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This article continues and generalizes the study "On the Similarity of Quasi-Geostrophic Vortices against the Background of Large-Scale Barotropic Currents" [6] (Oceanology, Zhmur, 2024, in print). In continuation of [6], a similar formulation is considered, but for other types of background currents. In the quasi-geostrophic description for small Rossby numbers, the problem of the evolution of an arbitrarily shaped liquid volume with homogeneous potential vorticity of all vortex core particles in an equidistant background flow—horizontal flow with vertical shear and equidistant flow with barotropic and baroclinic components—is presented. Ultimately, the problem boils down to an integrodifferential equation for the evolution of the vortex core boundary. The study of this equation in dimensionless form makes it possible to find a set of dimensionless parameters that determine the similarity condition of the studied vortices. [ABSTRACT FROM AUTHOR]

It is shown that the front of the flame of a thoroughly mixed diluted methane-oxygen mixture at 298 K and 100–300 Torr propagating to the ends of hollow cylindrical and conical obstacles does not form a von Kármán path (vortex shedding) behind them; however, this instability occurs under the same conditions in the flow of hot products after obstacles. The reason that vortex shedding is not observed behind an obstacle during flame propagation but appears in the course of propagation of a reflected stream of hot products is that thermal conductivity reduces the curvature of the flame and leads to its stabilization. Indeed, the convex areas of the chemical reaction zone in a combustible mixture give off more heat in relation to cold ones than in a flat flame: the heat from them is not only transmitted forward in the direction of flame propagation but also in the lateral directions. The resulting cooling of the reaction zone causes the flame regions that burst forward to lag behind. The opposite situation is observed in concave areas, where the temperature rises for the same reasons. The rate of reactions increases and they spread forward faster as the flame spreads. Thus, the surface of the curved front of the flame is evened out. In other words, thermal conductivity has a stabilizing effect on a curved flame. This effect is missing in non-reactive gas. This effect is absent in a nonreacting gas. Calculations based on the acoustic approximation of the Navier–Stokes equations for a compressible reacting medium make it possible to take into account the main observed feature of the flame front approaching an obstacle in the form of a cylinder: vortex shedding is not observed behind the obstacle during flame propagation. Thus, a qualitative model allows obtaining both the mode of the emergence of a von Kármán instability in a chemically inert gas and its absence during flame propagation. [ABSTRACT FROM AUTHOR]

Fully resolved direct numerical simulations are used to quantify the effect of evolving heat, due to idealized smoldering processes, on the aerodynamic forces of a spherical particle, representing an idealized fixed-shape firebrand particle. Firebrand particles are small glowing particles that are generated in fires and can be transferred long distances by the wind and create new spot fires. Understanding the transport of firebrands is of great importance in fire science. The simulations are performed at a Reynolds number of 500, relevant for a wide range of firebrand size and wind velocity combinations. The spatiotemporal variation of temperature over the surface of the particle is obtained using a detailed surface energy balance analysis. The firebrand particle is assumed to have the thermal and material properties of pine needles and has a Biot number larger than unity, which means that the particle undergoes notable internal temperature gradients. The results indicate that the buoyancy-induced flow around the particle significantly modifies the trailing vortices and produces two non-interacting tunnel-shaped plumes in the wake of the sphere as the particle's Richardson number increases. As a result, the particle's drag and lift coefficients show large deviations from those of a non-heated particle and an isothermal particle. The increased surface temperatures result in an increase in the drag force while inducing a negative lift. The significant variations seen in the aerodynamic forces as a function of the particle's instantaneous temperature indicate that the influence of the transient thermal conditions of firebrands should be considered in the prediction of the particles' trajectory and landing spots. [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]

One of the factors significantly influencing the flow structures and vortices formed on delta wings is the shape of the leading edge. This study examined the impact of needle vortex generators, inspired by owl wings, on the flow characteristics over a slender delta wing with a sweep angle of 65° to improve its aerodynamic performance. These nature-inspired vortex generators were designed to apply no additional flow blockage or drag force. Flow visualization tests were conducted in a smoke tunnel to gain deeper insights into the effects of the vortex generators on the flow physics over the delta wing. The experiments were performed at three angles of attack of 10°, 15°, and 20° and a flow velocity of 2.6 m/s on two delta wings, with and without needle vortex generators at the leading edge and a Reynolds number of Re = 2.6 × 10 4 . Flow visualization was conducted on six longitudinal sections, six transverse sections, one-floor surface section, and one leading edge section at three different angles of attack. In addition, the investigation involved assessing the vortex breakdown location and wake region. The formation of the vortices and the effects of the needle vortex generators on the temporal and instantaneous flow structures and vortices were also investigated. The results suggested that the use of the needle vortex generators along the leading edge of the delta wing made the vortices smaller and closer to the wing surface and wing axis, postponed the vortex breakdown by approximately 13% of the chord length, and decreased the fluctuations of vortex breakdown location. In addition, the use of needle vortex generators eliminated the secondary vortices. [ABSTRACT FROM AUTHOR]

With a global population estimated at 2000 individuals between Argentina and Chile, less than 1% of its historical population, the huemul (Hippocamelus bisulcus) is categorized as "Endangered". Through a population viability analysis, we sought to estimate the viability of two huemul populations under different threat scenarios. Through a sensitivity analysis, we expected to identify those threats, and environmental or population variables that are more relevant for each population survival. Our main goal is to contribute to the management of the species in Chile through threats prioritization seeking to focus future conservation strategies. This research involved huemul populations from the Nevados de Chillán-Laguna del Laja Biological Corridor Biosphere Reserve (NCLL) and the Cerro Castillo National Park (PNCC). The NCLL population showed a very low probability of survival with a mean time to extinction of 45.9 years; in contrast, PNCC population exhibited a higher probability of survival with a mean time to extinction of 68.6 years. Predation and harassment by dogs seem to have the most significant negative impact on both populations' fate. Additionally, populations were highly sensitive to the percentage of reproductive females and female mortality. Based on our findings, we proposed concentrating conservation efforts on reducing or eliminating dogs' chances to attacks and predate huemul, as well as to focus surveillance actions on females. [ABSTRACT FROM AUTHOR]

Expressions are obtained for the position of the maximum Imax of the Fourier transform of a Bessel–Gaussian beam (BGB) and its dependence on the topological charge is substantiated. It is found that Imax depends on the angle of the cone and the parameters of the Gaussian beam. Here, as the cone angle is reduced (and, therefore, the diffraction-free region increases), the distances between the maxima of the intensity distributions in the focal plane of the lens, corresponding to different magnitudes of the topological charge, increase. An expression is found for the position of the energy center of the Fourier transform of the BGB and it is shown that it also depends on the cone angle γ and the size of the Gaussian beam waist w0. As the product γw0 increases, the shift in the energy center of the BGB relative to the radius R of the annular Fourier spectrum in the approximation of geometric optics decreases. These results reveal the impossibility of forming perfect vortices with a BGB. Here the degree of their "imperfection" is determined by the deviation of the maximum of the intensity distribution in the focal plane of the lens on the parameter R which specifies the radius of the ring of the Fourier image of the Bessel beam, which is greater for beams with a larger diffraction-free region. [ABSTRACT FROM AUTHOR]

We propose a method for calculating the kinetics of ultrasonic coagulation of PM2.5 during fine gas cleaning that provides an order of magnitude higher calculation performance. Increased productivity is achieved through the proposed and justified method of reducing the original three-dimensional problem to a two-dimensional one. The proposed reduction method is based on the fact that the time of complete rotation of vortex acoustic flows turns out to be much shorter than the characteristic coagulation time during fine gas cleaning. This makes it possible to present the fractional composition of aerosol particles as a function of two stream functions instead of three coordinates. Calculations carried out using the proposed method make it possible to identify the possibility of increasing the efficiency of coagulation in three-dimensional flows due to the following mechanisms: a local increase in concentration caused by the inertial transfer of particles to the periphery of three-dimensional vortices in the gas phase, increasing the frequency of particle collisions due to three-dimensional turbulent disturbances in ultrasonic fields with a high amplitude of oscillatory velocity (more than 10 m/s), and increasing productivity and ensuring the possibility of continuous implementation of the process in flow mode due to the transfer of particles between the streamlines of the main vortices initiated by ultrasonic vibrations as well as due to external flows perpendicular to the plane of the vortices in three-dimensional space. The developed set of programs for implementing calculations can be used in the design of gas cleaning equipment. [ABSTRACT FROM AUTHOR]

Optimizing the slug bubble size specifically for ultra-thin flat sheet membranes in MBR systems can effectively enhance the scouring force and improve fouling control efficiency, thereby further advancing their targeted and widespread application. In this study, a three-dimensional model was developed based on the practical application to investigate the impact of slug bubbles on scouring performance in ultra-thin flat sheet MBR systems, encompassing their evolution, disturbance level, and shear stress. A membrane fouling probability index for quantifying the distribution of membrane fouling, along with a turbulence intensity index have been proposed. The findings revealed that the 20-mL slug bubble induced the highest disturbance level in the surrounding fluid, characterized by an instantaneous peak velocity of 0.63 m/s at the local system level, conducive to bubble scouring. And exerted the greatest shear stress effect, achieving the most effective reduction in membrane contamination, with a maximum shear stress of 1.82 Pa. The experimental validation conducted during the operational cycles confirmed that the scouring effect of 20-mL slug flow yielded in a maximum proportion of 48.16% within the low fouling probability region. The results provided evidence supporting the assertion that specific aeration conditions producing 20 mL of bubbles resulted in minimal membrane fouling, ensuring a more pronounced scouring effect. The combination anythsis of slug bubble characteristics and behaviors, integrating theoretical and experimental approaches, implied that 20 mL was the optimal bubble size in ultra-thin flat sheet MBR, which fulfilled the optimal air scouring effect. [ABSTRACT FROM AUTHOR]

This study presents an analysis of heat transmission and magnetic nanofluid flow in a minichannel with corrugated upper wall and exposed to a magnetic field. Choice of this geometry allows an improvement of heat transfer contrary to that of rectangular shape. This study is developed to complete the existing ones in the literature. In this two-dimensional study, flow is supposed to be laminar, and the chosen fluid is Fe3O4-water magnetic nanofluid which is used as cooling fluid. For this nanofluid, two volume fractions (0.6, 1%) were used. Several simulations were conducted for a series of Reynolds numbers which vary between 150 and 210 and magnetic field strengths which take values ranging from 0 up to 1400 G for two chosen configurations (a source located at 15 mm and two sources located, respectively, at 7.5 and 15 mm). The results obtained show that magnetic nanofluid subjected to a magnetic field seems as an active vortex generator which modifies the flow structure, allowing a good mixing of the fluid and consequently an improvement in heat transmission. For selected values of magnetic field intensities, an improvement in heat transmission was observed followed by a reduction in pressure drop. This is due to the separation of the fluid from the lower wall which reduces the friction effect. Rise in volume fraction does not modify the flow structure, and it allows an enhancement in heat transfer. According to results obtained, we note a maximum of 10.21% enhancement of heat transmission in the case of a source located at 15 mm and a maximum of 27.44% of improvement of heat transmission in in the case of application of two sources for the case where the volume fraction is equal 1%. With this study, we can locate the correct position of the magnets allowing a good heat transfer rate. [ABSTRACT FROM AUTHOR]

High-speed video recording was used to trace the matter transfer pattern of a free-falling water drop and of the deformation of the free surface of the target fluid at the intrusive mode when the available potential surface energy (APSE) exceeds the kinetic energy of the drop. The free surface of the unified drop-target fluid system remains convex at the initial submerging stage. The inflowing drop forms a lenticular intrusion in the fluid bulk, which gradually transforms into a vortex ring. A cavity begins to form with a time delay Δt = 10 to 12 ms. The cavity surface includes traditional flat, spherical, cylindrical and conical sections moving at different velocities. The temporal variability of the intrusion and cavity geometry was traced. The drop substance is preserved as individual fibers in the wake of the submerging ring. [ABSTRACT FROM AUTHOR]

The generation of chirality in supramolecular structures from achiral building blocks has remained a challenge for a long time. In this study, we present a vortex-assisted chiral supramolecular polymerization from a series of achiral C3-symmetric monomers, where the mechanism of symmetry-breaking is systematically investigated. By increasing the supersaturation, at the early stage of nucleation and growth, highly ordered assemblies can be generated as the initial chiral nuclei. Meanwhile, chiral assemblies from high supersaturation are hard to interwind into clusters, where clusters as nuclei are not conducive to being fractured by sheer force of vortex fluid. Therefore, it is concluded that chiral assemblies in the nucleation stage possess low energy barrier, so that chiral nuclei could be fractured and replicated by the vortex. By enlarging the initial chiral bias, the major chiral nuclei can evolute into the final chiral polymers. [ABSTRACT FROM AUTHOR]

The effect of the gap between the propeller tips and the inner wall of the duct ring on the thrust and available capacity of the ducted propeller propulsion system is investigated. The structure of vortex flow in a thin gap between the end surface of the propeller blades and the air ring of the ducted propeller is analyzed, as well as the features of the propeller blades flow at boost modes. [ABSTRACT FROM AUTHOR]

New-type vortex structures in a 3D ferromagnet—vortex rings—are predicted. It is established experimentally that these structures have finite energy. The nature of the interaction of pairs of such rings in the simplest cases is investigated. [ABSTRACT FROM AUTHOR]

A gun-track launcher that combines a balanced gun with a rocket track is an important technology for the non-destructive recovery of high-value projectile weapons. Given the restrictions imposed by the track and the interference caused by it, the muzzle jet of such launchers is significantly different from those of traditional artillery. Given this engineering background, this study examines the characteristics of the evolution of supersonic muzzle jets with different constrained boundaries. Results show that the structure of the muzzle jet undergoes a distortion that changes its symmetric circumferential shape into an asymmetric one, tilted above the center of the muzzle. Vortexes are generated below the track owing to lateral airflow, and their formation and evolution lead to significant changes in the pressure of the flow field. Moreover, the asymmetry of the flow field varies owing to the different structures of the side plates of the track, which leads to varying characteristics of the development of shock waves and vortexes in the muzzle jet. The content of this article provides a theoretical basis and necessary technical support for enriching the research connotation and engineering applications of shock wave fields. [ABSTRACT FROM AUTHOR]

Shear banding in amorphous metals originates from the activation and percolation of flow units. To uncover the self-assembly dynamics of flow units in metallic glasses, a rectangular sample with two flow units embedded in the matrix undergoing simple shearing was analyzed using finite element simulations. The vortex evolution behavior, including activation, growth, and collapse during the self-assembly of flow units, was revealed. It was found that the formation of a mature vortex indicates the onset of yielding, and the collapse of the vortex represents the percolation of flow units or shear localization. The effects of initial free volume distribution and the distance between flow units on vortex behavior were also studied. Increasing the initial free volume concentration within flow units or the matrix leads to a gentler vortex evolution process and better homogeneous plasticity. The shape of vortex tends to be "flatter" with the increase in flow units' spacing, and the optimal spacing was found to maximize the strength of the material. [ABSTRACT FROM AUTHOR]

Several researchers tended to study and develop vortex technologies to generate clean electric power, it generates a vortex updraft air stream while operating at a moderate temperature scale. The conventional solar air collector with a vortex engine has been shown to be insufficient for starting and maintaining updrafts by a previous model. So, this research sought to propose and design a new solar vortex engine system and improve the system by conducting a set of calculations carried out by the ANSYS 2020 R2 simulation program. The research focuses on increasing the performance of the proposed model by changing the angle of the Guide Vane to increase the vortex force generated where four angles are proposed. Where four different angles were proposed that are close to the angles of previous studies (10°, 15°, 20°, and 25°). The air intake speed has been changed on each proposed angle. The proposed model was validated by its general behavior, which is similar to previous studies in performance. After a comparison was made between the results of the proposed models, it was found that the angle of 20 deg gives the highest performance of the model that was designed and tested using the ANSYS program. [ABSTRACT FROM AUTHOR]

Southern chamois (Rupicapra pyrenaica) is a medium-sized and gregarious mountain ungulate with populations affected by periodic outbreaks of border disease virus (BD), infectious keratoconjunctivitis (IKC), and sarcoptic mange (SM). Even though the impact of each disease on chamois populations has been described in detail, there is a lack of information about the potential impact of concomitant epidemics and the synzootic potential (co-occurring enzootic or epizootic processes producing worse health outcomes in wildlife) on chamois populations. Furthermore, whether a specific order of apparition of epidemics is more or less harmful for the host population is practically unknown not only for chamois but also for most mammal populations. Using a population viability analysis (PVA), we studied the consequences of multiple disease outbreaks with synzootic potential on growth rates and probabilities of extinction of virtual populations exposed to hard winters, density dependence, and co-occurring BD, IKC, and SM outbreaks. Such infections are not under cross-immunity nor density-dependent processes and thus are supposed to affect population demography independently. Heavy snowfalls are also likely to occur in our simulated populations. Our simulations showed that a second outbreak, even caused by a low virulent pathogen, causes an increase in the probability of extinction of the host population with regard to the first outbreak. IKC-BD- and SM-BD-affected populations had a higher risk of becoming extinct in 50 years confirming the extra risk of multiple outbreaks on the viability of the affected populations. [ABSTRACT FROM AUTHOR]

The term "vortex" refers to a region in a fluid where the flow spin around an axis line, which could be flat or curved. Vortices can twist, stretch, move, and interact in several situations, once they are formed. The angular and linear momentum, along with some energy and mass, are all noticeable in a rotating vortex. Descriptions of vortices developed in various flows include smoke rings, dust devils, cyclones, and the wind surrounding a tropical tornado. The existence of vortices in the natural environment makes it important for researchers to explore them when and wherever they are encountered. Magnetic field effects include numerous technical applications such as: B. Extraction of geothermal energy, casting of metals, cooling of nuclear reactors. Hybrid nanofluids, on the other hand, are more effectively accepted as next-generation thermal systems in automotive cooling applications, heat exchangers, and HVAC due to their higher thermophysical properties. The purpose of this work is to study how local magnetic fields affect the magnetic flux of a hybrid nanofluid inside an enclosure induced by a magnetic source. We implement a single-phase model (SPM) to classify hybrid nanofluids and computationally evaluate the associated partial differential equations (PDEs). The results reflect that the localized magnetic field generates a counter-rotating vortex in the flow which breaks apart the other vortex and hence becomes strengthened. The vortex elongates along the direction of the localized magnetic field and tends to occupy a major part of the cavity. Magnetic field decreases in the thermal gradient near the horizontal walls of the enclosure. The faster-moving lids cause more rigorous mixing of the layer of fluid at different temperatures, which distorts the uniformity of the pattern of isotherms. Finally, heat transport is more affected by the magnetic field as compared to skin friction. [ABSTRACT FROM AUTHOR]

A review of fundamental theoretical publications is presented, wherein the flow of an incompressible fluid in the cores of three-dimensional vortex sheets formed in the case of the separated flow of low-aspect-ratio wings are considered. Problems concerning an inviscid-fluid flow in the core of a conical vortex sheet and a vortex sheet vanishing from the edges of a parabolic wing, as well as the problem of a viscous-fluid flow in the core of a conical vortex structure, are considered. [ABSTRACT FROM AUTHOR]

A review of fundamental theoretical studies concerning the theory and application of the nonsteady-state analogy to an incompressible fluid flowing around slender bodies is presented. Problems related to the application of nonsteady-state analogy to wings, to the wake behind an elliptically loaded wing, as well as methods for numerical calculation of the evolution of vortex sheets and for determining the positions of lines of low separation from solid surfaces are considered taking into account viscous-inviscid interactions. The issues of nonuniqueness and asymmetry of solutions for the problems of a separated flow moving around slender bodies are discussed. [ABSTRACT FROM AUTHOR]

A review of fundamental theoretical studies concerning plane vortex flows in an incompressible fluid is presented. Problems connected with flow in the vicinity of the point of a vortex sheet vanishing from a solid surface, with self-similar flows of an ideal and viscous fluid, with flow in the cores of spiral vortex sheets, with the stability and diffusion of vortex flows, and with the development of a theory of boundary-layer separation from a solid surface are considered. [ABSTRACT FROM AUTHOR]

The most important design index of water intakes is critical submergence depth of the intake. The depth at which the air core formed by the vortex is about to enter the intake. The emergence of a vortex and air entry into the intake increase head loss and decrease discharge coefficient. The reservoir geometric asymmetry, presence of unevenness in the bottom of the reservoir and angle of approach flow are among the factors that influence formation of the vortex and critical submergence depth. In this research, a physical model has been used to investigate the effect of reservoir geometry on the critical submergence depth. This model is designed in such a way that it can produce the strongest type of vortices with air core and with different strengths. The results showed that by creating asymmetry in the flow approaching the water intake (with side blockage in upstream), the presence of even 10% side blockage can have a great effect on the formed vortex and increase the critical submergence depth by about two times. To create uneven conditions on the reservoir bottom, blockages were created on the bottom of the reservoir upstream of the intake. The results showed that the blockage up to half of the height below the intake caused an increase of about 10–25% of the critical submergence depth, in low and high Froude numbers, respectively. However, in blockages more than half of the height below the intake, this effect increases about 60% of the critical submergence depth. In addition, the effect of the slope of the intake head wall on the order (type) of the vortex and its stability and instability was studied, and it was found that the order of the vortex decreases with the increase in the slope of the head wall toward the vertical position. Also, by increasing the slope of the head wall, the vortices form in an unstable manner. The vertical head wall can act as an anti-vortex structure and cause a reduction in critical submergence depth. [ABSTRACT FROM AUTHOR]

Policies and measures to control pandemics are often failing. While biological factors controlling transmission are usually well explored, little is known about the environmental drivers of transmission and infection. For instance, respiratory droplets and aerosol particles are crucial vectors for the airborne transmission of the severe acute respiratory syndrome coronavirus 2, the causation agent of the coronavirus 2019 pandemic (COVID-19). Once expectorated, respiratory droplets interact with atmospheric particulates that influence the viability and transmission of the novel coronavirus, yet there is little knowledge on this process or its consequences on virus transmission and infection. Here we review the effects of atmospheric particulate properties, vortex zones, and air pollution on virus survivability and transmission. We found that particle size, chemical constituents, electrostatic charges, and the moisture content of airborne particles can have notable effects on virus transmission, with higher survival generally associated with larger particles, yet some viruses are better preserved on small particles. Some chemical constituents and surface-adsorbed chemical species may damage peptide bonds in viral proteins and impair virus stability. Electrostatic charges and water content of atmospheric particulates may affect the adherence of virion particles and possibly their viability. In addition, vortex zones and human thermal plumes are major environmental factors altering the aerodynamics of buoyant particles in air, which can strongly influence the transport of airborne particles and the transmission of associated viruses. Insights into these factors may provide explanations for the widely observed positive correlations between COVID-19 infection and mortality with air pollution, of which particulate matter is a common constituent that may have a central role in the airborne transmission of the novel coronavirus. [ABSTRACT FROM AUTHOR]

This study aims to investigate the impact of cavitation states on the stability of cryogenic pumps. Steady and unsteady simulations of the internal flow were conducted based on an SST k–ω turbulence model and a modified Zwart cavitation model considering thermodynamic effects. The modified cavitation model was verified using the hydrofoil model and compared with the Hord test results. The results indicate that the variation in pressure at the pump inlet has a significant influence on the cavitation in the pump. The cavitation states and fluid flow directions vary across the different spans in the impeller channel. The smaller the distance from the front cover of the impeller, the more severe is the cavitation, in addition to the appearance of a vortex. The influence of the formation of a longitudinal vortex at the impeller outlet on the pressure fluctuation in the cavitation state was revealed. The rotation of the impeller has negligible influence on the pressure load distribution at the blade inlet. However, it has a higher influence on that of the second half of the blade, particularly when the blade passes through the volute tongue. Cavitation can exacerbate the instability of pump operation. The research results are significant for accurately predicting cavitation performance and improving the anti-cavitation capability of cryogenic pumps. [ABSTRACT FROM AUTHOR]

The decision to intervene in endangered species management is often complicated. Migratory species exemplify this difficulty because they experience diverse threats at different times and places that can act cumulatively and synergistically on their populations. We use population viability analysis (PVA) to compare potential conservation interventions on the critically endangered, migratory Orange-bellied Parrot Neophema chrysogaster. This species suffers high juvenile mortality, but it is not clear why this is so. Given uncertainty about the best recovery strategy, we compare PVA scenarios that simulate various ways of utilizing captive-bred parrots to support the wild population in the context of unresolved threatening processes. Increasing the number of juveniles entering the population each year had the greatest benefit for population growth rate and size. Directly lowering juvenile mortality rates is difficult given uncertainty about the drivers of mortality in the wild. In lieu of this, releasing 100 juveniles from captivity to the wild population each autumn (either as a stand-alone action, or in combination with other interventions) was the most feasible and straightforward intervention of the options we tested. However, our PVAs also show that unless substantial and sustainable reductions can be made to juvenile mortality rates, Orange-bellied Parrots will remain dependent on intensive conservation management. This study highlights the utility of PVAs for answering practical questions about how to implement species conservation. PVAs provide a way to incorporate the best available information in a replicable modelling framework, and to identify impacts of parameter uncertainty on demographic trends. [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]

This paper presents a numerical investigation of the interaction among wave, flow and a fixed cylinder using the naoe-FOAM-SJTU solver, which is a viscous solver for hydrodynamics based on OpenFOAM. The simulation considers the strong nonlinear interaction among a regular wave, flow, and a single fixed cylinder due to viscosity, which is common in offshore structures. The study focus on the vortex induced by viscosity and its significant role in hydrodynamic performance computation. A mesh convergence study is conducted prior to the simulation, and a proper set of mesh is chosen. The simultaneous generation of the regular wave and flow is realized using the numerical field boundary, and the wave propagation is validated. The results of wave elevation and pressures captured by wave gauges and probes around the fixed cylinder are compared with experiment results. The structure of vortices is displayed at significant times, and the phenomena of wave elevation and pressure changes around the cylinder are analyzed in detail using the Omega-Liutex identification method. [ABSTRACT FROM AUTHOR]

In this paper, a detailed analysis of the distribution of intensity of vortex circular airy beam (CAB) propagating in a turbulent atmosphere applying Fresnel–Kirchhoff diffraction integral equations is presented. A turbulent atmosphere consists of different types of aberrations. The existence of aberrations in an atmosphere under turbulence plays a vital part in affecting the quality of optical beams. Here, the effect of different aberrations such as z-tilt, defocus, astigmatism, coma, and spherical aberration on the intensity distribution and structure of vortex CAB at two different propagation distances under four different atmospheric turbulent conditions with topological charge m = 1 were investigated. The two different propagation distances which we have used in this scenario are z = 2000 m and z = 5000 m. A numerical analysis was performed for each aberration, and corresponding 3d and 2d plots were plotted. The results show that spherical aberration has the highest effect than the other four aberrations on the intensity distribution of vortex CAB and z-tilt aberration has the least effect. Also, the analysis shows that the quality of the beam reduces with an increase in propagation distance. A comparison study was also done to identify the difference between vortex CAB and non-vortex CAB. Based on the comparison results, it is revealed that the maximum intensity distribution and quality of beam could be achieved more with vortex CAB than with non-vortex CAB. [ABSTRACT FROM AUTHOR]

Using the RANS approach, the phenomenon of interference of the jet flow during its deceleration with the windward edge of an inclined groove on the streamlined surface and the tornado-like vortex generated at the groove inlet is established. Experiments confirmed emerging of extra-ordinary static pressure drop between the stagnation and rarefaction zones. The backflow velocity increases twice and this velocity magnitude exceeds the mass-average velocity. The study justifies the abnormal separated flow related to heat transfer enhancement for the cases of inclined grooves on a structured plate and the wall of the narrow channel. This phenomenon produces a multiple (up to 6–9 times) growth of the relative friction and heat fluxes inside the grooves (compared to the case of a plain wall). We observe also the acceleration in the near-wall stream caused by a set of single-row inclined groves arranged in a narrow channel. Here the maximum velocity in the stream core within this structured channel increases by more than 1.5 times as compared to peek velocity for a flow in a plane-parallel channel. The study is useful in the aerodynamic design of new energy-efficient groove-structures surfaces. [ABSTRACT FROM AUTHOR]

When mesoscale vortices interact with the flow, there are three variants of their behavior: rotation, nutational oscillations, and unlimited elongation. This work describes the physical conditions of vortex transformation into filaments. The proportion of vortices that are stretching out into filaments in the World Ocean and some regions, redistributing the energy from mesoscale to submesoscale, is calculated. [ABSTRACT FROM AUTHOR]

The hemodynamics of intracranial aneurysm (IA) comprises complex transient flow patterns that affect its growth and rupture. Owing to the combined effects of geometrical factors and pulsatile flow conditions, the transient flow patterns in the IA are still unclear. The purpose of this work is to reveal the effect of the aspect ratio (AR, sac height/neck width) on the evolution of the internal flow patterns and the hemodynamics of the IA. We proposed an easy method to fabricate three simplified elastic IA models and measured the transient flow characteristics by using particle image velocimetry (PIV). Transient vortex structures in the IA modes during a cardiac cycle were systemically measured and many new flow phenomena were found, including the vortex morphology (size, structure, and core location), a high-speed jet, wall compliance effects, and three flow modes during retrograde flow phase. The results show that the AR of the IA affects the transient flow patterns as well as the wall shear stress (WSS) in complex ways. The results could deepen our understanding of the transient flow behaviors in IA and guide related clinical studies. [ABSTRACT FROM AUTHOR]

To study the cavitation and induced pressure pulsation characteristics of the volute tongue of the centrifugal pump, the full channel numerical calculation of the centrifugal pump under different flow rates and available net positive suction head conditions was conducted, and the numerical calculation results were verified by experiments. The results show that cavitation near the tongue of the centrifugal pump occurs under large flow conditions, which is mainly caused by the separation vortex formed by flow separation. The frequency of vapor bubbles shedding at the tongue is equal to that of the separation vortex, both of which are blade passing frequencies. The change of vapor bubble volume in the process of vapor bubble shedding is consistent with the change trend of vorticity in the process of vortex shedding, both of which first increase and subsequently decrease. The pressure pulsation periods of different monitoring points near the tongue are identical. The amplitude of pressure pulsation near the impeller near the tongue is larger. The amplitude of pressure pulsation around the tongue decreases when tongue cavitation occurs. The pressure pulsation at this place mainly depends on the influence of the separation and attachment vortex at the tongue and the dynamic and static interference between the impeller and the tongue. The main frequency amplitude of pressure pulsation near the tongue gradually decreases with the occurrence and development of tongue cavitation, and broadband pulsation appears in the low-frequency band. [ABSTRACT FROM AUTHOR]

A spur dike is a hydraulic structure, protruding in a river or channel used for several purposes like protection of river-bank erosion and deepening of the main channel. The present paper discusses pre-existing research work on flow pattern and prediction of temporal and maximum scours depth around the spur dikes placed in different locations at 90 ∘ and 180° curved channels. The equations having approximately 2.367, 4.47, 0.17, and 0.271 (average) times with their corresponding experimental data. The parameters, influencing the scour process and flow pattern, have been identified as the ratio of flow intensity to critical velocity (V/Vc ≥ 1) is below 1 and special kind of bedding material is approximately 10 % greater than under live-bed condition and many more. The numerical value of the Froude number and the geometry of the bed surface material are also discussed in this paper. Based on these parameters, the empirical formulations and experimental studies on local scours around the straight, L-shaped, T-shaped spurs, placed at 30°, 45°, 60°, 120°, and 180° azimuthal angles have been discussed. Various numerical schemes proposed in almost seventy-five literatures have been summarized. A critical review of numerical and experimental results found in different works related to temporal and maximum scour depth, flow characteristics, and bed topography around the dike shows that the data and accompanying results are insufficient for the design of spurs used as river structures in curved channels. There are needs to carry out extensive experiments, under various flow conditions, to examine the flow behavior and scouring processes around the spurs. Due to complex flow pattern and scouring processes, taking place around the spur, it becomes difficult to understand the real physics behind these phenomenon and therefore, data-driven models are suggested to arrive at more reasonable relationships required to be used for design purposes. [ABSTRACT FROM AUTHOR]

The generation of noise by the flow of a compressible viscous gas over a circular cylinder as a result of the formation of vortices in it and the separation of them from the surface of the cylinder was considered. The sound field of this flow was calculated using the method of simulation of large vortices, and its acoustic characteristics were determined using the method of acoustic analogy based on the solution of the Ffowcs Williams–Hawkings equation. On the basis of the direct numerical simulation data on the indicated flow, its regimes at diff erent Reynolds numbers were investigated. The results of calculation of the acoustic characteristics of this flow within the framework of the two- and three-dimensional approaches to the solution of the Ffowcs Williams–Hawkings equation were compared. A good agreement has been obtained between the calculated gasdynamic and acoustic characteristics of a gas flow over a circular cylinder and the corresponding experimental and calculation data available in the literature. [ABSTRACT FROM AUTHOR]

A numerical study of the aerodynamics of a swirling turbulent flow and of the classification of particles in the vortex chamber of a pneumatic combined apparatus has been performed. The obtained results indicate the possibility of achieving a uniform distribution of the radial flow velocity along the height of the chamber in the particle separation zone in it by changing the shape of the rotor blades of the apparatus, which is a prerequisite for its efficient operation. The trajectories of motion of single particles in the vortex chamber are determined. A significant effect of turbulent flow pulsations on the efficiency of particle separation in it has been established. The reliability of the obtained results is confirmed by test studies and by their comparison with experimental data. [ABSTRACT FROM AUTHOR]

Past investigations of thermal counterflow in He II were mostly conducted in pipes/channels of constant cross-sections, which are often unduly influenced by the presence of walls. We devise and carry out an experiment using a spherically symmetric setup to study unbounded counterflow in order to gain better understanding of interactions between quantized vortices and counterflow; the preliminary analysis shows that this method is viable. [ABSTRACT FROM AUTHOR]

Recent studies proposed the two-band effect and the related type-1.5 superconductivity in ZrB12 single crystal. Here, by combining both macroscopic and microscopic measurements, the superconducting properties and the intricate vortex matter of ZrB12 are studied in detail. The vortex phase diagram is constructed, where the temperature dependence of the upper critical field can be well reproduced using a two-band Werthamer-Helfand-Hohenberg (WHH) model. A pronounced surface superconductivity is also found in the same temperature range, where the semi-Meissner state is observed. Both phenomena are attributed to the weakly coupled two-band effect. The direct visualization of the semi-Meissner state exhibits an inhomogeneous distribution of vortex clusters, vortex chains and large Meissner areas. With the increase of magnetic field, a transition from the semi-Meissner state to the mixed state is revealed and further supported by statistical analysis of the vortex pattern. Our results provide direct experimental evidence for the type-1.5 superconductivity in ZrB12. [ABSTRACT FROM AUTHOR]

Microfluidic devices can form monodisperse double emulsions, but the fabrication steps are complicated and require specialized equipment. Recently, a method to convert single emulsions into double emulsions using vortex mixers has been proposed. Using this method, we demonstrate the production of double emulsions using commercially available single-emulsion microfluidic chips. We characterize the effect of vortex speed, vortex duration and the number of vortex/flick cycles on the average diameter and coefficient of variation of the double emulsions. Using fluorescent nanoparticles as tracers, we show that droplet breakup occurs during the second emulsification (using the vortex), but did not observe any fusion between the cores of double emulsion droplets. We also found that some inverted double emulsion droplets containing the outer water phase in their core were produced during vortex emulsification. Finally, while commercial chips only exist with a finite range of channel size that sets the monodispersed emulsion droplet radius, we show that the double-emulsion droplet radius can be adjusted using osmotic pumping. Our method is simple, available and user-friendly for biomedical researchers. [ABSTRACT FROM AUTHOR]

An inviscid, nonlinear shallow water model is applied to study the formation of filaments and merging of potential vorticity (PV, π). We confirm that misalignment of vorticity with the streamlines is crucial to merger. Flow creates positive PV tendency (πt) on the lee side of π ridge, which increases the angle between streamlines and PV contours and the efficiency of vorticity transport along the parallel but oppositive direction in the positive quadrants of πt. So, the vortices move closer while rotating around each other. Filamentation starts as weak vorticity shatters from the outer edge of vortex core. The filament grows and rotates around the cores, but shows little effects to positive PV advection or vortex merging in the inner core, evidenced by the steady core area integrated PV trends. Consecutive PV transfer from lower to higher interval levels are observed during merger process while elongated filamentation is dissolving into the lower level PV regime. The vortices never merge when negative πt prevails between two vortices. Distance between the vortex cores show direct correspondence to positive πt between them. Hence, the advance of positive πt provides a simple mechanism of merging. The Rossby radius of deformation (LD) is confirmed to be another strong indicator for vortex pair merger where LD comparable or smaller than the initial vortex core separation length scale makes merger more likely due to geostrophic adjustment. The Rossby number (Ro) affected the overall flow interaction speed speed when LD is fixed. [ABSTRACT FROM AUTHOR]

Industrially important tubes, such as bundled risers or intake pipes, use spacers to prevent them from colliding with each other. However, these tubes vibrate elastically under currents, either individually or in groups. Therefore, a practical evaluation of tubes's elastic behavior is necessary. In this study, a towing tank experiment using a model of bundled two vertical elastic pipes were carried out to understand the flow-induced behavior of pipes assuming the angle and distance between the pipes as parameters. Furthermore, the two pipes' responses were classified into four different patterns, the experiment was repeated side-by-side and staggered arrangement, and the effect of flow direction on the motion of two pipes were also investigated. As a result, the elastic behavior of bundled two pipes could be classified into four behavior patterns when the distance between two pipes and the flow direction was changed from tandem arrangement to side-by-side arrangement. The patterns are (i) predominant translational motion, (ii) approaching and moving away, (iii) torsional motion, (iv) superposition of approaching and moving away and torsional motions. The classification of these four behavioral patterns provides knowledge for measuring the fluid forces acting on two pipes with elastic response. [ABSTRACT FROM AUTHOR]

The removal of Hg from solid waste plays a key role in environmental protection. In this study, a fast, simple, and effective method for the removal of Hg by acid extraction, using a combination of vortex agitation and ultrasonic irradiation along with hydrobromic acid (HBr), was established using Hg-containing solid wastes. The optimal durations of vortex agitation and ultrasonic irradiation with 48% v/v of HBr were 5 and 6 min, respectively, and total Hg (T-Hg) extraction was achieved within 21 min. The proposed method was validated using the Certified Reference Material (CRM) ERM CC580 (estuarine sediment) and CRM NMIJ 7302-a (marine sediment). Under the optimized conditions, the efficiency rates of T-Hg extraction in both CRMs were 99.5% and 94.2%, with repeatabilities of 3.21% RSD and 2.31% RSD, respectively. The proposed extraction method can also be used for the remediation of Hg in other environmental matrices. [ABSTRACT FROM AUTHOR]

The mixing process of pre-evaporated afterburner fuel at different positions upstream of the mixers and airflow was numerically simulated in a straight channel, with semicircular mixer, rectangular mixer, triangular mixer and chevron mixer respectively. The effects of vortices generated by mixers on fuel distribution and mixing characteristics were studied. The results show that: (1) The scale, strength and breaking speed of the streamwise vortex and the development speed of normal vortex are different downstream of the four mixers, which accelerate the mixing process of fuel and airflow. (2) The fuel distribution at the outlet of mixers, downstream of straight section and downstream of the crest and trough is mainly affected by secondary flow, the streamwise vortex and the normal vortex respectively. (3) The fuel mixing uniformity downstream of the four mixers is increased by about 80% compared with no mixer. In the limited distance, the mixing performance of chevron mixer is the best, while the triangular mixer is the worst Rectangular mixer has the fastest mixing speed and superior comprehensive performance. In addition, the effect of the channel wall on the mixing process downstream of mixers cannot be ignored. [ABSTRACT FROM AUTHOR]

A reduction correlation between the (3 + 1) -dimensional variable-coefficient Gross–Pitaevskii equation with the partially nonlocal nonlinearity under a harmonic potential and a (2 + 1) -dimensional constant-coefficient one is firstly erected. With the aid of solutions via the Hirota method for the (2 + 1) -dimensional constant-coefficient equation, the (3 + 1) -dimensional soliton analytical solutions with the Hermite–Gaussian envelope including vortex, diploe soliton and saddle-shaped soliton are firstly unfolded. Expanded and compressed evolutions of these (3 + 1) -dimensional soliton structures are presented in the periodic amplification and exponential diffraction decreasing systems. In the x - z plane, the eye-shaped structure appears in all soliton structures, and its number is related to the Hermite parameter. [ABSTRACT FROM AUTHOR]

A numerical solution for the problem of the flow around a periodically oscillating and rotating with a constant speed cylinder is presented. Streamlines of time-averaged flow fields are shown for several distinct values of rotational and oscillatory velocities. A comparison with a known solution for an oscillating cylinder without rotation is given. An asymptotic solution for the velocity field in the boundary layer is obtained and the stationary component is revealed. [ABSTRACT FROM AUTHOR]

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

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

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

This review attempts to elucidate the physical origin of aerodynamic lift of an airfoil using simple formulations and notations, particularly focusing on the critical effect of the fluid viscosity. The evolutionary development of the lift problem of a flat-plate airfoil is reviewed as a canonical case from the classical inviscid circulation theory to the viscous-flow model. In particular, the physical aspects of the analytical expressions for the lift coefficient of the plate-plate airfoil are discussed, including Newton's sine-squared law, Rayleigh's lift formula, thin-airfoil theory and viscous-flow lift formula. The vortex-force theory is described to provide a solid foundation for consistent treatment of lift, form drag, Kutta condition, and downwash. The formation of the circulation and generation of lift are discussed based on numerical simulations of a viscous starting flow over an airfoil, and the evolution of the flow topology near the trailing edge is well correlated with the realization of the Kutta condition. The presented contents are valuable for the pedagogical purposes in aerodynamics and fluid mechanics. [ABSTRACT FROM AUTHOR]

The momentum flow exchange between the impeller and side channel produces highly turbulent flows in side channel pumps. The turbulent flows feature complex patterns of vortex structures that are partly responsible for the dissipation of energy losses and unsteady pressure pulsations. The concept of turbulent flows in side channel pumps requires a reliable vortex identification criterion to capture and predict the effects of the vortex structures on the performance. For this reason, the current study presents the application of the new Ω-criterion to a side channel pump model in comparison with other traditional methods such as Q and λ2 criteria. The 3D flow fields of the pump were obtained through unsteady Reynolds-averaged Navier-Stokes (RANS) simulations. Comparative studies showed that the Ω-criterion identifies the vortex of different intensities with a standard threshold, Ω=0.52. The Q and λ2 criteria required different thresholds to capture vortex of different intensities thus leads to subjective errors. Comparing the Ω-criterion intensity on different planes with the entropy losses and pressure pulsation, the longitudinal vortex plays an important role in the momentum exchange development which increases the head performance of the pump. However, the rate of exchange is impeded by the axial and radial vortices restricted in the impeller. Therefore, the impeller generates the highest entropy loss and pressure pulsation intensities which lower the output efficiency. Finally, the findings provide a fundamental background to the morphology of the vortex structures in the turbulent flows which can be dependent upon for efficiency improvement of side channel pumps. [ABSTRACT FROM AUTHOR]