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Andreev–Bashkin entrainment makes the hydrodynamics of the binary superfluid solution particularly interesting. We investigate stability and motion of quantum vortices in such system. [ABSTRACT FROM AUTHOR]

Phase-space holes are well-known Bernstein–Greene–Kruskal (B.G.K.) modes and are formed by particle-trapping in solitary potential waveforms. They exhibit orbital particle trajectories in the phase-space, due to which they are also referred to as phase-space vortices. In this article, we develop the theory of phase-space hydrodynamics for electron and ion phase-space in collisionless plasmas. The analogy between ordinary two-dimensional fluids and 1 D − 1 V phase-space has been explored by introducing a momentum equation and a phase-space vorticity field, which enable the fluid-like analyses of the plasma phase-space. The developed kinetic-hydrodynamic equations are then employed to address the vortical nature of phase-space holes by exploring their fluid-analogous vortex-like characteristics, an identification technique of phase-space vortices, an exact derivation of the Schamel-df equations, and a measurable definition of the particle-trapping β parameter. This article introduces a new technique to the study of phase-space holes which focuses on the fluid-analogous vortical nature of the phase-space holes and prevents the need for an initial assumption of the trapped and free particle phase-space densities, thus presenting itself as a precursor to the Schamel-pseudopotential method. [ABSTRACT FROM AUTHOR]

In this study, a two-dimensional computational domain featuring gas and solid phases is computationally studied for Geldart-B-type particles. In addition to the baseline case of a uniform gas-phase injection velocity, three different inlet velocity profiles were simulated, and their effects on the fluidized bed hydrodynamics and bubble dynamics have been studied. An in-house computer program was developed to track the bubbles and determine the temporal evolution of their size and position prior to their breakup. This program also provides information on the location of bubble coalescence and breakup. The gas-solid interactions were simulated using a Two-Fluid Model (TFM) with Gidaspow's drag model. The results reveal that the bed hydrodynamics feature a counter-rotating vortex pair for the solid phase, and bubble dynamics, such as coalescence and breakup, can be correlated with the vortices' outer periphery and the local gradients in the vorticity. [ABSTRACT FROM AUTHOR]

Light levitation of droplets over a locally heated gas–liquid interface by an infrared focus laser has been recently reported, but the hydrodynamics of light levitated droplet evolution remains unclear. Herein, we report that the condensed droplet experiences a periodic damped vortex motion process before evolving to a stably levitated droplet. In the later stage of the periodic damped vortex motion, the velocity decay rate is linearly proportional to the growth of condensed droplets. The linear scaling factor approximates the dynamic viscosity of the ambient fluid, which is analogous to the shear stress–shear relationship in the Newtonian friction law. This study deepens the understanding of the underlying mechanism of light levitated droplet evolution. [ABSTRACT FROM AUTHOR]

For vortex particle methods relying on SPH‐based simulations, the direct approach of iterating all fluid particles to capture velocity from vorticity can lead to a significant computational overhead during the Biot‐Savart summation process. To address this challenge, we present a Monte Carlo vortical smoothed particle hydrodynamics (MCVSPH) method for efficiently simulating turbulent flows within an SPH framework. Our approach harnesses a Monte Carlo estimator and operates exclusively within a pre‐sampled particle subset, thus eliminating the need for costly global iterations over all fluid particles. Our algorithm is decoupled from various projection loops which enforce incompressibility, independently handles the recovery of turbulent details, and seamlessly integrates with state‐of‐the‐art SPH‐based incompressibility solvers. Our approach rectifies the velocity of all fluid particles based on vorticity loss to respect the evolution of vorticity, effectively enforcing vortex motions. We demonstrate, by several experiments, that our MCVSPH method effectively preserves vorticity and creates visually prominent vortical motions. [ABSTRACT FROM AUTHOR]

The work and life of Ippolit Stepanovich Gromeka is reviewed. Gromeka authored a classical set of eleven papers on fluid dynamics in just ten years before a tragic illness ended his life. Sadly, he is not well known to the western scientific community because all his publications were written in Russian. He is one of the three authors who independently derived an analytical solution for accelerating laminar pipe flow. He was the first to eliminate the contradiction between the theories of Young and Laplace on capillary phenomena. He initiated the theoretical basis of helical (Beltrami) flow, and he studied the movement of cyclones and anticyclones seventeen years before Zermelo (whose work is considered as pioneering). He is also the first to analyse wave propagation in liquid-filled hoses, thereby including fluid–structure interaction. [ABSTRACT FROM AUTHOR]

Fallback in core-collapse supernova explosions is potentially of significant importance for the birth spins of neutron stars and black holes. It has recently been pointed out that the angular momentum imparted onto a compact remnant by fallback material is subtly intertwined with its kick because fallback onto a moving neutron star or black hole will preferentially come for a conical region around its direction of travel. We show that contrary to earlier expectations such one-sided fallback accretion onto a neutron star will tend to produce spin-kick misalignment. Since the baroclinic driving term in the vorticity equation is perpendicular to the nearly radial pressure gradient, convective eddies in the progenitor as well as Rayleigh–Taylor plumes growing during the explosion primarily carry angular momentum perpendicular to the radial direction. Fallback material from the accretion volume of a moving neutron star therefore carries substantial angular momentum perpendicular to the kick velocity. We estimate the seed angular momentum fluctuations from convective motions in core-collapse supernova progenitors and argue that accreted fallback material will almost invariably be accreted with the maximum permissible specific angular momentum for reaching the Alfvén radius. This imposes a limit of |${\sim }10^{-2}\, \mathrm{M}_\odot$| of fallback accretion for fast-spinning young neutron stars with periods of |${\sim }20\, \mathrm{ms}$| and less for longer birth spin periods. [ABSTRACT FROM AUTHOR]

We present a higher-order convergent numerical solver for active polar hydrodynamics in three-dimensional domains of arbitrary shape, along with a scalable open-source software implementation for shared- and distributed-memory parallel computers. This enables the computational study of the nonlinear dynamics of out-of-equilibrium materials from first principles. We numerically solve the nonlinear active Ericksen–Leslie hydrodynamic equations of three-dimensional (3D) active nematics using both a meshfree and a hybrid particle-mesh method in either the Eulerian or Lagrangian frame of reference. The solver is validated against a newly derived analytical solution in 3D and implemented using the OpenFPM software library for scalable scientific computing. We then apply the presented method to studying the transition of 3D active polar fluids to spatiotemporal chaos, the emergence of coherent angular motion in a 3D annulus, and chiral vortices in symmetric and asymmetric 3D shapes resembling dividing cells. Overall, this provides a robust and efficient open-source simulation framework for 3D active matter with verified numerical convergence and scalability on parallel computers. [ABSTRACT FROM AUTHOR]

The strongly interacting transient state of quark-gluon plasma (QGP) medium created in ultra-relativistic collisions survives for a duration of a few fm/c. The spacetime evolution of QGP crucially depends on the equation of state (EoS), vorticity, viscosity, and external magnetic field. In the present study, we obtain the lifetime of a vortical QGP fluid within the ambit of relativistic second-order viscous hydrodynamics. We observe that the coupling of vorticity and viscosity significantly increases the lifetime of vortical QGP. The inclusion of a static magnetic field, vorticity, and viscosity makes the evolution slower. However, the static magnetic field slightly decreases the QGP lifetime by accelerating the evolution process for a non-rotating medium. We also report the rate of change of vorticity in the QGP, which will be helpful in studying the behavior of the medium in detail. [ABSTRACT FROM AUTHOR]

High-speed gas/vapour jets injected into a cross-moving sonic liquid signifies a vital phenomenon which bears useful applications in environmental and energy processes. In the present experimental study, a pulsating jet of supersonic steam was injected into cross-flowing water. Circulation zones of opposite vorticity owing to the interaction between the steam jet and cross-water flow were found. However, a large circulation appeared in front of the nozzle exit. Also, most small circulation regions were observed at higher water-flow rates (>2 m3/s). Among the prime mixing variables (i.e., turbulence kinetic energy (TKE) and Reynolds shear stress (RSS)), the RSS estimations backed a small diffusive phenomenon within a region far from the nozzle exit. Further information extracted from the PIV images indicated the existence of Kelvin–Helmholtz (KH) instabilities. The counter-rotating vortex pairs (CVPs) appeared to be significant in the region close to the nozzle exit, and they exhibited leeward side folds. Moreover, the effects of the operating conditions on the pressure recovery and mixing efficiency as well as the penetration and the separation height were evaluated to determine the optimisation of the phenomenon. By applying extreme difference analysis, the mixing efficiency was found as the most influential parameter. [ABSTRACT FROM AUTHOR]

This paper is aimed at eliciting consistency conditions for the existence of unsteady incompressible axisymmetric swirling viscous Beltrami vortices and explicitly constructing solutions that obey the conditions as well as the Navier–Stokes equations. By Beltrami flow, it is meant that vorticity, i.e., the curl of velocity, is proportional to velocity at any local point in space and time. The consistency conditions are derived for the proportionality coefficient, the velocity field and external force. The coefficient, whose dimension is of [length−1], is either constant or nonconstant. In the former case, the well-known exact nondivergent three-dimensional unsteady vortex solutions are obtained by solving the evolution equations for the stream function directly. In the latter case, the consistency conditions are given by nonlinear equations of the stream function, one of which corresponds to the Bragg–Hawthorne equation for steady inviscid flow. Solutions of a novel type are found by numerically solving the nonlinear constraint equation at a fixed time. Time dependence is recovered by taking advantage of the linearity of the evolution equation of the stream function. The proportionality coefficient is found to depend on space and time. A phenomenon of partial restoration of the broken scaling invariance is observed at short distances. [ABSTRACT FROM AUTHOR]

We present a Gaussian process (GP) approach, called Gaussian process hydrodynamics (GPH) for approximating the solution to the Euler and Navier-Stokes (NS) equations. Similar to smoothed particle hydrodynamics (SPH), GPH is a Lagrangian particle-based approach that involves the tracking of a finite number of particles transported by a flow. However, these particles do not represent mollified particles of matter but carry discrete/partial information about the continuous flow. Closure is achieved by placing a divergence-free GP prior ξ on the velocity field and conditioning it on the vorticity at the particle locations. Known physics (e.g., the Richardson cascade and velocity increment power laws) is incorporated into the GP prior by using physics-informed additive kernels. This is equivalent to expressing ξ as a sum of independent GPs ξl, which we call modes, acting at different scales (each mode ξl self-activates to represent the formation of eddies at the corresponding scales). This approach enables a quantitative analysis of the Richardson cascade through the analysis of the activation of these modes, and enables us to analyze coarse-grain turbulence statistically rather than deterministically. Because GPH is formulated by using the vorticity equations, it does not require solving a pressure equation. By enforcing incompressibility and fluid-structure boundary conditions through the selection of a kernel, GPH requires significantly fewer particles than SPH. Because GPH has a natural probabilistic interpretation, the numerical results come with uncertainty estimates, enabling their incorporation into an uncertainty quantification (UQ) pipeline and adding/removing particles (quanta of information) in an adapted manner. The proposed approach is suitable for analysis because it inherits the complexity of state-of-the-art solvers for dense kernel matrices and results in a natural definition of turbulence as information loss. Numerical experiments support the importance of selecting physics-informed kernels and illustrate the major impact of such kernels on the accuracy and stability. Because the proposed approach uses a Bayesian interpretation, it naturally enables data assimilation and predictions and estimations by mixing simulation data and experimental data. [ABSTRACT FROM AUTHOR]

Dark matter, if it exists, accounts for five times as much as the ordinary baryonic matter. Compared to hydrodynamic turbulence, the flow of dark matter might possess the widest presence in our universe. This paper presents a statistical theory for the flow of dark matter that is compared with N-body simulations. By contrast to hydrodynamics of normal fluids, dark matter flow is self-gravitating, long-range, and collisionless with a scale-dependent flow behavior. The peculiar velocity field is of constant divergence nature on small scale and irrotational on large scale. The statistical measures, i.e., correlation, structure, dispersion, and spectrum functions, are modeled on both small and large scales, respectively. Kinematic relations between statistical measures are fully developed for incompressible, constant divergence, and irrotational flow. Incompressible and constant divergence flow share the same kinematic relations for even order correlations. The limiting correlation of velocity ρ L = 1 / 2 on the smallest scale (r = 0) is a unique feature of collisionless flow ( ρ L = 1 for incompressible flow). On large scale, transverse velocity correlation has an exponential form T 2 ∝ e − r / r 2 with a constant comoving scale r2=21.3 Mpc/h that may be related to the horizon size at matter–radiation equality. All other correlation, structure, dispersion, and spectrum functions for velocity, density, and potential fields are derived analytically from kinematic relations for irrotational flow. On small scale, longitudinal structure function follows one-fourth law of S 2 l ∝ r 1 / 4 . All other statistical measures can be obtained from kinematic relations for constant divergence flow. Vorticity is negatively correlated for scale r between 1 and 7 Mpc/h. Divergence is negatively correlated for r > 30 Mpc/h that leads to a negative density correlation. [ABSTRACT FROM AUTHOR]

The gold–gold collisions at s N N = 7.7 and 11.5 GeV are simulated within the PHSD transport model. In each collision event, the spectator nucleons are separated and the fluidization procedure for the participants is performed. The local velocities are determined in the Landau frame and the kinematic and thermal vorticity fields are evaluated. We analyze the thermodynamic properties of the cells where Λs and Λ ¯ s were born or had their last interaction. Such cells contribute to the formation of the observed global polarization of hyperons induced by the thermal vorticity of the medium. The Λ ¯ polarization signal is found to be mainly determined by hot, dense, and highly vortical cells at the earlier stage of the collision, whereas the Λ polarization signal is accumulated over the longer time and includes cells with lower vorticity. The calculated global polarizations for both Λs and Λ ¯ s agree well with the experimental finding by the STAR collaboration at energy s N N = 11.5   G e V. For collisions at s N N = 7.7   G e V , we can reproduce the STAR data for Λ hyperons, but significantly underpredict the observed global polarization of Λ ¯ . Furthermore, we consider the centrality dependence of the hyperon polarization in collisions at 7.7 GeV. It increases with an increase of centrality, reaches a maximum at 65–75% and then starts decreasing rapidly for peripheral collisions. [ABSTRACT FROM AUTHOR]

We review recent studies of vortical motion and the resulting polarization of Λ hyperons in heavy-ion collisions at NICA energies, in particular, within the model of three-fluid dynamics (3FD). This includes predictions of the global Λ polarization and ring structures that appear in Au+Au collisions. The global Λ polarization in Au+Au collisions is calculated, including its rapidity and centrality dependence. The contributions of the thermal vorticity and meson-field term (proposed by Csernai, Kapusta, and Welle) to the global polarization are considered. The results are compared with data from recent STAR and HADES experiments. It is predicted that the polarization maximum is reached at s N N ≈ 3 GeV if the measurements are performed with the same acceptance. It is demonstrated that a pair of vortex rings are formed, one at forward rapidities and another at backward rapidities, in ultra-central Au+Au collisions at s N N > 4 GeV. The vortex rings carry information about the early stage of the collision, in particular, the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable R Λ , even in the midrapidity region at s N N = 5–20 GeV. At forward/backward rapidities, the R Λ signal is expected to be stronger. The possibility of observing the vortex-ring signal against the background of non-collective transverse polarization is discussed. [ABSTRACT FROM AUTHOR]

The work and life of Ippolit Stepanovich Gromeka is reviewed. Gromeka authored a classical set of eleven papers on fluid dynamics in just ten years before a tragic illness ended his life. Sadly, he is not well known to the western scientific community because all his publications were written in Russian. He is one of the three authors who independently derived an analytical solution for accelerating laminar pipe flow. He was the first to eliminate the contradiction between the theories of Young and Laplace on capillary phenomena. He initiated the theoretical basis of helical (Beltrami) flow, and he studied the movement of cyclones and anticyclones seventeen years before Zermelo (whose work is considered as pioneering). He is also the first to analyse wave propagation in liquid-filled hoses, thereby including fluid–structure interaction.

This article proposes a novel graphics processing unit‐based active nematic flow solver based on the smoothed particle hydrodynamics (SPH) method. Nematohydrodynamics equations are discretized using the SPH algorithm. Flow behavior, nematic ordering, topological defects, and vorticity correlation are calculated and discussed in detail. The spectrum of the kinetic energy with respect to the wavenumber is calculated at high particle resolution, and its slope at the different length scales is discussed. To exploit the SPH capabilities, pathlines of nematic particles are evaluated during the simulation. Finally, the mixing behavior of the active nematics is calculated as well and described qualitatively. The effects of two important parameters, namely, activity and elastic constant are investigated. It is shown that the activity intensifies the chaotic mixing nature of the active nematics, while the elastic constant behaves oppositely. [ABSTRACT FROM AUTHOR]

We propose an efficient model for the description of the three-dimensional (3-D) evolution of breaking water waves in the nearshore region. A fundamental property of the model is its intrinsic ability to account for the 3-D dynamics of vorticity and the energy dissipation induced by wave breaking. In particular, the vorticity evolution is achieved through the use of mollified operators, an approach similar in spirit to that adopted in smoothed particle hydrodynamics. Further, since the model is based on depth-semi-averaged equations with a core structure similar to that of nonlinear shallow-water equations, it takes advantage of well-known numerical methods for hyperbolic equations, while permitting computation of local flows. Finally, the model relies on a limited number of tunable parameters and a very simple breaking criterion. All the above aspects allow for a simple and reliable representation of the main features of wave breaking at the time and spatial scales typical of the nearshore wave dynamics. A number of benchmarks are used to explore the properties of the model, which is tuned only once for all cases. Wave height decay rates are well described for both sloshing (thin) and shoaling (thick) spillers, and a good description is also provided of the vorticity field. A final run of an impulsive wave over a submerged breakwater is used to illustrate the representation of the 3-D vorticity dynamics. [ABSTRACT FROM AUTHOR]

This companion paper presents the results of a series of numerical experiments examining the effects of a mitigation canal on the hydrodynamics of a tsunami-like turbulent bore proceeding over a horizontal bed. The hydraulic bores were generated by a dam-break setup which employed impoundment depths of do = 0.20 m, 0.30 m, and 0.40 m. The bore propagated downstream of the impoundments in the flume and interacted with a canal with varying geometry located downstream. The bore then left the flume through a drain located further downstream of the canal. In this study, the effect of the canal depth on the specific momentum and specific energy of hydraulic bores passing over a rectangular canal is numerically studied. The canal width was kept constant, at w = 0.6 m, while the canal depths were varied as follows: d = 0.05 m, 0.10 m, and 0.15 m. The time history of mean flow energy during the bore's passing over the mitigation canal indicates that the jet stream of the maximum mean flow energy is controlled by the canal depth. The time required to dissipate the jet stream of the maximum vorticity, the turbulent kinetic energy, and the energy dissipation rate all increased as the canal depth decreased. The effect of canal orientation on the bore hydrodynamics was also numerically investigated, and it was found that the impulsive momentum and specific energy reached the highest values for canal orientations of 45 and 60 degrees. For the same canal depth, the highest peak specific momentum occurred with the highest degree of canal orientation (θ = 60°). [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) is a ubiquitous numerical method for solving the fluid equations, and is prized for its conservation properties, natural adaptivity, and simplicity. We introduce the Sphenix SPH scheme, which was designed with three key goals in mind: to work well with sub-grid physics modules that inject energy, be highly computationally efficient (both in terms of compute and memory), and to be Lagrangian. sphenix uses a Density-Energy equation of motion, along with a variable artificial viscosity and conduction, including limiters designed to work with common sub-grid models of galaxy formation. In particular, we present and test a novel limiter that prevents conduction across shocks, preventing spurious radiative losses in feedback events. Sphenix is shown to solve many difficult test problems for traditional SPH, including fluid mixing and vorticity conservation, and it is shown to produce convergent behaviour in all tests where this is appropriate. Crucially, we use the same parameters within sphenix for the various switches throughout, to demonstrate the performance of the scheme as it would be used in production simulations. sphenix is the new default scheme in the swift cosmological simulation code and is available open source. [ABSTRACT FROM AUTHOR]

Namely, let the vorticity HT ht be supported on I N i point vortices HT ht , where HT ht are coordinates and HT ht is the strength of the I j i th point vortex in the plane HT ht . The function HT ht is the system's Hamiltonian for the standard Poisson bracket on HT ht weighted by the strengths HT ht . Consider a point HT ht on the real axis and an action of three other points on it. [Extracted from the article]

We study the active flow around isolated defects and the self-propulsion velocity of +1/2 defects in an active nematic film with both viscous dissipation (with viscosity ή) and frictional damping G with a substrate. The interplay between these two dissipation mechanisms is controlled by the hydrodynamic dissipation length ld = v ή/G that screens the flows. For an isolated defect, in the absence of screening from other defects, the size of the shear vorticity around the defect is controlled by the system size R. In the presence of friction that leads to a finite value of d, the vorticity field decays to zero on the lengthscales larger than d. We show that the self-propulsion velocity of +1/2 defects grows with R in small systems where R< d, while in the infinite system limit or when Rd, it approaches a constant value determined by d. [ABSTRACT FROM AUTHOR]

We develop a consistent hydrodynamic theory for ferrofluids that can be concentrated, strongly interacting, and polydisperse. We analyze the dynamics of ferrocolloids under imposed flow and magnetic field, from micro-, meso-, and macroscopic points of view. We settle the long-standing debate on the correct reactive contribution to magnetization dynamics near or far from equilibrium. We obtain a fundamental mesoscopic rotational fluctuation-dissipation relation, linking vortex viscosity and rotational self-diffusivity and with far-reaching consequences on ferrofluid hydrodynamics. It distinguishes from the traditional Stokes–Einstein–Debye relation that only applies to dilute and noninteracting systems. Furthermore, it is used to infer the size of structure units whose rotational diffusion is responsible for the primary Debye peak of water. The characteristic hydrodynamic radius is estimated to be ∼ 0.18 nm, considerably larger than the geometrical radius of water molecules. This is in contrast to the result obtained by naively employing the Stokes–Einstein–Debye relation. We revisit the magnetoviscous effect in ferrofluids and obtain novel expressions for the rotational viscosity, shedding new light on the effects of inter-particle correlations and particle packing. In particular, previous models usually confuse solvent vorticity with suspension vorticity and do not yield the actual rotational viscosity measured in experiments. We compare our theoretical predictions with recent simulations and find quantitatively good agreements. Our work is to be a cornerstone for understanding ferrofluid dynamics and of considerable importance to various applications. It can be also valuable for studying the hydrodynamics of other structured fluids. [ABSTRACT FROM AUTHOR]

This study examines the hydrodynamics and morphodynamics of open‐channel confluences characterized by subcritical flow, low flow discharge ratio, a 90° junction angle and dominant sediment supply coming from the tributary. The analysis is based on a novel data set comprised of the three‐dimensional time‐averaged velocity field, turbulence, bed morphology, and water surface levels acquired under controlled conditions in a laboratory setup. Confluence morphology at equilibrium stage was characterized by moderate bed discordance and pronounced bed erosion at the junction. This study suggests an updated conceptual model of flow hydrodynamics in realistic morphologically stable confluences. The near‐bed flow from the main channel proceeds underneath the tributary inflow into the tributary where it engages in the rotational motion of a strong secondary circulation observed within and downstream of the junction. The high‐speed near‐bed flow intensifies the stretching of the secondary cell past the downstream junction corner where it expands and aligns with slope of the bank‐attached bar. It is argued that the post‐confluence secondary cell is a result of flow separation at the tributary‐mouth bar and of the curvature of the shear layer, configuring a Prandtl's first kind of helical flow. Key Points: Strong secondary circulation was observed at the tributary‐mouth bar and downstream of the junctionThe near‐bank portion of flow coming from the main channel engaged in the rotational motion of the secondary cell at the tributary‐mouth barSecondary circulation was related to flow separation at the tributary‐mouth and distribution of secondary vorticity along the shear layer [ABSTRACT FROM AUTHOR]

Air-core vortex occurred at the hydraulic intakes deteriorates the performance and operation stability of hydraulic machineries. To investigate the evolution process and generation mechanism of the air-core vortex formed at the vertical intake, large-eddy simulation with the coupled level-set and volume-of-fluid method is performed in a pump sump. This paper elucidates the evolution of velocity distribution caused by pump suction, and associations between vortices motions and velocity evolution and the accompanying free-surface deformations are clarified, which reveals the generation mechanism and evolution characteristics of air-core vortex. Vortices are created by the disturbances of small recirculation zone around the intake pipe. The recirculation is caused by the interaction of the wall of vertical pipe and converging flows with opposite directions driven by the pump suction. The enhancement of vortices due to vortex distortion dominates the air-core vortex formation, and the vertical stretching effect accounts for about 70%. The meandering characteristics of air-core vortex are characterized through analyses of meandering scope and velocity distribution, and the convection of mean flow and sump wall take the leading role in causing its meandering. • Accurate two-phase simulation of the air-core vortex in a vertical intake is achieved. • Velocity distribution and associated vortices motions are elucidated during the air-core vortex formation. • The interaction of the wall of vertical pipe and converging flows with opposite directions creates vortices. • Vortex distortion dominates the enhancement of vertical vortices. • Causes of the air-core vortex meandering and its meandering region are revealed. [ABSTRACT FROM AUTHOR]

Based on the numerical and experimental visualization methods, the flow patterns around a uniformly moving plate located at an arbitrary angle of attack are studied. The study is based on the fundamental equations of continuity, momentum and stratifying substance transport for the cases of strong and weak stratified fluids, as well as potential and actually homogeneous ones. The visualization technique and computation codes were compiled bearing in mind conditions of internal waves, vortices, upstream, and downstream wakes registration, as well as the resolution of ligaments in the form of thin interfaces in schlieren flow images. The analysis was carried out in a unified mathematical formulation for a wide range of plate motion parameters, including slow diffusion-induced flows and fast transient vortex flows. The patterns of formation and subsequent evolution of the basic structural components, such as upstream disturbances, downstream wake, internal waves, vortices, and ligaments, are described both at start of motion and subsequent uniform movement of the plate. Calculations of forces acting on the obstacle in the flow were carried out to study effects of variations in fluid properties, flow conditions and plate parameters on the dynamic characteristics of the obstacle. The numerical and experimental results on the flow patterns around a plate are in a good agreement with each other for different flow regimes. [ABSTRACT FROM AUTHOR]

Both simulations and observations have shown that turbulence is a pervasive phenomenon in cosmic scenarios, yet it is particularly difficult to model numerically due to its intrinsically multiscale character which demands high resolutions. Additionally, turbulence is tightly connected to the dynamical state and the formation history of galaxies and galaxy clusters, producing a diverse phenomenology which requires large samples of such structures to attain robust conclusions. In this work, we use an adaptive mesh refinement (AMR) cosmological simulation to explore the generation and dissipation of turbulence in galaxy clusters, in connection to its assembly history. We find that major mergers, and more generally accretion of gas, is the main process driving turbulence in the intracluster medium. We have especially focused on solenoidal turbulence, which can be quantified through enstrophy. Our results seem to confirm a scenario for its generation which involves baroclinicity and compression at the external (accretion) and internal (merger) shocks, followed by vortex stretching downstream of them. We have also looked at the infall of mass to the cluster beyond its virial boundary, finding that gas follows trajectories with some degree of helicity, as it has already developed some vorticity in the external shocks. [ABSTRACT FROM AUTHOR]

In this work, the hydrodynamics, mixing and sedimentation is numerically investigated in the batch stirred vessel through CFD. The flow field obtained by performing transient CFD simulations using multiple reference frame (MRF) and sliding mesh approach along with standard k-ε turbulence model. The velocity field is investigated spatially and temporally and liquid circulation is quantified at various impeller speeds to find an optimum impeller speed. The importance of geometry of the draft tube baffles is investigated by quantifying the vorticity, mixing time, power requirement and quality of suspension in the batch stirred vessel. It is found that suspension quantity in a batch stirred vessel is strongly dependent on the hydrodynamics. The role of the draft tube and the inner baffles is further analyzed and found that proper positioning and length of the baffles is necessary to improve the turbulence characteristics and the quality of the suspension. [ABSTRACT FROM AUTHOR]

• The effects of a vortex generator (VG) and magneto hydrodynamics (MHD) on the thermal properties of nanofluids in a microchannel is numerically studied. • It was shown that at GR = 1.0, the strength of the vorticity is still high, which can act as a strong turbulator in the wake of the cylinder. • The numerical results demonstrate that when the MHD and VG effects are applied to the model, heat transfer increases by approximately 20%. • It is demonstrated that, for the analyzed models in this work, the effect of the VG mechanism is stronger than the influence of MHD. This paper investigates the effects of a vortex generator (VG) and magneto-hydrodynamics (MHD) on the thermal properties of nanofluids in a microchannel. A variety of test scenarios within the laminar flow regimes are numerically examined: nanofluids in a hot-walled simple channel (SC); nanofluids in a heated-walled channel where a circular cylinder is embedded within the channel and functions as a vortex generator (VG); nanofluids in a heated-walled channel that incorporates both a vortex generator and magneto-hydrodynamics (VG-MHD). The channel has a circular cylinder with a diameter of D that is fixed inside the channel with various gap ratios (GR = G/D) ranging from 0.5 to 4.0. Numerical investigations for laminar flow with Re ≤ 1,000 are carried out. The nanoparticle volume fractions range from 0 % to 7 %, and the magnetic field is set at 0.05 T. The best heat transmission conditions with the lowest skin friction coefficient are evaluated for the optimal GR. It is found that heat transfer is enhanced by approximately 20 % when MHD and VG effects are employed, in contrast to a traditional channel that does not utilize the MHD effect. [ABSTRACT FROM AUTHOR]

A major issue in smoothed particle hydrodynamics (SPH) approaches is the numerical dissipation during the projection process, especially under coarse discretizations. High‐frequency details, such as turbulence and vortices, are smoothed out, leading to unrealistic results. To address this issue, we introduce a vorticity refinement (VR) solver for SPH fluids with negligible computational overhead. In this method, the numerical dissipation of the vorticity field is recovered by the difference between the theoretical and the actual vorticity, so as to enhance turbulence details. Instead of solving the Biot‐Savart integrals, a stream function, which is easier and more efficient to solve, is used to relate the vorticity field to the velocity field. We obtain turbulence effects of different intensity levels by changing an adjustable parameter. Since the vorticity field is enhanced according to the curl field, our method can not only amplify existing vortices, but also capture additional turbulence. Our VR solver is straightforward to implement and can be easily integrated into existing SPH methods. [ABSTRACT FROM AUTHOR]

The present work deals with some recent developments regarding the inclusion of the Large-Eddy Simulation (LES) in the weakly compressible Smoothed Particle Hydrodynamics (SPH) framework. Previously {see the work of Di Mascio et al. [Phys. Fluids 29, 4 (2017)]}, this goal was achieved by applying a Lagrangian filter to the Navier–Stokes equations for compressible fluids and, then, approximating the differential operators in a SPH fashion. Since the Lagrangian nature of the derived scheme turned out to be an obstacle for accurate simulations of high Reynolds number problems, the above approach is here modified to obtain a quasi-Lagrangian LES-SPH model. This relies on the addition of a small velocity deviation to the actual Lagrangian velocity based on the particle shifting technique and on the inclusion of the tensile instability control technique for eliminating the onset of the tensile instability in the fluid regions characterized by large vorticity and negative pressure. The proposed model is successfully tested in both two-dimensional and three-dimensional frameworks by simulating the evolution of freely decaying turbulence problems and comparing the outputs with the available theoretical results and solutions from other numerical models. [ABSTRACT FROM AUTHOR]

Air wake distribution around the superstructure of a mega-yacht is a key concern for the designer because of various reasons such as comfort expectations in recreational deck areas, self-noise generation, air pollution and temperature gradients due to exhaust interactions, and safety of helicopter operations such as landing/take off and hovering. The Reynolds-averaged Navier-Stokes (RANS) technique in computational fluid dynamics (CFD) is frequently used in studies on mega-yacht hydrodynamics and aerodynamics with satisfactory results. In this article, a case study is presented for the utilization of CFD in a mega-yacht's superstructure design. The flow field in recreational open areas has been analyzed for the increase in velocity due to the existence of the superstructure. A reduction in self-noise of the mast structure has been aimed by reducing flow separation and vorticity. Time-dependent velocity data obtained with scale-resolving simulations are presented for the evaluation of helicopter landings. The capabilities and limitations of the RANS technique are discussed along with recent developments in modeling approaches. [ABSTRACT FROM AUTHOR]

A rotating superfluid forms an array of quantized vortex lines that determine its angular velocity. The spasmodic evolution of the array under the influence of deceleration, dissipation, and pinning forces is thought to be responsible for the phenomenon of pulsar glitches, sudden jumps in the spin frequency of rotating neutron stars. We describe and implement an N -body method for simulating the motion of up to 5000 vortices in two dimensions and present the results of numerical experiments validating the method, including stability of a vortex ring and dissipative formation of an Abrikosov array. Vortex avalanches occur routinely in the simulations, when chains of unpinning events are triggered collectively by vortex–vortex repulsion, consistent with previous, smaller scale studies using the Gross–Pitaevskii equation. The probability density functions of the avalanche sizes and waiting times are consistent with both exponential and lognormal distributions. We find weak correlations between glitch sizes and waiting times, consistent with astronomical data and meta-models of pulsar glitch activity as a state-dependent Poisson process or a Brownian stress-accumulation process, and inconsistent with a threshold-triggered stress-release model with a single, global stress reservoir. The spatial distribution of the effective stress within the simulation volume is analysed before and after a glitch. [ABSTRACT FROM AUTHOR]

In this article, we consider the ideal magnetic Bénard problem in both two and three dimensions and prove the existence and uniqueness of strong local-in-time solutions, in Hs for s > n\2 + 1, n = 2; 3. In addition, a necessary condition is derived for singularity development with respect to the BMO-norm of the vorticity and electrical current, generalizing the Beale- Kato-Majda condition for ideal hydrodynamics. [ABSTRACT FROM AUTHOR]

We analyzed patterns of aggregation and spatial distribution of the epizoic barnacle Xenobalanus globicipitis on the flukes of Mediterranean striped dolphins, Stenella coeruleoalba, assessing its potential use as an indicator of the host's hydrodynamics based on data from 55 dolphins. Barnacles occurred along the trailing edge with the cirri oriented towards the oncoming flow. Nearest neighbor analyses suggested that new recruits actively seek placement next to already settled barnacles, forming aggregations possibly to facilitate copulation. The probability of spanwise settlement strongly increased with fluke width (presumably enabling prolonged leading‐edge vorticity), and with chordwise length where pressure is predicted to be positive. Consequently, clustering tended to increase nonlinearly towards the fluke notch. Furthermore, it was three times more likely for barnacles to occur on the dorsal vs. ventral side of flukes, at an average abundance ca. 12 times higher. This difference could result from a host's asymmetric oscillation of the tail, which would alter leading‐edge vorticity, and/or an interaction between the wake produced by the dorsal fin and the flow associated with flukes. Both processes could primarily enhance cyprid contact and/or attachment on the dorsal side. This study offers a starting point for future comparison with other cetaceans. [ABSTRACT FROM AUTHOR]

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

An analytical approach to the determination of optimal disturbances is developed. The approach, suitable for flows with piecewise-constant vorticity distributions, is based on the equation of disturbance energy balance and explicit expressions for the growth rate of the energy or the final-to-initial energy ratio. The corresponding expressions are functions of the initial parameters and the optimal disturbance parameters are determined from an extremization of these functions. Within the framework of the approach the classical Rayleigh problem of the free shear layer instability and the problem of the instability of a system consisting of two counter-streaming jet flows in a rotating shallow water layer are considered. The parameters of the optimal disturbances are compared with those of growing normal modes. [ABSTRACT FROM AUTHOR]

Acoustic streaming was proposed to drive rotary motors, where a gas layer exists between the stator and the rotor. With numerical simulations for this kind of noncontact ultrasonic motors, the influences of the parameters of the air flow on the performance of the motors are calculated and analyzed. The results show that the replacement of invariant viscosity by the temperature-dependent viscosity decreases the rotor velocity by ∼11%. Heat conduction is found to play a trivial role. It is also revealed that the rotor velocity increases more and more rapidly as the thickness of the air gap becomes smaller and smaller. Most importantly, we demonstrated that this kind of motor is very stable, and the rotor velocity is insensitive to the working temperature of the environment. [ABSTRACT FROM AUTHOR]

Flows generated near hydro‐engineering structures are characterized by energetic three‐dimensional flow structures that are markedly different from naturally occurring fish habitats. The current study evaluated the interaction of Nile tilapia (Oreochromis niloticus) with spanwise rollers in the turbulent wake of a cylinder in both the wake bubble and the vortex shedding further downstream. The flow field hydrodynamics were measured using an acoustic Doppler velocimeter for Reynolds number (ReD) regimes ranging from 3,730 to 33,590, over a streamwise length of six diameters downstream of the cylinder, and revealed a pair of alternating vortices rotating about a spanwise axis, which were rendered asymmetric by the bed boundary proximity. Fish avoided areas where vorticity, turbulence intensity, turbulent kinetic energy, eddy size, and Reynolds shear stress were highest. Events of stability loss, referred to as spills, were significantly correlated to the turbulence integral length scale relative to fish standard length, with the peak number of spills occurring when the eddy length approached 45% to 50% of the fish length. Spill events significantly depended on ReD, Reynolds stress, and vorticity and varied according to fish length and weight. Among zones of similar Reynolds stress and vorticity magnitude, spills were most frequent when Reynolds shear stress was positive, downward acting and eddies rotated clockwise, which highlights the importance of direction and orientation of flow structures in determining the hydrodynamic forces that affect fish swimming stability. Recommendations are made for the inclusion of these metrics in the design and refinement of hydro‐engineering schemes. Key Points: The interaction of fish with spanwise vortices was examined by considering habitat use and swimming stabilityFish avoided areas of highest turbulent heterogeneity, while loss of stability peaked when turbulence length scale was 45–50% of fish lengthHighest magnitudes of downward‐acting Reynolds stresses and negative vorticity corresponded to the highest rate of spill occurrence [ABSTRACT FROM AUTHOR]

Seaweed and fish have slippery outer surfaces because of the secretion of a layer of mucus. Navier slip arises when the component of the tangential velocity at a wall is proportional to the strain. The hydrodynamics of a three-dimensional flexible plate with Navier slip was explored by using the immersed boundary method in an effort to scrutinize the effects on plate hydrodynamics of a slip boundary mimicking the mucus layers of seaweed and fish. For comparison, simulations with the no-slip condition were also performed. Two cases were chosen for simulation: a flexible plate with a fixed leading edge and a flexible plate with a heaving leading edge in a uniform flow. For the fixed plate, the velocity gradient and the total drag were determined to examine the influence of the slip surface. Drag was significantly reduced by the slip. The slip surface lessens the velocity gradient near the wall and suppresses the flapping motion. The drag reduction process was characterized by using the distributions of vorticity and pressure. The hydrodynamics of the heaving flexible plate with Navier slip was explored in terms of thrust generation. The flapping motion was mainly governed by the input heaving condition and a large form drag was exerted on the flexible plate. The net thrust, input power, and Froude efficiency were determined as a function of the bending rigidity. A large net thrust for the heaving plate was generated by the slip. The velocity ratio was employed to interpret the correlation between the slip velocity and the flapping motion. [ABSTRACT FROM AUTHOR]

In this work, we investigate the phenomenon of vortex generation and formation of a vortex ring when a liquid drop impinges on a miscible liquid surface. Although the formation of a vortex ring for this system has been studied for more than a century, little is known about its exact mechanism of generation and how its hydrodynamics is related to the shape of the drop. This is due to the complexity involved in the conversion of the initially generated vorticity into a vortex ring. To cast light on this intriguing phenomenon, time-resolved high-speed imaging with high magnification is used. This allows us to probe deeper into the vortex generation process and study the formation of the ring. We make a comprehensive study of the effect of drop impingement height and drop shape at the time of impact on the vortex generation and the hydrodynamics of the ring. The effect of crater evolution on the hydrodynamics of the vortex ring is studied in terms of its diameter and translational velocity. By examining the role of the shape of the crater on vortex ring penetration, we answer the question why the most penetrating vortex rings are generated by a prolate shaped drop. [ABSTRACT FROM AUTHOR]

Nonequilibrium interacting systems can evolve to exhibit large-scale structure and order. In two-dimensional turbulent flow, the seemingly random swirling motion of a fluid can evolve toward persistent large-scale vortices. To explain such behavior, Lars Onsager proposed a statistical hydrodynamic model based on quantized vortices. Here, we report on the experimental confirmation of Onsager’s model. We dragged a grid barrier through an oblate superfluid Bose–Einstein condensate to generate nonequilibrium distributions of vortices. We observed signatures of an inverse energy cascade driven by the evaporative heating of vortices, leading to steady-state configurations characterized by negative absolute temperatures. Our results open a pathway for quantitative studies of emergent structures in interacting quantum systems driven far from equilibrium. [ABSTRACT FROM AUTHOR]

The present study investigated the effect of impeller speed and vortex ingestion on vortex shape, gas holdup, and bubble size distribution in an unbaffled stirred tank using optical probe measurements. Further, the ability of the volume of the fluid model to predict vortex shape was examined. Without vortex ingestion, an increase in impeller speed resulted in a significant variation in vortex shape, whereas it had a negligible effect on vortex shape with ingestion. This suggests that when vortex ingestion occurred, most of the energy was consumed for the dispersion of gas rather than the deformation of the gas‐liquid interface. It was observed that a large number of gas bubbles were entrained into the vortex core around the impeller region, which led to a lower gas holdup at the top axial locations. An increase in the impeller speed also resulted in the formation of larger bubbles. The absence of baffles limits shear for bubble break up, resulting in larger bubbles above the impeller plane. [ABSTRACT FROM AUTHOR]

The article deals with the impact of the hydrodynamic feature of the vortex granulator operation and intensity of the heat transfer agent’s directional vortex motion on the structure and quality of the porous surface layer and internal nanoporous structure in the ammonium nitrate granules. The analysis results of the porous ammonium nitrate quality indices, obtained in different hydrodynamic regimes, were demonstrated. The structure of a granule, obtained in the vortex gas flow with different twisting intensity, was studied. The received data make the base to create the engineering calculation method of granulators as a part of the unit to obtain 3D nanostructured porous surface layer on the ammonium nitrate granule. The obtained porous ammonium nitrate (PAN) samples were tested to define the explosive features of the industrial explosive “Ammonium Nitrate/Fuel Oil” (ANFO). The detonation velocity of ANFO was determined by the Dotrish method (it is based on the comparison of the known detonation velocity of the detonating chord with the unknown velocity of ANFO detonation). The industrial explosive (ANFO) charges based on the 95 % of PAN and 5 % of the diesel fuel distillate reliably detonate from the intermediate charge – trotyl block, which is initiated by the electric detonator. The ANFO detonation velocity was 2.2- 2.3 km/s. It is possible to regulate the process regarding the nanostructured porous layer formation with the specified properties owing to the selection of the optimal hydrodynamic regime to lay the humidifier’s film and granules heat treatment. The results of the theoretical and experimental research carried out by authors enable to perform the optimization projection of the main equipment in the unit to obtain PAN, i.e. the vortex granulator. [ABSTRACT FROM AUTHOR]