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

The perforated drip irrigation emitter (PDIE) is a novel drip irrigation emitter incorporating multiple energy dissipation mechanisms, chiefly hedging, deflection, and friction. To characterize the influences of structural parameters and vortices on the hydraulic performance of PDIE, the discharge exponent, discharge rate, and emitter unit constant were analyzed via hydraulic performance experiments and numerical simulation. The key findings are: (1) Discharge exponents of PDIE ranged from 0.478 to 0.515; average high-pressure hydraulic performance exceeded low pressure by 4.882%. (2) The four key structural parameters impacted hydraulic performance from large to small as follows: the width of the perforation (a), the angle of the scalariform perforation plate (α), the distance of the two perforations (b), and the length of the channel cavity (c). Among them, the discharge exponent changes significantly with a and α. (3) Vortex-retaining PDIE exhibited a lower emitter discharge exponent versus vortex-removed versions. However, vortices increase discharge rate and reduce energy consumption of PDIE. After optimization, the emitter discharge exponent of the PDIE with the reserved vortex is 0.461, which is relatively improved by 3.556%. This study can provide a theoretical reference for the structural design of new drip irrigation emitters and functional analysis of vortices. HIGHLIGHTS The hydraulic performance of the perforated drip irrigation emitterr is optimized.; Key structural parameters and the vortex were explored for their effects on the hydraulic performance of the perforated drip irrigation emitter.; By retaining vortices and adjusting key structural parameters, the hydraulic performance of PDIE can be optimized.; The emitter of PDIE with better hydraulic performance is put forward.;

In order to determine the most suitable turbulence model for studying the aerodynamic performance of bus, the effects of different turbulence models on the aerodynamic characteristics of bus were investigated. A comparative analysis was conducted on five turbulence models (IDDES, DDES, DES, LES, URANS). The pressure distribution on the cross section at x=0 and y=0 is also analyzed for each model. The results reveal that IDDES accurately captures the negative pressure at the rear of the bus and predicts the pressure gradients more effectively than other models. IDDES also captures more vortices at the head of the bus and predicts the wake flow more widely than other models. DDES has obvious shedding phenomenon in the wake flow, while IDDES provides a relatively smooth airflow trajectory, but its prediction of airflow trajectory at a distance is less clear. Through quantitative and qualitative analyses of the aerodynamic characteristics of bus under different turbulence models, it can be concluded that IDDES is the most suitable turbulence model to study the aerodynamic characteristics of bus.

The possibilities of simulation of viscous incompressible fluid flows with lattice Boltzmann method are considered. Unlike the traditional discretization approach based on the use of Navier–Stokes equations, the lattice Boltzmann method uses a mesoscopic model to simulate incompressible fluid flows. Macroscopic parameters of a fluid, such as density and velocity, are expressed through the moments of the discrete probability distribution function. Discretization of the lattice Boltzmann equation is carried out using schemes D2Q9 (two-dimensional case) and D3Q19 (three-dimensional case). To simulate collisions between pseudo-particles, the Bhatnaga r–Gross–Crooke approximation with one relaxation time is used. The specification of initial and boundary conditions (no penetration and no-slip conditions, outflow conditions, periodic conditions) is discussed. The patterns of formation and development of vortical flows in a square cavity and cubic cavities are computed. The results of calculations of flow characteristics in a square and cubic cavity at various Reynolds numbers are compared with data available in the literature and obtained based on the finite difference method and the finite volume method. The dependence of the numerical solution and location of critical points on faces of cubic cavity on the lattice size is studied. Computational time is compared with performance of fine difference and finite volume methods. The developed implementation of the lattice Boltzmann method is of interest for the transition to further modeling non-isothermal and high-speed compressible flows.

The problem of an approximate solution to hydrodynamic problems is the consideration of pressure. To exclude it from the equations, the transition to “non-primitive variables” (vortex and velocity vector divergence) is made. In this case, there are difficulties in the algorithmization of new equations for solving the inverse problem of hydrodynamics and a lot of internal iterative calculations. The object of this study includes equations in “non-primitive” variables. The research methods are based on the transformation without simplifications and assumptions of hydrodynamic equations into a form containing “non-primitive” variables and the demonstration of the possibilities of solving the equations. The GAMS programming language was used for approximate solutions for the first time. The aim of this paper is to demonstrate the possibility of solving the full equations in “non-primitive” variables for various conditions. The results showed the possibility of considering the compressibility of the medium when solving the inverse problem of hydrodynamics; the identity of solutions of the proposed system of equations and equations using the potential; and the possibility of using optimizing programming languages for hydrodynamics problems. The scientific novelty of this research consists of solving the full equations of hydrodynamics with the use of “non-primitive” variables but without the use of the current function. Doi: 10.28991/ESJ-2024-08-02-021 Full Text: PDF

Optical elements based on nanomaterials are becoming major avenues to satisfy the technological requirements of compact, lightweight, and tunable elements of the emerging terahertz (THz) field. A new generation of diffractive components integrating specific geometry with additional features (flexibility, stretchability, rotation, and other approaches for tuning properties) extends the functionality of wavefront control. Here, an innovative approach is demonstrated to control the THz wavefront via a layered composition of spiral zone plates (SZPs) with tunable mutual orientation and scaling. As a proof of concept, the SZP is designed using Laguerre‐Gauss mode analysis with further fabrication and experimental characterization of the resultant vortex beams. For each single SZP, a flexible element is proposed based on a thin film of single‐walled carbon nanotubes deposited on a stretchable substrate. Thus, this diffraction element can be tuned not only by rotation (along the azimuthal direction), but also by its stretching (in the radial direction). The spatial tuning of the developed SZPs (spiral zone plates) opens up an efficient, convenient, and highly customizable approach for the manipulation of vortex beams. [ABSTRACT FROM AUTHOR]

Facing an increasingly hostile ecological environment, the imperative for advancing hydrogen fuel cell vehicles has become more pronounced. This paper establishes a three-dimensional computational fluid dynamics model of a Roots-type hydrogen circulating pump by utilizing the generalized type line equation of the Roots rotor. Delving deep into the intricate interplay of backflow phenomena on the internal flow dynamics and operational efficiency of the Roots-type hydrogen circulation pump across various scenarios. The results reveal that mass flow rate and velocity vary continuously and with the same pulsation frequency as rotation angle or time during a complete rotation cycle. As the rotational speed increases, the number of backflow occurrences decreases, the frequency of backflow currents in the rotor basin decreases, and the temperature rise in both the suction and exhaust chambers decreases. It becomes evident that the rotational speed wields a more profound influence on the Roots pump's performance than temperature: the volumetric and isentropic efficiencies of the Roots-type hydrogen circulating pump decrease by 3.5% and 4.6%, respectively, with increasing temperature, while the volumetric and isentropic efficiencies of the pump increase by 32.6% and 24.0%, respectively, with increasing rotational speed. • The numerical simulation of hydrogen circulation pump using dynamic mesh technique. • Focus on the occurrence and impacts of backflow of hydrogen circulation pumps. • The influence of backflow on internal flow characteristics at different speeds and temperatures. • The general link between return frequency and flow pulsation is discussed in detail. [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]

In proceeding with the advanced development of small unmanned aerial vehicles (UAVs), which are small flying machines, understanding the flight of insects is important because UAVs that use flight are attracting attention. The figure-eight trajectory of the wing tips is often observed in the flight of insects. In this study, we investigated the more efficient figure-eight motion patterns in generating lift during the hovering motion and the relationship between figure-eight motion and Reynolds number. For this purpose, we compared the ratios of the cycle-averaged lift coefficient to the power coefficient generated from each motion by varying the elevation motion angle, which is the rotational motion that represents the figure-eight motion, and the Reynolds number. The result showed that the motion with a smaller initial phase of the elevation motion angle ( φ e 0 ≤ 90 ° ) could generate lift more efficiently at all Reynolds numbers. In addition, the figure-eight motion was more effective when the Reynolds number was low. [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]

Multi-principal element alloys (MPEAs) exhibit outstanding strength attributed to the complex dislocation dynamics as compared to conventional alloys. Here, we develop an atomic-lattice-distortion-dependent discrete dislocation dynamics framework consisted of random field theory and phenomenological dislocation model to investigate the fundamental deformation mechanism underlying massive dislocation motions in body-centered cubic MPEA. Amazingly, the turbulence of dislocation speed is identified in light of strong heterogeneous lattice strain field caused by short-range ordering. Importantly, the vortex from dislocation flow turbulence not only acts as an effective source to initiate dislocation multiplication but also induces the strong local pinning trap to block dislocation movement, thus breaking the strength-ductility trade-off. [ABSTRACT FROM AUTHOR]

Considering the importance of wind turbine tower, its vibration under multi-hazard action consisting of vortex-induced load and seismic load needs to be controlled, especially as the height of the wind turbine tower increases, it increases the risk of its higher-order vibration. To address this issue, theoretical equations for vortex-induced load based on the governing equation of particle damping system are put forward, the vibration control of a 1/20 scale wind turbine model is studied, and the experimental and numerical analyses are conducted. Many studies have shown that wind turbine tower equipped with tuned mass damper (TMD) can result in an RMS response reduction ratio ranging from 20% to 40%. Compared to TMD, particle tuned mass damper (PTMD) has better vibration control effect under single seismic load, and still achieves good vibration control ability with a maximum RMS (root–mean–square) reduction ratio of 35.55% under multi-hazard action. Furthermore, MPTMD (multiple particle tuned mass damper) is proposed for controlling higher-order vibration mode, achieving a maximum RMS reduction ratio of 65.93%. Combining the spectrum diagram result, the ability to control higher-order mode vibration of MPTMD is confirmed. [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]

The particles of micron and submicron sizes (PM 2.5 and less) in gas environments pose a significant danger to humanity due to the emergence of specific and very dangerous diseases of the cardiovascular, respiratory, and immune systems of the human body. Such particles are the most difficult to detect; therefore, their effects on human health have only been discovered in recent decades. Classical ultrasonic coagulation by sinusoidal action turns out to be ineffective for PM 2.5 due to the peculiarities of the physical mechanisms of hydrodynamic and orthokinetic interaction realized in gaseous media. This article presents a theoretical justification for choosing ways to increase the efficiency of ultrasonic coagulation of PM 2.5 by creating special conditions under which nonlinear disturbances of the velocity and pressure of the gas phase in the ultrasonic field occur. The authors performed simulations of ultrasonic coagulation under nonlinear disturbances of the velocity (vortex) and the pressure (shock waves), which has numerical difficulties due to the instability of existing methods. As a result of the numerical analysis, the possibility of increasing the coagulation rate of particles in the submicron size range up to limit values (13 times due to nonlinear pressure disturbances, and an additional increase of at least 2 times due to aerosol compaction in the vortex field of gas velocity) was shown. [ABSTRACT FROM AUTHOR]

In this paper, we consider the formation of vortices in multilayer stacks of Bose–Einstein condensates with tilted dipoles by numerical simulations of the Gross–Pitaevskii equation. Different dependencies of critical rotation frequency (CRF) and optical lattice height, vortex number, and rotation frequency are studied, depending on the direction of the dipole axis and dipole strength. Our results show that the CRF in z = 0 is minimum. When the optical lattice height is gradually increased, the CRF decreases gradually. Reducing of dipole strength in anisotropic dipole–dipole interaction (DDI) favours the formation of vortices, and such decline in isotropic DDI hinders the creation of vortices. The reason for this difference is that the repulsive interaction is favorable and the attractive interaction is disadvantageous for the vortex formation. In addition, we study the first-order correlation function and focus on variation of coherence. For small rotation frequency, the break of coherence occurs earlier in the case of purely repulsive interaction. With an increase in rotation frequency, the coherence concurrently disappears in layer z = 2. Moreover, we also investigate the quenched dynamics, showing that the increase of angular momentum is induced by changing the direction of dipoles and in this process the vortex number remains unchanged. [ABSTRACT FROM AUTHOR]

Development in hydropower technology leads to modern and efficient technology. The emergence of gravitational vortex water turbine (GVWT) is a promising invention. It is suitable for harnessing energy from low head and flow rate water sources, ranging from approximately 0.7–2 m and 0.03–5 m3/s. A series of experimental studies had been conducted to develop the GVWT with a propeller runner. The objective of this study is to analyze the effect of runner design, including the number of blades, runner diameter and runner installation position, on the GVWT's performance. A preliminary study on a dual-stage GVWT was carried out to increase the single-stage GVWT performance. The experimental result shows that 4-blade and 5-blade runners provide better performance than 3-blade runner and 6-blade runner. For a 5-blade runner, the optimal installation position is between 60% and 70% of depth. Installing a runner in the basin produces a blockage effect, which increase the runner performance. An extremely large blockage ratio causes stoppage which is undesirable. The maximum allowed blockage ratio is 0.8. The preliminary study on the dual-stage GVWT proves that it increases the GVWT's performance. The efficiency of GVWT ranges from 25% − 50%. [ABSTRACT FROM AUTHOR]

This study addresses the challenge of performance degradation in waterjet pumps due to non-uniform suction flow. Utilizing the Proper Orthogonal Decomposition (POD) method, it decomposes and reconstructs the flow features within a waterjet pump under non-uniform inflow into a series of modes ranked in descending order of energy. By analyzing the modes with dominant energy, which contain complex information about the flow field, it is revealed that modes 1 and 2 predominantly represent the formation of a concentrated vortex, whereas modes 3 and 4 illustrate its spatial offset. Notably, in the hub section, mode 3 exhibits a delayed flow separation caused by the reduction of circumferential vortex (CV), with a consequent lift in blade loading at the leading edge and a higher head compared to mode 1. In the shroud section, the delayed flow separation in mode 3 suppressed reverse flow and the concentrated separation vortex (CSV) and then increased the blade loading, ultimately enhancing the pump head. The findings provide significant insights into optimizing waterjet pump performance by detailing the interactions between various flow structures and pump components, effectively filling a knowledge gap in applying dimensionality reduction techniques within the distorted flow fields of water jet pumps. [ABSTRACT FROM AUTHOR]

Objectives: The aims of this study were to assess the vortex characteristics of left ventricle (LV) in fetuses with coarctation of the aorta (CoA) using high–frame rate ultrasound with blood speckle‐tracking (BST) and explore its relationships with cardiac function and morphology parameters. Methods: Thirty fetuses with CoA and 30 gestational‐age matched normal fetuses were included in this cross‐sectional study. The area, length, width, and position of the vortex in the LV were recorded and quantitatively analyzed by BST echocardiography. The associations of vortex properties with ventricular function and morphology were also determined. Results: Based on BST imaging, the LV vortex can be observed in 93% of the fetuses. The fetuses with CoA exhibited significantly larger and wider vortex than the controls (P <.05). Linear regression analysis indicated that vortex area was positively related to sphericity index of LV as well as isovolumic relaxation time (r =.52, P =.003 and r =.42, P =.021). There was a negative correlation between vortex area and mitral valve size (r = −.443, P =.014). No significant association was found between vortex area and myocardial performance index and aortic isthmus size. Conclusions: It is feasible to quantitatively evaluate the left ventricular vortex in fetuses by BST. The fetuses with CoA exhibited greater vortex area and width, and the altered vortex property is associated with geometry of LV. This will facilitate our comprehension of the unique flow patterns and early cardiac remodeling in fetuses with CoA. [ABSTRACT FROM AUTHOR]

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Controlled assembly of nanoparticles (NPs) has garnered much interest over the past two decades. Beyond established techniques, new methods utilizing local short‐range or large‐scale long‐range interactions remain to be explored to achieve diverse micro‐ and nanoscale structures. Here, we report the controlled emergence of vortex‐pair arrays within monodispersed gold nanorods by applying a direct current electric field across a pair of sawtooth electrodes. By employing in situ darkfield microscopy and particle collective analysis, we elucidate the mechanism behind the formation and stabilization of the NP vortices, attributing it to the combined effects of the electrode shape, high NP density, and high solution viscosity. We further explore the controllability of the vortex‐pair arrays and obtain multiple complex vortice patterns. Our findings will facilitate the investigation of efficient and controlled dynamic assembly of NPs under external fields and help manufacture next‐generation optoelectronic functional materials. [ABSTRACT FROM AUTHOR]

Under the influence of crosswind, when high-speed trains (HSTs) meet on a bridge, they produce complex vortexes, strong aerodynamic loads, and other aerodynamic effects. The purpose of this paper is to reveal the influences of crosswind and windbreaks on the vortexes generated by HSTs, the pressure distributions on the surfaces of the trains, and the aerodynamic load coefficients of the trains when they meet on a bridge, as well as the influence of the pressure waves generated by the trains on the windbreaks. The three-dimensional incompressible improved delayed detached eddy simulation (IDDES) method based on the SST k-ω turbulence model is used for numerical calculation purposes, and the overset grid method is used to realize the relative motions of the trains. The results show that the windbreaks can reduce the negative pressure (NP) imposed on the train surface and effectively improve the pressure distribution; crosswinds have a significant impact on the vortexes generated by trains, and the vortexes generated by the upstream train affect the stability of the downstream train; windbreaks can reduce the aerodynamic load applied when trains meet and thus improve the safety of the trains; and the head and tail waves generated by trains impose pressure on the windbreaks, which affects the reliability of the windbreaks installations. The simulation results can provide a preliminary reference for future research. [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]

In order to study the unsteady flow and vortex characteristics of tongue cavitation, numerical calculation is carried out for the whole flow channel given different conditions. Then, the calculation results are verified experimentally. The results show that after the occurrence of tongue cavitation in the centrifugal pump, it deteriorates with the decrease of NPSHa. However, when NPSHa is reduced to 3.78 m, it does not change significantly anymore with the decrease of NPSHa. The extrusion of fluid by the vapor at the tongue promotes the formation of the separation vortex, and the re-jet flow caused by the separation vortex leads to vapor shedding. The frequency of cavitation shedding is consistent with the frequency of vortex shedding. In the vorticity transport equation, the relative vortex stretching term and the relative vortex dilatation term dominate the vapor shedding by controlling the change in vorticity. The baroclinic torque term mainly affects the change of vorticity at the vapor-liquid interface, but to a much lesser extent than the first two terms. [ABSTRACT FROM AUTHOR]

Planning and analysis of infrastructure involving cylindrical shapes such as bridge platform pillars and offshore sea piping systems are needed to ensure user safety. This study aims to determine the effect of variations in cylinder diameter on fluid flow profiles with OpenFOAM software in laminar conditions with Reynolds numbers 60, 100, and 200. The computational domain used is a rectangle with a length of 32D and a width of 20D, where D is the cylinder diameter, which in this study is varied by D, 2D, and 4D. We placed the cylinder at a distance of 8D in the direction of the x-axis and a length of 10D in the direction of the y-axis. The simulation results show that variations in cylinder diameter affect the fluid flow profile, and the drag coefficient increases with increasing variations in cylinder diameter. In addition, variations in diameter also affect the formation of vortex structures as the Reynolds number increases.

Under the influence of crosswind, when high-speed trains (HSTs) meet on a bridge, they produce complex vortexes, strong aerodynamic loads, and other aerodynamic effects. The purpose of this paper is to reveal the influences of crosswind and windbreaks on the vortexes generated by HSTs, the pressure distributions on the surfaces of the trains, and the aerodynamic load coefficients of the trains when they meet on a bridge, as well as the influence of the pressure waves generated by the trains on the windbreaks. The three-dimensional incompressible improved delayed detached eddy simulation (IDDES) method based on the SST k-ω turbulence model is used for numerical calculation purposes, and the overset grid method is used to realize the relative motions of the trains. The results show that the windbreaks can reduce the negative pressure (NP) imposed on the train surface and effectively improve the pressure distribution; crosswinds have a significant impact on the vortexes generated by trains, and the vortexes generated by the upstream train affect the stability of the downstream train; windbreaks can reduce the aerodynamic load applied when trains meet and thus improve the safety of the trains; and the head and tail waves generated by trains impose pressure on the windbreaks, which affects the reliability of the windbreaks installations. The simulation results can provide a preliminary reference for future research.

In order to study the unsteady flow and vortex characteristics of tongue cavitation, numerical calculation is carried out for the whole flow channel given different conditions. Then, the calculation results are verified experimentally. The results show that after the occurrence of tongue cavitation in the centrifugal pump, it deteriorates with the decrease of NPSHa. However, when NPSHa is reduced to 3.78 m, it does not change significantly anymore with the decrease of NPSHa. The extrusion of fluid by the vapor at the tongue promotes the formation of the separation vortex, and the re-jet flow caused by the separation vortex leads to vapor shedding. The frequency of cavitation shedding is consistent with the frequency of vortex shedding. In the vorticity transport equation, the relative vortex stretching term and the relative vortex dilatation term dominate the vapor shedding by controlling the change in vorticity. The baroclinic torque term mainly affects the change of vorticity at the vapor-liquid interface, but to a much lesser extent than the first two terms.

The Fuzzy C-means (FCM) method with Fourier coefficient-based distance was firstly used to construct the vortex features and analyze the large-scale unsteady flow pattern around the building by the transient ensemble velocity magnitude and Q criterion value. The performance of the unsteady Reynolds-averaged Navier-Stokes (URANS) turbulence models, including Standard$k - \varepsilon $model, Realizable$k - \varepsilon $, Renormalization Group (RNG) theory$k - \varepsilon $and Shear-Stress Transport (SST) $k - \omega $models on the flow structures around a high-rise building, was examined and compared by data analysis. The transient data was analyzed to identify the root of the different flow structures. The vortex structure was used to distinguish the different turbulence simulation performance directly. The result indicated that the RNG$k - \varepsilon $model shown the best simulation results on the mean velocity and total turbulent kinetic energy fields. The RNG $k - \varepsilon $ model could simulate the modest scales of vortices which approximates the experiment data around the building, while the SST$k - \omega $model could simulate the abundant scales of vortices which led larger turbulence viscosity coefficient. In addition, the nature pressure difference ventilation partition method was proposed and verified in simulating the nature pressure difference around a single building.

Comparing the Gutenberg Galaxy with what he called the Marconi Constellation (Understanding Media, 1964), Marshall McLuhan discussed “the effects of radio [as being] quite independent of its programming” (that is, “the medium is the message”), noting that electronic media represent “an ever-simultaneous flow which is a very far cry indeed from the one direction, one level flow of the printed page, or of the lecture platform.” Thinking of what he calls “the typographic trance of the West [that] has endured until today” (Playboy interview, 1969), McLuhan prophesized the shift from the visual culture of print to the acoustic culture of the electronic: “[T]he Gutenberg Galaxy is being eclipsed by the constellation of Marconi.” I propose that this concept has its roots in McLuhan’s deep interest in modernism but also that it leaves its imprint on his progressive pedagogy as formulated in “Education in the Electronic Age” (1967, 1970) where he proposes an experiential, collaborative, student-centered, project-based, integrated learning as a way of “the training of [students’] perception.” In this paper, I compare two brief passages, one from T.S. Eliot’s The Waste Land (1922) and the other from McLuhan’s Counterblast (1954) as examples of the progressive heuristic tool of exploration McLuhan called “mosaic” and offered as a tool for the training of readers’/students’ perception. Eliot’s poem offers a paradigm of a modernist experiment in which the reader is invited to inhabit the text’s intervals, learning to read the page which, though visual, aspires to be polyphonic, simultaneous, and (in McLuhan’s terms) acoustic--instead of just visual. The paper therefore argues that McLuhan’s emerging, radical, future-looking, electronic, post-modernist poetics is firmly rooted in the modernist praxis of “making it new” that looks both to its modernist past and the electronic/media/digital future.

The formation of vortices behind the gates of diversion dams is an operational challenge. Such vortices lead to vibration and corrosion in the gate, reducing the lifetime and raising the operational cost of the dam. This study investigated these vortices and their formation. It was found that the gate or cutoff wall was not the only explanation for the vortices; the closed side gates also contribute to vortex formation. Furthermore, an increase in the gate width reduced vorticity; the vortex size experienced a 200% reduction as the gate size increased by 200%. The cutoff wall diameter was another determinant. An increase in the cutoff wall diameter raised vorticity. The vortices increased by 50% as the wall diameter increased by 150%.

In the field of hydrogen safety and combustion, the effect of obstacles on hydrogen deflagration is a topic of general interest to scholars. In previous studies, scholars usually used uniform obstacles under various operating conditions and obtained conclusions by changing their number and positions. However, in practice, the shapes of obstacles at an accident site are often not the same and regular. In this paper, a series of obstacles with variations in length were investigated, and the effects of the obstacles on hydrogen deflagration under different working conditions were analyzed. The configuration of the obstacles with gradually increasing lengths amplified the vortices in the flow field so that the propagation direction of the flame front surface was reversed after passing three obstacles. The variations in the lengths of the obstacles had a significant stretching effect on the propagation of the flame and a considerable acceleration effect on the propagation speed of the flame. The main reason for the acceleration was the rapid propagation of the flame achieved by the vortex when rupture occurred. The change in the pressure gradient that occurred at the center of rotation caused rapid movement of the combustion gases, which ultimately led to an increase in the flame propagation speed. A configuration with gradually increasing lengths of the obstacles promoted the overpressure. A configuration with gradually decreasing lengths of the obstacles suppressed the overpressure. The reason for the formation of the local high-pressure area was that unburned gas was accumulated there by pressure waves and the obstacle walls, and then the thermal expansion formed a high pressure. The Rayleigh–Taylor and Kelvin–Helmholtz instabilities caused the overpressure to rise further. The results can provide a theoretical basis for hydrogen transportation, storage, and safety.

In recent years, vanadium dioxide (VO2) has drawn enormous attention in dynamic electromagnetic (EM) manipulation, owing to its mild phase change condition and prominent diversity of optical characteristics. In this paper, anisotropic meta-atoms integrating VO2 are proposed to obtain four polarization-multiplexing channels. The meta-atom is composed of two stacking metal–insulator–metal (MIM) structures. For the modulation of EM wavefront in desired manners, a meta-atom database composed of 256 meta-atoms is elaborately designed. Applying the meta-atom database and the degree of freedom in interfacial phase distribution, two metasurfaces are demonstrated in the verification of four-channel polarization-multiplexed vortex beams. The firstly proposed metasurface realizes the generation of four vortex beams with different topological charges. Each channel is dependent on the polarization of the incident wave and VO2 state. The further investigated metasurface achieves simultaneous control over the reflection direction, quantity, and mode of vortex beams under different VO2 states and polarization states of incident wave. In addition, designed metasurfaces exhibit wideband effect for over 100 GHz. The proposed design method enables four-channel generation of vortex beams using a single metasurface, and may have potential applications in dynamic and integrated terahertz communication.

Abstract Controlled assembly of nanoparticles (NPs) has garnered much interest over the past two decades. Beyond established techniques, new methods utilizing local short‐range or large‐scale long‐range interactions remain to be explored to achieve diverse micro‐ and nanoscale structures. Here, we report the controlled emergence of vortex‐pair arrays within monodispersed gold nanorods by applying a direct current electric field across a pair of sawtooth electrodes. By employing in situ darkfield microscopy and particle collective analysis, we elucidate the mechanism behind the formation and stabilization of the NP vortices, attributing it to the combined effects of the electrode shape, high NP density, and high solution viscosity. We further explore the controllability of the vortex‐pair arrays and obtain multiple complex vortice patterns. Our findings will facilitate the investigation of efficient and controlled dynamic assembly of NPs under external fields and help manufacture next‐generation optoelectronic functional materials.

As a new perspective on the influences of the electrically charged air and electric field on the air flow, the natural air flow on a negatively charged forward-inclined step is analyzed. The electric field formed by the charged step pushes away the negative charge and attracts the positive charge in natural air, so that only the positive charge density is analyzed. A two-dimensional model of flow and electric field is set and solved on COMSOL Multiphysics FEM solver coupling three physics, that is, flow, electrostatics, and charge-transport. The pressure power spectra at the point around the vortex shedding region are calculated in the case of neutral air / uncharged step and charged air / charged step combinations. Whereas the former has large power below 1Hz, the latter has small power below 1Hz but with a larger peak at 30Hz, that is the vortex shedding frequency. In order to analyze the cause of the difference, the electric force effects are evaluated. The result shows that the upper portion of the vortex has forces in the same direction to the mainstream, and it degrades to the lower portion, which accelerates the vorticity of the vortex. Also, the vortex region has a strong downward force. Adding that, the curl of the electric force on the charged air is calculated to show that the upstream half of the vortex has the same direction curl as the vortex rotation, and the downstream half has an opposite curl because of the gradient charge density. These forces strengthen the vortices and raise their negative pressures and are estimated to suppress the fluctuation of the pressures so that the pressure’s spread spectrum reduces. In addition, the results of an experiment using a desktop wind tunnel are given as extra information.

The present paper focuses on the synchronization behavior of vortex shedding in in-line tube banks with and without acoustic resonance. We have studied the characteristics of acoustic resonance generated by in-line tube banks with a tube pitch ratio of 2.8 in the flow direction. The single high peak in the sound pressure level spectrum was formed at the gap velocity from 5.0 m/s to 48.0 m/s. As the gap velocity increased, the peak frequency increased. The Strouhal number became approximately 0.145. At the gap velocity of 23.0 m/s, the acoustic resonance of the first mode occurred in the transverse direction. The flow patterns and vortex shedding of in-line tube banks at acoustic resonance have been experimentally investigated. The vortex flow field in the tube banks was measured by PIV with and without the acoustic resonance phenomenon. The alternative vortices were shed from each tube in tube banks with and without the acoustic resonance. A pair of vortices has been created at the top and bottom of the jet stream flowing between the gaps of two tubes. On the other hand, the phase-aligned alternative vortices were occasionally shed from each tube in tube banks. No acoustic resonance occurred, the phase-aligned alternative vortices were shed for 11.7 % of the 0.4 s period. When acoustic resonance occurred, the proportion of phase-aligned alternate vortices increased from 11.7 % to 31.0 %. The rate of increase in wall sound pressure is approximately equal to the rate of increase in vortex synchronization. The increase in wall sound pressure due to acoustic resonance is primarily due to the synchronization of vortices in the tube banks during the occurrence of weak resonance phenomena.

In this study, we conducted a numerical analysis of the flow characteristics and heat transfer mechanism of a Tesla valve. Our aim was to illustrate the improvement in heat transfer by presenting velocity clouds, temperature clouds, pressure clouds, velocity vectors, and local flow lines. The findings of our study indicate that the formation of different vortices at the inlet of the Tesla valve has varying effects on heat transfer and fluid flow in forward and reverse flow scenarios. During forward flow, longitudinal vortices are more likely to form, whereas transverse vortices tend to form during reverse flow. These vortices have the ability to disrupt the boundary layer and enhance heat transfer, resulting in improved heat transfer efficiency, albeit with a slight pressure drop. When the flow angle was increased from 40° to 80°, we observed a decrease in the Nusselt number (Nu) by 17.8 % and 8.1 % in forward and reverse flows, respectively. Conversely, the friction factor (f) increased by 22.6 % and 3.1 %, while the Dittus-Boelter factor (Dit) increased by 11.8 %. In addition, the extension of the lateral groove length from 10 cm to 18 cm resulted in a decrease of 7.5 % and 11.7 % in Nu for forward and reverse flows, respectively. Similarly, f decreased by 13.8 % and 9.1 %, while Dit decreased by 5.2 %. Moreover, mathematical equations were developed to describe the relationship between the lead angle, side channel length, Re, Nu, and f. These findings aim to offer valuable insights for the design and implementation of Tesla valves.

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]

There are various secondary flow types in turbodrill's blade cascades, and all kinds of secondary flow have a significant effect on flow loss. In this paper, the stator cascade of φ160 mm turbodrill is taken as the research object, and the CFD method is used to analyze the secondary flow and its evolution. The origin and evolution mechanism of secondary flow is explained from the flow mechanism. The results show that when the working rotary speed is lower than the design rotary speed, the secondary flows are composed of suction surface separation vortex, horseshoe vortex, and passage vortex coexisting. The intensity of secondary flows increases with the decrease of rotary speed. When the working rotary speed is near the design rotary speed, the secondary flows include horseshoe vortex, passage vortex, and corner vortex. When the working rotary speed is higher than the design rotary speed, the secondary flows consist of pressure surface separation vortex and suction surface trailing edge separation vortex. Regardless of rotary speed, secondary flow intensity in the shroud region is greater than the hub region, which has a greater influence on the mainstream. In addition, compared with high rotary speeds, secondary flow intensity is greater at low rotary speeds, resulting in greater flow losses. [ABSTRACT FROM AUTHOR]

By numerically solving the Gross–Pitaevskii equation with phenomenological dissipation term, we study the vortex formation properties of a three-dimensional dipolar Bose–Einstein condensate of 164Dy atoms. We studied the influence of the contact interaction between atoms on the formation mechanism of vortices. We also study how the dipole orientation affects the vortex formation properties and the number of vortices. We find that enhancing the interaction of short-range repulsion interaction or dipolar repulsion interaction can shorten the time to form a stable vortex structure and increase the number of vortices. [ABSTRACT FROM AUTHOR]

In this study, the critical submergence of deep well pumps is analyzed. The critical submergence, which is an important parameter for centrifugal pumps and water intakes that usually have a certain diameter, is determined using dimensionless quantities. The innovative aspect of this study is that three different water inlet opening models are created for two shaft pumps with different nominal diameters, these models are related to the water inlet diameters and the critical submergence is defined using dimensionless quantities. The critical submergence of the pumps was determined using a vacuum measurement method and the critical submergence of each model at different flow rates was compared with Froude number dependent submergence equations developed by other researchers. The aim of this study is to determine the critical submergence of the pumps and to use the flow models developed at these depths with the aid of mathematical equations to ensure the operation of the pumps in the reliable zone (vortex-free). The physical models were found to be effective for vortex formation depth and vortex shape. The physical models found Fcr (critical Froude number) ≤1.40 for pump P1 and Fcr ≤1.44 for pump P2, these values can also be used to determine the suction lift of the pumps. The critical Weber and Reynolds numbers decrease as the water suction area of the pumps increases. Considering the depth of vortex formation, it would be appropriate to use the original (D0) physical models for both pumps. As a result, dimensionless quantities can be used to determine the critical submergence of deep well pumps. [ABSTRACT FROM AUTHOR]

To reveal how aircraft affects the internal flow of the ejector nozzle, we have constructed three model types in this article. These include the model of SR-71 aircraft, the model that only contains ejector nozzle with third auxiliary valve, and the model that integrates the previous two. The results showed that in the transonic regime (Ma = 1.2), the third auxiliary flow mainly stems from the boundary layer of the aircraft body. Indeed, a large-scale flow separation phenomenon near the third auxiliary door may require a more nuanced description. The mainstream flow is always in an overexpansion state and results in a Mach plate structure at the exit of the nozzle. However, after integration, the rates of the third auxiliary and the secondary flow are reduced by 18.15% and 5.26%, respectively. Meanwhile, the mainstream flow demonstrates higher overexpansion levels, the position of the Mach plate further downstream changes, and the thrust coefficient decreases by 1.75%. It is worthwhile noting that a strong pressure gradient occurs in the circumferential direction near the connecting structure, which induces lateral flow. This lateral flow breaks away from the wall under the reverse pressure gradient of the nozzle, thus forming three vortex pairs. [ABSTRACT FROM AUTHOR]

Obstruction of the LVAD flow path can occur when blood clots or tissue overgrowth form within the inflow cannula, pump body, or outflow graft, and it can lead to thrombus, embolism, and stroke. The goal of this study was to measure the impact of progressive pump inflow obstruction on the pressure and flow dynamics of the LVAD-supported heart using a mock circulatory loop. Pump obstruction (PO) was produced by progressively blocking a fraction of the LVAD inlet area. Pressures, flows, and the midplane velocity field of the LV were measured for three LVAD speeds and six PO levels. Pressure and flow decreased with PO, shifting more of the flow through the aortic valve such that the total flow decreased by 6–11% and decreased the efficiency of the work of the native heart up to 60%. PO restricts diastolic flow through the LVAD, which reduces mitral inflow and decreases the strength and energy of the intraventricular vortices. The changes in flow architecture produced by PO include flow stasis and increased shear, which predispose the system to thromboembolic risk. Analysis of the contributions to external work may enable early detection, which allows time for therapeutic intervention, reducing the likelihood of pump replacement and the risk of complications. [ABSTRACT FROM AUTHOR]

The objectives of this paper are to pursue an accurate numerical method of unsteady cavitating flow at a reasonable calculation cost and investigate the unsteady cavitating flow characteristics of a centrifugal pump. Firstly, the cavitating flow simulations of a centrifugal pump were performed using the partially-averaged Navier–Stokes (PANS) turbulence model and its improved model to evaluate the numerical methods based on experimental data. Compared with the experimental results, the improved PANS turbulence model can better predict the cavitating flows in the pump and has better applicability. Further, the unsteady cavitating flow characteristics of the centrifugal pump, such as the vapour volume fraction, the cavitation-vortex dynamics and the pressure and head fluctuations, were simulated by improved PANS model and discussed. The liquid flow vortex at the end of the cavitation in the impeller is an important reason for the periodic change of the cavitation shape. The periodic change of cavity volume has a certain impact on the pressure pulsation in the impeller and the pump head. [ABSTRACT FROM AUTHOR]

The T-junction structure with one inlet and two outlets is ubiquitous in natural and aerospace systems. However, previous research has mainly focused on vortex breakdown under steady-state flow in symmetrical structures. Limited research has been conducted on vortex breakdown in asymmetric structures, where the radii of the two channels differ. This creates a flow rate difference between the outlets, and the ratio of mass flow rate in the small channel to the large channel is defined as the splitting ratio. To study the appearance of vortex structures in the outlet channel under different flow rates and splitting ratios, a split-type asymmetrical circular cross-section pipeline experimental system that can be flexibly disassembled was designed and built. Pressure signals of each channel using pressure sensors were measured and analyzed. It is worth noting that a string tracing technology combined with particle image velocimetry (PIV) technology to monitor the outlet channel was adapted to visualize the flow. Results show that the pressure oscillations in the channels of the T-junction are related to the splitting ratio. Besides, asymmetric T-junction structure exhibits different large vortex structure formation and breakup processes in the two outlet channels, and these processes are influenced by the splitting ratio. • A new split-type asymmetrical T-junction experimental system was designed • Splitting ratio plays important part in pressure oscillation and vortex formation • A string tracing technology was first adapted to visualize the flow • Particle image velocimetry (PIV) technology was modified to visualize the flow • Flow characteristics exhibit a non-linear correlation with the splitting ratio [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]

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