Individual Jets Research Articles

Jets of the Antarctic Circumpolar Current in the central part of the Drake Passage based on the survey data in October–November of 2008

The horizontal structure of the jets of the Antarctic Circumpolar Current (ACC) is analyzed on the basis of CTD- and LADCP- sounding performed during a hydrophysical survey with a 10-mile spatial resolution in the central part of the Drake Passage in October–November of 2008. According to the modern multijet classification of the ACC, the survey area covered the zones of three jets of the South Polar Current (SPC), which is the middle branch of the ACC. The current jets revealed a fine horizontal thermohaline structure, which was manifested even in the case of the confluence of individual jets into a “superjet.”

Interaction of multiple atmospheric-pressure micro-plasma jets in small arrays: He/O2 into humid air

Arrays of atmospheric-pressure plasma jets are being considered as a means to increase the area being treated in surface modification and in plasma medicine in particular. A unique challenge of scaling plasma jet arrays is that individual plasma jets in an array tend to interact with each other, which can lead to quenching of some individual jets. To investigate these potential interactions, a computational study of one-, two- and three-tube arrays of micro-plasma jet arrays was performed. An atmospheric-pressure He/O2 = 99.8/0.2 mixture was flowed through the tubes into humid room air. We found that the jets interact through electrostatic, hydrodynamic and photolytic means. The hydrodynamic interactions result from the merging of individual He channels emerging from individual tubes as air diffuses into the extended gas jets. Ionization waves (IWs) or plasma bullets, which form the jets on the boundaries of an array, encounter higher mole fractions of air earlier compared with the center jet and so are slower or are quenched earlier. The close proximity of the jets produces electrostatic repulsion, which affects the trajectories of the IWs. If the jets are close enough, photoionizing radiation from their neighbors is an additional form of interaction. These interactions are sensitive to the spacing of the jets.

Experimental Research on the Attenuation Rules of Personalized Air-Conditioning Nozzle Jet Flow in Aircraft Cabins

A full size simulation laboratory aircraft cabin comprising three rows of seats has been built. This represents the Airbus A320 and the China C919 aircraft. Experimental research on the attenuation rule of the individual air-conditioning isothermal jet flow from nozzles positioned above the seats was conducted. The results show that axial air velocity continuously decreases with increasing cross-sectional distance. For a distance x < 0.4 m, (the axis air velocity sharp attenuation area), the velocity of attenuation slows. When 0.7 m x < 0.9 m, the velocity remains at about 1m.s-1 with the vents fully open, and at about 0.5 m.s-1 with the vents half open. The air velocity distribution of different cross-sections is axisymmetric and basically in line with the circular outlet jet flow rule. Combined with empirical formulae, the turbulent coefficient values of the isothermal jet flow in the airplane cabin was established as 0.1021 with the vents fully open and 0.1776 with the vents half open. The spread angles α of jet flow for these two conditions were found to be 19.14° and 31.12° respectively. The axial velocity attenuation rule was also confirmed. The experimental results align with those anticipated by calculation.

Twisted symmetry in multiple impingement jets at low Reynolds number

In this study, the cooling effect of nine confined jets arranged in square in-line array is investigated experimentally. The individual jet diameter is 3 mm, the jet-to-jet spacing ratio is two times as much as the jet diameter and the jet-to-plate spacing varies from 1 to 4 times as much as the jet diameter. The jet Reynolds number varies up to 880. An infrared camera is used for quantitative temperature measurement on the rear face of the impingement plate and a PIV system is installed to obtain the velocity field on different planes. The results show a twisted symmetry pattern of the flow field and heat transfer on the impingement plate when the confined ratio equals to jet-to-jet spacing ratio. This condition is produced only for the square in line array configuration and is due to the different interactions of central jet with lateral and corner jets.

Experimental investigation on behavior of multiple vertical buoyant jets discharged into a stagnant ambient

The behavior of merging buoyant jets discharged from uni-directional diffuser has been examined considering the interaction of individual axi-symmetric jets. Some series of experiments have been performed to define the range of merging transition based on the variations of local flow properties. The properties for the large eddies on the boundaries; passing frequency, vortex spacing, and Strouhal number, are also measured to investigate the evolution of individual jets to a merged flow. The results of this study show that the local flow properties change from those of axi-symmetric to merged flow over a merging transition where b/ps = 0.3 to 1.2. The flapping motion is observed as the individual jets get merged with neighboring ones. After the merging transition (b/ps = 0.3 to 1.2), the flows show a typical behavior of plane flows with a constant value of Strouhal number.

High-order harmonic generation from a dual-gas, multi-jet array with individual gas jet control

We present a gas jet array for use in high-order harmonic generation experiments. Precise control of the pressure in each individual gas jet has allowed a thorough investigation into mechanisms contributing to the selective enhancement observed in the harmonic spectra produced by dual-gas, multi-jet arrays. Our results reveal that in our case, the dominant enhancement mechanism is the result of a compression of the harmonic-producing gas jet due to the presence of other gas jets in the array. The individual control of the gas jets in the array also provides a promising method for enhancing the harmonic yield by precise tailoring of the length and pressure gradient of the interaction region.

Causal connection in parsec-scale relativistic jets: results from the MOJAVE VLBI survey

We report that active galactic nucleus (AGN) jets are causally connected on parsec scales, based on 15 GHz Very Long Baseline Array (VLBA) data from a sample of 133 AGN jets. This result is achieved through a new method for measuring the product of the jet Lorentz factor and the intrinsic opening angle Gamma*theta_j from measured apparent opening angles in flux density limited samples of AGN jets. The Gamma*theta_j parameter is important for jet physics because it is related to the jet-frame sidewise expansion speed and causal connection between the jet edges and its symmetry axis. Most importantly, the standard model of jet production requires that the jet be causally connected with its symmetry axis, implying that Gamma*theta_j < 1. When we apply our method to the MOJAVE flux density limited sample of radio loud objects, we find Gamma*theta_j = 0.2, implying that AGN jets are causally connected. We also find evidence that AGN jets viewed very close to the line of sight effectively have smaller intrinsic opening angles compared with jets viewed more off-axis, which is consistent with Doppler beaming and a fast inner spine/slow outer sheath velocity field. Notably, gamma-ray burst (GRB) jets have a typical Gamma*theta_j that is two orders of magnitude higher, suggesting that different physical mechanisms are at work in GRB jets compared to AGN jets. A useful application of our result is that a jet's beaming parameters can be derived. Assuming Gamma*theta_j is approximately constant in the AGN jet population, an individual jet's Doppler factor and Lorentz factor (and therefore also its viewing angle) can be determined using two observable quantities: apparent jet opening angle and the apparent speed of jet components.

Performance of jet substructure techniques for large-R jets in proton-proton collisions at $ \sqrt{s}=7 $ TeV using the ATLAS detector

Abstract This paper presents the application of a variety of techniques to study jet substructure. The performance of various modified jet algorithms, or jet grooming techniques, for several jet types and event topologies is investigated for jets with transverse momentum larger than 300 GeV. Properties of jets subjected to the mass-drop filtering, trimming, and pruning algorithms are found to have a reduced sensitivity to multiple proton-proton interactions, are more stable at high luminosity and improve the physics potential of searches for heavy boosted objects. Studies of the expected discrimination power of jet mass and jet substructure observables in searches for new physics are also presented. Event samples enriched in boosted W and Z bosons and top-quark pairs are used to study both the individual jet invariant mass scales and the efficacy of algorithms to tag boosted hadronic objects. The analyses presented use the full 2011 ATLAS dataset, corresponding to an integrated luminosity of 4.7 ± 0.1 fb−1 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy of $ \sqrt{s}=7 $ TeV.

Computational Aerodynamic Predictions of Supersonic Retropropulsion Flowfields

Supersonic retropropulsion, or the initiation of a retropropulsion phase at supersonic freestream conditions, is an enabling decelerator technology for high-mass planetary entries at Mars. Supersonic retropropulsion relies on retrothrust to decelerate the vehicle. A thrust-driven interaction of underexpanded jet flow with the shock layer of a blunt body alters the aerodynamic characteristics of the vehicle. Little literature exists on analytical and computational modeling approaches for supersonic aerodynamic-propulsive interactions at moderate thrust levels and flight-relevant conditions. This investigation is an exploratory application of a steady, turbulent computational approach to supersonic retropropulsion flowfields using modern and historical test cases. The results obtained from this approach agree reasonably well with experimental data for the locations of the bow shock, stagnation point, and Mach disk for a retropropulsion configuration with a single nozzle at the nose. The surface pressure distributions agree less favorably, showing a pressure rise toward the shoulder that was not observed in the original experiment. The flowfield structures for a peripheral retropropulsion configuration agree qualitatively with the expected structures, but proper inboard jet flow expansion and interactions between individual jet flows are likely not being captured; accordingly, pressure is preserved inboard of the nozzles to higher thrust than was observed experimentally.

Time resolved characteristics of gaseous jet injected by a group-hole nozzle

In this study, we investigate the evolution of a transient gaseous helium jet issuing from a multi-hole fuel injector at pressure ratios of 2, 3, 4 and 5. High speed Schlieren was used to visualize the jet development process and a digital edge detection method applied to determine time resolved jet penetration and tip speed. Both near and far field regions of the jet were investigated. Measurement of jet tip axial penetration and speed revealed that jet formation is comprised of three stages: emergence of individual jets, merging individual jets into the final stage of a merged single jet and penetration of the single merged jet. Penetration of the jet tip was found to be more sensitive to nozzle pressure ratio while the jet spread showed sensitivity to the stage of the jet evolution. Little sensitivity in jet parameters was found for the jet emergence and merge stages where it is likely that nozzle-opening processes play an important role. Scaling of the jet parameters based on those typical of free jets revealed the single merged jet to be similar to that of a free jet, although the form of the scaling depends on the parameters used to define the nozzle diameter and jet speed.

Planar Laser-Induced Fluorescence of Mars Science Laboratory Reaction Control System Jets

Nitric-oxide planar laser-induced fluorescence was used to visualize the flow in the wake of a Mars Science Laboratory entry capsule with activated reaction control system jets in NASA Langley Research Center’s 31 in. Mach 10 air tunnel facility. Images were processed using the virtual diagnostics interface method, which brings out the three-dimensional nature of the flow visualization data while showing the relative location of the data with respect to the model. Comparison of wind-on and wind-off results illustrates the effect that the hypersonic crossflow has on the trajectory and structure of individual reaction control system jets. The visualization and comparison of both single and multiple activated jets indicate low levels of jet–jet interaction. Quantitative streamwise velocity was also obtained via molecular tagging velocimetry.

Merging of high speed argon plasma jets

Formation of an imploding plasma liner for the plasma liner experiment (PLX) requires individual plasma jets to merge into a quasi-spherical shell of plasma converging on the origin. Understanding dynamics of the merging process requires knowledge of the plasma phenomena involved. We present results from the study of the merging of three plasma jets in three dimensional geometry. The experiments were performed using HyperV Technologies Corp. 1 cm Minirailguns with a preionized argon plasma armature. The vacuum chamber partially reproduces the port geometry of the PLX chamber. Diagnostics include fast imaging, spectroscopy, interferometry, fast pressure probes, B-dot probes, and high speed spatially resolved photodiodes, permitting measurements of plasma density, temperature, velocity, stagnation pressure, magnetic field, and density gradients. These experimental results are compared with simulation results from the LSP 3D hybrid PIC code.

A Three-decade X-band VLBI Study of 3CR Lobe-dominated Quasar Nuclei

We report X-band VLBI observations of several 3CR lobe-dominated quasar nuclei from 1981 to 2010, mostly obtained with the NRAO VLBA. The goal is to follow flux density outbursts and to fully determine the jet morphology and kinematics on 1-100 pc scales. In 3C207, the core region has flux outbursts at mean intervals of ~7 yr; one of these is actually a double outburst from a stationary true core and a swinging component ~0.5 mas apart. The position angle (PA ) of the swinging component varies by ~40°, while the PA values of the jet components span ~25°. The jet extends to ~25 mas. Average superluminal speeds are ~10c . One component shows apparent acceleration from 7c to 14c at 2-3 mas from the true core, in a jet recollimation zone that redirects the flow toward PA ~90°. Individual jet components expand until reaching the recollimation zone. In 3C263 and other objects, some of the same phenomena are seen, including ejection of jet components over a range in PA , superluminal motion, and apparent acceleration, but to a lesser degree. Possible physical interpretations involving beaming, orientation, projection, precession, and magnetic effects are discussed.

MULTIPLE PLASMA EJECTIONS AND INTERMITTENT NATURE OF MAGNETIC RECONNECTION IN SOLAR CHROMOSPHERIC ANEMONE JETS

The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are about 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of ~4 km s–1. In some events, a downward moving blob with a speed of ~35 km s–1 was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.

Dynamic interaction of multiple buoyant jets

AbstractAn array of closely spaced round buoyant jets interact dynamically due to the pressure field induced by jet entrainment. Mutual jet attraction can result in a significant change in jet trajectories. Jet merging also leads to overlapping of the passive scalar fields associated with the individual jets, resulting in mixing characteristics that are drastically different from those of an independent free jet. A general semi-analytical model for the dynamic interaction of multiple buoyant jets in stagnant ambient conditions is proposed. The external irrotational flow field induced by the buoyant jets is computed by a distribution of point sinks with strength equal to the entrainment per unit length along the unknown jet trajectories and accounting for boundary effects. The buoyant jet trajectories are then determined by an iterative solution of an integral buoyant jet model by tracking the changes in the external entrainment flow and dynamic pressure fields. The velocity and concentration fields of the jet group are obtained by momentum or kinetic energy superposition for merged jets and plumes, respectively. The modelling approach is supported by numerical solution of the Reynolds-averaged Navier–Stokes equations. The model shows that jet merging and mixing can be significantly affected by jet interactions. Model predictions of the multiple jet trajectories, merging height, as well as the centreline velocity and concentration of the buoyant jet group are in good agreement with experimental data for: (i) a clustered momentum jet group; (ii) a turbulent plume pair; and (iii) a rosette buoyant jet group. Dynamic interactions between a jet group are shown to decrease with the addition of an ambient cross-flow.

Liquid film falling behaviour on horizontal circular cylinder

The flow pattern behaviour of falling liquid film over three horizontal cylinders was evaluated. These flows can take three forms: discrete droplets, individual jets, and continuous sheet, and special attention is paid to the effects of the physical properties and geometrical parameters of the first two forms (droplets and jets) because these forms are more important in heat-transfer behaviour and less research has been published for these forms. The flow modes and experimental results were successfully compared with previous experimental literatures, and also the effects of liquid flow rate, tube diameter, and tube spacing on departure site spacing, in both drop and jet modes, were evaluated in the low Galileo number and high viscosity fluid (cooking oil), to help developing criteria for determining falling film modes and their transitions, and to understand the heat transfer characteristics associated with each mode.

Factorization and resummation for dijet invariant mass spectra

Multijet cross sections at the LHC and Tevatron are sensitive to several distinct kinematic energy scales. When measuring the dijet invariant mass ${m}_{jj}$ between two signal jets produced in association with other jets or weak bosons, ${m}_{jj}$ will typically be much smaller than the total partonic center-of-mass energy $Q$, but larger than the individual jet masses $m$, such that there can be a hierarchy of scales $m\ensuremath{\ll}{m}_{jj}\ensuremath{\ll}Q$. This situation arises in many new-physics analyses at the LHC, where the invariant mass between jets is used to gain access to the masses of new-physics particles in a decay chain. At present, the logarithms arising from such a hierarchy of kinematic scales can only be summed at the leading-logarithmic level provided by parton-shower programs. We construct an effective field theory, ${\mathrm{SCET}}_{+}$, which is an extension of soft-collinear effective theory that applies to this situation of hierarchical jets. It allows for a rigorous separation of different scales in a multiscale soft function and for a systematic resummation of logarithms of both ${m}_{jj}/Q$ and $m/Q$. As an explicit example, we consider the invariant mass spectrum of the two closest jets in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}3$ jets. We also give the generalization to $pp\ensuremath{\rightarrow}N$ jets plus leptons relevant for the LHC.

Experimental study on solid circulation in a multiple jet fluidized bed

AbstractParticle image velocimetry was used to investigate the evolution of multiple inlet gas jets located at the distributor base of a two‐dimensional fluidized bed setup. Results were used to estimate the solid circulation rate of the fluidized bed as well as particle‐entrainment into the individual jets. The effects of fluidization velocity, orifice diameter, orifice pitch, particle diameter, and particle density were studied. It was determined from this study that the solid circulation rate linearly increased with an increase in the fluidization velocity until the multiple jet system transitioned from isolated to an interacting system. In the interacting system of jets, the solid circulation increased with fluidization velocity but at a much lower rate. For multiple jet systems, this phenomenon may indicate the presence of an optimum operating condition with high circulation rate and low air input in the bed. © 2011 American Institute of Chemical Engineers AIChE J, 58: 3003–3015, 2012

Atmospheric-Pressure Microplasma Jets From Linear Arrays of Hollow-Core Optical Fibers for Biomedical Applications

Atmospheric-pressure microplasma jets from a linear array of five hollow-core optical fibers are described. All plasma plumes from the array were quite narrow but long enough to apply the direct treatments to a very small object. The optical intensities from five individual plasma jets were also stable and had a good uniformity. The variation of the optical intensities of individual plasma plumes was within 15%. This plurality of the small-sized plasma jets can be utilized to target some groups of different cells simultaneously in an in vitro biomedical application.

Mathematical modelling of abrasive waterjet footprints for arbitrarily moving jets: Part I—single straight paths

It is notoriously well-known that abrasive waterjet milling (AWJM) is difficult to perform controlled-depth owing to variable geometries of the footprints that depends not only on jet energy and the exposure time upon the workpiece, but also on the orientation of the jet relative to the target surface. An attempt is made to develop a model that can be generally applied to different machine system and to predict individual jet footprints that are one of the key steps for controlled-depth AWJM. To address this, the paper breaks new ground in geometrical modelling of AWJM with the benefit of having few variables for predicting the footprints obtained under the following conditions: (i) any time exposures (i.e. V f , jet feed speeds); (ii) jet orientations ( θ) relative to the target surface; (iii) arbitrarily moving straight jet-paths ( β). These conditions reflect the real industrial conditions under which the process is run. The geometrical model results in a non-linear partial differential equation, a method to evaluate the material specific erosion rate from the characteristics of a shallow trench obtained experimentally using high jet feed speeds. Under these conditions, the governing equations can be linearised and solved analytically. The model validation for full profile of trenches generated at various tilt angles ( θ=70–90°), jet feed rates ( V f =500–1000 mm/min) and jet path directions ( β=0–270°) indicates that a high degree of accuracy (mean of the residuals R M <3% and root-mean-square error of residuals R RMS<6%) has been achieved. This innovative footprint modelling approach has the key advantage of being independent of the properties of the workpiece material and/or machine setup, since it calibrates the specific etching rate. By considering any orientation of the jet plume vector relative to the target surface, this approach becomes a powerful tool for the development of advanced jet path strategies to enable AWJM of complex geometries.