Jet Shape Research Articles

Picturing QCD jets in anisotropic matter: from jet shapes to energy energy correlators

Recent theoretical developments in the description of jet evolution in the quark gluon plasma have allowed to account for the effects of hydrodynamic gradients in the medium modified jet spectra. These constitute a crucial step towards using jets as tomographic probes of the nuclear matter they traverse. In this work, we complement these studies by providing leading order calculations of widely studied jet observables, taking into account matter anisotropies. We show that the energy distribution inside a jet is pushed towards the direction of the largest matter anisotropy, while the away region is depleted. As a consequence, the jet mass and girth gain a non-trivial azimuthal dependence, with the average value of the distribution increasing along the direction of largest gradients. However, we find that, for these jet shapes, matter anisotropic effects can be potentially suppressed by vacuum Sudakov factors. We argue that the recently proposed measurements of energy correlations within jets do not suffer from such effects, with the azimuthal dependence being visible in a large angular window, regardless of the shape of the distribution.

Numerical modelling and experimental validation of dripping, jetting and whipping modes of gas dynamic virtual nozzle

PurposeThis study aims to develop an experimentally validated three-dimensional numerical model for predicting different flow patterns produced with a gas dynamic virtual nozzle (GDVN).Design/methodology/approachThe physical model is posed in the mixture formulation and copes with the unsteady, incompressible, isothermal, Newtonian, low turbulent two-phase flow. The computational fluid dynamics numerical solution is based on the half-space finite volume discretisation. The geo-reconstruct volume-of-fluid scheme tracks the interphase boundary between the gas and the liquid. To ensure numerical stability in the transition regime and adequately account for turbulent behaviour, the k-ω shear stress transport turbulence model is used. The model is validated by comparison with the experimental measurements on a vertical, downward-positioned GDVN configuration. Three different combinations of air and water volumetric flow rates have been solved numerically in the range of Reynolds numbers for airflow 1,009–2,596 and water 61–133, respectively, at Weber numbers 1.2–6.2.FindingsThe half-space symmetry allows the numerical reconstruction of the dripping, jetting and indication of the whipping mode. The kinetic energy transfer from the gas to the liquid is analysed, and locations with locally increased gas kinetic energy are observed. The calculated jet shapes reasonably well match the experimentally obtained high-speed camera videos.Practical implicationsThe model is used for the virtual studies of new GDVN nozzle designs and optimisation of their operation.Originality/valueTo the best of the authors’ knowledge, the developed model numerically reconstructs all three GDVN flow regimes for the first time.

Transition of Edney shock–shock interactions due to the whipping phenomenon of liquid jet in supersonic crossflow

In this paper, we experimentally study the unsteady dynamics of shock–shock interaction between the bow shock generated by a liquid jet in supersonic crossflow (LJISC) and an oblique shock. Images of shock–shock interactions were captured using high-speed focusing schlieren. Due to the whipping nature of the liquid jet, a coupling happens between the instantaneous bow shock shape and violent oscillations of the liquid jet. Proper orthogonal decomposition reveals that the dominant coherent structures of LJISC are convective and flapping modes, and these modes are responsible for unsteady variation in the local bow shock angle. An oblique shock emanating from a wedge is made to interact with the oscillating bow shock of a liquid jet near the sonic line. At this shock interaction location and for a constant momentum flux ratio between liquid jet and crossflow, unsteady transitions between the types of Edney shock–shock interactions were observed. The types of Edney shock–shock interactions that can occur depend on the local average bow shock angle and the momentum flux ratio. Support vector machine (SVM) model was used to classify three types of Edney shock–shock interactions based on ten features related to the nearest knee point, shock interaction point, and maximum penetration height. Using the SVM model, three dominant features that affect the type of shock–shock interaction were identified. Experimental results, when compared with shock polar, reveal some short-duration abnormal presence of overall regular interaction instead of overall Mach interaction regime.

Effect of vent area on vented ammonia-hydrogen-air deflagrations in a 1-m-long duct

Although ammonia-hydrogen blended fuel has become a research hotspot, it is essential to recognize that adding hydrogen to ammonia increases the potential explosion hazard before considering the development of ammonia-hydrogen fuel. In this study, the effect of vent area on vented deflagrations of ammonia-hydrogen-air mixtures is investigated in a 1-m-long horizontal rectangular duct with a right end opening at an initial temperature of 293 K and an initial pressure of 101 kPa. A dimensionless vent coefficient Kv is used to define the vent area in this work to clarify the evolution of flame structures and overpressure inside and outside the duct. For a specific Kv, the amplitude of the maximum internal explosion overpressure (Pmax) monitored at the left end of the duct (LE) has a greater difference compared with other pressure monitoring points. The maximum amplitude of Pmax is always reached at the LE for Kv ≤ 3.2, while the difference in the maximum amplitude of Pmax between different monitoring points decreased significantly for Kv > 3.2. With the increasing of Kv from 2.2 to 20.1, Pmax obtained at the right end of the duct (RE) and the center of the duct increases monotonously, but Pmax monitored at the LE shows a non-monotonic increasing trend. A spike structure of penetrating flame bubbles resulting from negative pressure balance is only observed inside the duct for Kv ≤ 5.6. Two types of oscillations (Helmholtz and Acoustic oscillations) can be distinguished in some tests, and only acoustic oscillations of overpressure can be clearly found in tests with Kv > 7.8. With the increasing of Kv from 2.2 to 20.1, the shape of the external fireball will change significantly. As Kv increases from 2.2 to 5.6, the external fireball shapes are always mushroom-shaped. However, the shapes of the fireball become elongated for Kv > 7.8, and even the external fireball presents a jet shape for Kv = 20.1. With the increasing of Kv from 2.2 to 20.1, The maximum external overpressure increases first, thereafter decreases, and finally increases.

Influence of impingement jet designs on solar air collector performance

The present work shows the impact of jet shapes and absorber plate spacing on the performance of heat transfer and pressure drop in solar air collectors experimentally. Absorber wall temperature, outlet temperature, useful heat gain, Nusselt number, friction factor, and thermal-hydraulic performance (THP) are the parameters under investigation. The experiment is conducted at heat fluxes of 900 W/m2 and 1000 W/m2, and Reynolds numbers ranging from 3000 to 19000. The results indicate that, in comparison to the Nusselt numbers for square and triangular jets, the Nusselt number for the circular jet is greater by 11.64% and 18.94%, respectively. The average useful heat gain of the circular jet is 6.45% higher than that of the square jet and 15.19% higher than that of the triangular jet. The maximum useful heat gain is provided by lower absorber plate spacing values. When the ratio of absorber plate spacing to jet diameter is 3.3, the THP for circular and triangular jets is 0.96 and 1.04, respectively. As a function of the geometrical and flow characteristics, the jet's Nusselt number and friction factor correlations are proposed, which forecast the current experimental findings.

Jet modification in absence of QGP-medium: the role of multiparton interactions and color reconnection* *D. Banerjee acknowledges the Inspire Fellowship research grant (DST/INSPIRE Fellowship/2018/IF180285)

Recent studies on high-multiplicity events in small collision systems (proton-proton and proton-lead) have drawn considerable research interest toward the possibility of the formation of partonic medium in such systems. One of the important consequences of the formation of dense partonic medium is the quenching of high-momentum final-state particles, resulting in several experimental observations such as suppression in nuclear modification factor , modification of jet shape observable and jet fragmentation ( ) distributions, etc. In this work, we study and for inclusive charged-particle jets in proton-proton (pp) collisions at = 13 TeV using the PYTHIA 8 Monash 2013 Monte Carlo simulation. We show that the color reconnection (CR) and multiparton interaction (MPI) mechanisms in PYTHIA 8 can lead to an increased rate of jet production. We also find that the mechanisms of MPI and CR and change in the gluonic contribution in high-multiplicity events result in significant modification of and compared to those in minimum bias events for 10 20 GeV/c. We notice a direct connection of and gluonic contribution with the amount of modification in : the larger the number of MPIs and/or gluonic contribution, the larger the amount of modification of .

Kinematics and Collimation of the Two-sided Jets in NGC 4261: VLBI Study on Subparsec Scales

We report multifrequency VLBI studies of the subparsec scale structure of the two-sided jets in the nearby radio galaxy NGC 4261. Our analyses include new observations using the source frequency phase referencing technique with the Very Long Baseline Array at 44 and 88 GHz, as well as archival data at 15 and 43 GHz. Our results show an extended double-sided structure at 43/44 GHz and provide a clear image of the nuclear region at 88 GHz, showing a core size of ∼0.09 mas and a brightness temperature of ∼1.3 × 109 K. Proper motions are measured for the first time in the two-sided jets, with apparent speeds ranging from 0.31 ± 0.14 c to 0.59 ± 0.40 c in the approaching jet and 0.32 ± 0.14 c in the receding jet. The jet-to-counterjet brightness ratio allows us to constrain the viewing angle to between ∼54° and 84° and the intrinsic speed to between ∼0.30 c and 0.55 c. We confirm the parabolic shape of the upstream jet on both sides of the central engine, with a power-law index of 0.56 ± 0.07. Notably, the jet collimation is found to be already completed at subparsec scales, with a transition location of about 0.61 pc, which is significantly smaller than the Bondi radius of 99.2 pc. This behavior can be interpreted as the initial confinement of the jet by external pressure from either the geometrically thick, optically thin advection-dominated accretion flows or the disk wind launched from it. Alternatively, the shape transition may also be explained by the internal flow transition from a magnetically dominated to a particle-dominated regime.

Numerical simulation and experimental study of optimized jet shape in electric arc electrochemical composite machining

A favorable flow field enhances the product transport capacity and also increases the electrochemical mass transfer rate. In this paper, an end-side connected electrode suitable for electric arc electrochemical composite milling was proposed based on the existing flushing form. The aim is to simultaneously enhance the machining of the groove surface and the side. The flushing form was optimized by the flow field, and it was shown that the internal flushing increased the area of the high flow rate zone of the bottom gap. In the experiments, it was found that the internal flushing reduced the secondary discharge probability, the accumulation of re-solidified material on the groove surface was decreased, and the surface dissolution was uniform with low oxidation. However, the central jet is lost along the course and a zero velocity zone exists at the corners of the groove. Therefore, the sidewall open flow field is proposed to reduce the sidewall recast layer. It was verified that the sidewall slots of the positive flow type improved both the surface quality of the groove surface and the side wall. It was also found that the increase in the number of open grooves facilitates the generation of uniform debris removal.

Optimal Injection Distance in Ultrasonic Water Flow Cleaning

Cleaning tests with ultrasound-superposed water jets are performed to explore the optimal injection distance from the jet nozzle to a glass plate spin-coated with small silica particles (as a cleaning sample). The cleaning performance is evaluated based on particle removal efficiency (PRE) that is calculated using the haze method. Visualization of the water jet and liquid film flow over the cleaning target shows that the jet flow with short injection distance tends to be in a steady state, while the water jet shape instability grows for long injection distance, leading to atomization of the jet. The cleaning tests with varying the injection distance suggest that there exists an optimal injection distance at which the PRE becomes maximal.

Search for medium effects using jets from bottom quarks in PbPb collisions at [formula omitted

The first study of the shapes of jets arising from bottom (b) quarks in heavy ion collisions is presented. Jet shapes are studied using charged hadron constituents as a function of their radial distance from the jet axis. Lead-lead (PbPb) collision data at a nucleon-nucleon center-of-mass energy of sNN=5.02TeV were recorded by the CMS detector at the LHC, with an integrated luminosity of 1.69nb−1. Compared to proton-proton collisions, a redistribution of the energy in b jets to larger distances from the jet axis is observed in PbPb collisions. This medium-induced redistribution is found to be substantially larger for b jets than for inclusive jets.

CMS pythia 8 colour reconnection tunes based on underlying-event data

New sets of parameter tunes for two of the colour reconnection models, quantum chromodynamics-inspired and gluon-move, implemented in the pythia 8 event generator, are obtained based on the default CMS pythia 8 underlying-event tune, CP5. Measurements sensitive to the underlying event performed by the CMS experiment at centre-of-mass energies sqrt{s}=7 and 13,text {Tehspace{-.08em}V}, and by the CDF experiment at 1.96,text {Tehspace{-.08em}V} are used to constrain the parameters of colour reconnection models and multiple-parton interactions simultaneously. The new colour reconnection tunes are compared with various measurements at 1.96, 7, 8, and 13,text {Tehspace{-.08em}V} including measurements of the underlying-event, strange-particle multiplicities, jet substructure observables, jet shapes, and colour flow in top quark pair ({{text {t}} {}{bar{text {t}}}}) events. The new tunes are also used to estimate the uncertainty related to colour reconnection modelling in the top quark mass measurement using the decay products of {{text {t}} {}{bar{text {t}}}} events in the semileptonic channel at 13,text {Tehspace{-.08em}V}.

Effect of 3D submerged jet shape on maximum pressure of plunge pool bottom

Effect of 3D submerged jet shape on maximum pressure of plunge pool bottom

The effect of gravity on self-similarity of Worthington jet after water entry of a two-dimensional wedge

The effect of gravity on the self-similarity of jet shape at late stage of Worthington jet development is investigated by experiment in the study. In addition, the particle image velocimetry (PIV) method is introduced to analyze the development of flow field. There is a linear scaling regarding the axial velocity of the jet and the scaling coefficient increases with the Froude number.

Flood-driven jet flow and sedimentary regime in a river-dominated estuary

Sediment dynamics under floods are critical for estuarine morphological evolution. A two-dimensional coupled hydrodynamic/sediment transport numerical modeling was adapted to investigate the flood-driven jet structure and the resultant sedimentary regime in a river-dominated estuary, Modaomen Estuary, Pearl River Delta, China. The results show that the flow velocity of flood jet exhibits a Gaussian distribution in the transverse direction and shows a linear decreasing trend in the longitudinal direction. Moreover, a distinct zonation, including a zone of flow establishment (ZOFE) and a zone of established flow (ZOEF), was detected. The ZOFE was the core area of high turbidity and strong erosion and provided sufficient sediments to the ZOEF, where sediment diffused and settled. Due to the settling lag, the sediment diffusion and deposition areas were larger than those of the jet. Estuarine geomorphology regulates the shape of flood jet, which shows an asymmetry configuration with the main body located at the west side of the bifurcated estuary. Tidal dynamics play a crucial role in altering the range of jet diffusion, especially in the longitudinal direction. Increased flood intensity has little effect on the jet structure and erosion/deposition pattern, but significantly increases the magnitude of seaward current velocities and bed level changes, as well as the transverse diffusion range of jet and sedimentation.

Jet substructure in neutral current deep inelastic e+p scattering at the upcoming Electron-Ion Collider

Predictions are made for the jet substructure of one-jet events produced in electron-proton neutral current deep inelastic scattering at the future Electron-Ion Collider for exchanged four-momentum squared, $Q^2 > 125$ GeV$^2$. Data are simulated using Monte Carlo event generators PYTHIA 8.304 and RAPGAP 3.308 at the center of mass energies $\sqrt{s}$ = 63.2, 104.9 and 141 GeV. Jets and subjets are produced by longitudinally invariant $k_T$ cluster algorithm. The subjet multiplicity distributions and differential jet shapes are measured for different jet sizes and varying jet-resolution parameter. A comparison is presented between the $k_T$ and anti-$k_T$ cluster algorithms for the study of jets and subjets using the simulated data and the HERA data.

Simulation Study on Jet Formation and Penetration Capability of Double-layer Cylinder-cone Shaped Charges with Different Outer Liner Materials

In order to discuss the effect of different outer liner material on the performance of the double cylinder-cone shaped charge, the nonlinear dynamics software Autodyn-2D was used to carry out numerical simulation, and the jet shape and penetration of steel target were analysed when copper, nickel, tungsten, tantalum and steel were used as outer liner materials and copper was used as inner cover material. The result shows that the jet head is formed by the cylindrical part of the inner liner, and all the outer liner forms a slug. The total length of the projectile is the longest when the outer liner material is copper. The jet head velocities are the biggest when the outer liner materials are nickel and steel 4340. The shaped charge with copper outer liner yields much longer depths.

Vertically neutral collapse of a pulsating bubble at the corner of a free surface and a rigid wall

Vertically neutral collapse of a pulsating bubble occurs when the boundaries above or below the bubble balance the buoyancy effect over a pulsation. In this study, the vertically neutral collapse of a bubble near a vertical rigid wall below the free surface is investigated. The boundary integral method (BIM) is employed to model the bubble dynamics with an open-domain free surface. Moreover, this method is validated against several buoyant bubble experiments. Bubble dynamics in such conditions are associated with three dimensionless parameters: the bubble-free surface distance $\gamma _{{f}}$ , bubble–wall distance $\gamma _{{w}}$ and buoyancy parameter $\delta$ . We derive the Kelvin impulse of a spherical bubble and the algebraic relationship for vertically neutral collapse, which proves to be accurate for predicting vertically neutral collapse when the bubble is relatively far from the boundaries. Four patterns of the vertically neutral collapse of the bubble for different $\gamma _{{w}}$ and $\gamma _{{f}}$ are identified: (i) formally downward jet; (ii) annular collapse; (iii) horizontal jet; and (iv) weak jet. Despite the downward jet shape, the ‘formally downward jet’ is in the vertically neutral collapse state in terms of the profile of toroidal bubbles and the orientation of local high-pressure zones around the bubble at jet impact. A bulge with a high curvature above the bubble in the ‘annular collapse’ pattern is formed during bubble collapse under two local high-pressure zones at the left and right extremities of the bubble. The ‘horizontal jet’ pattern has the greatest potential to attack the wall, and the power laws of the moment of the jet impact, jet velocity and bubble displacement with respect to the theoretical Kelvin impulse are discussed. In particular, we quantitatively illustrate the role of the free surface on bubble migration towards the wall through the variational power-law exponents of the bubble displacement with respect to $\gamma _{{w}}$ .

Smoothed particle hydrodynamics method for pinch plasma simulation with non-ideal MHD model

When plasma is compressed by magnetic forces, a pinch phenomenon is observed. Pinch plasma has received significant attention as an efficient source of radiation and a way for high-density plasma physics analysis. In this study, a non-ideal magnetohydrodynamics (MHD) model is applied to a smoothed particle hydrodynamics (SPH) framework to analyze pinch plasmas whose local resistivity varies with temperature and pressure. The proposed SPH model incorporates several numerical treatments, such as a correction term to satisfy the ∇·B constraint and some artificial dissipation terms to govern the shock wave. Moreover, it includes the evaluation of a novel SPH discretization for non-ideal MHD terms, including current density calculations. Furthermore, the proposed model is validated with three benchmark cases: (1) Brio and Wu shock tube (ideal MHD), (2) resistive MHD shock simulation, and (3) magnetized Noh Z-pinch problem. The simulation results are compared with the results of some reference Eulerian MHD simulations and analytical solutions. The simulations agree well with the reference data, and the introduced numerical treatments are effective. Finally, X-pinch simulations are performed using the proposed model. The simulations well produce the micro Z-pinch and jet shapes, which are important X-pinch features. Overall, the proposed SPH model has extensive potential for studying the complex pinch plasma phenomena.

Physics of moderately stretched electrified jets in electrohydrodynamic jet printing.

Electrohydrodynamic (EHD) jet printing involves the deposition of a liquid jet issuing from a needle stretched under the effect of a strong electric field between the needle and a collector plate. Unlike the geometrically independent classical cone-jet observed at low flow rates and high applied electric fields, at a relatively high flow rate and moderate electric field, EHD jets are moderately stretched. Jetting characteristics of such moderately stretched EHD jets differ from the typical cone-jet due to the nonlocalized cone-to-jet transition. Hence, we describe the physics of the moderately stretched EHD jet applicable to the EHD jet printing process through numerical solutions of a quasi-one-dimensional model of the EHD jet and experiments. Through comparison with experimental measurements, we show that our simulations correctly predict the jet shape for varying flow rates and applied potential difference. We present the physical mechanism of inertia-dominated slender EHD jets based on the dominant driving and resisting forces and relevant dimensionless numbers. We show that the slender EHD jet stretches and accelerates primarily due to the balance of driving tangential electric shear and resisting inertia forces in the developed jet region, whereas in the vicinity of the needle, driving charge repulsion and resisting surface tension forces govern the cone shape. The findings of this study can help in operational understanding and better control of the EHD jet printing process.

Time variability of the core-shift effect in the blazar 3C 454.3

Measuring and inferring the key physical parameters of jets in active galactic nuclei (AGN) requires high-resolution very long baseline interferometry (VLBI) observations. Using VLBI to measure a core-shift effect is a common way of obtaining estimates of the jet magnetic field strength, a key parameter for understanding jet physics. The VLBI core is typically identified as the bright feature at the upstream end of the jet, and the position of this feature changes with the observed frequency, rcore ∝ ν−1/kr. Due to the variable nature of AGN, flares can cause variability of the measured core shift. In this work, we investigated the time variability of the core-shift effect in the luminous blazar 3C 454.3. We employed a self-referencing analysis of multi-frequency (5, 8, 15, 22−24, and 43 GHz) Very Long Baseline Array (VLBA) data covering 19 epochs from 2005 to 2010. We found significant core-shift variability ranging from 0.27 to 0.86 milliarcsec between 5 GHz and 43 GHz. These results confirm the core-shift variability phenomenon observed previously. Furthermore, we also found time variability of the core-shift index, kr, which was typically below one, with an average value of 0.85 ± 0.08 and a standard deviation of 0.30. Values of kr below one were found during flaring and quiescent states. Our results indicate that the commonly assumed conical jet shape and equipartition conditions do not always hold simultaneously. Even so, these conditions are typically assumed when deriving magnetic field strengths from core-shift measurements, which can lead to unreliable results if kr significantly deviates from unity. Therefore, it is necessary to verify that kr = 1 actually holds before using core-shift measurements and the equipartition assumption to derive physical conditions in the jets. When kr = 1 epochs are selected in the case of 3C 454.3, the magnetic field estimates are consistent, even though the core shift varies significantly with time. Subsequently, we estimated the magnetic flux in the jet of 3C 454.3 and found that the source is in the magnetically arrested disc state, which agrees with earlier studies. Finally, we found a good correlation of the core position with the core flux density, rcore ∝ Score0.7, which is consistent with increased particle density during the flares.