Jet Propagation Research Articles

The influence of the gap width of the blade on the performance of the mixing pump

Abstract The spiral axial flow gas-liquid mixed pump has some problems, such as unsteady flow and sharp decline in performance, when it runs in the biased condition with high gas content. Based on the principle of fluid flow and the design concept of slot drainage, a slit blade is proposed in this study to improve the degree of gas-liquid separation inside the mixing pump. The slit connects the pressure surface of the blade of the mixing pump with the suction surface. The pressure difference between the pressure surface and the suction surface leads to the generation of slit jet, which plays a “blowing” role in the adhesion of the gas phase on the suction surface inside the mixing pump. And make the stagnant air mass in the flow passage move again, so as to slow down the gas-liquid separation in the mixed transport pump. This study provides theoretical reference for the design and optimization of spiral axial flow gas-liquid mixed pump.

Experiments for control of boundary layer transition by plasma actuators

Plasma flow control technology is a new type of active flow control technology, and this paper carries out certain research on the basic principle of plasma flow control technology and its application on the wing model. The paper introduces the theory of plasma discharge and analyzes how plasma can control the flow field. A parallel dielectric barrier discharge plasma exciter is then designed and tested by using the Particle Image Velocimetry (PIV) technique to investigate the spatial flow field distributions of single-stage and three-stage actuators, and the mechanism of jet generation by the actuator is analyzed. Finally, the plasma actuator was utilized to control flow separation on a super-zero-boundary airfoil, and the oil droplet interferometric method was used to study the actuator’s role in controlling boundary layer transition. The experiment revealed that increasing the actuator discharge voltage can further reduce wall drag and more effectively delay the transition. Under the given conditions of a head-on angle of 6° and the incoming wind speed of 20 m/s, a two-stage actuator’s continuous discharge parameter was set to an output voltage of 12 kV and an output frequency of 4.7 kHz. The results showed that the transition position can be delayed by 13%, indicating the effectiveness of the actuator’s jet effect in enhancing the stability of the boundary layer flow.

A semi-analytical model for the propagation of a relativistic jet in a magnetized medium

ABSTRACT The merger of two magnetized compact objects, such as neutron stars, forms a compact object which may launch a relativistic and collimated jet. Numerical simulations of the process show that a dense and highly magnetized medium surrounds the system. This study presents a semi-analytical model that models the effects that a static magnetized medium with a tangled field produces in relativistic, collimated, and non-magnetized jets. The model is a first approximation that addresses the magnetic field present in the medium and is based on pressure equilibrium principles between the jet, cocoon, and external medium. A fraction of the ambient medium field is allowed to be entrained in the cocoon. We find that the jet and cocoon properties may be affected by high magnetic fields (≳ 1015 G) and mixing. The evolution of the system may vary up to $\sim 10{{\ \rm per\ cent}}$ (compared to the non-magnetized case). Low-mixing may produce a slower broader jet with a broader and more energetic cocoon would be produced. On the other hand, high-mixing could produce a faster narrower jet with a narrow and less-energetic cocoon. Two-dimensional hydrodynamical simulations are used to validate the model and to constrain the mixing parameter. Although the magnetic field and mixing have a limited effect, our semi-analytic model captures the general trend consistent with numerical results. For high magnetization, the results were found to be more consistent with the low mixing case in our semi-analytic model.

Analysis of Sound Propagation Behaviors for Supersonic Jet on Far Field Region by Computational Aero-Acoustics (CAA) Simulation

Noise emission is an essential issue for the aviation industry, as it harms health and induces various physiological responses. The noise generated by supersonic jets is very intense. It will cause fatigue and even damage the human hearing system in the surrounding area of jet operation. Besides, the experimental and prototyping cost for the jet model is prohibitive, and it is a vast project and process that takes a lot of time to run. The purpose of this study is to determine the sound propagation behaviours of a supersonic jet in the far-field region and to analyse the consequences of the velocity of a supersonic jet on sound propagation of supersonic jet by using computational fluid dynamics (CFD) and computational aeroacoustics (CAA) simulations. This study focused on the perspective of observing the distance of the receiver when receiving the sound propagation of a supersonic jet, the observed angle of the receiver when receiving the sound propagation of a supersonic jet, and the velocity of the supersonic jet. The CFD and CAA analyses were performed in transient state simulation and the 2-inch Acoustics Reference Nozzle (ARN2). The result shows that the overall SPL throughout the frequency is proportional to the jet velocity of the supersonic jet. However, the distance and angle of the receiver gave different results in sound propagation behaviour. The results also conclude that as the distance between the receiver and jet nozzle exit increases, the overall SPL trend will decrease throughout the frequency increase. As the vertical distance between the receiver and the axisymmetric line of the jet nozzle increases, the frequency of the receiver starts to observe will decrease.

Asymmetric jet shapes with two-dimensional jet tomography

Two-dimensional (2D) jet tomography is a promising tool to study jet medium modification in high-energy heavy-ion collisions. It combines gradient (transverse) and longitudinal jet tomography for selection of events with localized initial jet production positions. It exploits the transverse asymmetry and energy loss that depend, respectively, on the transverse gradient and jet path length inside the quark-gluon plasma (QGP). In this study, we employ 2D jet tomography to study medium modification of the jet shape of γ-triggered jets within the linear Boltzmann transport (LBT) model for jet propagation in heavy-ion collisions. Our results show that jets with small transverse asymmetry (ANn⃗) or small γ-jet asymmetry (xJγ=pTjet/pTγ) exhibit a broader jet shape than those with larger ANn⃗ or xJγ, since the former are produced at the center and go through longer path lengths while the later are off center and close to the surface of the QGP fireball. In events with finite values of ANn⃗, jet shapes are asymmetric with respect to the event plane. Hard partons at the core of the jet are deflected away from the denser region while soft partons from the medium response at large angles flow toward the denser part of QGP. Future experimental measurements of these asymmetric features of the jet shape can be used to study the transport properties of jets and medium responses. Published by the American Physical Society 2024

Observational evidence to support a dense ambient medium shaping the jet in 3C 84

Highly collimated relativistic jets are a defining feature of certain active galactic nuclei (AGN), yet their formation mechanism remains elusive. Previous observations and theoretical models have proposed that the ambient medium surrounding the jets could exert pressure, playing a crucial role in shaping the jets. However, a direct observational confirmation of such a medium has been lacking. In this study, we present very long baseline interferometric (VLBI) observations of 3C 84 (NGC 1275), located at the center of the Perseus Cluster. Through monitoring observations with the Very Long Baseline Array (VLBA) at 43 GHz, a jet knot was detected to have been ejected from the sub-parsec scale core in the late 2010s. Intriguingly, this knot propagated in a direction significantly offset from the parsec-scale jet direction. To delve deeper into the matter, we employed follow-up VLBA 43 GHz observations, tracing the knot’s trajectory until the end of 2022. We discovered that the knot abruptly changed its trajectory in the early 2020s, realigning itself with the parsec-scale jet direction. Additionally, we present results from an observation of 3C 84 with the Global VLBI Alliance (GVA) at 22 GHz, conducted near the monitoring period. By jointly analyzing the GVA 22 GHz image with a VLBA 43 GHz image observed about one week apart, we generated a spectral index map, revealing an inverted spectrum region near the edge of the jet where the knot experienced deflection. These findings suggest the presence of a dense, cold ambient medium characterized by an electron density exceeding ∼105 cm−3, which guides the jet’s propagation on parsec scales and significantly contributes to the overall shaping of the jet.

Very long baseline interferometry observations of the high-redshift X-ray-bright blazar SRGE J170245.3+130104

Aims. The X-ray luminous and radio-loud active galactic nucleus (AGN) SRGE J170245.3+130104 discovered at z ∼ 5.5 provides unique chances to probe the growth and evolution of a supermassice black hole (SMBH) with powerful jets in the early Universe. Methods. We present 1.35 − 5.1 GHz Very Long Baseline Array (VLBA) results regarding the radio continuum emission and a spectral analysis of this quasar in a low-flux-density state. Results. This source is unresolved at three frequencies, with total flux densities of 8.35 ± 0.09 Jy beam−1, 7.47 ± 0.08 Jy beam−1, and 6.57 ± 0.02 Jy beam−1 at 1.73 GHz, 2.26 GHz, and 4.87 GHz, respectively. Meanwhile, the brightness temperature is higher than 109 K. Conclusions. Compared with previous radio observations with arcsecond-scale resolution, nearly all the radio emission from this source is concentrated in the very central milliarcsecond (mas) scale area. We confirm this source is a bright blazar at z > 5. This young AGN provides a great opportunity to understand the mechanisms behind the generation of strong jets in the early Universe.

Study on the jet molding of Cu-W-Zrx alloy liner

With the rapid development of armored weapons, the improvement of armor-breaking weapons is imminent, and the liners as the core component of armor-breaking has attracted much attention. As a result, the paper uses AUTODYN-2D kinetic simulation software to simulate the generation of jets in the erosion process of Cu-W alloy liner and Cu-W-Zr alloy liner materials. The results demonstrate that the jet created by Cu-W-Zr alloy is longer than that formed by Cu-W alloy, and it has good erosion ability with high head velocity during the jet creation process, which can be used to develop liners.

A sub-100 nm thickness flat jet for extreme ultraviolet to soft X-ray absorption spectroscopy.

Experimental characterization of the structural, electronic and dynamic properties of dilute systems in aqueous solvents, such as nanoparticles, molecules and proteins, are nowadays an open challenge. X-ray absorption spectroscopy (XAS) is probably one of the most established approaches to this aim as it is element-specific. However, typical dilute systems of interest are often composed of light elements that require extreme-ultraviolet to soft X-ray photons. In this spectral regime, water and other solvents are rather opaque, thus demanding radical reduction of the solvent volume and removal of the liquid to minimize background absorption. Here, we present an experimental endstation designed to operate a liquid flat jet of sub-micrometre thickness in a vacuum environment compatible with extreme ultraviolet/soft XAS measurements in transmission geometry. The apparatus developed can be easily connected to synchrotron and free-electron-laser user-facility beamlines dedicated to XAS experiments. The conditions for stable generation and control of the liquid flat jet are analyzed and discussed. Preliminary soft XAS measurements on some test solutions are shown.

Wall confinement effects on the dynamics of cavitation bubbles in thin tubes

Cavitation is a common phenomenon in nature and has numerous applications. In contrast to a cavitation bubble in a free domain, a cavitation bubble in a thin tube is restricted by the tube wall, which is expected to significantly affect bubble evolution, but its mechanism is still unclear. In this study, the dynamics of a cavitation bubble in a thin circular tube is studied by numerical simulation, focusing on the confinement effects of the tube. The results show that besides affecting the size and lifetime of the bubble, the confinement effects of the tube lead to the generation of counter jets and a ring jet during the contraction process of the bubble, and the curvature of the two counter jets determines the ring jet's peak velocity. When the bubble deviates from the midpoint of the tube in the axial direction, the two sides of the bubble along the axial direction show asymmetric behaviors, which results in the bubble migrating toward the midpoint. The tube diameter, tube length, liquid viscosity, and initial bubble position can significantly influence the degree of confinement effects, which can be characterized by the variations of several key indicators, such as bubble size, lifetime, degree of deformation, counter jet velocity, ring jet velocity, and axial migration of the bubble.

A large-scale cold plasma jet: generation mechanism and application effect

Atmospheric pressure cold plasma jets (APCPJs) typically exhibit a slender, conical structure, which imposes limitations on their application for surface modification due to the restricted treatment area. In this paper, we introduce a novel plasma jet morphology known as the large-scale cold plasma jet (LSCPJ), characterized by the presence of both a central conical plasma jet and a peripheral trumpet-like diffuse plasma jet. The experimental investigations have identified the factors influencing the conical and the trumpet-like diffuse plasma jet, and theoretical simulations have shed light on the role of the flow field and the electric field in shaping the formation of the LSCPJ. It is proved that, under conditions of elevated helium concentration, the distributions of impurity gas particles and the electric field jointly determine the plasma jet’s morphology. High-speed ICCD camera images confirm the dynamic behavior of plasma bullets in LSCPJ, which is consistent with the theoretical analysis. Finally, it is demonstrated that when applied to the surface treatment of silicone rubber, LSCPJ can achieve a treatment area over 28 times larger than that of APCPJ under equivalent conditions. This paper uncovers the crucial role of impurity gases and electric fields in shaping plasma jet morphology and opens up the possibility of efficiently diversifying plasma jet generation effects through external electromagnetic fields. These insights hold the promise of reducing the generation cost of plasma jets and expanding their applications across various industrial sectors.

Linear Boltzmann transport for jet propagation in the quark-gluon plasma: Inelastic processes and jet modification

Linear Boltzmann transport for jet propagation in the quark-gluon plasma: Inelastic processes and jet modification

Experimental study of the noise suppression of supersonic impinging jets with chevrons

Supersonic impinging jets may cause many adverse ground effects, including surface erosion, nonuniform surface heat transfer, lift loss, and acoustic loading. In this study, chevron nozzles are used to suppress the noise generation of supersonic impinging jets originated from a circular convergent nozzle with the jet Mach number of 1.2. An array of microphones is used to measure the far-field acoustic fields, and a schlieren system is employed to measure the near-field flow structures. Three impinging distances are considered to examine the differences between the impinging jets and the free jet, and to assess the effect of impinging distance on the noise characteristics. Two chevron nozzles with different penetration angles are designed to investigate the potentials of chevron nozzles in controlling the supersonic-impinging-jet noise. Results show that the chevron nozzles do not alter the directivity of overall sound pressure levels, but significantly reduce the amplitude at all emission angles. The discrete tones in the impinging jets are dramatically mitigated or eliminated, and the levels of broadband noise are also significantly reduced over a wide range of frequency band, regardless of the impingement distance. The influences of chevrons on the near-field flow structures are checked with the root-mean-square values and proper orthogonal decomposition of schlieren images, which provide more evidence on the noise suppression mechanism with chevrons.

Shock wave induced by the collapse of a bubble cluster with each bubble distributed randomly

The phenomenon of bubble collapse is ubiquitous in both natural and industrial settings, often manifesting in the form of bubble clusters. Despite its prevalence, there has been limited research on the dynamics of bubble clusters. In order to gain a better understanding of shock wave emission, liquid jet propagation, and the resulting pressure loads during bubble cluster collapse, we have developed a high-fidelity numerical approach aimed at accurately capturing shock waves and phase interfaces. The interface compression technique is introduced into the compressible two-phase model to improve the sharpness of the phase interface. We solve the physical model using the BVD (Boundary Variation Diminishing) principle. Both the 5th order WENO (Weighted Essentially Non-Oscillatory) scheme and the interface capturing function THINC (Tangent of Hyperbola for INterface Capturing) are utilized to reconstruct primary variables at cell boundaries, effectively minimizing numerical dissipation. For further resolution improvement, we implement these numerical methods on the AMR (Adaptive Mesh Refinement) mesh. Our numerical results demonstrate that the distance between the wall and the bubble cluster, as well as the nearest bubble to the wall, significantly influence the wall peak pressure. However, they have a minimal impact on the overall evolution of the bubble cluster and the peak pressure induced in the flow field. Remarkably, the spatial distribution of bubbles and the total number of bubbles play a crucial role in shaping the dynamic behavior of the bubble cluster and the pressure loads exerted both on the solid wall and in the flow field. The crucial findings offer profound insights into a range of applications, including cavitation erosion, underwater explosions, and drug delivery.

Investigations on the jets and shock waves of a cavitation bubble collapsing between a wall and a particle

The simultaneous presence of particles and cavitation bubbles has a deleterious effect on the performance and safety of hydraulic machinery through the generation of jets and shock waves. In the present paper, the mechanisms responsible for the generation and the evolution of jets and shock waves from a collapsing cavitation bubble situated between a spherical particle and a wall are simulated using a compressible two-phase flow solver. Specifically, the effects of bubble position on jet and shock wave behavior are qualitatively analyzed. The simulations and experiments reveal three typical cases of jet behavior: a jet toward the wall, double jets, and a jet toward the particle. Needle jets and shock waves are commonly generated by collisions of the bubble interface. In some cases, needle jets are associated with a high impact velocity. It is found that the smaller the distance between the particle and the wall, the higher the pressure generated by the jets and the shock waves on the wall.

Magnetic and thermal acceleration in extragalactic jets

Aims. Relativistic jets launched from active galactic nuclei accelerate up to highly relativistic velocities within a length scale of between a few parsecs and tens of parsecs. The precise way in which this process takes place is still unclear. While magnetic acceleration is known to be able to accelerate relativistic outflows, little attention has been paid to the role of thermal acceleration. The latter has been assumed to act only on compact regions very close to the central engine, and to become negligible on parsec scales. However, this holds under the assumption of small internal energies relative to the magnetic ones, and whether or not this assumption is valid and what happens when we drop this assumption are open questions. Methods. We used a 2D relativistic magnetohydrodynamical code to explore jet acceleration from subparsec to parsec scales. As initial conditions for our models, we used observational constraints on jet properties derived by means of very long-baseline interferometry observations for a Fanaroff Riley I radio galaxy, NGC 315. We investigated the parameter space established for this source and performed a number of simulations of magnetically, thermally, or kinetically dominated jets at injection, and compared our results with the observations. Furthermore, we employed different models to characterize our jets, involving different magnetic field configurations (i.e., force-free vs. nonforce-free) and varying shear layer thicknesses. Results. Our simulated jets show that when thermal energy is comparable to or exceeds magnetic energy, thermal acceleration becomes significant at parsec scales. This result has important consequences, potentially extending the acceleration region far beyond the collimation scales, as thermal acceleration can effectively operate within a conically expanding jet. In all the models, we find acceleration to be driven by expansion, as expected. A number of our models allow us to reproduce the acceleration and opening angles observed in NGC 315. Finally, our results indicate that disk-launched winds might play an important role in jet propagation. Namely, when the jet has an initial force-free magnetic field configuration, thicker shear layers are needed to shield the internal spine from the action of the external medium and thus delay the growth of instabilities.

Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova

Follow-up observations of short gamma-ray bursts (sGRBs) have continuously unveiled late extended/plateau emissions, attributed to jet launch due to late engine activity, the nature of which remains enigmatic. Observations of GW170817 have confirmed that sGRBs are linked to neutron star (NS) mergers, and discovered a kilonova (KN) transient. Nevertheless, the origin of the early blue KN in GW170817 remains unclear. Here, we investigate the propagation of late jets in the merger ejecta. By analytically modeling jet dynamics, we determine the properties of the jet-heated cocoon, and estimate its cooling emission. Our results reveal that late jets generate significantly brighter cocoons compared to prompt jets, primarily due to reduced energy loss by adiabatic cooling. Notably, with typical late jets, emission from the cocoon trapped inside the ejecta can reproduce the blue KN emission. We estimate that the forthcoming Einstein Probe mission will detect the early cocoon emission at a rate of ∼2.1−1.6+3.2 yr−1, and that optical/UV follow-ups in the LIGO-Virgo-KAGRA O5 run will be able to detect ∼1.0−0.7+1.5 cocoon emission events. As an electromagnetic counterpart, this emission provides an independent tool to probe NS mergers in the Universe, complementing insights from sGRBs and gravitational waves.

Atmospheric pressure argon plasma jets I – Measurements of spatial distribution for visible emission spectrum and vacuum ultraviolet

AbstractThis paper describes the observed position dependent emission spectrum and vacuum ultraviolet (VUV) to clarify the optical structure of argon atmospheric pressure plasma jets (APJs). Visible emission spectra of argon, nitrogen, and OH molecules were measured as a function of position from the nozzle of plasma jet generator to gas flow direction. From the results, we realized that a certain electric field is required for producing high energy excited atoms of argon in the jet from the high voltage electrode in the device to the ground positioned at downstream side. Moreover, VUV was detected along the plasma jet through the downstream direction. Thus, we could picture that the light pattern of plasma jet of which intensity weaken depend to the distance from the nozzle is sustained by the above two factors with the present steady state experiments.

Design of field shaper suitable for plate and experimental research on welding of dissimilar materials

Magnetic pulse welding realizes solid-state connection through a high-speed collision of materials, which can effectively overcome the welding difficulties of light metal materials. In the magnetic pulse welding system, in order to improve the welding efficiency, a field shaper is usually applied between the multi-turn coil and the workpiece to concentrate the magnetic field in the welding area, thereby improving the electromagnetic force. However, a large number of researchers are currently on the tube-welded field shaper, and very few researchers have studied the structure of the plate-welded field shaper. Therefore, this paper proposed a new field shaper for plate welding. The effect of the structure parameter of the field shaper on the magnetic field and electromagnetic force on the aluminum plate was analyzed in the COMSOL multiphysics software. The optimal structure parameters of the field shaper were selected. The plastic deformation and the generation of jets under different voltages and the welding of the same/dissimilar metal materials at different standoff distances were studied experimentally, which verifies the feasibility of the new field shaper.

Thermodynamic analysis of nano-electrospray induced gas jets

Nano-electrospray (nES) produces a plume of charged liquid droplets which have drag interactions with the surrounding gas after they are emitted from a source capillary. The resulting induced gas flow has often been considered unimportant, but we have demonstrated that a gas microjet of significant velocity up to 10s of m/s can be produced. In this work we present a thermodynamic framework that enables analysis of gas jet generation from electrosprays and introduce the important metrics for such analysis, effectiveness (a measure of momentum transfer from the electrosprayed aerosol to gas) and efficiency (a measure of energy conversion from electrical energy generating the electrospray to gas kinetic energy). This analytical framework is applicable to any two-phase flows consisting of discrete conservative-force-driven particles which exchange momentum with an inert, otherwise quiescent fluid medium to yield a co-flowing two-phase jet. We apply this framework to sprays of water from nano-electrospray emitters to demonstrate that increasing the applied electrical potential difference, increasing liquid mass flowrate, and decreasing droplet size all can increase electrospray induced gas jet strength, but only the latter two do so while also increasing the momentum transfer effectiveness and energy conversion efficiency.