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The vortex-ring interaction of synchronous jets has been paid more attention by predecessors, while the research of asynchronous jets (i.e. there is a time difference between the start of jets) of parallel dual nozzles has been studied less. Therefore, the interaction between vortex rings and the vortex structure evolution of the dual-nozzle asynchronous jets with different time differences (Δt) is studied in this paper. Numerical results obtained can be divided into four intervals: 1. Synchronous jets (Δt = 0); 2. Critical interval (Δt < 0.1t, where t is the jet time), having similar vortex structure evolution modes and dynamic characteristics as the synchronous jet; 3. Strong interaction interval (0.2t ≤ Δt ≤ 0.4t), in which the main vortex ring shows obvious acceleration, and the streamwise vortex structure is found in the wake; 4. weak interaction interval (Δt ≥ 0.6t), in which the interaction between vortex rings is much less strong and the streamwise vortex structure also appears in the wake. In addition, it is found that pressure on the nozzle outlet plane increases and the vortex dissipation in the downstream flow field slows down significantly due to the vortex-ring interaction on the condition of asynchronous jets.

We introduce a model of a passive optical cavity based on a novel variety of the two-dimensional Lugiato–Lefever equation, with a localized pump carrying intrinsic vorticity S, and the cubic or cubic–quintic nonlinearity. Up to S=5, stable confined vortex ring states (vortex pixels) are produced by means of a variational approximation and in a numerical form. Surprisingly, vast stability areas of the vortex states are found, for both the self-focusing and defocusing signs of the nonlinearity, in the plane of the pump and loss parameters. When the vortex rings are unstable, they are destroyed by azimuthal perturbations, which break the axial symmetry. The results suggest new possibilities for mode manipulations in passive nonlinear photonic media by means of appropriately designed pump beams.

We analyse the dynamical properties of three-dimensional solitary waves in cylindrically trapped Bose-Einstein condensates. Families of solitary waves bifurcate from the planar dark soliton and include the solitonic vortex, the vortex ring and more complex structures of intersecting vortex lines known collectively as Chladni solitons. The particle-like dynamics of these guided solitary waves provides potentially profitable features for their implementation in atomtronic circuits, and play a key role in the generation of metastable loop currents. Based on the time-dependent Gross-Pitaevskii equation we calculate the dispersion relations of moving solitary waves and their modes of dynamical instability. The dispersion relations reveal a complex crossing and bifurcation scenario. For stationary structures we find that for the solitonic vortex is the only stable solitary wave. More complex Chladni solitons still have weaker instabilities than planar dark solitons and may be seen as transient structures in experiments. Fully time-dependent simulations illustrate typical decay scenarios, which may result in the generation of multiple separated solitonic vortices.

We present clinical measurements and a theoretical model for the decay of the left ventricular (LV) vortex ring. Previous works have postulated that the formation of the vortex ring downstream of the mitral annulus is affected by LV diastolic impairment. However, no previous works have considered how the strength of the vortex ring will decay inside the ventricle after its formation. Although the vortex ring formation relates to the very initial stage of the filling, the decay process is governed by a large portion of the diastolic time and will be affected by the interaction of the ventricle walls and the vortex ring. Here we used in-vivo measurements and presented a mechanistic model to calculate the evolution of the vortex ring strength and predict the rate of vortex ring decay within the left ventricle. The results demonstrated the actual circulation decay rate was universal, remaining nearly unchanged across all subjects of varying LV geometry or diastolic function. Furthermore, using the model-predicted circulation decay rate, differentiation between normal and abnormal filling was observed.

Development of the fetal heart is a fascinating process that involves a tremendous amount of growth. Here, we performed image-based flow simulations of 3 human fetal left ventricles (LV), and investigated the hypothetical scenario where the sizes of the hearts are scaled down, leading to reduced Reynolds number, to emulate earlier fetal stages. The shape and motion of the LV were retained over the scaling to isolate and understand the effects of length scaling on its fluid dynamics. We observed an interesting cut-off point in Reynolds number (Re), across which the dependency of LV wall shear stress (WSS) on Re changed. This was in line with classical fluid mechanic theory where skin friction coefficient exhibited first a decreasing trend and then a plateauing trend with increasing Re. Below this cut-off point, viscous effects dominated, stifling the formation of LV diastolic vorticity structures, and WSS was roughly independent of Reynolds number. However, above this cut-off, inertial effects dominated to cause diastolic vortex ring formation and detachment, and to cause WSS to scale linearly with Reynolds number. Results suggested that this transition point is found at approximately 11 weeks of gestation. Since WSS is thought to be a biomechanical stimuli for growth, this may have implications on normal fetal heart growth and malformation diseases like Hypoplastic Left Heart Syndrome.

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

This paper investigates the evolution properties of the flow field structure for axial descent rotor based on the unsteady momentum source method combined with the Computational Fluid Dynamics (CFD). The study focuses on analyzing the speed critical value during the onset of or exit from the Vortex Ring State (VRS), and its changing characteristics of the flow field structure. Results from the Lagrangian Coherent Structure (LCS) analysis reveal the switch particularity between the tubular slipstream and the annular vortex, suggesting the criticality change character on flow field structure which occurs in the evolution process of VRS. These criticality features, that is the VRS boundaries described by the flow structure change, as determined by this method, are consistent with the existing theoretical and experimental results, verifying the feasibility of the established analysis method in the study of such boundaries. This work provides a robust framework for studying VRS boundaries and offers insights for further research on the underlying flow mechanism.

The characteristics of wet micro burst are more complex, which will cause some deviation on the artillery range, side deviation and other parameters, and have a great influence on the artillery shooting accuracy. Taking 155 mm artillery explosive shell as the research object, based on vortex ring principle and fluid mechanics, the micro-downburst and raindrop motion model was established, which was integrated into the wet micro-downburst model suitable for ballistic analysis and calculation. The wet micro-downburst model was combined with the 6-DOF external ballistic model of artillery. Simulation and analysis of the effect of different initial vortex ring center induced velocity on the firing accuracy of flat firing and curved firing. The experimental results show that for long-range firing, the range of the artillery decreases with the increase of the induction velocity of the initial vortex ring center, which seriously affects the firing accuracy and killing effect of the artillery.

A numerical simulation of the gasdynamic processes accompanying the formation and propagation of vortex rings obtained with the use of a piston-type generator has been performed. The formation of a vortex ring, the capture of particles of a disperse admixture by it, and their carry by the ring are considered. The numerical calculations were conducted with the use of nonstationary Navier–Stokes equations, and the movement of particles was defined using the discrete-trajectory method. The distribution of the admixture particles in a vortex ring was determined depending on the conditions of its formation. The influence of the characteristics of a vortex ring on the carry of a passive admixture by it was investigated. The reasons for the qualitative and quantitative differences between the losses of particles in a vortex ring in the path of its movement in different regimes are discussed.

Due to their complex aerodynamics, helicopters may enter different dangerous aerodynamic conditions under certain adverse circumstances. In this paper, we examine one such phenomenon—the Vortex Ring State (VRS). We present a simulation of the formation and evolution of a vortex ring around a helicopter’s main rotor. The calculations were carried out by solving Navier–Stokes equations using the Ansys CFX code. The simulations modeled a real helicopter using the rotor wing concept, assuming that only the main rotor blade’s geometry was modeled. A sensitivity study assessed the impact of the calculation domain and mesh size on main rotor thrust and required moment parameters. Simulations were conducted to determine the VRS region by observing the transition of the helicopter from a level flight, with the main rotor blades held at a fixed pitch position, to a gradual increase in vertical descent. The VRS region was compared with experimental results obtained from other authors, revealing sufficient coincidences. The main characteristics of the identified region were then described.