Large Jet Research Articles

The Influence of Large‐Scale Spatial Warming on Jet Stream Extreme Waviness on an Aquaplanet

AbstractThe effect of modified equator‐to‐pole temperature gradients on the jet stream by low‐level polar warming and upper‐level tropical warming is not fully understood. We perform aquaplanet simulations to quantify the impact of different sea surface temperature distributions on jet stream strength, large wave amplitudes and extreme waviness. The responses to warming in the waviness metrics Sinuosity Index and Local Wave Activity are sensitive to the latitude range over which they are calculated. Therefore, we use a latitude range that accurately represents the position of the jet. The uniform warming scenario strengthens the jet and reduces large wave amplitudes. Reductions in meridional temperature gradients lead to weakened mid‐latitudinal jet strength and show significant decreases in large wave amplitudes and jet stream waviness. These findings contradict the mechanism that weakened jet streams increase wave amplitudes and extreme jet stream waviness. We conclude that weakened jet streams do not necessarily become wavier.

Jet quenching parameter in QCD kinetic theory

We study the jet quenching parameter q^ in a nonequilibrium plasma using the QCD effective kinetic theory. We discuss subleading terms at large jet momentum p, show that our expression for q^ reproduces thermal results at small and large transverse momentum cutoffs for infinite p, and construct an interpolation between these limits to be used in phenomenological applications. Using simple nonequilibrium distributions that model pertinent features of the bottom-up thermalization scenario, we analytically assess how anisotropy, underoccupation, or overoccupation affect the jet quenching parameter. Our work provides more details on the q^ formula used in our preceding work [ ] and sets the stage for further numerical studies of jet momentum broadening in the initial stages of heavy-ion collisions from QCD kinetic theory. Published by the American Physical Society 2024

Numerical simulation of unsteady characteristics of large flow rate jet interference

Numerical simulation of unsteady characteristics of large flow rate jet interference

A model-based study of the dynamics of Arctic low-level jet events for the MOSAiC drift

Low-level jets (LLJs) are studied for the period of the ship-based experiment MOSAiC 2019/2020 using the regional climate model Consortium for Small-scale Model—Climate Limited area Mode (CCLM). The model domain covers the whole Arctic with 14 km resolution. CCLM is run in a forecast mode (nested in ERA5) and with different configurations of sea ice data for the winter. The focus is on the study of LLJs for the MOSAiC site. LLJs are detected using model output every 1 h. We define LLJ events as LLJs that last at least 6 h. Case studies of LLJ events are shown using wind lidar and radiosonde data as well as CCLM simulations. LLJs are not local events but are embedded in large jet structures extending for hundreds of kilometers that are advected toward the MOSAiC site. CCLM simulations are used to study the statistics of LLJs of all profiles and of LLJ events as well as the dynamics. LLJs are found in about 40% of the hourly profiles, but only 26% of the hourly profiles are associated with LLJ events. Strong LLJs (≥15 m/s) are detected in 13% of the hourly profiles, which is about the same fraction as for strong LLJ events. The mean duration of events is about 12 h. The LLJ events are characterized using dynamical criteria for the wind speed profile and the evolution of the jet core. A fraction of 35% of the LLJ events are baroclinic, but more than 40% of the LLJ events show a large contribution of advection to the initial generation as well as for the evolution of the jet core. Only very few events fulfill the criteria of inertial oscillations. LLJ events occur for all months, but strong events have a higher frequency during winter. The turbulent kinetic energy in the lower atmospheric boundary layer (ABL) is twice (4 times) as large for LLJs (strong LLJs) than for situations without LLJs, which underlines the impact of LLJs on turbulent processes in the ABL.

X-ray emission from large scale jets of AGNs at high redshifts

The limited angular resolution of the existing telescopes, operating in radio, optical and X-ray wavebands, hinder the study on multi-spectral component (MSC) emissions from the large scale jet of AGNs. This is particularly strenuous for the sources located at high redshifts. Though a few of them were resolved in radio-optical wavebands, their X-ray counterparts have been rarely discovered. This poses a bigger challenge in understanding their emission mechanism. At high redshifts, the X-ray emission from the large scale jets are generally interpreted as inverse-Compton scattering of cosmic microwave background photons (IC/CMB), due to the increase in CMB photon density. However, recent Fermi γ-ray flux upper limit estimates on two high redshift (z>3.5) AGN jets (J1510+5702 and J1421-0643), question the validity of the IC/CMB model. Here, we propose a model by considering the advection of electrons from the sites of particle acceleration (Rahman et al., 2022), to interpret the MSC emission from these sources. We show that observed radio/optical/X-ray emissions can be explained by the synchrotron emission from the advected and accelerated electron distribution. We also show that the IC/CMB spectrum of this composite electron distribution satisfies the constraints drawn from Fermi observations.

AGN Feedback Signatures in UV Emission

Supermassive black holes (SMBH) are believed to influence galaxy evolution through AGN (active galactic nuclei) feedback. Galaxy mergers are key processes of galaxy formation that lead to AGN activity and star formation. The relative contribution of AGN feedback and mergers to star formation is not yet well understood. In radio-loud objects, AGN outflows are dominated by large jets. However, in radio-quiet objects, outflows are more complex and involve jet, wind, and radiation. In this review, we discuss the signatures of AGN feedback through the alignment of radio and UV emissions. Current research on AGN feedback is discussed, along with a few examples of studies such as the galaxy merger system MRK 212, the radio-quiet AGN NGC 2639, and the radio-loud system Centaurus A. Multi-frequency observations of MRK 212 indicate the presence of dual AGN, as well as feedback-induced star-forming UV clumps. The fourth episode of AGN activity was detected in radio observations of the Seyfert galaxy NGC 2639, which also showed a central cavity of 6 kpc radius in CO and UV maps. This indicates that multi-epoch jets of radio-quiet AGN can blow out cold molecular gas, which can further reduce star formation in the center of the galaxies. Recent UV observations of Cen A have revealed two sets of stellar population in the northern star-forming region, which may have two different origins. Recent studies have shown that there is evidence that both positive and negative feedback can be present in galaxies at different scales and times. High-resolution, multi-band observations of large samples of different types of AGN and their host galaxies are important for understanding the two types of AGN feedback and their effect on the host galaxies. Future instruments like INSIST and UVEX will be able to help achieve some of these goals.

Thermal-hydraulic performance of turbulent flows across a heated round tube installed through several perforated twisted tapes

PurposeThe purpose of this study is to advance turbulent thermal convection inside the constant heat-flux round tube inserted by multiple perforated twisted tapes.Design/methodology/approachThe novel design of this study is accomplished by inserting several twisted tapes and drilling some circular perforations near the tape edge (C1, C3, C5: solid tapes; C2, C4, C6: perforated tapes). The turbulence flow appearances and thermal convective features are examined for various Reynolds numbers (8,000–14,000) using the renormalization group (RNG) κ−ε turbulent model and Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm.FindingsThe simulated outcomes reveal that inserting more perforated-twisted tapes into the heated round tube promotes turbulent thermal convection effectively. A swirling flow caused by the twisted tapes to produce the secondary flow jets between two reverse-spin tapes can combine with the main flow passing through the perforations at the outer edge to enhance the vortex flow. The primary factors are the quantity of twisted tapes and with/without perforations, as the perforation ratio remains at 2.5 in this numerical work. Weighing friction along the tube, C6 (four reverse-spin perforated-twisted tapes) brings the uppermost thermal-hydraulic performance of 1.23 under Re = 8,000.Research limitations/implicationsThe constant thermo-hydraulic attributes of liquid water and the steady Newtonian fluid are research limitations for this simulated work.Practical implicationsThe simulated outcomes will avail the inner-pipe design of a heat exchanger inserted by multiple perforated twisted tapes to enhance superior heat transfer.Originality/valueThese twisted tapes form tiny circular perforations along the tape edge to introduce the fluid flow through these bores and combine with the secondary flow induced between two reverse-spin tapes. This scheme enhances the swirling flow, turbulence intensity and fluid mixing to advance thermal convection since larger perforations cannot produce large jet velocity or the position of perforations is too far from the tape edge to generate a separated flow. Consequently, this work contributes a valuable cooling mechanism toward thermal engineering.

Intermittent Emission of Particles from a Bose‐Einstein Condensate in a 1D Lattice

AbstractParticle emission from a Bose‐Einstein condensate with periodically modulated interactions is investigated in a 1D lattice. Within perturbative analysis, which leads to instabilities for discrete modes, the main regimes are obtained where the system can emit a large particle jet, and the distinctly intermittent rather than continuous emission is found. The time evolution of the trapped particles exhibits a stair‐like decay, and a larger drive induces a more significant intermittency. This study further sheds light on the dynamics of the stimulating process, and demonstrates that instead of a real suspension, the intermittency represents a build‐up stage of the system. The theoretical framework might be generalized to the explorations on multiple‐site systems with analogous configurations and couplings, and offer new insights into other fundamental nonequilibrium problems.

On the preferred flapping motion of round twin jets

Linear stability theory (LST) is often used to model the large-scale flow structures in the turbulent mixing region and near pressure field of high-speed jets. For perfectly expanded single round jets, these models predict the dominance of azimuthal wavenumbers $m=0$ and $m = 1$ helical modes for the lower frequency range, in agreement with empirical data. When LST is applied to twin-jet systems, four solution families appear following the odd/even behaviour of the pressure field about the symmetry planes. The interaction between the unsteady pressure fields of the two jets also results in their coupling. The individual modes of the different solution families no longer correspond to helical motions, but to flapping oscillations of the jet plumes. In the limit of large jet separations, when the jet coupling vanishes, the eigenvalues corresponding to the $m=1$ mode in each family are identical, and a linear combination of them recovers the helical motion. Conversely, as the jet separation decreases, the eigenvalues for the $m=1$ modes of each family diverge, thus favouring a particular flapping oscillation over the others and preventing the appearance of helical motions. The dominant mode of oscillation for a given jet Mach number $M_j$ and temperature ratio $T_R$ depends on the Strouhal number $St$ and jet separation $s$ . Increasing both $M_j$ and $T_R$ independently is found to augment the jet coupling and modify the $(St,s)$ map of the preferred oscillation mode. Present results predict the preference of two modes when the jet interaction is relevant, namely varicose and especially sinuous flapping oscillations on the nozzles’ plane.

Boosting dark matter searches at muon colliders with machine learning: The mono-Higgs channel as a case study

Abstract The search for dark matter (DM) candidates at high-energy colliders is one of the most promising avenues to understand the nature of this elusive component of the universe. Several searches at the Large Hadron Collider (LHC) have strongly constrained a wide range of simplified models. The combination of the bounds from the LHC with direct-detection experiments exclude the most minimal scalar-singlet DM model. To address this, lepton portal DM models are suitable candidates where DM is predominantly produced at lepton colliders since the DM candidate only interacts with the lepton sector through a mediator that carries a lepton number. In this work, we analyze the production of DM pairs in association with a Higgs boson decaying into two bottom quarks at future muon colliders in the framework of the minimal lepton portal DM model. It is found that the usual cut-based analysis methods fail to probe heavy DM masses for both the resolved (where the decay products of the Higgs boson can be resolved as two well-separated small-R jets) and the merged (where the Higgs boson is clustered as one large-R jet) regimes. We have then built a search strategy based on boosted-decision trees (BDTs). We have optimized the hyperparameters of the BDT model to both have a high signal-to-background ratio and to avoid overtraining effects. We have found very important enhancements of the signal significance with respect to the cut-based analysis by factors of 8–50 depending on the regime (resolved or merged) and the benchmark points. Using this BDT model on a 1D parameter space scan, we found that future muon colliders with $\sqrt{s}=3$ TeV and ${\cal L} = 1~{\rm ab}^{-1}$ can exclude DM masses up to 1 TeV at the 95% confidence level.

Next-to-Leading BFKL for Mueller–Navelet Dijets with Large Rapidity Separation and Jet Veto

Next-to-Leading BFKL for Mueller–Navelet Dijets with Large Rapidity Separation and Jet Veto

Large area inkjet-printed OLED fabrication with solution-processed TADF ink

This work demonstrates successful large area inkjet printing of a thermally activated delayed fluorescence (TADF) material as the emitting layer of organic light-emitting diodes (OLEDs). TADF materials enable efficient light emission without relying on heavy metals such as platinum or iridium. However, low-cost manufacturing of large-scale TADF OLEDs has been restricted due to their incompatibility with solution processing techniques. In this study, we develop ink formulation for a TADF material and show successful ink jet printing of intricate patterns over a large area (6400 mm2) without the use of any lithography. The stable ink is successfully achieved using a non-chlorinated binary solvent mixture for a solution processable TADF material, 3‐(9,9‐dimethylacridin‐10(9H)‐yl)‐9H‐xanthen‐9‐one dispersed in 4,4’-bis-(N-carbazolyl)-1,1’-biphenyl host. Using this ink, large area ink jet printed OLEDs with performance comparable to the control spin coated OLEDs are successfully achieved. In this work, we also show the impact of ink viscosity, density, and surface tension on the droplet formation and film quality as well as its potential for large-area roll-to-roll printing on a flexible substrate. The results represent a major step towards the use of TADF materials for large-area OLEDs without employing any lithography.

Abstract 18572: Mimickers of Chiari Network in the Left Atrium

Case: 84-year-old female with ischemic cardiomyopathy and severe secondary mitral regurgitation with restricted leaflet mobility due to chordae tethering and a large central regurgitant jet. She underwent trans-catheter edge to edge repair with Mitra Clip NTW. The clip was aligned in the 12 to 6 o'clock position in the middle of A2/P2 scallop and appropriate graft was obtained with good tissue bridging. The trans mitral gradient at the end of the procedure was 3 mmHg and final V-waves at 10 mmHg. After the guiding catheter was moved back to the right atrium, the transesophageal echocardiogram (TEE) showed the presence of an echo dense flickering, bubble-like mobile structure around the right upper pulmonary vein. The heart team agreed that it looked like an endothelial disruption induced by the guiding catheter. After careful consideration and using shared decision making, the patient was maintained on Eliquis for 6 months without evidence of thromboembolic phenomena. Repeat TEE showed a healed dissection flap and no echo dense structure seen previously. Discussion: Unlikely to be thrombus or air bubbles, this structure looked like what we would see in a Chiari network. Complications after Mitra Clip procedure have been well described and can be broadly divided into procedure related and device related. Endothelial disruption with the imaging characteristics shown in this case has not been described. There are no evidence-based guidelines on how to proceed with this type of complication. It is well known that endothelial damage increases the risk for thrombosis and embolic phenomena. Due to concerns of a stroke, the decision was made to start anticoagulation with the plan of redo TEE. This case demonstrates the importance of performing TEE after Mitra Clip procedure to look for lesions that would increase the risk of stroke. It also demonstrates that patients with endothelial disruption after Mitra clip may benefit from short term anticoagulation for stroke prevention.

Prediction of the performance of the pressure-regulating valve in a large high-speed jet wind tunnel

Prediction of the performance of the pressure-regulating valves in a large high-speed jet wind tunnel is important for obtaining and adjusting a high-quality flow field in the test section. In this work, we proposed a prediction method that corrects the theoretical characteristics of the pressure-regulation of the valve based on the experimental testing data of the ratio between the high- and low-pressure of the valve. The current method was validated for a given Mach number of 0.8, and the results showed that compared with the theoretical characteristics, the displacement deviation of the spool was reduced by 9.84%, and the total pressure deviation of the settling chamber was reduced by 43.61%. The results also show that compared with the single low-pressure ratio correction characteristic, the displacement deviation of the spool was reduced by 0.94%, and the total pressure deviation of the settling chamber was reduced by 3.4%. This method can consider the variation of the pressure loss for different pressure ratios and improve the pressure prediction of the valve.

Numerical simulation of lateral jet interaction with rarefied hypersonic flow over a two-dimensional blunt body

Reaction Control System (RCS) is a direct force control system that successfully adjusts a craft's attitude or orbit using the reaction force created by jet flow. RCS is frequently employed in the management of near-space vehicles due to its properties of fast response time and effective control efficiency. When the near-space vehicle is navigating at high altitude in a low density atmosphere, the Navier–Stokes equation is no longer applicable. The numerical approach utilized in this study is known as the Conserved Discrete Unified Gas Kinetic Scheme, and the governing equation is the Boltzmann equation, which is not constrained by the continuum hypothesis. In velocity space, an unstructured mesh is utilized, which minimizes the amount of discrete velocity points and considerably increases computation efficiency. The numerical results are in good agreement with the direct simulation Monte Carlo code DS2V when modeling large Knudsen number lateral jet flow. The interaction flow field between hypersonic free stream and lateral jet is then simulated at altitudes of 60–90 km using argon as the working gas and a two-dimensional blunt cone with lateral jet as the study object. Under a fixed jet pressure ratio, preliminary research was conducted on the variation of the lateral jet interference flow field characteristics with the freestream Knudsen number and angle of attack. The differences in surface pressure and heat flux caused by jet opening and shutting are compared. Under rarefied atmospheric conditions, the variation of the force/moment amplification coefficient is given. The numerical results show that when the angle of attack is 0°, the separation area in front of the nozzle and a pair of opposite vortices, which are common in the jet interference flow field, gradually disappear with increasing altitude, but the separation vortex reappears when the angle of attack of the freestream is increased. The high-pressure region generated upstream of the nozzle is the primary cause of the extra force/moment. The density of the main flow decreases as altitude increases, various shock wave patterns of the interference flow field gradually dissipate and the force/moment amplification factor changes considerably. The rarefied gas effect has a significant effect on the lateral jet interference flow.

Experimental study on the effect of injection schemes on fuel spray and combustion characteristics in a compact combustor

Fuel injection schemes based on close-coupled injection are usually used in compact combustor design. In this paper, an experimental method is adopted to study the fuel spray Sauter mean diameter (SMD) and combustion characteristics when different fuel injection schemes, strut cavity structures, and fuel/air jet momentum flux ratios are applied. Four fuel injection schemes based on close-coupled injection schemes and premixed injection schemes are proposed for use in a compact integrated combustor to compare the effects of the fuel injection schemes. Three struts are designed to study the influence of the cavity on the close-coupled fuel injection scheme. The results show that the spray and combustion characteristics of the close-coupled injection scheme differ from those of premixed injection schemes. Specifically, the SMD in the close-coupled scheme is in the range of 70-150 μm, which is larger and more uneven than that of the premixed scheme (15-40 μm), and the close-coupled scheme has better ignition performance at a temperature of 450 K. The flame structure of the close-coupled injection schemes with reverse mainstream inside the cavity has better radial uniformity, but more fuel is attached to the strut surface, resulting in a lower flame intensity and increased diffusion flame. The cavity on the strut sidewall can effectively promote fuel atomization by approximately 25% when the jet momentum flux ratio is low, make the fuel more uniform in the strut radial direction, increase the flame intensity, and reduce diffusion flame zone. In the close-coupled injection scheme, the large jet momentum ratio will lead to the collision and fusion of multiple fuel streams downstream of the struts, thus increasing the fuel droplet size and limiting the promoting effect of the strut wall structure. In summary, this paper provides further understanding of the combustor spray and combustion characteristics of different fuel injection schemes.

Impact of jet velocity profile on the propulsive performance and vortex ring formation of pulsed jet propulsion

A squid-inspired jet propulsion system that indudes a deformable body and a nozzle exit attached to it is numerically studied. By prescribing the body deformation during a single discharge, we examine the impact of jet speed profiles on the vortex ring formation and propulsion performance of the system. Our results show that a secondary vortex ring following the leading vortex ring can be produced by the reverse cosine jet speed pattern at a given maximum stroke ratio, and for the other profiles (i.e., constant, cosine, reverse cosine, half cosine and rever half cosine styles) only distributed vortices are seen behind the leading vortex ring. The constant jet speed produces the largest time-averaged thrust due to jet momentum flux related thrust associated with its large jet speed. Except for the constant speed style, the largest mean thrust production and propulsion factor are obtained by the reverse cosine profile among the other four styles attributed to the formation of the secondary vortex ring. Nevertheless, this secondary vortex ring would not be produced at a small maximum stroke ratio for the reverse cosine speed fashion. We also find that the mean thrust production can reach a maximum under a specific maximum stroke ratio (Γm = 7.60) when two vortex rings are produced. This work may provide insight into the mechanical and control design of jet-based biomimetic propellers and robots.

Probing the Heart of Active Narrow-line Seyfert 1 Galaxies with VERA Wideband Polarimetry

We explored the parsec-scale nuclear regions of a sample of radio-loud narrow-line Seyfert 1 galaxies (NLSy1s) using the VLBI Exploration of Radio Astrometry wideband (at a recording rate of 16 Gbps) polarimetry at 22 and 43 GHz. Our targets include 1H 0323+342, SBS 0846+513, PMN J0948+0022, 1219+044, PKS 1502+036, and TXS 2116-077, which are all known to exhibit γ-ray emission indicative of possessing highly beamed jets similar to blazars. For the first time, we unambiguously detected Faraday rotation toward the parsec-scale radio core of NLSy1s, with a median observed core rotation measure (RM) of 2.7 × 103 rad m−2 (or 6.3 × 103 rad m−2 for redshift-corrected). This level of RM magnitude is significantly larger than those seen in the core of BL Lacertae objects (BLOs; a dominant subclass of blazars), suggesting that the nuclear environment of NLSy1s is more gas-rich than that in BLOs. Interestingly, the observed parsec-scale polarimetric properties of NLSy1s (low core fractional polarization, large core RM and jet–EVPA misalignment) are rather similar to those of flat-spectrum radio quasars (FSRQs). Our results are in accordance with the scenario that NLSy1s are in an early stage of active galactic nucleus evolution with their central black hole masses being smaller than those of more evolved FSRQs.

Computational Analysis of Air/Mist Film Cooling Using a Sweeping Jet Fluidic Oscillator–Part I: Sweeping Air-Only Jet With Detailed Analysis of Vortex Dynamics

Abstract The sweeping jet can be a promising candidate in film cooling applications since it has a large lateral jet spreading which can be considered an advantage when compared to the regular steady jet film cooling. Fluidic oscillators can generate a sweeping jet without the need for any moving parts. In addition, they can be more conveniently manufactured by additive manufacturing techniques. This two-part paper presents a numerical study to investigate the application of using air/mist sweeping jets in film cooling for protecting turbine airfoils. Part I focuses on validating the computational mode by comparing the thermal-flow and heat transfer behavior between steady and sweeping air-only jets to ensure they are consistent with published information. Part II focuses on the mist behavior and its effect on heat transfer enhancement in the sweeping jet film cooling by adding micro-liquid droplets. An unsteady Reynolds-averaged Navier–Stokes (URANS) simulation accompanied by the k–ω shear stress transport (SST) turbulence model was used in this study. A comparison is made between steady and sweeping jets at two blowing ratios (BR = 1 and 2). The results show that the steady jet provided better film cooling performance along the centerline compared to that of the sweeping jet for both blowing ratios. However, the sweeping jet provided better and more uniform film cooling performance in the spanwise direction. Both jets experienced a significant jet-liftoff when the blowing ratio was 2. The entrainment was significant in the sweeping jet case for both blowing ratios. The sweeping jet caused an increase of 9.5% in total pressure losses compared to the steady jet. It was found that for the sweeping jet, a pair of counter-rotating vortices is inward-rushing toward the wall in the center rather than outward-rushing as in a typical steady jet film cooling flow field. A detailed analysis is presented to understand the instantaneous vortex dynamics of the sweeping jet that leads to the inward rotating counter-rotating vortex pair (CRVP) (i.e., reversed CRVP). The result shows that the pair of counter-rotating vortices is just a time-averaged image of a single vortex sweeping back and forth in the domain; it does not actually exist in real time.

Recurrent 3He-rich solar energetic particle injections observed by Solar Orbiter at ∼0.5 au

We report Solar Orbiter observations of six recurrent solar energetic particle injections in 2022 March 3−6 at ∼0.5 au. All but one were associated with jets emanating from a plage near a large sunspot in active region 12 957. We saw large jets in injections with high 3He and Fe enrichments and minor jets in injections with no or lower enrichments. Furthermore, the event with the highest enrichment showed a more compact configuration of the underlying photospheric magnetic field. The higher fluences as well as harder spectra were seen in the event with a simultaneous jet and wider eruption. However, in this case, the energy buildup time in the source might be required to produce such spectra. Extreme-ultraviolet images from Solar Orbiter revealed a number of intersecting loops at the base of jets not seen from 1 au that might be a precondition for the recurrent events.