomagnetic latitude of registration of vortex centers coincides with the latitude of the maximum amplitude of geomagnetic pulsations (field line resonances) and decreases by ~15° toward the early hours of MLT. The observed dynamics of Pc5 pulsations and vortices is assumed to reflect MHD wave propagation in the magnetosphere.

Исследование особенностей азимутального распространения геомагнитных Pс5-пульсаций и их эквивалентных токовых вихрей по данным наземных и спутниковых наблюдений

Using phase delays at spaced stations and satellite observations in the magnetosphere during two events, we have studied azimuthal propagation of resonant bursts of geomagnetic pulsations in the Pc5 range. We have also examined propagation of equivalent current vortices during these events. It has been found that the pulsations, observed in the magnetosphere and ionosphere, and the equivalent current vortices in the ionosphere propagate in the azimuthal direction from the dayside to the nightside. Propagation velocities according to ground-based observations are 5–25 km/s; according to satellite observations, 114–236 km/s. Propagation velocities according to satellite observations do not exceed the Alfvén velocity in the magnetosphere, which is 620–1006 km/s. According to data from various instruments, there are signatures of fast magnetosonic and Alfvén waves at a time in one of the events on the satellite. This clearly reflects the transformation of these waves. The geomagnetic latitude of registration of vortex centers coincides with the latitude of the maximum amplitude of geomagnetic pulsations (field line resonances) and decreases by ~15° toward the early hours of MLT. The observed dynamics of Pc5 pulsations and vortices is assumed to reflect MHD wave propagation in the magnetosphere.

Numerical indication that center vortices drive dynamical mass generation in QCD

The first calculation of the response of the momentum space quark propagator to center vortices in the ground state fields of QCD is presented. Center vortices are identified on 2+1-flavor dynamical gauge fields with mπ≃156 MeV to obtain the vortex-removed and vortex-only quark propagator. Dynamical mass generation is found to vanish upon vortex removal, while the vortex-only field is able to generate dynamical mass. These new signatures strengthen the lattice QCD evidence indicating that center vortices underpin both dynamical chiral symmetry breaking and quark confinement. Published by the American Physical Society 2024

A two-cell vortex model

A two-cell vortex solution to the Navier–Stokes equations is derived in this article. The theoretical analysis provides expressions for the velocity components, vorticity, and pressure distributions of the two-cell vortex flow. A key feature of this new modeling approach is the presence of a “vortex eye” region, which is absent in classical single-cell vortex models. The derived tangential velocity profile is kept general, allowing for the recovery of the single-cell profile as a special case. The model parameters are constrained by the boundary conditions inherent to two-cell vortices. The model explicitly demonstrates that the two-cell vortex flow exhibits two regions of recirculating flow structures in the meridional plane. The analysis shows that near the vortex core, fluid descends from above and diverges outward. This downward flow meets the incoming flow from the vortex's outer region at a distance known as the “eye-wall” radius. The merging of these two streams results in an upward deflection, generating the two-cell fluid motion. Unlike in single-cell vortices, where vorticity reaches its maximum at the vortex center, the present results indicate that in two-cell vortices, the vorticity peaks at the eye-wall radius.

Two Types of Transitions to Relatively Fast Spinup in Tropical Cyclone Simulations with Weak-to-Moderate Environmental Vertical Wind Shear

Abstract Tropical cyclone intensification is simulated with a cloud-resolving model under idealized conditions of constant SST and unidirectional environmental vertical wind shear maximized in the middle troposphere. The intensification process commonly involves a sharp transition to relatively fast spinup before the surface vortex achieves hurricane-force winds in the azimuthal mean. The vast majority of transitions fall into one of two categories labeled S and A. Type S transitions initiate quasi-symmetric modes of fast spinup. They occur in tropical cyclones after a major reduction of tilt and substantial azimuthal spreading of inner-core convection. The lead-up also entails gradual contractions of the radii of maximum wind speed rm and maximum precipitation. Type A transitions begin before an asymmetric tropical cyclone becomes vertically aligned. Instead of enabling the transition, alignment is an essential part of the initially asymmetric mode of fast spinup that follows. On average, type S transitions occur well after and type A transitions occur once the cyclonically rotating tilt vector becomes perpendicular to the shear vector. Prominent temporal peaks of lower-tropospheric CAPE and low-to-midlevel relative humidity averaged over the entire inner core of the low-level vortex characteristically coincide with type S but not with type A transitions. Prominent temporal peaks of precipitation and midlevel vertical mass flux in the meso-β-scale vicinity of the convergence center characteristically coincide with type A but not with type S transitions. Despite such differences, in both cases, the transitions tend not to begin before the distance between the low-level convergence and vortex centers divided by rm reduces to unity.

Center vortex geometry at finite temperature

The geometry of center vortices is studied in SU(3) gauge theory at finite temperature to capture the key structural changes that occur through the deconfinement phase transition. Visualizations of the vortex structure in temporal and spatial slices of the lattice reveal a preference for the vortex sheet to align with the temporal dimension above the critical temperature. This is quantified through a correlation measure. A collection of vortex statistics, including vortex and branching point densities, and vortex path lengths between branching points, are analyzed to highlight internal shifts in vortex behavior arising from the loss of confinement. We find the zero-temperature inclination of branching points to cluster at short distances vanishes at high temperatures, embodying a rearrangement of branching points within the vortex structure. These findings establish the many aspects of center vortex geometry that characterize the phase transition in pure gauge theory. Published by the American Physical Society 2024

Characterization of tornado-induced wind pressures on a multi-span light steel industrial building

This study presents the characteristics of external wind pressures of a multi-span light steel industrial building through wind pressure measurements conducted in a tornado simulator. The test model is designed as a three-span low-rise building with gable roofs according to the practical measured sizes and shapes of the light steel industrial building destroyed in the Shengze tornado, China (2021). The distance from the tornado-like vortex center to the building, building orientation, roof angle, and swirl ratio are considered as experimental parameters. The effects of the parameters on the most unfavorable peak and mean pressure coefficients of each surface are analyzed. The roof zoning specified in ASCE 7–16 was re-analyzed based on the characteristics of wind pressure coefficients, and the tornado design pressure coefficients were calculated. The results of the analysis illustrate that the wind-ward roof surface at a distance of around one vortex core radius from the center experience the most severe pressure coefficient under tornado, the most unfavorable zone of the pressure coefficients on the building roof changes with the building orientation, the model with a smaller roof angle has smoother pressure coefficient contours than that with a larger roof angle because of the cutting effect of the ridge, and the simulated tornado with the lower swirl ratio generate higher external pressure coefficients on the building model. Moreover, the roof zoning in ASCE 7–16 for the boundary layer wind is not precise for tornado, thus an updated roof zoning for the tornado design pressure coefficients is defined.

Age-related alterations in vortex veins on indocyanine green angiography.

To determine age-related alterations in vortex veins in healthy subjects. A total of 228 healthy subjects (aged 4 to 86 years) were recruited and divided into four groups (G1, <21 years; G2, 21-40 years; G3, 41-60 years; and G4, 61-86 years). The clinical characteristics of the participants were recorded, and parameters including the number of vortex vein roots (NVVR), the central vortex vein diameter (CVVD), the mean root area of the vortex vein (MRAVV), and the weighted mean of the thickest branch diameter (WMTBD) were obtained by marking the vortex veins on indocyanine green angiography (ICGA). The NVVR in the age group over 60 years old was significantly lower than that in other age groups (P<0.05). The CVVD, MRAVV, and WMTBD of all age groups increased with increasing age (P<0.05). The NVVR was unevenly distributed among the quadrants (P<0.001). The proportions of type four vortex veins (complete systems including ampulla) and anastomotic branches of the vortex veins were significantly increased in elderly participants over 50 years of age (P<0.05). Subfoveal choroidal thickness was significantly correlated with age, NVVR, CVVD and MRAVV (P<0.05). This is the first study to reveal age-related alterations in vortex veins on ICGA in a healthy population. Aging may lead to partial vortex occlusion and residual vortex dilation. As age increases, anastomotic branches increasingly appear between the originally independent vortex veins. Translational relevance: Aging may lead to partial vortex occlusion and residual vortex dilation.

Semiclassics for the QCD vacuum structure through T2-compactification with the baryon-’t Hooft flux

We study QCD vacuum structure with the topological θ angle using a recently proposed semiclassical approach on ℝ2 × T2 with the ’t Hooft and baryon magnetic fluxes. Under the assumption of adiabatic continuity in this setup, the confining vacuum can be described by the dilute gas of center vortices. With this semiclassical approach, we derive the 2d effective description at small T2 and successfully explain the reasonable theta dependence of the QCD vacuum: in the one-flavor QCD at θ = π, the CP symmetry is spontaneously broken for quark mass above a critical value and restored for a subcritical mass, while the CP symmetry is always spontaneously broken in the multi-flavor QCD at θ = π. From our semiclassical description, we discuss implications to the 4d chiral Lagrangian and propose how the η′ meson should be incorporated in consistent with known global structures: the periodicity of the η′ should be extended from the naive one 2π to 2πN. Additionally, we revisit the phase diagram of Nf = 1 + 1 and Nf = 1 + 1 + 1 QCD on the up and down quark mass plane, confirming and refining the existence of the CP-broken Dashen phase.