Motion Of Jet Research Articles

Quantifying eddy structures and very-large-scale motions in turbulent round jets

Abstract

The black hole transient MAXI J1348–630: evolution of the compact and transient jets during its 2019/2020 outburst

ABSTRACT We present the radio and X-ray monitoring campaign of the 2019/2020 outburst of MAXI J1348–630, a new black hole X-ray binary (BH XRB) discovered in 2019 January. We observed MAXI J1348–630 for ∼14 months in the radio band with MeerKAT and the Australia Telescope Compact Array, and in the X-rays with MAXI and Swift/XRT. Throughout the outburst, we detected and tracked the evolution of compact and transient jets. Following the main outburst, the system underwent at least four hard-state-only re-flares, during which compact jets were again detected. For the major outburst, we observed the rise, quenching and reactivation of compact jets, as well as two single-sided discrete ejecta travelling away from the BH, launched ∼2 months apart. These ejecta displayed the highest proper motion (≳100 mas d−1) ever measured for an accreting BH binary. From the jet motion, we constrain the ejecta inclination and speed to be ≤46○ and ≥0.69 c, and the opening angle and transverse expansion speed of the first component to be ≤6○ and ≤0.05 c. We also infer that the first ejection happened at the hard-to-soft state transition, before a strong radio flare, while the second ejection was launched during a short excursion from the soft to the intermediate state. After travelling with constant speed, the first component underwent a strong deceleration, which was covered with unprecedented detail and suggested that MAXI J1348–630 could be located inside a low-density cavity in the interstellar medium, as already proposed for XTE J1550–564 and H1743–322.

Numerical study on edge tone with compressible direct numerical simulation: Sound intensity and jet motion

A two-dimensional model of the edge tone is studied by a highly accurate and reliable method of direct numerical simulation of the compressible Navier-Stokes equations, and used to verify key features observed in previous experimental and numerical studies, and to discover new features related to the jet motion and the edge tone generation mechanism. The first and second modes of the edge tone that are numerically reproduced agree well with Brown’s equation. In the mode transition region, dynamical mode transition is observed at a fixed jet velocity. For both first and second modes, the pressure distributions are antisymmetric with respect to the edge plate, and the sound intensity is proportional to the fifth power of the jet velocity. These results are consistent with the edge tone being radiated from a dipole-like source. Spatial profiles of the velocity and the velocity variance of the oscillating jet are also investigated for each mode over a range of the jet velocity including the mode transition regime. The amplitude of the velocity oscillation becomes constant with increasing jet velocity, while a measure of the amplitude of the velocity variance profile, which is introduced to characterize the strength of the jet fluctuation and named the ’fluctuation strength’, is proportional to the third power of the jet velocity. Some properties of the fluctuation strength correspond to properties of the sound intensity, including the first mode having larger amplitude than the second mode, and the way of deviating from the power law at smaller values of jet velocity and in the mode transition region. It is proposed that the third-power law exhibited by behavior of the fluctuation strength could be related to the increase of the skewness observed in the velocity profile with increase of jet velocity, and a model calculation is used to support this proposal.

Effects of Temperature on Melt Electrospinning: Experiment and Simulation Study

In this study, the jet formation progress, jet motion, resultant fiber diameter, fiber mat morphology, inner structures and mechanical properties of the fibers prepared at different heating temperatures via melt electrospinning system were studied, in a comprehensive and systematic manner. The temperature distribution of the melt electrospinning configuration was simulated, in order to provide a good deal of insight into the experimental results. High-speed photography was adopted to capture the images of jet formation process and jet motion during melt electrospinning. The experimental results showed that higher heating temperature at the spinneret results in shorter jet formation time, smaller fiber diameter, more disordered fiber mat, lower degree of crystallinity and strength. The simulation works was carried out, aimed at facilitating to deeply understand the experimental results.

Novel Self-Directing Single-Polymer Jet Developing Layered-Like 3D Buckled Microfibrous Scaffolds for Tissue Engineering Applications.

Electrospinning is a promising technique for the fabrication of bioscaffolds in tissue engineering applications. Pertaining issues of multiple polymer jets and bending instabilities result in random paths which lend poor controllability over scaffolds morphology for affecting the porosity and mechanical stability. The present study alleviates these challenges by demonstrating a novel self-directing single jet taking a specifically patterned path to deposit fibers into circular and uniform scaffolds without tuning any externally controlled parameters. High-speed camera observation revealed that the charge retention and dissipation on the collected fibers caused rapid autojet switching between the two jetting modes, namely, a microcantilever-like armed jet motion and a whipping motion, which sequentially expand the area and thickness of the scaffolds, respectively, in a layered-like fashion. The physical properties showed that the self-switching dual-jet modes generated multilayered microfibrous scaffolds (MFSs) with dual morphologies and varied fiber packing density, thereby establishing the gradient porosity and mechanical strength (through buckled fibers) in the scaffolds. In vitro studies showed that as-spun scaffolds are cell-permeable hierarchical 3D microporous structures enabling lateral cell seeding into multiple layers. The cell proliferation on days 6 and 9 increased 21% and 38% correspondingly on MFSs than on nanofibrous scaffolds (NFSs) done by conventional multijets electrospinning. Remarkably, this novel and single-step process is highly reproducible and tunable for developing fibrous scaffolds for tissue engineering applications.

Asymptotic Behavior of Small Perturbations for Unsteady Motion an Ideal Fluid Jet

The stability problem of unsteady rotating circular jet motion of an ideal fluid is reduced to solving an initial-boundary value problem for Poincare–Sobolev type equation with an evolutionary condition on the jet free initial boundary. The solution of this problem is constructed by the method of variables separation. The asymptotic amplitudes behavior perturbations of the free jet boundary at t → ∞ is found. The results obtained are compared with the known results on the stability of the potential jet motion

The Extraordinary Outburst in the Massive Protostellar System NGC 6334 I-MM1: Spatiokinematics of Water Masers during a Contemporaneous Flare Event

Abstract Following an eruptive accretion event in NGC 6334I-MM1, flares in the various maser species, including water masers, were triggered. We report the observed relative proper motion of the highly variable water masers associated with the massive star-forming region, NGC 6334I. High velocity H2O maser proper motions were detected in five maser clusters, CM2-W2 (bow-shock structure), MM1-W1, MM1-W3, UCHII-W1, and UCHII-W3. The overall average of the derived relative proper motion is 85 km s−1. This mean proper motion is in agreement with the previous results from VLA multiepoch observations. Our position as well as the velocity variance and covariance matrix analyses of the maser proper motions show its major axis to have a position angle of −79.°4, cutting through the dust cavity around MM1B and being aligned in the northwest–southeast direction. We interpret this as the axis of the jet driving the CM2 shock and the maser motion. The complicated proper motions in MM1-W1 can be explained by the combined influence of the MM1 northeast–southwest bipolar outflow, the CS(6−5) north–south collimated bipolar outflow, and the radio jet. The relative proper motions of the H2O masers in UCHII-W1 are likely not driven by the jets of the MM1B protostar but by MM3-UCHII. Overall, the post-accretion burst relative proper motions of the H2O masers trace shocks of jet motion.

Экспериментальное исследование влияния канала малого диаметра на пробивное действие кумулятивной струи

The paper focuses on experiments carried out to determine the effect of a small-diameter channel, passed by a shaped-charge jet before interacting with an obstacle, on its penetrating action. These experiments were conducted in relation to the study of the features of shaped-charge jet motion through the cavity of an elongated solenoid with electromagnetic stabilization of the jet stretching process. For this purpose, steel sleeves with a channel were installed in front of the shaped charge, which made it possible to simulate the mechanical factors affecting the shaped-charge jet when it moves in the air channel. For the conditions implemented in the experiments, it was found that in the absence of collisions of the shaped-charge jet with the channel walls, the penetration depth decreases insignificantly, i.e. within 5%. In experiments in which there were traces of contact interaction with the shaped-charge jet on the channel surface, a significant decrease in the penetrating action was recorded.

Generation of Surfaces With Isotropic and Anisotropic Wetting Properties by Curved Water Jet-Guided Laser Micromachining

Abstract This experimental work utilizes a newly developed method, curved water jet-guided laser micromachining, to generate microfeatures on metallic surfaces. During the process, material is removed by a high-power nanosecond laser beam, which is transmitted through a high-pressure microwater jet via total internal reflection. To achieve intricate texturing patterns, a secondary motion component is superimposed on the XY motion of the workpiece provided by the motion stage. The secondary motion is generated by deflecting the water jet trajectory by a controllable dielectrophoretic force. The induced secondary motion of the water jet cuts the processing time to one half when generating texture patterns for isotropic wetting as compared to processes with only XY motion. The ability to alter the water jet's trajectory by tens of microns at high frequencies, which is beyond the capability of conventional CNC machines, allows a wide range of different micropatterns to be generated, profoundly increasing the flexibility and efficiency of the process as compared to conventional approaches. As a demonstration, surface textures for isotropic and anisotropic behaviors are generated on stainless steel surfaces. The influence of feature spacing, motion speed (frequency), and texturing patterns on surface wettability is studied.

Construction of Natural Loofah/Poly(vinylidene fluoride) Core-Shell Electrospun Nanofibers via a Controllable Janus Nozzle for Switchable Oil-Water Separation.

Developing microstructure and multifunctional membranes toward switchable oil-water separation has been highly desired in oily wastewater treatment. Herein, a controllable Janus nozzle was employed to innovatively electrospin natural loofah/poly(vinylidene fluoride) (PVDF) nanofibers with a core-shell structure for gravity-driven water purification. By adjusting flow rates of the PVDF component, a core-shell structure of the composite fibers was obtained caused by the lower viscosity and surface tension of PVDF. In addition, a steady laminar motion of fluids was constructed based on the Reynolds number of flow fields being less than 2300. In order to investigate the formation mechanism of the microstructure, a series of Janus nozzles with different lengths were controlled to study the blending of the two immiscible components. The gravity difference between the two components might cause disturbance of the jet motion, and the PVDF component unidirectionally encapsulated the loofah to form the shell layer. Most importantly, the dry loofah/PVDF membranes could separate oil from an oil-water mixture, while the water-wetted membrane exhibited switchable separation that could separate water from the mixtures because of the hydroxyl groups of the hydrophilic loofah hydrogen-bonding with water molecules and forming a hydration layer. The composite fibers can be applied in water remediation in practice, and the method to produce core-shell structures seems attractive for technological applications involving macroscopic core-shell nano- or microfibers.

Jet motion and fiber properties arising from a parallel electric field in melt-electrospinning

It is well known that the electric field has a great influence on the diameter and properties of fiber prepared via the melt-electrospinning technique. In this paper, two parallel metal discs were introduced to create a controllable electric field in the experiments. In addition, a three-dimensional electric field was calculated by the numerical simulation method and the jet motion was captured by taking advantage of high-speed photography technology. The influences of electric field distribution on the fiber jet, fiber diameter, fiber mat area and fiber crystallinity were studied in an in-depth and systematical manner. Both whipping amplitude and whipping frequency were also used to describe the characteristics of the jet. The above-mentioned results have proven that increasing the distance between the two parallel metal discs leads to the decrease of electric field intensity and the increase of electric field action time on the fiber, which together determine the diameter and crystallinity of the fiber. With the increase of the outer diameter of the upper disc, the distribution of the electric field becomes more uniform, making it capable of steadily controlling the behavior of the jet, and thus effectively reducing the diameter of the fiber and improving the crystallinity of the fiber.

Three-dimensional deflecting oscillation of turbulent planar opposed jets confined in an open cavity under crossflow

In this work, the flow dynamics of two isothermal turbulent opposed water jets issuing from rectangular slot nozzles and confined inside an open cubical cavity with vertical crossflow in a rectangular duct are studied experimentally using time-resolved stereo particle image velocimetry. The turbulent structure and the deflecting oscillation of the colliding jets have been investigated for fixed nozzle separation and a crossflow Reynolds number of 3000 for three jets’ Reynolds numbers of Rej = 1500, 3000, and 5000. The probability density function of the fluctuations for the three nondimensional velocity components measured at the mean impingement height of the jets has been calculated for three different positions along the cavity span. The experimental results confirm that as Rej increases, departure from Gaussian behavior has been noted, with stronger skewness and larger scatters observed for Rej = 5000. The oscillation dynamics of the flapping jets has been characterized and examined with high spatial and temporal resolution by identifying phase-averaged velocity and vorticity fields and Reynolds stresses at several specific phases. Analysis shows that the value of Rej plays a significant role in the motion and behavior of the switching jets. A proper orthogonal decomposition (POD) analysis of the coherent structure organization of the turbulent flow has been performed to construct a reduced-order model of the turbulent flow. The results show that the first four POD modes contain about 17% of the total kinetic energy (the first 120 modes up to 79%) and that the complexity of the most energetic flow structures increases with an increase in the Rej number.

The Role of Electrical Polarity in Electrospinning and on the Mechanical and Structural Properties of As-Spun Fibers.

Electric field strength and polarity in electrospinning processes and their effect on process dynamics and the physical properties of as-spun fibers is studied. Using a solution of the neutral polymer such as poly(methyl methacrylate) (PMMA) we explored the electrospun jet motion issued from a Taylor cone. We focused on the straight jet section up to the incipient stage of the bending instability and on the radius of the disk of the fibers deposited on the collecting electrode. A new correlation formula using dimensionless parameters was found, characterizing the effect of the electric field on the length of the straight jet, This correlation was found to be valid when the spinneret was either negatively or positively charged and the electrode grounded. The fiber deposition radius was found to be independent of the electric field strength and polarity. When the spinneret was negatively charged, was longer, the as-spun fibers were wider. The positively charged setup resulted in fibers with enhanced mechanical properties and higher crystallinity. This work demonstrates that often-overlooked electrical polarity and field strength parameters influence the dynamics of fiber electrospinning, which is crucial for designing polymer fiber properties and optimizing their collection.

A Relativistic Orbit Model for Temporal Properties of AGN

We present a unified model for X-ray quasi-periodic oscillations (QPOs) seen in Narrow-line Seyfert 1 (NLSy1) galaxies, γ-ray and optical band QPOs that are seen in Blazars. The origin of these QPOs is attributed to the plasma motion in corona or jets of these AGN. In the case of X-ray QPOs, we applied the general relativistic precession model for the two simultaneous QPOs seen in NLSy1 1H 0707-945 and deduce orbital parameters, such the radius of the emission region, and spin parameter a for a circular orbit; we obtained the Carter’s constant Q, a, and the radius in the case of a spherical orbit solution. In other cases where only one X-ray QPO is seen, we localized the orbital parameters for NLSy1 galaxies REJ 1034+396, 2XMM J123103.2+110648, MS 2254.9-3712, Mrk 766, and MCG-06-30-15. By applying the lighthouse model, we found that a kinematic origin of the jet based γ-ray and optical QPOs, in a relativistic MHD framework, is possible. Based on the inbuilt Hamiltonian formulation with a power-law distribution in the orbital energy of the plasma consisting of only circular or spherical trajectories, we show that the resulting Fourier power spectral density (PSD) has a break corresponding to the energy at ISCO. Further, we derive connection formulae between the slopes in the PSD and that of the energy distribution. Overall, given the preliminary but promising results of these relativistic orbit models to match the observed QPO frequencies and PSD at diverse scales in the inner corona and the jet, it motivates us to build detailed models, including a transfer function for the energy spectrum in the corona and relativistic MHD jet models for plasma flow and its polarization properties.

Enhanced electrospinning: Multi-level fiber alignment by control of electrohydrodynamic jet motion for tissue engineering

This paper proposes a novel electrospinning method for controllable fiber alignment and deposition on a dielectric substrate by the electric field manipulation using nanosecond rise time high-voltage pulse generators. A peculiarity of the proposed technical solution is the ability to control polymer jet localization in the interelectrode space with the possibility of stabilization and retention of the jet at an arbitrary point. A preliminary numerical simulation shows electric field distribution in proposed geometry with a syringe and two cylindrical collectors. Samples of oriented materials based on a polyamide 6/66 copolymer with 2–4° degrees of disorientation were obtained. The study of thermal and mechanical behavior of oriented materials based on polyamide was carried out, and macromolecular orientation was established by X-ray diffraction in small and wide angles. The possibility to create material by stacking multiple layers with given fiber orientation at 65° and 90° and polymer spinning on various dielectric materials by means of the reverse polarity operating principle is demonstrated. The ability to control fiber alignment in electrospinning will expand the possibilities of high-performance production of polymeric nonwoven materials with a given architecture and unique physicochemical characteristics required for solving a whole range of medical and technological challenges of a different profile.

Damage to Polystyrene Polymer Film by Shock Wave Induced Bubble Collapse.

Metallic surfaces that are in contact with solutions are commonly used in numerous applications where these surfaces can be damaged by shock wave induced bubble collapse. Use of polymer films that coat such surfaces to prevent them from damage requires a better understanding of how much harm collapsing bubbles produce in the films. In this study, we report the results from coarse-grained molecular dynamics simulations to study the damage to polystyrene (PS) films coating a hard surface. The damage was caused by a collapsing nanobubble located in the proximity of the film and interacting with an impinging shock wave. This collapse produces a high-speed water jet that impacts the PS film with a greater force than the shock front and creates cavities/pits in the PS film. We observed that polymer molecules located in the jet vicinity undergo conformational extension in the direction perpendicular to the jet motion, while chain molecules in the rest of the film undergo compression. We also observed that damage to the film is sensitive to the strength of the shock wave.

Flow dynamics of a fluidic oscillator with internal geometry variations

An experimental study is conducted to examine the impact of internal geometry of a fluidic oscillator on its working mechanisms, i.e., the widths of the inlet wedge W1, mixing chamber W2, and exit throat W3, normalized by the width of the inlet throat W0. Using time-resolved particle image velocimetry, the flow dynamics both inside and outside the oscillator are measured simultaneously. The phase-averaged flow fields are obtained using proper orthogonal decomposition analysis based on which the pressure fields are computed. It is found that the external jet spreading angle and the oscillation frequency are proportional to the width of the inlet wedge up to W1/W0 = 2. This is because the inlet wedge controls the feedback flow and accordingly the recirculation bubble in the mixing chamber. At a critical lower value of W1/W0 = 0.8, there is no feedback flow with a stable external sweeping jet. The mixing chamber width W2/W0 controls the size of the recirculation bubble, which has a notable proportional control on the spreading angle. With a small mixing chamber of W2/W0 = 2.9, it is also found that the strong feedback flow can still produce a stable sweeping jet motion but with a small spreading angle. The exit throat width W3/W0 has non-monotonous control on the external jet spreading angle and the oscillation frequency. It is noteworthy that the jet can still produce a stable sweeping motion even with a large value of W3/W0 = 4.2, which can significantly reduce the blocking effect of the exit.

Experimental and Numerical Characterization of a Liquid Jet Injected into Air Crossflow with Acoustic Forcing

The current work presents a study on spray dynamics in aeronautical injectors. More particularly, the experimental characterization of a liquid jet in an oscillating gaseous cross flow (LJIOGCF) atomization is presented and compared to numerical simulations. The experimental setup consists of a water jet transversally injected into an oscillating subsonic air flow at ambient conditions. In a first step, a cross-comparison is performed in order to validate the numerical model and the tools used to quantitatively analyze the experimental data in the case of steady air flows. In a second step, the air flow is submitted to longitudinal acoustic waves using a pneumatic loudspeaker. A detailed database, representative of the actual dynamics of LJIOGCF configurations, is obtained using both experiments and numerical simulations. Visualizations with a back lighting approach are employed to characterize the liquid jet close to the injection location while phase doppler anemometry is used to determine the characteristics of the crossflow and the spray in terms of droplet size, velocity and concentration. Phase-averaging is performed to characterize the response of the liquid jet, the air velocity field and the spray oscillations during the excitation cycle. The numerical simulation relies on a multi-scale large eddy simulation approach. This method couples a multi-fluid solver for the liquid jet main body with a dispersed phase solver for the atomized spray. The acoustic perturbation is imposed as a fluctuating air inflow condition. The experimental results show that the acoustic forcing induces a flapping motion of the liquid jet. As a consequence, velocity and concentration waves travelling downstream the liquid jet appear. Coupling phenomena between the crossflow, the atomization of the liquid jet and the transport of droplets are observed, revealing different wave transport velocities. It further appears that spray dynamics are both driven by liquid column and crossflow oscillations. The numerical simulation is able to capture the global flapping dynamics of the liquid jet’s main body. More quantitative comparisons show a very good agreement between simulation and experiments regarding the jet trajectories over the entire excitation cycle. Numerical droplet average velocities are also in good agreement with experiments. Finally, the numerical simulation partly reproduces the coupling between acoustics and spray dynamics observed in the experiments.

The Effects of Electric Field on Jet Behavior and Fiber Properties in Melt Electrospinning

The electric field and temperature are the two important factors that influence the diameter and properties of fiber in the melt electrospinning process. It is commonly known that the polymer jet behavior is governed by the electric field within spinning area. In present work, a comprehensively-designed and properly-conducted analysis was carried out to investigate into the effects of electric field on the jet behaviors, diameters, crystalline structure and mechanical properties of the resultant fibers. An auxiliary electrode was invited to enhance the electric field strength. The high-speed photography was adopted to capture the jet motion, and also, the numerical simulation was used to understand the electric field distribution. By making use of the whipping amplitude and whipping frequency, the characteristics of jet behavior were described. It was found that by applying an auxiliary electrode, the average fiber diameter reduced from 61.01 µm to 9.06 µm, and the crystallinity and strength of the fiber was improved with the help of the higher electric filed intensity. In addition, the more uniform electric field would produce finer and more uniform fiber because of the more stable jet motion.

On experimental and numerical study of the dynamics of a liquid metal jet hit by a laser pulse

In this paper, we present an experimental and numerical study of the laser pulse impact on the liquid metal jet target. The jet motion was recorded with the stroboscopic ultrafast shadow photography. Simulations were carried out in a two-step approach. At the first step, we simulated laser interaction with the target using the radiation hydrodynamics code 3DLINE, which accounts for a number of effects: liquid–gas phase transition, dynamics of ionization, radiation transfer, laser reflection, refraction and absorption. However, this code cannot be used on a deeply refined mesh near the liquid surface and does not account for the surface tension, which strongly affects liquid motion on the microsecond timescale after the laser pulse ends. Therefore, for the second step we employed the OpenFOAM solver, based on the volume-of-fluid method, which overcomes these limitations. The simulated target dynamics is found to be in a fairly good agreement with the experiment.