Vortex Motion Research Articles

Modelling of gas-dynamic processes in the design of small-sized installation for the production of micro-powders by gas spraying melt quenching in a horizontal reactor.

A new scheme for obtaining metal powders by gas spraying is present. The atomization takes place in a horizontal reactor where the interacting flows of the melt and the atomizing gas are perpendicular. The theoretical calculations performed within the selected approximation, quantitative values of process parameters, describing the interaction of flows were obtained as a result. The penetration depth of the gas stream into the melt jet at different pressures and gas flow rates was appreciated. The liquid melt jet, in initial approximation, as a flow of non-reactive particles of a spherical shape with a diameter in the range 40-250 μm in order to evaluate the selected parameters of the design of the spray chamber (atomizer) was considered. A relationship between the distribution of gas flow velocities and the distribution of the velocities of condensed particles in the atomizer chamber was modelled. We have found the areas of the atomizer in which the “reverse” flow of light particles (with a diameter of less than 80 μm). The vortex motion of the gas in the chamber induces this effect. We have found and modeled the correlation between the distribution of gas flow velocities and the distribution of the velocities of condensed particles in the atomizer chamber. The simulation results show that the investigated range of gas-dynamic characteristics in the sprayer of the chosen design ensures the production of powder materials of a given dispersion.

Research on the Aerodynamic Noise Characteristics of Heat Exchanger Tube Bundles Based on a Hybrid URANS-FWH Method

This paper examines the aerodynamic noise characteristics of heat exchanger tube bundles, with the objective of exploring the frequency and directional features of noise under nonacoustic resonance conditions, to provide assistance in determining acoustic resonance. To predict the flow-induced noise of tube bundles, this study employs a hybrid URANS-FWH method. The transition SST model of URANS is used to accurately simulate the turbulent flow field and obtain precise statistical data on turbulence. The FWH equation is utilized to predict and evaluate the intensity and spectral characteristics of the tube bundle noise. The research findings indicate that the noise generated by the heat exchanger tube bundle is affected by pressure pulsations resulting from vortex motion in the deeper regions of the tube bundles. Notably, within specific frequency ranges, the noise intensity experiences a significant enhancement, potentially triggering complex modes of acoustic resonance. This resonance phenomenon poses safety concerns for equipment and threatens the wellbeing of personnel. Consequently, this study provides a solid theoretical foundation for predicting and controlling noise in heat exchanger tube bundles, offering valuable guidance for practical applications.

How hydraulic jumps form downstream of a negative step with channel expansion: experimental and numerical investigations of the transitions between wave jumps and submerged jets

AbstractWeirs and sills, particularly negative steps, play a pivotal role in modulating water flow, inducing hydraulic jumps that efficiently dissipate downstream energy. Beyond their aesthetic appeal, these features hold crucial engineering significance. This study combines physical experiments and numerical simulations downstream of a negative step featuring an abrupt width expansion. The spontaneous alteration of water flow conditions upstream and downstream of the step results in distinct flow regimes. By considering the critical Froude number to sustain an undular jump without wave breaking on a flatbed, we establish a framework for evaluating energy loss. Our analysis successfully delineates the transition limit between wave jumps and submerged jets downstream of a negative step. The co-existence regime of both jumps is explained by the analysis showing that the additional energy loss induced by the negative step is larger for the wave jump compared to the submerged jet. The abrupt width expansion at the negative step significantly reduces the transition depth between the submerged jet and wave jump, attributed to energy loss with intricate three-dimensional vortex motions—exceeding losses incurred by the negative step alone. We delve into the detailed mechanisms of these transitions through a three-dimensional numerical simulation of the energy-loss process and water surface profiles downstream of the step with expansion. The maximum energy loss by the undular jump and the minimum energy loss by the submerged jet are defined by the wave steepness at the limit of maintaining the undular jump and the jet plunging angle capable of sustaining the submerged jet, respectively.

New Physical Insight into High-Spin Physics: Double Helix Level Scheme A nuclear structure data approach

To present a new nuclear structure data concept of a level scheme, we redesign the high-spin level scheme of 171Yb nucleus. We start with the description of the property of repeatability of the Eγ data based on which Eγ can be parametrized by the 2c(2I + k − 1) formula with I the nuclear spin and k an integer band offset different from band to band. This describes a beam of parallel and equidistant lines whose 2c average slope and k numbers can be determined by a least-squares fit to the experimental bands, which characterize the average rotational behavior of the experimental bands. Based on repeatability the level scheme of 171Yb nucleus can be shaped as a discrete 3D double helix structure, with the experimental bands superimposed as decay paths. Double helix suggests that semiclassically nuclear rotation can be seen as a vortex motion.

Vortex flow induced self-assembly in CsPbI3 rods leads to an improved electrical response towards external analytes.

We present a facile and versatile strategy for enabling CsPbI3 rods to self-assemble at an air-water interface. The CsPbI3 rods, which float at the air-water interface, align under the influence of the rotational flow field due to the vortex motion of a water subphase. The aligned CsPbI3 rods could be transferred onto various substrates without involving any sophisticated instrumentation. The temperature of the subphase, the concentration of the CsPbI3 aliquot, the rotational speed inducing vortex motion, and the lift-off position and angle of the substrate were optimized to achieve high coverage of the self-assembled rods of CsPbI3 on glass. The Rietveld refinement of the XRD profile confirms that the aligned CsPbI3 is in the pure orthorhombic phase ascribed to the Pnma space group. The hydrophilic carboxylic group of the oleic acid attaches to the Pb atoms of the halide perovskite rods, while their hydrophobic tails encapsulate the rods within their shell, creating a shielding barrier between the water and the perovskite surface like a reverse micelle. The aligned CsPbI3 rods exhibit a nearly 47-fold increment in current upon exposure to ammonia gas (amounting to 5.6 times higher sensitivity in ammonia sensing) compared to the non-aligned CsPbI3 rods.

Statistical analysis of vortex condensate motion in two-dimensional turbulence

An inverse turbulent cascade in a periodic square box produces a coherent system-sized vortex dipole. We study the statistics of its motion by carrying out direct numerical simulations performed for various bottom friction α, pumping intensity ε, and fluid hyperviscosity ν. In the main approximation, coherent vortices can be considered as point vortices, and within this model, they drift at the same dipole velocity, which is determined by their circulation and mutual arrangement. The characteristic value of the dipole velocity is more than an order of magnitude smaller than the polar velocity inside coherent vortices. Turbulent fluctuations give rise to a relative velocity between the vortices, which changes the distance between them. We found that for a strong condensate, the probability density function of the vector ρ, describing the difference in the mutual arrangement of coherent vortices from half the diagonal of the computational domain, has the form of a ring. The radius of the ring weakly depends on control parameters and its width is proportional to parameter δ=ϵ−1/3L2/3α, where ϵ is the inverse energy flux and L is the system size. The random walk around the ring, caused by turbulent fluctuations, has superdiffusion behavior at intermediate times. It results in a finite correlation time of the dipole velocity, which is of the order of turnover time τK=L2/3ϵ−1/3 of system-size eddies produced by an inverse turbulent cascade. The results obtained deepen the understanding of the processes governing the motion of coherent vortices.

Modeling of ergodic processes in dynamic graphs of computer networks

Summary: For a mathematical model of mobile wireless computer networks, the random process of alternating network connectivity and disconnection was studied using several mobility models: isotropic random walk with reflection from the boundaries of the network location area, partially directed random walk, random walk with elements of vortex motion. The probability distribution functions of the durations of periods of network connectivity and disconnection are found, the ergodicity of the process and the uncorrelated nature of the period durations are shown. A large positive asymmetry of the distributions was noted, indicating the presence of a relatively small number of periods of long duration in the process. The analysis was carried out using simulation methods. The results of the analysis are presented as dependency plots.

Numerical Investigation of Inner Flow Characteristics of a Prototype Pump Turbine with a Single Pier in Draft Tube at Part Load Conditions

Pump turbines operate under various off-design conditions, resulting in complex internal flow patterns. This study employs Reynolds-averaged Navier–Stokes (RANS) numerical methods to investigate the flow characteristics of a prototype pump turbine with a single draft tube pier in turbine mode, and then, the flow characteristics inside the draft tube are discussed with emphasis. Asymmetry between the pier-divided draft tube passage flows is inevitable due to the elbow section’s curvature. Most of the fluid flows out of one passage, while vortex motion dominates the interior of the other one, resulting in completely different pressure fluctuation characteristics for the two flow passages. The large-flow passage is mainly characterized by the wide band in the frequency domain, corresponding to the recirculation zone, while some of the measured points in the low-discharge passage exhibit frequency splitting under kinematic progression. Further analysis demonstrates a low-frequency peak corresponding to the complementary shape between the vortex rope and the recirculation zone. This work elucidates the effects of the pier on the flow behavior and pressure fluctuation characteristics inside the draft tube and fills the research gap on piers in the field of pump turbines.

Clustering of Floating Tracers in a Random Velocity Field Modulated by an Ellipsoidal Vortex Flow

The influence of a background vortex flow on the clustering of floating tracers is addressed. The vortex flow considered is induced by an ellipsoidal vortex evolving in a deformation. The system exhibits various vortex motion regimes: (1) a steady state, (2) oscillation and (3) rotation of the ellipsoidal vortex core. The latter two induce an unsteady velocity field for the tracer, thus leading to irregular (chaotic) tracer motion. Superimposing a stochastic divergent velocity field onto the deterministic vortex flow allows us to observe significantly different tracer evolution. An ellipsoidal vortex has ellipsoidal symmetry, and the tracer’s trajectories exhibit the same symmetry inside the vortex. Outside the vortex, the external deformation flow symmetry dominates. Diffusion scattering and chaotic advection give tracers the opportunity to leave the region of ellipsoidal symmetry and form a picture of shear flow symmetry. We use the method of characteristics to integrate the floating tracer density evolution equation and the Euler Ito scheme for obtaining the floating tracer trajectories with a random velocity field. The cluster area and cluster mass from the statistical topography are used as the quantitative diagnostics of a floating tracer’s clustering. For the case of a steady ellipsoidal vortex embedded into the deformation flow with a random velocity field component, we found that the clustering characteristics were weakened by the steady vortex. For the cases of an unsteady ellipsoidal vortex, we observed clustering in the floating tracer density field if the contribution of the divergent component was greater than or equal to that of the rotational (nondivergent) component. Even when the initial floating tracer patch was set on the boundary of the oscillating ellipsoidal vortex, we observed the formation of clusters. In the case of a rotating ellipsoidal vortex, we also observed pronounced clustering. Thus, we argue that unsteady ellipsoidal vortex regimes (oscillation and rotation), which induce chaotic motion of the nearby passive tracer’s trajectories, are still conducive to clustering of floating tracers observed in the density field, despite the intense deformation introduced by strain and shear.

Analysis of the influence of swirling flow on the boiling heat transfer characteristics of two-phase flow

The Eulerian-Eulerian (EE) simulation approach + GENeralized TwO Phase (GENTOP) concept and two-fluid three-flow field with droplet were used to simulate the heat and mass transfer. Analysis encompassed the examination of steam and liquid phase distributions, as well as flow pattern transitions. Heat transfer enhancements were quantified using a comprehensive heat transfer factor. The disturbance intensity of the secondary flow was characterized by the absolute vortex flux. Results revealed a correlation between the intensity of the secondary flow and axial length, indicative of progressive fluid disturbance enhancement. Additionally, the maximal motion of the steam phase vortex was observed both near the wall and channel center. The EE+GENTOP concept exhibited superior capability in reproducing multi-scale flow including small-scale dispersed bubbles and large-scale continuous steam (coalescence and break-up). For investigations into the entrainment and deposition of liquid droplets in annular flow, the selection of a two-fluid three-flow field with the droplet model is recommended.

Radiated waves and rotational flows generated by cylindrical Oscillating Water Columns

This paper is concerned with the radiated wave and the rotational flow fields generated by the forced oscillations of the water columns within surface-piercing hollow cylinders. The present study utilised Open Foam as the viscous flow solver to numerically model the forced oscillations. An investigation of the radiated waves in the fields near the water columns confirms two distinct nonlinear characteristics. These are progressively reduced amplitude and progressively reduced phase difference. An evaluation of the rotational flow fields around the mouths of the water columns helps explain their origins. This study confirms that the nonlinear characteristics in the near-field are physically caused by the formation and motion of vortex ring at the bottom edge of the cylinder. Interestingly, the progressively reduced amplitude is not evident in the far-field. All these new findings support the confirmation regarding the appropriateness of linear radiation theory and the implication of the vortex motion on the effective draft of a fixed cylindrical Oscillating Water Column (OWC).

SPECTRAL STUDY LOWER SOLAR ATMOSPHERE OF THE ACTIVE REGION SITE WITH THE ELLERMAN BOMB AND ACCOMPANYING Hα-EJECTIONS

The results of studying in details the features formation and development of the Ellerman bomb (EB) and accompanying Hα-ejections arose on the NOAA 11024 active region site, are presented. This site was in the region of emerging new magnetic flux. Spectral data with high spatial and temporal resolution were obtained with the French–Italian solar telescope THEMIS on July 4, 2009. Spectra with the Hα line and with the spectral region λλ ≈ 630 nm were used. Stokes I profiles were obtained with an interval corresponding to 160 km on the Sun surface. The Hα line profiles obtained for different periods of EB development were asymmetric with an excess of emission in the short-wavelength wing. The temporal variations of intensity in the Hα line wings at distances ±0.1 and ±0.16 nm from its center indicated that two periods can be distinguished in EB evolution: the preheating phase and the flaring phase, during which the gradual and pulse energy release occurred. Hα-ejections (surges) are small-scale eruptions of cold matter in the solar atmosphere. In all spectra they were visible in the absorption. The surge profiles were projected onto the blue or red Hα line wing. Its Doppler shifts were used to calculate the line-of-sight velocities (Vlos) of chromospheric matter in surges. The velocity distribution in the surges indicated their multi-flow structure. One of the surges showed signs of plasma vortex motions. Most surges occurred with a high velocity – Vlos up reached -110 km/s, and down to 90 km/s. We obtained temporal Vlos variations in a wide interval (140 ─ 490 km) of photospheric heights for the area of EB development and its immediate surroundings. At all photospheric levels predominantly upward motions were found. In the central part of the EB in the upper layer of the photosphere the Vlos varied between -0.5 ÷ 0.2 km/s, in the lower layer – -1.1 ÷ -0.1 km/s. An increase the core intensity of all photospheric lines was correlated in time with an increase of the emission intensity in the Hα line wings. The new observational data for the Ellerman bomb and accompanying Hα-ejections, which have been obtained and analyzed, can be used to verify existing and create new theoretical models.

Superfluid Rivers in Spinning-down Neutron Stars

We study the motion of neutron superfluid vortices in a spinning-down neutron star, assuming axisymmetry of the flow and ignoring the motion of vortices about the rotation axis. We find that the vortex array, if initially rectilinear, is soon substantially deformed as the star spins down; vortices are swept outward by the Magnus force, accumulating in regions of the inner crust where they pin, accompanied by significant bending of the vortex array. As the star spins down to below a spin rate of ∼20 Hz (twice the spin rate of the Vela pulsar), the Magnus and pinning forces gradually compress the vortex array into dense sheets that follow spherical shells. In some cases, the vortex array bends on itself and reconnects, forming one or more tori of vortex rings that contain superfluid “rivers” with significant angular momentum. Vortex sheets are likely to form near the base of the inner crust in the regime of nuclear pasta.

Dynamics of two vortices on a finite flat cylinder

In this work, a model that describes the motion of point vortices in an ideal incompressible fluid on a finite flat cylinder is obtained. The case of two vortices is considered in detail. It is shown that the equations of motion of vortices can be represented in Hamiltonian form and have an additional first integral. A procedure of reduction to a fixed level of the first integral is proposed. For the reduced system, phase portraits are constructed, fixed points and singularities of the system are indicated.

One sight on sound generation and absorption by vortices

Vortices generate sound and absorb sound. A. Powell and M. S. Howe deduced the equations and showed that the exterior product of vortex and local velocity took part in sound generation and absorption. However, it is difficult to image its physical phenomena. In this paper, as one example, the interaction of sound and vortices at the throat of a cavity with grazing flow is investigated by CFD simulation. As the results, it is found that sound absorbing regions and sound generating regions are locally distributed and moving. It is also found that when counterclockwise vortices turn to the left, they absorb sound and when they turn to the right, they generate sound. Based on these results, 'Floating Vertical Bar Model (FVB Model)' is proposed to image the sound generation and absorption phenomena, in which a vortex is simulated as a bar floating vertically on the water surface, because a vortex has coherent structure along its axis like a bar. When a vortex (a bar) is accelerated perpendicular to its axis, pressure fluctuation (water wave) is easily generated. And when sound wave (water wave) shakes a vortex (a bar), sound energy is absorbed by a vortex (a bar) motion.

Turbulence and Pollutant Statistics around a High-Rise Building with and without Overhangs

Wind flow around an isolated building is highly turbulent. Facade appurtenances can further increase the complexity of the flow, which strongly affects the gas dispersion around the building. This study investigated the turbulence and pollutant statistics around a high-rise building with large-eddy simulations and determined the influence of overhangs on the local wind flow and dispersion. Large-scale periodic vortex motion was detected. The results indicated that both the oncoming flow and the flow around the building followed a standard Gaussian distribution, whereas the occurrence frequencies of pollutant concentrations were far from Gaussian for pollutants discharged from both the rooftop and the ground behind the building. Near the pollutant sources, the positive concentration fluctuations occurred more frequently; occasionally, positive and negative fluctuations occurred equally. For the majority of areas far from the source, negative fluctuations were more common, but the maximum positive fluctuations were much larger. Overhangs changed the local flow structures near the building facade. Both the maximum concentration fluctuation and the maximum occurrence frequency decreased in the region between overhangs because turbulence was restricted.

Guided vortex motion in a ferromagnet-superconductor bilayer

Vortex motion in ferromagnetic-superconducting bilayers constituted by thin manganite La0.67Sr0.33MnO3 film deposited on the top of thin YBa2Cu3O7−δ film has been investigated. Both films were deposited on uniformly twinned single-crystalline substrates and patterned into strips directed at different angles to the twin lines pattern. These conditions lead to the guided vortex motion at different angles to the periodic pinning potential. It has been established that critical current and flux flow resistance in such an anisotropic pinning landscape-scale follow the elliptic dependence on the angle of the direction of the strip.

Model Verification and Experimental Study of The Turbomachinery Wake Flow Field Reconstruction

Abstract A clear understanding of the turbomachinery wake flow field is one of the key problems in developing turbomachinery aerodynamics. The theoretical model of helical vortices is established in cylindrical coordinates (r,θ,z), and the model corresponds to the experimental scheme, which verifies the feasibility of reconstructing flow field by interpolation in r-z plane under different θ. This model shows that theta should not exceed 20 degrees in order to reconstruct the flow field more accurately. Taking rotors as the representative of the turbomachinery, Particle image velocimetry (PIV) is used to measure the velocity field in the rotor wake. Interpolating reconstruction of spacing between different measurement planes, the reconstruction results are relative to the theory, which plane spacing should be less than 20 deg. Using the vorticity weighted average method to calculate the central position of the vortex core, the wandering motion of the tip vortex is obtained. On this basis, a correct conditional average algorithm is proposed to eliminate this effect. Through the analysis method of the circulation, it is proved that the point where the second derivative of the circulation with respect to the radius is 0 corresponds to the radius of the vortex core, and the evolution law of the growth of the vortex core radius is proportional to the square root of the vortex ages. The results provide a reliable experimental method for the quantitative study of the spatio-temporal evolution of complex vortex structures in the three-dimensional flow of turbomachinery wakes.

Restriction of vortex motion in superconducting NbN film via ion irradiation

Restriction of vortex motion in superconducting NbN film via ion irradiation

Study on improving liquid carrying performance of annular jet pump gas well with static mixer

AbstractIn the process of natural gas extraction, the phenomenon of liquid loading will affect the efficiency of gas well extraction and reduce the life of the well. Compared with conventional drainage gas extraction technology, the jet pump can not only reduce the bottom back pressure and ensure the stable production of gas reservoirs but also promote the final recovery rate. Since the jet pump relies on the interaction between fluid particles to transfer energy, the energy loss is large and the efficiency is low. To maximize the advantages of the gas‐driven jet pump, this study innovatively combines a static mixer with an annular jet pump. Utilizing the cyclonic effect produced by the static mixer, the original gas‐liquid axial motion is transformed into a stronger vortex motion, and the liquid droplets are changed into a liquid film that is easier to carry, which significantly improves the discharge efficiency of the jet pump. This study uses a combination of numerical simulation and experimental analysis to compare the associated effects of the new annular jet pump (NAJP) and the conventional annular jet pump (CAJP) on the liquid‐carrying performance of gas wells in terms of cyclonic effect, droplet breakage ratio, and pump efficiency. The results show that, compared with CAJP, NAJP increases the mass flow rate of the sucked fluid. The droplet breakage ratio increases by 15.4% year‐on‐year, while the critical liquid‐carrying flow rate is reduced by about 10.7%, resulting in a maximum pumping efficiency of 37%, an increase of about 30.7% year‐on‐year. At the same time, the reduction of the energy coefficient means lower energy consumption. In summary, NAJP is better than CAJP in terms of liquid‐carrying effect and efficiency.