Development Of Jet Research Articles

Hard jet substructure in a multistage approach

We present predictions and postdictions for a wide variety of hard jet-substructure observables using a multistage model within the framework. The details of the multistage model and the various parameter choices are described in []. A novel feature of this model is the presence of two stages of jet modification: a high-virtuality phase [modeled using the modular all twist transverse-scattering elastic-drag and radiation model ()], where modified coherence effects diminish medium-induced radiation, and a lower virtuality phase [modeled using the linear Boltzmann transport model ()], where parton splits are fully resolved by the medium as they endure multiple scattering induced energy loss. Energy-loss calculations are carried out on event-by-event viscous fluid dynamic backgrounds constrained by experimental data. The uniform and consistent descriptions of multiple experimental observables demonstrate the essential role of modified coherence effects and the multistage modeling of jet evolution. Using the best choice of parameters from [], and with no further tuning, we present calculations for the medium modified jet fragmentation function, the groomed jet momentum fraction zg and angular separation rg distributions, as well as the nuclear modification factor of groomed jets. These calculations provide accurate descriptions of published data from experiments at the Large Hadron Collider. Furthermore, we provide predictions from the multistage model for future measurements at the BNL Relativistic Heavy Ion Collider. Published by the American Physical Society 2024

Late-time X-Ray Observations of the Jetted Tidal Disruption Event AT2022cmc: The Relativistic Jet Shuts Off

The tidal disruption event (TDE) AT2022cmc represents the fourth known example of a relativistic jet produced by the tidal disruption of a stray star, providing a unique probe of the formation and evolution of relativistic jets in otherwise dormant supermassive black holes (SMBHs). Here we present deep, late-time Chandra observations of AT2022cmc extending to t obs ≈ 400 days after disruption. Our observations reveal a sudden decrease in the X-ray brightness by a factor of ≳14 over a factor of ≈2.3 in time, and a deviation from the earlier power-law decline with a steepening α ≳ 3.2 (F X ∝ t −α ), steeper than expected for a jet break, and pointing to the cessation of jet activity at t obs ≈ 215 days. Such a transition has been observed in two previous TDEs (Swift J1644+57 and Swift J2058+05). From the X-ray luminosity and the timescale of jet shut-off, we parameterize the mass of the SMBH in terms of unknown jet efficiency and accreted mass fraction parameters. Motivated by the disk–jet connection in active galactic nuclei, we favor black hole masses ≲105 M ⊙ (where the jet and disk luminosities are comparable), and disfavor larger black holes (in which extremely powerful jets are required to outshine their accretion disks). We additionally estimate a total accreted mass of ≈0.1 M ⊙. Applying the same formalism to Swift J1644+57 and Swift J2058+05, we favor comparable black hole masses for these TDEs of ≲ a few × 105 M ⊙, and suggest that jetted TDEs may preferentially form from lower-mass black holes when compared to nonrelativistic events, owing to generally lower jet and higher disk efficiencies at higher black hole masses.

Structured Jet Model for Multiwavelength Observations of the Jetted Tidal Disruption Event AT 2022cmc

AT 2022cmc is a recently documented tidal disruption event that exhibits a luminous jet, accompanied by fast-declining X-ray and long-lasting radio and millimeter emission. Motivated by the distinct spectral and temporal signatures between the X-ray and radio observations, we propose a multizone model involving relativistic jets with different Lorentz factors. We systematically study the evolution of faster and slower jets in an external density profile, considering the continuous energy injection rate associated with time-dependent accretion rates before and after the mass fallback time. We investigate time-dependent multiwavelength emission from both the forward shock (FS) and reverse shock (RS) regions of the fast and slow jets, in a self-consistent manner. Our analysis demonstrates that the energy injection rate can significantly impact the jet evolution and subsequently influence the lightcurves. We find that the X-ray spectra and lightcurves could be described by electron synchrotron emission from the RS of the faster jet, in which the late-time X-ray upper limits, extending to 400 days after the disruption, could be interpreted as a jet break. Meanwhile, the radio observations can be interpreted as a result of synchrotron emission from the FS region of the slower jet. We also discuss prospects for testing the model with current and future observations.

Fluid–structure interaction analysis of curved wedges entering into water

The water entry of wedges with curvature differs significantly from that of linear wedges, which have been fully investigated and formulated. The safety and integrity of structures prompt an urgent investigation into the mechanism by which the curvature affects slamming loads and structural responses during water entry. This study examines the slamming force characteristics, pressure distributions, fluid jet evolutions, and structural response behaviors of two-dimensional curved wedge sections, considering five different curvatures and two panel thicknesses. A two-way coupling fluid–structure interaction (FSI) solver has been proposed within an open-source framework. The FSI solver was validated against published literature to ensure its high-fidelity. The small deadrise angle results in a more complicated time-domain characteristics for the slamming pressure, with a gradual transition from a single peak to a double peak. The half-peak pressure duration time were defined, and the quantitative results reveal that the hydroelastic effect of the linear wedge is significantly higher than the curved wedges. When considering the geometric curvature, the elastic wedges do not consistently reduce the peak slamming pressure and lengthen the pulse time. Additionally, large deformations generated by the panel vibrations alter the evolutionary pattern of the fluid jet. In contrast to the linear wedge, the structural responses of the curved wedges show distinctive two-stage behaviors.

Multi-scale flow atomization characteristics of Jatropha biodiesel swirl liquid film breakup

The characteristics of the spray and droplets produced by liquid film breakup are crucial for understanding the atomization process in industrial furnace atomizers. This study employed high-speed camera technology to capture images of Jatropha biodiesel (JB) spray at various pressures and Ohnesorge numbers (Oh). Image processing methods were employed to analyze the evolution morphology and proper orthogonal decomposition (POD) of fuel swirl spray, revealing the instability, breakup length, spray cone angle, fractal characteristics of the liquid film breakup zone, and droplet distribution characteristics. The results indicated that the JB jet evolution progressed through stages: cylindrical jet, torsion liquid film, open swirl, complete swirl, and fully developed mode. The evolution and disintegration of the liquid film exhibited a complex structure with ligaments, perforations, and droplet separation. Flow disturbances induced the Klystron effect, characterizing microscopic droplet motion. As spray pressure increased, the growth rate of the disturbance wave increased, the breakup length decreased, the atomization cone angle enlarged, and the fractal dimension (FD) of the liquid film breakup zone increased. The droplet size distribution followed a log-normal distribution, with a substantial increase in the number of small droplets as injection pressure increased. This study provides valuable insights into the multi-scale flow atomization of biodiesel in industrial furnace, and is of great significance for the design, operation, and optimization of spraying systems in various industrial applications.

Observation of Enhanced Long-Range Elliptic Anisotropies Inside High-Multiplicity Jets in pp Collisions at sqrt[s]=13 TeV.

A search for collective effects inside jets produced in proton-proton collisions is performed via correlation measurements of charged particles using the CMS detector at the CERN LHC. The analysis uses data collected at a center-of-mass energy of sqrt[s]=13 TeV, corresponding to an integrated luminosity of 138 fb^{-1}. Jets are reconstructed with the anti-k_{T} algorithm with a distance parameter of 0.8 and are required to have transverse momentum greater than 550GeV and pseudorapidity |η^{jet}|<1.6. Two-particle correlations among the charged particles within the jets are studied as functions of the particles' azimuthal angle and pseudorapidity separations (Δϕ^{*} and Δη^{*}) in a jet coordinate basis, where particles' η^{*}, ϕ^{*} are defined relative to the direction of the jet. The correlation functions are studied in classes of in-jet charged-particle multiplicity up to N_{ch}^{j}≈100. Fourier harmonics are extracted from long-range azimuthal correlation functions to characterize azimuthal anisotropy for |Δη^{*}|>2. For low-N_{ch}^{j} jets, the long-range elliptic anisotropic harmonic, v_{2}^{*}, is observed to decrease with N_{ch}^{j}. This trend is well described by MonteCarlo event generators. However, a rising trend for v_{2}^{*} emerges at N_{ch}^{j}≳80, hinting at a possible onset of collective behavior, which is not reproduced by the models tested. This observation yields new insights into the dynamics of jet evolution in the vacuum.

Optical study on spray mixing, flame propagation and jets evolution within visible methanol active pre-chamber for turbulent jet ignition

Methanol spray impingement, mixing, flame propagation and jet evolution within the narrow-confined active pre-chamber (APC) with complex walls were experimentally observed by optical method for the first time. The effects of injection pressure and duration was investigated on an actual-geometry optical APC assembled in constant volume combustion chamber (CVC). Exploration on APC internal processes within static environments forms the basis for optimization of APC and analysis of jet formation. Mie scattering coupled with flame natural luminosity imaging were used to record spray mixing and combustion. The results show that in the APC with narrow-confined space, methanol spray undergoes three wall impingements, inducing a tumble that promotes mixing. High injection pressure enhances rapid spray tip penetration, while long injection duration slows methanol diffusion. In longer injection duration cases, the spray tip after the third impingement interferes with subsequent sprays. For higher injection pressure, this interference occurs in the APC cone section due to a larger spray cone angle, whereas for lower pressure, it happens in the APC duct section. Higher injection pressure also causes more spray to impact the APC bottom after the first wall impingement, hindering flame acceleration in the duct section. Irregular flame propagation is observed in the APC cone section due to wider space and uneven mixture conditions, while the convergent geometry from the APC throat to the duct section significantly accelerates flame propagation. The APC jet appears due to the pressure difference between the APC and the main chamber, with the brightness and length of the visible flame jet increasing with APC flame luminosity and pressure difference. A Mach ring structure is observed initially, but the jet velocity decreases as the Mach ring disappears during the APC inner flame extinguishing process. Through this study, the actual spraying and combustion process in APC is experimentally captured and revealed, which are an important contribution for APC optimization and development.

The effect of electric field uniformity on electrospun jet evolution and fiber morphology

Electric field distribution has a considerable impact on jet motion and resultant fibers’ diameter and morphology in electrospinning process. This study aims to explore the effect of electric field uniformity on jet evolution and fiber morphology by using auxiliary electrodes. Four disc auxiliary electrodes with different external diameters were designed. A high-speed photography equipment was employed to capture the jet motion. The morphology the fibers obtained from different locations of the jet were observed by the SEM to investigate jets evolution under different electric fields. The three-dimensional electric field were calculated by the ANSYS Maxwell software to simulate and quantify the electric field distribution throughout the electrospinning process. The results show that the larger diameter of the auxiliary electrode creates more uniform electric field distribution, smaller jet straight lengths, larger whipping amplitude, and lower the jet velocity. These factors result in finer and more uniform fibers. It was found that the morphology of fiber surface, beads shape and size also influenced by the uniformity of electric field distribution. This research indicates that a controllable uniform electric field was essential in preparing high-performance fibers.

A γ-Ray-emitting Blazar at Redshift 3.64: Fermi-LAT and OVRO Observations of PKS 0201+113

High-redshift (z > 3) γ-ray blazars are rare, but they are crucial for our understanding of jet evolution, γ-ray production and propagation, and the growth of supermassive black holes in the early Universe. A new analysis of Fermi-LAT data reveals a significant (5σ), spectrally soft (Γ ≃ 3.0) γ-ray source in a specific 4 month epoch, cospatial with PKS 0201+113 (z = 3.64). Monitoring of PKS 0201+113 at 15 GHz by the Owens Valley Radio Observatory 40 m telescope from 2008 to 2023 shows a prominent flare that dominates the radio light curve. The maximum of the radio flare coincides with the γ-ray flare, strongly suggesting an association (p-value = 0.023) between the γ-ray and the radio sources. PKS 0201+113 is only the third γ-ray blazar to be identified with z > 3.5, and it is the first such object to be identified by the detection of quasi-simultaneous γ-ray and radio flares. The jet properties of this peculiar blazar have been investigated. A detailed study of a two-zone leptonic model is presented that fits the broadband spectral energy distribution. An alternative scenario is also briefly discussed.

The variable radio jet of the accreting neutron star the Rapid Burster

ABSTRACT The Rapid Burster is a unique neutron star low-mass X-ray binary system, showing both thermonuclear v-I and accretion-driven Type-II X-ray bursts. Recent studies have demonstrated how coordinated observations of X-ray and radio variability can constrain jet properties of accreting neutron stars – particularly when the X-ray variability is dominated by discrete changes. We present a simultaneous very large array, Swift, and INTErnational Gamma-Ray Astrophysics Laboratory observing campaign of the Rapid Burster to investigate whether its jet responds to Type-II bursts. We observe the radio counterpart of the X-ray binary at its faintest-detected radio luminosity, while the X-ray observations reveal prolific, fast X-ray bursting. A time-resolved analysis reveals that the radio counterpart varies significantly between observing scans, displaying a fractional variability of $38 \pm 5$ per cent. The radio faintness of the system prevents the robust identification of a causal relation between individual Type-II bursts and the evolution of the radio jet. However, based on a comparison of its low-radio luminosity with archival Rapid Burster observations and other accreting neutron stars, and on a qualitative assessment of the X-ray and radio light curves, we explore the presence of a tentative connection between bursts and jet: i.e. the Type-II bursts may weaken or strengthen the jet. The former of those two scenarios would fit with magnetorotational jet models; we discuss three lines of future research to establish this potential relation between Type-II bursts and jets more confidently.

Inertial oscillation modelling of low-level jets: an application to the complex terrain and double-nosed wind profiles

This study investigates the role of inertial oscillations in the evolution of a nocturnal Low-Level Jet (LLJ) in complex terrain and explores the impacts of local perturbations on wind dynamics. Specifically, a conceptual model based on inertial oscillations (Van de Wiel et al. J Atmos Sci 67(8):2679–2689 (2010)) is used to replicate the evolution of an LLJ in a gentle-sloping valley ensuring to capture its long-period dynamics under weak synoptic forcing. The analysis is performed on an already-analysed case study from the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) data set, taking advantage of the known local flow characteristics and the existence of a temporary anomaly in the LLJ shape called double-nosed LLJ. In an attempt to capture this last flow feature, a model modification is introduced, revealing appropriate to capture the double-nosed shape of the LLJ. Further observational studies will be needed to corroborate the operational use of this model and explore its application potential in different wind and energy sectors.

Characteristics of the jet shear layer of a round elevated jet in crossflow

The present research aims at an experimental study to investigate the effect of velocity ratio (R) on the evolution of elevated round jet issued from a stack having an aspect ratio (AR) of 9.0 in a uniform crossflow at a Reynolds number of 2000. The experiments are conducted in a low-speed, recirculating water tunnel. Laser Doppler Velocimetry (LDV) is employed to characterize the water tunnel. Particle Image Velocimetry (PIV) is used to measure the flow field, and the dye visualization technique is utilized to capture the accompanying instantaneous flow structures. Depending on the velocity ratio (R = 0.16 - 1.5), distinct jet shear layer (JSL) structures are observed in the symmetric plane (XY), confirmed by both the flow visualization and PIV data. These structures include clockwise vortices, anticlockwise vortices, swing-induced mushroom vortices, and jet-like vortices. For R<0.5, entrainment of a substantial amount of jet fluid into the stack-wake region (downwash) has been observed. At R=0.5, the streak image captured in the wall parallel plane reveals the ring-like vortices that appear to wrap around the jet core while upright vortices are detected downstream on the lee side of the jet. Additionally, variations in average velocity and turbulent fluctuations in the near field, contingent on different velocity ratios, are discussed.

The Evolution of Flow Structures and Coolant Coverage in Double-Row Film Cooling with Upstream Forward Jets and Downstream Backward Jets

The spatiotemporal evolution of the flow structures and coolant coverage of double-row film cooling with upstream forward jets and downstream backward jets, having a significant impact on film-cooling performance, is studied using the simplified thermal lattice Boltzmann method (STLBM). Moreover, the effect of the inclination angle of downstream backward jets is considered. The high-performance simulations of film cooling have been conducted by using our verified in-house solver. Results show that special flow structures, such as a sand dune-shaped protrusion, appear in double-row film cooling with upstream forward jets and downstream backward jets, which is mainly because of the blockage effect resulting from the coolant jet with backward injection. The interaction among structures results in the generation of an anti-counterrotating vortex pair (anti-CVP). The anti-CVP with the downwash motion can result in the attachment of coolant to the bottom wall, which promotes the stability and lateral coverage of coolant film. The momentum and heat transport are strengthened as the backward jet is injected into the boundary layer of the mainstream. Although the downstream evolution of the backward jet is not very smooth, its core attaches closely to the bottom wall due to the downwash motion of anti-CVP. Moreover, there is an obvious backflow zone shown in the trailing edge of the downstream backward jet with a large inclination angle. The obvious backflow makes the coolant attach to the bottom wall well. Therefore, the film cooling effectiveness is improved as the inclination angle of the downstream backward jet varies from αdown=135° to αdown=155°, with a constant blowing ratio of BR=0.5. In addition, the fluctuation of the bottom wall’s temperature is weak due to the stable coverage of the coolant layer under αdown=155°. The film-cooling performance with an inclination angle of αdown=155° is the best among all the cases studied in this work. This work provides essential insights into film cooling with backward coolant injection and contributes to obtaining a complete understanding of film cooling with backward coolant injection.

Effects Of The Nozzle Exit Section Shape On The Velocity Field And Heat Transfer Of Impinging Synthetic Jets

"The versatility and effectiveness of synthetic impinging jets for cooling applications have pushed the scientific community to optimize the design of such devices investigating the effects of all the relevant flow parameters, such as the stroke length, the Reynolds number and the shape of the driving wave. The current work focuses on the influence of different nozzle exit section shapes on the flow field evolution and heat transfer behavior of synthetic jet. In work presented herein, the actuator consists of a loudspeaker oscillating inside a cavity provided with a nozzle that has a circular entry section and a variable-shape exit section with a fixed hydraulic diameter (equal to 20 mm). The exit section shapes investigated in the current work are the circular, the triangular, the square and rectangular one with aspect ratio equal to 2. Simultaneous synchronized two component particle image velocimetry and infrared thermography measurements are performed. Consistent results are found both in terms of flow fields as well as Nusselt patterns: small nozzle-to-plate distances exhibit less spreading of the jet combined with a less spreaded, although more intense, Nu pattern. Smaller nozzle-to-plate distances also reveal the shape of the nozzle in the thermal pattern: this behavior can be seen for every nozzle, and it is associated with the presence of a Nu peak in correspondence of every corner of the shape, where the three-lobe footprint of the triangular nozzle exit section shape is clearly visible. Larger nozzle-to-plate distances are associated with a higher spreading in the jet and a lower vertical velocity in the vicinity of the impinged plate. "

Flow dynamics and mixing of jet in crossflow with cylindrical cavity

The flow dynamics and mixing characteristics of an air jet issued from a cylindrical cavity in an air crossflow are numerically studied using a large-eddy-simulation technique. The cavity, aligned concentrically with the jet, is located beneath the crossflow wall. The jet-to-crossflow velocity ratio is 4, and the Reynolds number for the jet flow is 1.39×104 based on its diameter and centerline velocity. The presence of the cavity significantly influences the early evolution of the jet and its interaction with the crossflow. Complex vortical structures are observed. Notably, windward vortices on the jet surface increase in size, accompanied by a reduction in the Strouhal number. For a deep cavity, these vortices break down and result in small vortical tubes in the jet streamwise direction due to secondary instability. Also examined are leeward shear-layer vortices, hanging vortices, wake vortices, and the recirculating flow within the cavity. Their roles in the mixing between the jet fluid and the crossflow are identified. The cavity enhances mixing. The effect is significant in the near field but diminishes in the far field. By adjusting the cavity radius and depth, it is determined that the cavity depth exercises a more profound impact on jet evolution and mixing than the cavity radius. The most substantial influence occurs when a narrow and deep cavity is implemented. These findings may serve as guidelines for optimizing cavity design for effective modulation of jet behaviors.

Jet substructure

Jet substructure observables hold the keys to identifying the inner working of the quark–gluon plasma through its imprints in jet modification patterns. Because of the multi-scale nature of jet evolution, the strategy has focused on developing jet reclustering-based and jet shape-based observables to specifically probe different stages of jet evolution, which provide multi-dimensional quantification of jet particle distribution phase spaces. The developments of jet substructure in the past few years allowed us to explore the correlations among jet observables. The richer information beyond single-observable modifications could give provides a crucial step beyond the energy loss paradigm. This review surveys the theory and phenomenology of modern jet substructure observables, which help constraining the energy scales of medium interactions and identifying heavy flavor quarks within jets. Also, the peculiar soft activities point to more refined studies of medium responses to jets.

Numerical study on ignition start-up process of an underwater solid rocket motor across a wide depth range

Solid rocket motors have important applications in the propulsion of trans-media vehicles and underwater launched rockets. In this paper, the ignition start-up process of an underwater solid rocket motor across a wide depth range has been numerically studied. A novel multi-domain integrated model has been developed by combining the solid propellant ignition and combustion model with the volume of fluid multiphase model. This integrated model enables the coupled simulation of the propellant combustion and gas flow inside the motor, along with the gas jet evolution in the external water environment. The detailed flow field developments in the combustion chamber, nozzle, and wake field are carefully analyzed. The variation rules of the internal ballistics and thrust performance are also obtained. The effects of environmental medium and operating depth on the ignition start-up process are systematically discussed. The results show that the influence of the operating environment on the internal ballistic characteristics is primarily reflected in the initial period after the nozzle closure opens. The development of the gas jet in water lags significantly compared with that in air. As the water depth increases, the ignition delay time of the motor is shortened, and the morphology evolution of the gas jet is significantly compressed and accelerated. Furthermore, the necking and bulging of the jet boundary near the nozzle outlet and the consequent shock oscillations are intensified, resulting in stronger fluctuations in the wake pressure field and motor thrust.

A Case Study Featuring the Time Evolution of a Fire‐Induced Plume Jet Over the Rum Creek Fire: Mechanisms, Processes, and Dynamical Interplay

AbstractResults are presented from the Rum Creek fire during the California Fire Dynamics Experiment (CalFiDE). An instrumented payload aboard the NOAA Twin Otter (TO) aircraft, which included a scanning micro‐pulsed Doppler lidar (DL) and in situ chemistry packages, was used to address the evolution of a buoyant plume jet (BPJ) and transport dynamics over the southwest corner of the fire between 09/01/2022 and 09/02/2022. An approach previously developed to isolate updrafts was modified to account for the Gaussian core structure when addressing the evolution of the updraft, plume‐top entrainment, lateral entrainment, and the role of fire‐atmosphere interactions on the characteristics of the BPJ during four overpasses. A persistent cross‐valley flow leading up to the BPJ was observed for all four overpasses, with flow enhancement during the second overpass that coincided with changes in the BPJ structure and turbulence characteristics surrounding the BPJ. Length scales and entrainment rates were estimated at the lateral edges and the top of the plume. In the case of the latter, an analytical form of the BPJ profile above the vertical velocity maximum of the updraft was derived using a simplified form of the vertical momentum equation following a partial budget analysis that accounted for plume‐top entrainment and the boundary layer (BL) inversion. Velocity core strength and characteristics were analyzed away from the updraft with similar relationships between depth‐to‐widths of velocity cores found in a forthcoming study focused on wildfire plumes.

Numerical investigation of a diesel jet at high injection pressure - several parametric studies

The purpose of this work is to investigate the dynamic behaviour of a diesel spray. To this end, the calculation code used to simulate the spray is Fluent. The evolution of the jet is simulated using an averaged approach according to the Navier-Stokes equations. To complete the system of the averaged equations, we tested many turbulence models. The multiphase structure of the spray diesel is modelled within the Volume of Fluid (and its coupling with Level-Set models). The comparison of the penetration length of our numerical study by the experiment and by the calculation code AVBP gives a good agreement. Finally, we investigate the impact of several parameters (the ambient density, the diameter of the injection nozzle…) on the evolution of the diesel jet. The calculation results have contributed to an understanding of some physical phenomena governing the evolution of the diesel spray.

Limiting attractors in heavy-ion collisions

We study universal features of the hydrodynamization process in heavy-ion collisions using QCD kinetic theory simulations for a wide range of couplings. We introduce the new concept of limiting attractors, which are obtained by extrapolation to vanishing and strong couplings. While the hydrodynamic limiting attractor emerges at strong couplings and is governed by the viscosity-related relaxation time scale τR, we identify a bottom-up limiting attractor at weak couplings. It corresponds to the late stages of the perturbative bottom-up thermalization scenario and exhibits isotropization on the time scale τBMSS=αs−13/5/Qs. In contrast to hydrodynamic limiting attractors, at finite couplings the bottom-up limiting attractor provides a good universal description of the pre-hydrodynamic evolution of jet and heavy-quark momentum broadening ratios qˆyy/qˆzz and κT/κz. We also provide parametrizations for these ratios for phenomenological studies of pre-equilibrium effects on jets and heavy quarks.