Particles In Jet Research Articles

Role of density ratio on particle dispersion in a turbulent jet

The behavior of dispersed particles in a turbulent round jet is experimentally investigated. The role of particle-to-fluid density ratio ρp/ρf is analyzed by inspecting particle velocity fields and preferential concentration at four different ratios, from 0.7 to 19.3. The jet near-field region, i.e., up to X/D=11, is analyzed and compared to the unladen case. Particle-to-fluid density ratio is reported to have a strong impact on particle velocity field structure, in terms of jet transition and self-similar region as well as on turbulent fluctuations. Concentrations of particles show that increasing particle density corresponds to larger departure from uniformity. This occurrence is limited to the region X/D<5, where also the largest differences of average and fluctuating velocities with respect to the unladen case are measured.

POLİESTER MONOFİLAMENTTEN ÜRETİLMİŞ BİYOMEDİKAL TEKSTİL İÇİN YÜZEY İŞLEMİ

Foreign Body Reaction is a critical issue to be addressed when polyethylene terephthalate textile implants are considered in the medical field to treat pathologies involving hernia repair, or heart valve replacement. The natural porosity of textile materials tends to induce exaggerated tissue ingrowth which may prevent the implants from remaining flexible. One hypothesized way to limit the Foreign Body Reaction process is to increase the material surface roughness. Supercritical jet particle projection is a technique that provides enough velocity to particles in order to generate plastic deformation on the impacted surface. The aim of this study is to investigate the influence of micro particles laden supercritical nitrogen jet projection parameters like jet static pressure, standoff distance and particle size on the roughness of polyethylene terephthalate fabric surfaces. Results bring out that particles projected by supercritical nitrogen jet generate craters on the surface of monofilament as well as monofilament fabric, allowing topographical modifications at the yarn scale. Thus, this treatment increased the roughness of the monofilament fabric from 0.78 μm to 1.22 μm. Regarding the strength of the textile material, it is only slightly modified with the treatment process, as the tenacity of the yarns decreases by only 10%. In this work, it is revealed that the obtained structures tend to limit the adhesion and slow down the proliferation of human fibroblasts. The results obtained in this work show that it is possible to create a roughness on a polyethylene terephthalate fabric using the nitrogen jet technology.

3D PIC Simulations for relativistic jets with a toroidal magnetic field

ABSTRACT We have investigated how kinetic instabilities such as the Weibel instability (WI), the mushroom instability (MI), and the kinetic Kelvin–Helmholtz instability (kKHI) are excited in jets without and with a toroidal magnetic field, and how such instabilities contribute to particle acceleration. In this work, we use a new jet injection scheme, where an electric current is self-consistently generated at the jet orifice by the jet particles, which produce the toroidal magnetic field. We perform five different simulations for a sufficiently long time to examine the non-linear effects of the jet evolution. We inject unmagnetized e± and e−– p+ (mp/me = 1836), as well as magnetized e± and e−– i+ (mi/me = 4) jets with a top-hat jet density profile into an unmagnetized ambient plasmas of the same species. We show that WI, MI, and kKHI excited at the linear stage, generate a non-oscillatory x-component of the electric field accelerating, and decelerating electrons. We find that the two different jet compositions (e± and e−– i+) display different instability modes, respectively. Moreover, the magnetic field in the non-linear stage generated by different instabilities is dissipated and reorganized into new topologies. A 3D magnetic field topology depiction indicates possible reconnection sites in the non-linear stage, where the particles are significantly accelerated by the dissipation of the magnetic field associated to a possible reconnection event.

Investigation of Metal Powder Injection into a Combustion Chamber by Large Eddy Simulation for Power to X Studies

AbstractThe numerical modeling and simulation of particle dispersion during the filling process of a tubular combustion chamber are presented. By means of multiphase large eddy simulations (LES) the particle distribution inside a circular diffuser‐reactor chamber is studied to analyze the two‐phase flow dynamics for metal powder combustion in a tubular reactor with flame propagation. Typical particle accumulations are found that form close to the reactor wall and also particles tend to segregate and preferentially concentrate at vortex surfaces in particle bands. Particle segregation and accumulation effects aside vortex structures are analyzed using the LES approach. The causes of particle segregation and inhomogeneities are studied and measures for its reduction by changes in the reactor design are discussed. Alterations of the diffuser geometry are adapted to minimize the central particle jet formation and the particle distribution inhomogeneities during the filling process.

X-Ray Spectral Analysis of the Jet Termination Shock in Pictor A on Subarcsecond Scales with Chandra

Hot spots observed at the edges of extended radio lobes in high-power radio galaxies and quasars mark the position of mildly relativistic termination shock, where the jet bulk kinetic energy is converted to the internal energy of the jet particles. These are the only astrophysical systems where mildly relativistic shocks can be directly resolved at various wavelengths of the electromagnetic spectrum. The western hot spot in the radio galaxy Pictor A is an exceptionally good target in this respect, due to the combination of its angular size and high surface brightness. In our previous work, after a careful Chandra image deconvolution, we resolved this hot spot into a disk-like feature perpendicular to the jet axis, and identified it as the front of the jet termination shock. We argued for a synchrotron origin of the observed X-ray photons, which implied electron energies reaching at least 10–100 TeV at the shock front. Here, we present a follow-up on that analysis, proposing, in particular, a novel method for constraining the shape of the X-ray continuum emission with subarcsecond resolution. The method is based on a Chandra hardness map analysis, using separately deconvolved maps in the soft and hard X-ray bands. In this way, we have found there is a systematic, yet statistically significant gradient in the hardness ratio across the shock, such that the implied electron energy index ranges from s ≤ 2.2 at the shock front to s > 2.7 in the near downstream. We discuss the implications of the obtained results for a general understanding of particle acceleration at mildly relativistic shocks.

Formation and Penetration Properties of a Shaped Charge with Zr41.2Ti13.8Cu12.5Ni10Be22.5 Liner.

In the military field, determining how to increase the hole-expanding ability of shaped charge warheads is a key and difficult issue with respect to warhead development. Amorphous alloys have grains or grain boundaries, with unique mechanical properties. Zr41.2Ti13.8Cu12.5Ni10Be22.5 can be used as the liner material of shaped charges, resulting in high-speed particle flows that differ from those of traditionally shaped charges. In this paper, based on the analysis of the mechanical response characteristics of Zr41.2Ti13.8Cu12.5Ni10Be22.5 and its fracture morphology under impact, combined with the formation theory of shaped charge jets, a semi-empirical formula is derived to calculate the velocity of non-cohesive high-speed particle flow considering the elastic strain energy loss. Additionally, the reliability of the proposed theoretical model is verified through experiments. The penetration process of Zr-based amorphous alloy high-speed particle flow into a concrete target is theoretically analyzed, and the penetration stages of the high-speed particle flow into the target are clearly distinguished. Combined with the penetration theory of shaped charge particle jets, a high-speed particle flow penetration model is proposed, and a pore expansion model is established through an energy method. The experimentally obtained data on depth of penetration are in agreement with the theoretical calculation results.

Numerical simulation of flow field and residence time of nanoparticles in a 1000-ton industrial multi-jet combustion reactor

In this work, by establishing a three-dimensional physical model of a 1000-ton industrial multi-jet combustion reactor, a hexahedral structured grid was used to discretize the model. Combined with realizable k–ε model, eddy-dissipation-concept, discrete-ordinate radiation model, hydrogen 19-step detailed reaction mechanism, air age user-defined-function, velocity field, temperature field, concentration field and gas arrival time in the reactor were numerically simulated. The Euler–Lagrange method combined with the discrete-phase-model was used to reveal the flow characteristics of particles in the reactor, and based on this, the effects of the reactor aspect ratios, central jet gas velocity and particle size on the flow field characteristics and particle back-mixing degree in the reactor were investigated. The results show that with the decrease of aspect ratio in the combustion reactors, the velocity and temperature attenuation in the reactor are intensified, the vortex phenomenon is aggravated, and the residence time distribution of nanoparticles is more dispersed. With the increase in the central jet gas velocities in reactors, the vortex lengthens along the axis, the turbulence intensity increases, and the residence time of particles decreases. The back-mixing degree and residence time of particles in the reactor also decrease with the increase in particle size. The simulation results can provide reference for the structural regulation of nanoparticles and the structural design of combustion reactor in the process of gas combustion synthesis.

Study of a new method for the instant preparation of ice particles in ice abrasive air jet

The ice abrasive air jet is a clean surface treatment technology, which currently has limitations such as high energy consumption, uncontrollable particle size and hardness. Realizing the instant preparation and utilization of ice particles are crucial for solving the energy consumption problem. This paper based on the icing principle of heterogeneous nucleation, proposed a new method of ice making, the heat transfer mechanism of low temperature droplets was studied, and the method was proved to be feasible. Using the FLUENT solidification and melting model combined with the VOF model to calculate the freezing process of droplets, the effects of droplet particle size, initial temperature, and wall temperature on the freezing time were analyzed, and the calculation equation of the freezing time was determined, which was corrected by the icing test results. The results showed that the outside of the droplet freezes first, the liquid–solid boundary is parabolic, and the parabolic concavity increases with time and droplet size. In the freezing process, the larger the droplet size, the longer the droplet phase transition time; the higher the droplet initial temperature, the longer it took to reach the phase transition; the higher the wall temperature, the longer the ice formation time.

Elucidating the jet cross-section in pp and pPb collisions at sNN = 5.02TeV

In this paper, we present the charged particles jet cross-section study in [Formula: see text] and [Formula: see text] collisions at [Formula: see text],TeV using PYTHIA8 (PYTHIA8.186 and PYTHIA8.306) and HIJING 2.0 models, in kinematic range of [Formula: see text],GeV/c for [Formula: see text] collisions and [Formula: see text],GeV/c for [Formula: see text] collisions. The jets are reconstructed for [Formula: see text], 0.3, 0.4 and 0.6 for the pseudorapidity interval of [Formula: see text] 0.9-R. The jets algorithms: cell jet and slow jet inside PYTHIA8.186 and anti-[Formula: see text] algorithm using HIJING 2.0 have been used for Monte Carlo simulations. The simulation results are then compared with measurements of the ALICE experiment. It is observed that all models’ predictions are lower than experimental data up to [Formula: see text],GeV/c; after that, the Monte Carlo study of Cell and slow jet satisfies the experimental data. The CR tunes could not explain the ALICE data at high [Formula: see text] values due to nonperturbative QCD effects. We have also calculated the nuclear modification factor [Formula: see text], and no clear suppression has been seen in the case of [Formula: see text] collisions. The results from the models indicate that the QGP is not formed and that the cold nuclear matter effect exists in pPb collisions.

Ignition and combustion of a dense powder jet of micron-sized aluminum particles in hot gas

Aiming at the potential implementation of aluminum as a primary fuel in powder-fueled ramjets or engines, this work seeks to investigate the ignition and combustion characteristics of a dense gas-suspended jet of micron-sized aluminum particles in a hot flow with controlled temperature and compositions. Aluminum particles with a mean diameter of 40 µm are aerosolized using a custom-made feeder and carried into the burner by a nitrogen stream. The powder jet with a particle density of up to 1–3 kg/m3 can be ignited and burned violently at a surrounding gas temperature as low as 1500 K. The lowered ignition temperature of the powder jet can be attributed to a cooperative mechanism resulting in fast reactions. Meanwhile, the ignition delay time decreases from ∼25 to ∼5 ms when the surrounding temperature increases from 1500 to 2200 K. The burning powder jet generates strong luminance and AlO emission signals detected by a spectrometer. Particle image velocimetry (PIV) and camera pyrometry are used to derive the two-dimensional velocity and average projected temperature distribution, respectively. Furthermore, a high-speed camera with a microscopic lens captures the transition from dispersed combustion to group combustion that forms a large-scale flame column wrapping the entire powder jet. The aluminum oxide produced in the columnar flame forms a large number of nanosized smoke particles in the condensation region. Finally, a numerical model considering the collective effect of the powder jet is developed to predict the particle temperature history during the ignition stage, which shows good agreement with the temperature profiles derived from camera pyrometry and PIV techniques.

Simulation of particle interception of seamless knitted composite filter material based on the discrete phase model

In this research, a three-dimensional geometric model of knitted cylindrical air filter material is constructed. Due to the isotropy of the three-dimensional structure, a certain cyclic structure is selected for the flow calculation domain in this research. According to the principle of air filter particle testing, the pressure drop of the filter material and the particle collection efficiency are simulated and calculated. Applying ANSYS finite element analysis software, based on Fluent's fluid Lagrangian discrete model, the geometric model is meshed and the particle materials and boundary conditions are set. Air is the continuous phase, and its velocity is set at 0.27 m/s. The jet particles are used as discrete phases to track the particle trajectory in real time. Based on the above conditions, the simulation of the capture efficiency of weft-knitted tubular air filter material for different particle sizes can not only predict and evaluate the filtering efficiency of the knitted tubular air filter material, but also provide a theoretical reference for fluid simulation of the knitted filter material.

Comprehensive coverage of particle acceleration and kinetic feedback from the stellar mass black hole V404 Cygni

ABSTRACT We present analysis of comprehensive radio observations of the black hole V404 Cyg during its 2015 outburst. These data represent the best ever coverage of jet production and particle acceleration from any black hole. We report for the first time a clear and near-linear flux–rms correlation in the radio flux densities. Investigation of individual flares reveals in nearly all cases the peak corresponds to the transition from optically thick to thin to synchrotron emission, but an extended phase of particle acceleration is required in contrast to simple impulsive injection models. The largest radio flare is preceded by a phase of optical oscillations and followed one day later by a smaller but optically thin flare, likely due to ejecta interacting with the interstellar medium. Comparing the radio emission to contemporaneous X-ray and optical data, we find that the X-ray and radio measurements are correlated on all time-scales from seconds to one day. Correlation with the optical flux densities is weak at short time-scales, but becomes significant on time-scales greater than a few hours. We evaluate the physical conditions (size, magnetic field, and internal energy) associated with 86 individual radio flares, which in turn allows us to place a lower limit on the kinetic feedback over the 15 d of intense activity. If this energy was deposited locally to the source, as implied by the failure to detect jets on angular scales larger than milliarcsec, then we predict that a nova-like shell could have been formed.

Resonant enhancement of particle emission from a parametrically driven condensate in a one-dimensional lattice

Motivated by recent experiments, we investigate particle emission from a Bose-Einstein condensate in a one-dimensional lattice, where the interaction strength is periodically modulated. The modulated interactions parametrically excite a collective mode, leading to density oscillations. These collective oscillations in turn drive particle emission. This multistep process amplifies the drive, producing larger particle jets. We find that the amplitude dependence of the emission rate has a characteristic threshold behavior, as seen in experiments.

Study on dynamic behaviors from non-circular dense granular jet impact

Dynamic behaviors of non-circular dense granular jets impacting a sufficiently large target are studied by experiment and DEM simulation. Effects of the granular jet velocity, particle diameter, and aspect ratio on the anisotropic pattern were investigated. Results show that the anisotropy of particle concentration of the granular sheet is enhanced with increasing aspect ratio. Interestingly, despite the significant differences in flux, the particle velocities are approximately consistent along the long and short axes. Unlike liquid, a dead zone is present in the impact zone, and the axial-to-radial transformation of the velocity is achieved by similar circular motion along the dead zone. Because the dead zone is adaptively adjusted with the cross section, the particle fluxes are anisotropic. Frequent collisions and frictions contribute to the homogenization of velocity in azimuths. Increasing particle diameter causes the enhancement of velocity fluctuations, the circular motion cannot be maintained and particles become scattered and isotropic. • The anisotropy in velocity and flux of particles from non-circular dense particle jet impact is characterized. • The effects of the velocity, aspect ratio, and particle diameter on anisotropy are assessed. • The mechanism of the anisotropy of the granular sheet is simulated by DEM.

Application and assessment of the improved delayed detached eddy simulation model to the cold spray process: Toward high fidelity computation fluid dynamics simulations

Despite many years of research about the comprehension of fluid-dynamic related phenomena and improvements in the performance of cold spray systems, ensuring high fidelity simulations of gas and particle flow remains a challenge. In this work, a detailed high fidelity modeling, namely, improved delayed detached eddy simulation, in axisymmetric geometries was proposed and compared with a more usual numerical framework, the Reynolds averaged Navier–Stokes model. After its validation against literature data in three different nozzle configurations, the new model could demonstrate more accurate predictions of phenomena such as oblique shocks, bow shock, and particle–gas flow coupling. Finally, thanks to the high fidelity numerical framework, a new nozzle geometry with a narrower extension of the particle jet was proposed and assessed.

Carbon-Filled E-Glass Fibre-Reinforced Epoxy Composite: Erosive Wear Properties at an Angle of Impingement

In the current study, multiwalled carbon nanotubes (MWCNTs) and carbon particles (micron size) were employed to create carbon particle dispersions. At different impact angles, the erosion of abrasive particles in an air jet is examined. Carbon particles dispersed across a metal matrix increased the fibre bonding but decreased the mechanical strength. In the sample, carbon nanotubes make up 5% of the total. The strength of carbon nanotubes in matrix materials overcomes the growth in carbon particle length significantly. When carbon particles are present, the matrix material weakens and becomes brittle. Due to the effect of attrition on exposed surfaces, materials that are subjected to particle impingement are more vulnerable to erosive processes. Carbon has significantly improved the matrix material’s surface property. The research findings significantly affect 5% of the CNT composite. At 30°, 0.0033 g/min showed the least proportion of abrasive wear. Erosive wear decreases at the lowest impingement angle but increases as the impact angle increases. Since it causes brittleness, increasing the weight percentage of carbon particles is discouraged.

Numerical Simulation of the Flow in Two-Phase Supersonic Underexpanded Gas–Particle Jets Exhausting into a Slotted Submerged Space

A simplified 2D model for calculating two-phase gas–particle flows in a slot space has been developed. The model can be used for fast calculation and estimation of supersonic-flow parameters in the slot space. Using this model, a numerical simulation of the flow in two-phase gas–particle supersonic jets exhausting into a submerged slot space bounded by two parallel disks was performed. The presence of particles led to the splitting of the gas jet into an internal two-phase jet and an external gas jet. In the present study, we investigated the structure of a two-phase jet as dependent on the spacing between the disks for conditions of cold spraying. A new effect was found in the flow at a small spacing between the disks (of the order of 0.2 mm) and a high-velocity internal two-phase gas–particle jet was formed. The distribution of the concentration of particles in the particle jet proved to be essentially non-uniform, with a caustic formed at the upper jet boundary.

Searches for Heavy Resonances with Substructure

In the past decade, the Large Hadron Collider (LHC) has probed a higher energy scale than ever before. Most models of physics beyond the standard model (BSM) predict the production of new heavy particles; the LHC results have excluded lower masses of such particles. This makes the high-mass regions especially interesting for current and future searches. In most BSM scenarios of interest, the new heavy resonances decay to standard model particles. In a subset of these models, the new particles have large couplings to the top quark, the W and Z bosons, or the Higgs boson. The top quark and W, Z, and Higgs bosons often decay to quarks, giving rise to jets of particles with substructure; event selection based on substructure is used to suppress standard model backgrounds. This review covers the key concepts in experimental searches based on the jet substructure and discusses recent results from the ATLAS and CMS experiments.

Ionization process and distinctive characteristic of atmospheric pressure cold plasma jet driven resonantly by microwave pulses

In the present study, a coaxial transmission line resonator is constructed, which is always capable of generating cold microwave plasma jet plumes in ambient air in spite of using argon, nitrogen, or even air, respectively. Although the different kinds of working gas induce the different discharge performance, their ionization processes all indicate that the ionization enhancement has taken place twice in each pulsed periods, and the electron densities measured by the method of microwave Rayleigh scattering are higher than the amplitude order of 1018 m−3. The tail region of plasma jets all contain a large number of active particles, like NO, O, emitted photons, etc, but without O3. The formation mechanism and the distinctive characteristics are attributed to the resonance excitation of the locally enhanced electric fields, the ionization wave propulsion, and the temporal and spatial distribution of different particles in the pulsed microwave plasma jets. The parameters of plasma jet could be modulated by adjusting microwave power, modulation pulse parameters (modulation frequency and duty ratio), gas type and its flow rate, according to the requirements of application scenarios.

Particle-based fast jet simulation at the LHC with variational autoencoders

We study how to use deep variational autoencoders (VAEs) for a fast simulation of jets of particles at the Large Hadron Collider. We represent jets as a list of constituents, characterized by their momenta. Starting from a simulation of the jet before detector effects, we train a deep VAE to return the corresponding list of constituents after detection. Doing so, we bypass both the time-consuming detector simulation and the collision reconstruction steps of a traditional processing chain, speeding up significantly the events generation workflow. Through model optimization and hyperparameter tuning, we achieve state-of-the-art precision on the jet four-momentum, while providing an accurate description of the constituents momenta, and an inference time comparable to that of a rule-based fast simulation.