Mechanism Of Jet Formation Research Articles

Mechanisms of electrospray jet formation and atomized droplet motion in pulsed-jet mode

Mechanisms of electrospray jet formation and atomized droplet motion in pulsed-jet mode

Candidates for downstream jets at interplanetary shocks

Abstract Localised dynamic pressure enhancements arising from kinetic processes are frequently observed downstream of the Earth’s bow shock. These structures, called jets, modify their plasma surroundings and participate in particle energisation. Here, we report the first observations of jet-like structures at a non-planetary shock environment: downstream of interplanetary shocks. We introduce an analysis approach suitable for such conditions and apply it to Wind spacecraft data. We present one event with a Mach number similar to the Earth’s bow shock as a benchmark, as well as two low Mach number, low beta shocks: a parameter range that is difficult to access at planets. The jet-like structures we find are tens of ion inertial lengths in size, and some are observed further away from the shock than in a limited magnetosheath. We find that their properties are similar to those of magnetosheath jets: in the frame of the shock these structures are fast, cold, and most have no strong magnetic field variations. All three interplanetary shocks feature foreshock activity, but no strongly compressive waves. We discuss the implications these findings have for the proposed jet formation mechanisms.

Calcium Bright Knots and the Formation of Chromospheric Anemone Jets on the Sun

Space-based observations show that the solar atmosphere from the solar chromosphere to the solar corona is filled with small-scale jets and is linked with small-scale explosions. These jets may be produced by mechanisms similar to those of large-scale flares and such jets may be related to the heating of the corona and chromosphere as well as the acceleration of solar wind. The chromospheric anemone jets on the Sun remain puzzling because their footpoints (or bright knots) have not been well resolved and the formation process of such enigmatic small-scale jets remains unclear. We propose a new model for chromospheric jets using the 3D magnetohydrodynamic simulations, which show that the continuous, upward rising of small-scale twisted magnetic flux ropes in a magnetized solar chromosphere drives small-scale magnetic reconnection and the launching of several small-scale jets during the evolution of the chromospheric anemone jets. Our new, self-consistent, 3D computer modeling of small-scale, but ever-changing flux rope emergence in the magnetized solar atmosphere is fully consistent with observations and provides a universal mechanism for nanoflare and jet formation.

Numerical simulation of water jet load induced by spherical bubble collapse under underwater explosion

In this study, a numerical method combining the HLLC solver and FV-WENO scheme is proposed to accurately simulate the behavior of multiphase compressible fluids and investigate the formation process of water jets. The HLLC solver approximates the conservation equations of the fluid by using numerical fluxes from the approximate Riemann problem, while the FV-WENO scheme improves the accuracy of the numerical solution by employing the weighted essentially non-oscillatory (WENO) reconstruction method. The combination of these methods allows for a more accurate simulation of the behavior of multiphase compressible fluids, leading to an accurate depiction of the formation process of water jets. By simulating the interaction between underwater shock waves from explosions and single or multiple spherical bubbles, we study the generation, development, and collapse of water jets during the bubble collapse process. By revealing the characteristics of the load during the formation of water jets and the interaction mechanisms between bubbles, our study provides support for further research on water jet phenomena. The formation process of water jets is of great significance for understanding the propagation of underwater shock waves and structural damage. Through this study, we delve into the mechanism of water jet formation, providing a new perspective on the propagation of underwater shock waves and structural damage. Our research results demonstrate that the application of the HLLC solver and FVWENO scheme in water jet simulation effectively improves the accuracy and precision of the numerical solution.

Mechanisms of Low-Level Jet Formation in the U.S. Mid-Atlantic Offshore

Abstract Low-level jets (LLJs), in which the wind speed attains a local maximum at low altitudes, have been found to occur in the U.S. mid-Atlantic offshore, a region of active wind energy deployment as of 2023. In contrast to widely studied regions such as the U.S. southern Great Plains and the California coastline, the mechanisms that underlie LLJs in the U.S. mid-Atlantic are poorly understood. This work analyzes floating lidar data from buoys deployed in the New York Bight to understand the characteristics and causes of coastal LLJs in the region. Application of the Hilbert–Huang transform, a frequency analysis technique, to LLJ case studies reveals that mid-Atlantic jets frequently occur during times of adjustment in synoptic-scale motions, such as large-scale temperature and pressure gradients or frontal passages, and that they do not coincide with motions at the native inertial oscillation frequency. Subsequent analysis with theoretical models of inertial oscillation and thermal winds further reveals that these jets can form in the stationary geostrophic wind profile from horizontal temperature gradients alone—in contrast to canonical LLJs, which arise from low-level inertial motions. Here, inertial oscillation can further modulate the intensity and altitude of the wind speed maximum. Statistical evidence indicates that these oscillations arise from stable stratification and the associated frictional decoupling due to warmer air flowing over a cold sea surface during the springtime land–sea breeze. These results improve our conceptual understanding of mid-Atlantic jets and may be used to better predict low-level wind speed maxima. Significance Statement The purpose of this work is to identify and characterize the atmospheric mechanisms that result in an occasional low-level maximum in the wind speed off the U.S. mid-Atlantic coastline. Our findings show that these low-level jets form due to horizontal temperature gradients arising from fronts and synoptic systems, as well as from the land–sea breeze that forces warmer air over the cold ocean surface. This work aids predictability of such jets, improves our understanding of this coastal environment, and has implications for future deployment of offshore wind energy in this region.

Formation mechanism of blazar jets

In research of astronomy, cosmology and the basic theoretical physics, the black hole is one of the most concerned celestial bodies. AGN is a kind of observation source with supermassive black hole as the central core, among which Blazar is the key observation subclass of the observer whose jet is facing the Earth. Therefore, the study of the jet has become an crucial subject of black hole research. In this paper, I start with the basic structure model of AGN, briefly describe the characteristics and mechanisms of each structure, especially the jet, and afterward introduce the observed spectral bimodal characteristics, focusing on the analysis of the existing jet formation mechanism from the radio band. Through the existing observations and data fitting, that is, the logarithmic linear fitting of the jet power to the luminosity of the accretion disc and the jet power to the mass and spin parameters of the black hole, corresponding to the Blandford&Payne and the Blandford&Znajek mechanism respectively. Finally, we analyze the conclusion of the two methods and draw the possibility of the two processes and the complementary relationship in theory. Incidentally, the model theory of mixed interpretation of the two mechanisms and processes is obtained.

Establishment of a one-dimensional physical model for electrospinning multiple jets of spinnerets

Electrospinning is a technique used to prepare nanofiber material where an electrically charged jet of polymer solution is accelerated and stretched by electrostatic forces. There are two stages in electrospinning, the stable jet and bending instability. Almost all electrospinning research involves the theory and model of a single jet’s movement. Many devices for the mass production of nanofibers have been developed and studied to date. The multiple jets of spinnerets can form throughput nanofibers. However, a greater understanding is needed on the formation mechanism of these multiple jets, which would allow researchers to control nanofiber productivity and instruct spinneret design. In this work, we investigated the formation mechanism of multiple jets based on an annular spinneret. A one-dimensional physical model was established and multiple equations were combined; the wavelength [Formula: see text] with respect to the applied voltage [Formula: see text] was obtained based on the derivation of the theoretical formulation. The theory order relationship was verified with experiments using multiple jets containing the annular spinneret.

Characteristics of the low‐level jets observed over Dunkerque (North Sea French coast) using 4 years of wind lidar data

AbstractThis study investigates the occurrence and characteristics of low‐level jets (LLJs) up to 200 m above sea level in the North Sea area, specifically in the southernmost part of the basin, at the entrance of the English Channel. Using a short‐range Doppler lidar installed in Dunkerque Port, on the northern coast of France, wind profiles were recorded for 4 years and analyzed statistically. LLJs were detected on more than 11,000 of the 10‐min average wind profiles (5% of time), with similar jet core height and core speed distributions as in other sites in the southern North Sea area, and a similar annual cycle. However, there were differences in the core directions and the daily cycle, with afternoon northeastly jets being the most frequent in Dunkerque, whereas southwesterly nocturnal jets were dominant in the other North Sea sites. This suggests that wind channeling in the Dover Strait is likely a major factor for LLJ formation in Dunkerque region. The study also examined the conditions of LLJ occurrence using European Centre for Medium‐Range Weather Forecast (ECMWF) reanalysis v5 and ultrasonic anemometer data, but the different types of LLJs sharing the same core direction and occurrence conditions made it difficult to quantify specific jet formation mechanisms. This is the first experimental study on the North Sea shore, and at the entrance of the English Channel, providing valuable insights into the LLJ behavior in the region.

Experimental Study of the Formation and Evolution of Gas Jets in Supersonic Combustion Chambers

A simple and efficient flow field visualization method (based on shadow imaging) was applied in a direct-connect test to explore the influence of the momentum flux ratio and the jet angle on the formation and evolution of nitrogen jets in supersonic combustion chambers. The test setup adopts a rectangular flow passage to simulate a flight condition with Mach number of 6 and altitude of 25 km. The experimental results showed that (a) the flow field visualization method adopted in this paper can clearly register the formation and evolution of the shock wave structure in the flow field and the windward shear vortex on the jet surface. (b) The evolution process of the windward shear vortex is significantly affected by the jet angle. In particular, the stretching position of the windward shear vortex changed when the jet angle was obtuse. (c) The bow shocks showed local distortion due to the periodic generation of large-scale shear vortexes. (d) Under the working conditions of the test, the largest instability of the flow field was found for a jet angle of 120°. This work provides, on one hand, the experimental basis for clarifying the formation and evolution mechanism of transverse gas jets, and on the other, valuable data that can be used to validate numerical simulations.

Simulation of the “Central Engine” of Astrophysical Jets within the Plasma Focus Facility

Laboratory plasma ejections within the plasma focus facilities (the structure of their electric currents, rotation, shock wave arising from interaction with the ambient medium) reproduce all the main elements of jets from young stars. On the other hand, the physical processes responsible for the launch of a plasma ejection are still not well understood, and therefore there is still no unequivocal answer to the question of how adequately the laboratory experiment reproduces the mechanism of astrophysical jet formation. In this paper, we formulated the conditions under which the similarity of physical processes can also take place in the “central engine” of a laboratory experiment leading to the launch of a plasma ejection, based on the analysis of the effects of nonideal magnetohydrodynamics.

The jet formation mechanism of gamma-ray narrow-line Seyfert 1 galaxies

ABSTRACT Under a coronal magnetic field, we estimate the maximal jet power of the Blandford–Znajek (BZ) mechanism, Blandford–Payne (BP) mechanism, and hybrid model. The jet power of the BZ and hybrid model mechanisms depends on the spin of the black hole, while the jet power of the BP mechanism does not depend on the spin of the black hole. At high black hole spin, the jet power of the hybrid model is greater than that of the BZ and BP mechanisms. We find that the jet power of almost all gamma-ray narrow-line Seyfert 1 galaxies (γNLS1s) can be explained by the hybrid model. However, one source with jet power ∼0.1–1 Eddington luminosity cannot be explained by the hybrid model. We suggest that a magnetic field dragged inward by the accretion disc with magnetization-driven outflows may accelerate the jets in this γNLS1.

Jet Formation Mechanism of the Gamma-Ray-emitting Narrow-line Seyfert 1 Galaxies

We use a large sample of gamma-ray narrow-line Seyfert 1 galaxies (γ-NLS1s) to study the jet formation mechanisms. We find that the jet power of γ-NLS1s is lower than the maximum jet power of the Blandford–Payne (BP) mechanism. At the same time, we find that there is a significant correlation between jet power and accretion disk luminosity. Moreover, the contribution rates of the accretion to the jet power are larger than that of black hole mass to jet power. These results further suggest that the jet of γ NLS1s is mainly produced by the BP mechanism.

Laser bioprinting without donor plate

A promising laser bioprinting technology based on the effect of laser-induced direct transfer is rapidly developing and is already actively used in biotechnology and medicine today. Typically, such technologies use donor plates with an absorbent coating, from which gel microdroplets with living cells and microorganisms are transferred to an acceptor substrate under the action of a laser pulse. This article proposes a new bioprinting technology that makes it possible to transfer microdroplet not only without an absorbing coating, but also without the donor plate itself. The essence of this method is that the transfer to the surface of the acceptor is carried out by a series of nanosecond pulse with a wavelength of 3 μm directly from the surface of a liquid with microorganisms. The mechanism of a liquid jet and microdroplets formation upon absorption of a laser pulse in a thin surface liquid layer is discussed in detail. It has been shown that microorganisms transferred using the new bioprinting technology are viable and can be successfully cultivated on a dense nutrient medium.

Velocity tracking of shaped charge wire formation and propagation toward the target

ABSTRACT The formation of shaped charge jets is traditionally studied experimentally using flash X-ray and high-speed camera images. Sequential images obtained through these methods provide insight into the overall properties of the jet, such as jet tip velocity and outline shape. Numerical methods are validated using experimental results of the macroscopic properties by taking absolute velocity contours through the jet and comparing the outline shape. These methods do not describe where, and in which order, discrete parts of the shaped charge liner are located in the jet after formation. Shaped charge jet formation is studied here numerically by tracking the velocity in the flow field using stationary gauges and by placing dynamic gauges on the shaped charge liner. This method provides insight into the physical mechanism of jet formation. It is generally assumed that the shaped charge jet forms from liner inversion, where the liner tip becomes the jet tip that first penetrates the target. This work shows that the liner tip does not form part of the jet but is rather absorbed into the slug. Similarly, PER theory assumes that the outer part of the liner (next to the explosive) flows into the slug and the inner part flows into the jet. It is shown here that this assumption is not valid in all cases. This study is a proof of concept to highlight the advantages of using the method of simultaneous liner and flow field velocity tracking to aid shaped charge optimization activities.

A novel designed 3D multi-microhole plasma jet device driven by nanosecond pulse at atmospheric pressure

A novel designed three-dimensional (3D) multi-microhole helium plasma jet device excited by nanosecond pulse is developed in atmospheric air. Systematical investigations about the discharge characteristics are carried out to get insights into the formation mechanisms of 3D plasma jets. Results show that the 3D plasma jets originated from the branching of a single ionization wave to present a hexagonal-like structure including bottom jet (BJ) and side jets (SJ1 and SJ2). The BJ always keeps a stable performance while the SJ displays a remarkably turbulent mode. The dynamic evolution, and the propagation velocity and distance for BJ and SJ demonstrate significant differences, with a delay effect between BJ and SJ bullets propagation being observed. The optical emission spectra show that 3D jets possess a high yield of the spatial distribution of reactive species in jet plumes. The formation mechanism of 3D jets is determined by the hydrodynamic (He flow distribution) and electrical interactions (distribution of electric field force) in the discharge tube emerging from individual holes with different radial directions. The direct treatment of water using this developed underwater 3D plasma device results in the production of plasma activated water with a lower pH value, higher conductivity, and greater concentrations of reactive oxygen and nitrogen species, compared to the indirect treatment. Especially, the concentration of H2O2 can remarkably increase 141 folds from 1.43 to 202.12 μM within 5 min after the direct 3D plasma treatment. This novel-designed 3D jets-based technique is a promising platform for 3D application scenarios, especially in the case of underwater microbubble discharge, which is of great significance for water activation in emerging applications.

A multi-scale E-jet 3D printing regulated by structured multi-physics field

Micro/nano scale structure as important functional part have been widely used in wearable flexible sensors, gas sensors, biological tissue engineering, microfluidic chips super capacitors and so on. Here a multi-scale electrohydrodynamic jet (E-jet) 3D printing approach regulated by structured multi-physics fields was demonstrated to generate 800 nm scale 2D geometries and high aspect ratio 3D structures. The simulation model of jetting process under resultant effect of top fluid field, middle electric field and bottom thermal field was established. And the physical mechanism and scale law of jet formation were studied. The effects of thermal field temperature, applied voltage and flow rate on the jet behaviors were studied; and the range of process parameters of stable jet was obtained. The regulation of printing parameters was used to manufacture the high resolution gradient graphics and the high aspect ratio structure with tight interlayer bonding. The structural features could be flexibly adjusted by reasonably matching the process parameters. Finally, polycaprolactone/polyvinylpyrrolidone (PCL/PVP) composite scaffolds with cell-scale fiber and ordered fiber spacing were printed. The proposed E-jet printing method provides an alternative approach for the application of biopolymer materials in tissue engineering.

Study of formation mechanism of double metal plasma jets in a low-current pulsed vacuum arc discharge

Plasma jet formation was studied in a vacuum arc configured with a conical cathode located inside a hollow cylindrical anode. The outside of this anode was insulated, except at a 0.4 mm diameter micropore. The grounded vacuum chamber also served as an anode. The hollow cylindrical anode was connected to the grounded chamber anode through a resistor R. 170 A 14 μs arcs were excited by a pulse generator comprised of a series connection of a 0.1 F capacitor bank charged to 12 kV, a 200 μH inductor, and a 30 Ω resistor. Two plasma jets formed during the arc discharge, one originating from the cathode tip and the other through the micropore. It was found that when R was increased from 0 Ω to 1 MΩ, (1) the plasma jet originating at the micropore weakened, (2) the peak current to the hollow cylindrical anode decreased from 73 A to 0, and (3) the peak arc current decreased from 176 A to 150 A. Plasma jet velocities for R = 0 were inferred from the difference between electron current peak times at two probes, to be 9 km/s for the plasma jet from the cathode and 27 km/s for the plasma jet at the micropore.

Ouzo Column under Impact: Formation of Emulsion Jet and Oil-Lubricated Droplet.

We investigated the dynamics of a liquid column consisting of ouzo emulsion under the impact generated when the liquid container lands on a hard ground. At a cavitation number of 0.36, where cavitation is expected to occur, our high-speed videography captured the traveling jet and cavitation bubbles while the oil microdroplets in ouzo after different runs of impact were visualized by an optical microscope. Importantly, the impact on an ouzo column can eject a focused jet of the emulsion and deposit a small volume of emulsion on a solid substrate. As revealed by our still photography, the deposited emulsion formed an oil-lubricated drop immediately. Our findings have implications for jetting applications such as inkjet printing of emulsions or fast deposition of self-lubricating drops for assembling supraparticles. We also discuss the jet formation mechanism in terms of the existence of oil microdroplets.

Identifying Black Hole Central Engines in Gamma-Ray Bursts

Abstract The nature of the gamma-ray burst (GRB) central engine still remains an enigma. Entities widely believed to be capable of powering the extreme jets are magnetars and black holes. The maximum rotational energy that is available in a millisecond magnetar to form a jet is ∼1052 erg. We identify eight long GRBs whose jet-opening angle-corrected energetics of the prompt emission episode are >1052 erg with high confidence level and, therefore, their central engines are expected to be black holes. The majority of these GRBs present significant emission in the sub-GeV energy range. The X-ray afterglow light curves of these bursts do not show any shallow decay behavior such as a plateau; however, a few cases exhibit flares and multiple breaks instead of a single power-law decay. For a minimum mass of the black hole (∼2 M ⊙), we find the efficiency of producing a jet from its rotational energy to range between 2% and 270%. Highly energetic jets requiring high efficiencies implies that either the mass of these black holes are much larger or there are, in addition, other sources of energy that power the jet. By considering the Blandford–Znajek mechanism of jet formation, we estimate the masses of these black holes to range between ∼2 and 60 M ⊙. Some of the lighter black holes formed in these catastrophic events are likely candidates to lie in the mass-gap region (2–5 M ⊙).

A numerical study on laboratory plasma dynamics validated by low current x-pinch experiments

The computational study of x-pinch plasmas driven by pulsed power generators demands the development of advanced numerical models and simulation schemes, able to enlighten the experiments. The capabilities of PLUTO code are here extended to enable the investigation of low current produced x-pinch plasmas. The numerical modules of the code used and modified are presented and discussed. The simulations results are compared to experiments, carried out on a table-top pulsed power plasma generator implemented in a mode of producing a peak current of ∼45 kA with a rise time (10%–90%) of 50 ns, loaded with Tungsten wires. The structural evolution of plasma density is studied and its influence on the magnetic field is analyzed with the help of the new simulation data. The simulated areal mass density is compared with the experimentally measured dense opaque region to enlighten the dense plasma evolution. In addition, the measured areal electron density is compared to the simulation results. Moreover, the new simulation data offer valuable insights to the main jet formation mechanisms, which are further analyzed and discussed in relation to the influence of the J × B force and the momentum.