Intense Jet Research Articles

Short-duration gamma-ray bursts from Kerr–Newman black hole mergers

Black hole (BH) mergers are natural sources of gravitational waves (GWs) and are possibly associated with electromagnetic events. Such events from a charged rotating BH with an accretion on to it could be more energetic and ultra-short-lived if the magnetic force dominates the accretion process because the attraction of ionized fluid with a strong magnetic field around the rotating BH further amplifies the acceleration of the charged particle via a gyromagnetic effect. Thus a stronger magnetic field and gravitational pull will provide an inward force to any fluid displaced in the radial direction and move it toward the axis of rotation with an increasing velocity. After many twists during rotation and the existence of restoring agents, Such events could produce a narrow intense jet starts in the form of Poynting flux along the axis of rotation resembling the Blandford–Znajek (BZ) mechanism. We investigated a charged rotating BH and obtained characteristic results (e.g., the remnant mass, magnetic field strength, luminosity, opening angle, viewing angle, and variation of viewing angle on the SGRB luminosity detection) that have a nice coincidence with rare events having GW associated with EM counterparts. This study gives a new insight into events with a strongly magnetized disk dominating the accretion process of energy extraction.

Effect of pre-chamber volume and nozzle number on turbulent jet combustion characteristics of GDI engines

There are few studies on the effect of turbulent jets on the combustion characteristics of passive pre-chamber (PC) gasoline engines, and their mechanism needs to be elucidated. Therefore, a 3-D simulation was performed using CONVERGE software. The results reveal that a modest expansion in the PC volume contributes to combustion due to the increased jet energy, but when it is too large, the above effect is weakened. In this study, at a smaller 0.8 ml volume, the combustion is still similar to traditional spark plug ignition. At middle 1.6 ml volume, the mixture concentration in the PC increases and the uniformity is better, resulting in the highest jet velocity and shortest jet duration, thus achieving the fastest flame propagation and the highest heat release rate (HRR). However, at a larger 1.8–2.0 ml volume, the mixture concentration near the spark-plug is sharply reduced, thus the reduced combustion rate in the PC leads to insufficient jet energy in the subsequent jets and resulting deterioration in combustion. An appropriate increase in nozzle number also improves combustion by introducing more ignition sources. But more nozzles not always improving the combustion. In the eight-nozzle case, three nozzles are close to the exhaust valve so that the intake is inhibited, resulting in a worsening of the ignition. The combustion under six-nozzle shows the highest HRR and shortest combustion duration. However, the combustion deteriorates at eight-nozzle, since the increase in the ignition point is not enough to compensate for the negative impact of the reduced jet intensity on combustion.

Effective and environment-friendly oil removal with microbubble jet

Effective removal of oil contaminants from solid surfaces is crucial for various applications. However, traditional cleaning methods often involve the use of hazardous chemicals. Because of their stability and ability to adsorb pollutants, microbubbles are considered as a promising alternative for environmentally friendly cleaning. This study explores the enhancement of oil cleaning efficiency using a microbubble water jet. The properties of the microbubbles generated via ultrasonic agitation are examined under varying water temperatures, ultrasonic amplitudes, and surfactant concentrations. The microbubble jet demonstrates approximately 29 % enhanced cleaning efficiency compared with a single-phase water jet. Visualization techniques, including particle image velocimetry, reveal that this enhancement is driven by the behavior of microbubbles consistently adsorbing oil through hydrophobic interactions as well as the instability and increased turbulence intensity of the microbubble jet. Additionally, the higher (by 7 %) spreading velocity of the microbubble jet indicates the free surface of bubbles results in a drag reduction. Consequently, this enables the jet to cover wider regions to be cleaned effectively. The present findings demonstrate the potential of microbubble jets as an effective and eco-friendly alternative for oil removal and offer insights for their practical implementation in diverse fields utilizing microbubbles.

Signature of the western boundary currents in local climate variability.

The western boundary currents are characterized by narrow, intense ocean jets and are among the most energetic phenomena in the world ocean. The importance of the western boundary currents to the mean climate is well established: they transport vast quantities of heat from the subtropics to the midlatitudes1, and they govern the structure of the climatological mean surface winds2-6, precipitation4-6 and extratropical storm tracks7-13. Their importance to climate variability is much less clear, as the tropospheric response to extratropical sea surface temperature (SST) variability is generally modest relative to the internal variability in the midlatitude atmosphere12-14. Here we exploit novel local analyses based on high-spatial-resolution data to demonstrate that SST variability in the western boundary currents has a more robust signature in climate variability than has been indicated in previous work. Our results indicate that warm SST anomalies in the major boundary currents of both hemispheres are associated with a distinct signature of locally enhanced precipitation and rising motion anomalies that extend throughout the depth of the troposphere. The tropospheric signature closely mirrors that of ocean dynamical processes in the boundary currents. Thus, the findings indicate a distinct and robust pathway through which extratropical ocean dynamical processes influence local climate variability. The observational relationships are also reproducible in Earth system model simulations but only when the simulations are run at high spatial resolution.

Dynamics of single cavitation bubble collapse jet under particle-wall synergy

The interaction between a particle and a cavitation bubble significantly influences the erosive effect on the wall surface of flow passage components in fluid machinery. This paper investigates the dynamics of a single bubble collapse jet under the synergetic effects of a particle and a wall, using Kelvin impulse theory and high-speed photographic experiments. A theoretical model to predict the intensity and direction of the collapse jet at arbitrary locations near the particle and the wall is constructed on the basis of the image method and Weiss's theorem. The accuracy of the model is verified by comparison with a large number of experimental results. The mechanisms underlying the relative contributions of the particle and wall to the behavior of jet intensity and direction are explored. The effects of key parameters on jet intensity and direction are also quantitatively analyzed, including the relative positions of the particle, wall, and the bubble and the dimensionless particle radius. The main conclusions are as follows: (1) the particle will cause a deflection in the direction of the collapse jet near the wall, leading to the formation of a jet attraction zone. The proposed theoretical model effectively predicts the spatial location of this zone. (2) There exists a region in which the jet is weak, and there is a jet equilibrium point with zero impulse between the particle and the wall. The position of this equilibrium point gradually approaches the wall in a nonlinear manner with increasing particle size and in a quasi-linear manner with decreasing particle–wall distance. (3) When the particle and the bubble are the same distance from the wall, the jet direction gradually changes from toward the particle to vertical to the wall in a nonlinear manner as the bubble–particle distance increases. Moreover, the effective range of the particle's influence on the jet direction decreases as the particle–wall distance decreases.

Dominant Role of Eurasian Evaporation on the Moisture Sources of the Interannual Variations in Central Asian Summer Precipitation

Abstract The precipitation changes in arid and semiarid central Asia have great impacts on the local fragile ecosystem. The summer precipitation in central Asia shows obvious interannual variations, but the corresponding crucial moisture transporting processes remain unclear. Therefore, this study employs the Lagrangian flexible particle (FLEXPART) diffusion model to achieve this goal. Results show that the moisture of climatological summer precipitation in central Asia is mainly from the local regions, the surrounding western and northern Eurasian regions. The contribution of local evaporation from western central Asia is about 2 times that from eastern central Asia. At the interannual time scale, the moisture variations are mainly influenced by the local regions and western Eurasia, while the local evaporation is mainly from western central Asia. Totally, the Eurasian evaporation plays a dominant role in the interannual variations of central Asian summer precipitation by contributing more than 90% of the total moisture. The moisture transports associated with central Asian summer precipitation interannual variations are impacted by the anomalous cyclones over the western and northeastern parts of central Asia during the wet years, which enhance the moisture convergence and hence increase the summer precipitation in central Asia. The anomalous cyclone over the western part of central Asia is correlated with the changes in the intensity of Eurasian summer subtropical westerly jet (ESSWJ), while the anomalous cyclone over the northeastern part of central Asia is correlated with both ESSWJ and the British–Baikal Corridor pattern teleconnection in association with the polar front jet.

Effect of welding gap on electromagnetic pulse welding of a copper-aluminum alloy joint

ABSTRACT Electromagnetic pulse welding (EMPW) is commonly used for welding copper and aluminum alloy. The welding gap is important in the EMPW process. The research focused on the effect of welding gap on the welding process and the mechanical property of joints. During the EMPW experiments, the deformation, collision, and metal jet were recorded with a high-speed camera. The joint mechanical property was tested. SEM and EDS were employed to examine the bonding interface. Results indicated that the welding gap length did not significantly influence the aluminum alloy plate motion behavior when it was long enough. With the welding gap width increasing, the collision velocity initially increased and subsequently decreased, and the angle between the two plates when they first collided increased continuously. The intensity and duration of the metal jet and the joint mechanical properties also increased first and then decreased. The welding marks widened first and then narrowed.

The effect of jet disturbance on flame propagation characteristics of multi-component natural gas/hydrogen mixed fuel

Gas explosions mostly occur in turbulent environments in practical situations. Meanwhile, the current research on the explosion characteristics of hydrogen-doped natural gas is mostly methane/hydrogen mixed fuel, ignoring the influence of other components of natural gas on the explosion characteristics of the actual situation. Therefore, the effects of different jet intensities (Pjet), hydrogen-doping ratios (XH2) and equivalence ratios (φ) on the explosion characteristics of multi-component natural gas/hydrogen mixed fuel are experimentally investigated in cylindrical tanks of 30 L. Additionally, it extensively explored the dual influence of jet disturbance and gas inerting effect on the flame propagation characteristics of multi-component natural gas/hydrogen mixed fuel. With the increase of Pjet, both Pmax and (dp/dt)max initially increase and then decrease, while τ continuously decreases. When Pjet = 0.4 MPa, the promotion effect on Pmax and (dp/dt)max is most significant. The lifting of XH2 leads to a gradual increase in Pmax and decreasing τ. (dp/dt)max exhibits a trend of initially increasing and then decreasing with the elevation of XH2, reaching its maximum at XH2 = 40%. The introduction of jet flow significantly reduces the promotion or inhibition effect on explosions of high hydrogen blending ratio mixtures. Furthermore, the introduction of jet flow is more effective in promoting the explosive performance of multi-component natural gas/hydrogen mixed fuel with high equivalence ratios and low hydrogen doping ratios under rich fuel conditions. This study can provide a key reference for the explosion hazard assessment during the practical application of natural gas/hydrogen mixed fuel.

What Drives the Spread and Bias in the Surface Impact of Sudden Stratospheric Warmings in CMIP6 Models?

Abstract This study evaluates the representation of the composite-mean surface response to sudden stratospheric warmings (SSWs) in 28 CMIP6 models. Most models can reproduce the magnitude of the SLP response over the Arctic, although the simulated Arctic SLP response varies from model to model. Regarding the structure of the SLP response, most models exhibit a basin-symmetric negative Northern Annular Mode (NAM)-like response with a cyclonic Pacific SLP response, whereas the reanalysis shows a highly basin-asymmetric negative NAO-like response without a robust Pacific center. We then explore the drivers of these model biases and spread by applying a multiple linear regression (MLR). The results show that the polar cap temperature anomalies at 100 hPa (ΔT100) modulate the magnitude of both the Arctic SLP response and the cyclonic Pacific SLP response. Apart from ΔT100, the intensity and latitudinal location of the climatological eddy-driven jet in the troposphere also affect the magnitude of the Arctic SLP response. The compensation of model biases in these two tropospheric metrics and the good model representation of ΔT100 explain the good agreement between the ensemble mean and the reanalysis on the magnitude of the Arctic SLP response, as indicated by the fact that the ensemble mean lies well within the reanalysis uncertainty range and that the reanalysis mean sits well within the model distribution. The Niño-3.4 SST anomalies and North Pacific SST dipole anomalies together with ΔT100 modulate the cyclonic Pacific SLP response. In this case, biases in both oceanic drivers work in the same direction and lead to the cyclonic Pacific SLP response in models that are not present in the reanalysis. Significance Statement Sudden stratospheric warmings (SSWs) represent an important source of skill for forecasting winter weather on subseasonal-to-seasonal time scales. To what extent SSWs could be used to improve the prediction of surface weather depends on how well stratosphere–troposphere coupling associated with SSWs is represented in climate models. Therefore, we evaluate the representation of stratosphere–troposphere coupling associated with SSWs in 28 state-of-the-art climate models. The representation is found to diverge widely among climate models, and some are biased noticeably from the reanalysis. The models’ spread and bias are largely driven by five major factors and can be reduced substantially by making bias corrections to these factors.

The effect of AGN feedback on the Lyman-α forest signature of galaxy protoclusters at z∼ 2.3

ABSTRACT The intergalactic medium in the vicinity of galaxy protoclusters are interesting testbeds to study complex baryonic effects such as gravitational shocks and feedback. Here, we utilize hydrodynamical simulations from the SIMBA and The Three Hundred suites to study the mechanisms influencing large-scale Lyman-$\alpha$ transmission in $2\lt z\lt 2.5$ protoclusters. We focus on the matter overdensity-Lyman-$\alpha$ transmission relation $(\delta _m-\delta _F)$ on Megaparsec-scales in these protoclusters, which is hypothesized to be sensitive to the feedback implementations. The lower density regions represented by the SIMBA-100 cosmological volume trace the power-law $\delta _m-\delta _F$ relationship often known as the fluctuating Gunn–Peterson approximation. This trend is continued into higher density regions covered by simulations that implement stellar feedback only. Simulations with active galactic nucleus (AGN) thermal and AGN jet feedback, however, exhibit progressively more Lyman-$\alpha$ transmission at fixed matter overdensity. Compared with the seven protoclusters observed in the COSMOS field, only two display the excess absorption expected from protoclusters. The others exhibit deviations: four show some increased transparency suggested by AGN X-ray thermal feedback models while the highly transparent COSTCO-I protocluster appears to reflect intense jet feedback. Discrepancies with the stellar-feedback-only model suggests processes at play beyond gravitational heating and/or stellar feedback as the cause of the protocluster transparencies. Some form of AGN feedback is likely at play in the observed protoclusters, and possibly long-ranged AGN jets in the case of COSTCO-I. While more detailed and resolved simulations are required to move forward, our findings open new avenues for probing AGN feedback at Cosmic Noon.

Influence of temperature dependent short-term storage on thermal runaway characteristics in lithium-ion batteries

In practical applications, lithium-ion batteries inevitably encounter short-term exposure to high or low temperatures due to geographical climate variations and specific usage scenarios. This study explored the impact of short-term storage at temperatures ranging from −40 to 60 °C on the thermal stability of batteries. Combustion behavior, onset time (tTR) and onset temperature (TTR) of thermal runaway (TR), flame heat flux and mass loss were measured. It demonstrates that following short-term high/low temperature storage, the amount of gas in the exhaust phase increased significantly, and the intensity of the flame jet was enhanced. The experimental results showed that the tTR and TTR initially increased and then decreased with the storage temperature decreased from 20 °C to −40 °C. High temperature storage led to earlier TR and lower TTR. Interestingly, storage at 0 °C caused a delay in the occurrence of TR. Furthermore, an analysis of the heat transfer process, spanning from the safety valve opening to the onset of TR, was performed by leveraging the characteristic time and temperature parameters observed during the TR process. The findings of this research contribute to enhancing the safety and reliability of battery applications, particularly in scenarios involving temperature variations and potential thermal risks.

Experimental study of jet and cavity coupling under vertical motion of underwater vehicle

After the underwater vehicle detaches from the launch tube and starts its engine, the interaction between the tail cavity and the high-speed jet significantly impacts its motion stability and engine efficiency. Therefore, it is crucial to study the evolution mechanism of cavities in vertical motion. However, in traditional water tunnel experiments, the evolution of the cavity differs from the actual situation of vertical launch due to the influence of buoyancy. This study investigates the dynamics and motion trajectories of tail cavities and high-speed gas jets in the vertical movement of vehicles under different Froude numbers and nozzle stagnation pressure ratios through experimentation. The experimental results show two modes of tail cavity evolution: intact cavity (IC) and foam-conical cavity (FC-CC). Increasing the Froude numbers and stagnation pressure ratios facilitates the transition of the cavity from the IC mode to the FC-CC mode, effectively suppressing the formation and intensity of re-entrant jets, thereby reducing its impact on the bottom of the vehicle and enhancing motion stability. By deriving the formula for the length of the jet core area, it was found that the jet length is linearly related to the nozzle stagnation pressure, further revealing the mechanism of cavity evolution. These findings offer a new perspective for a deeper understanding and prediction of the dynamic behavior of underwater vehicles.

Deepening mechanisms of cut-off lows in the Southern Hemisphere and the role of jet streams: insights from eddy kinetic energy analysis

Abstract. Cut-off lows (COLs) exhibit diverse structures and lifecycles, ranging from confined upper-tropospheric systems to deep, multi-level vortex structures. While COL climatologies are well documented, the mechanisms driving their deepening remain unclear. To bridge this gap, a novel track matching algorithm applied to ERA-Interim reanalysis investigates the vertical extent of Southern Hemisphere COLs. Composite analysis based on structure and eddy kinetic energy budget differentiates four COL categories: shallow, deep, weak, and strong, revealing similarities and disparities. Deep, strong COLs concentrate around Australia and the southwestern Pacific, peaking in autumn and spring, while shallow, weak COLs are more common in summer and closer to the Equator. Despite their differences, both contrasting types evolve energetically via anticyclonic Rossby wave breaking. The distinct roles of jet streams in affecting COL types are addressed: intense polar front jets correlate with more deep COLs, whereas stronger subtropical jets relate to fewer shallow COLs. The COL deepening typically occurs in the presence of a robust upstream polar front jet, which enhances ageostrophic flux convergence and baroclinic processes. The subtropical jet positively correlates with COL intensity but weakens when considering the seasonality, suggesting uncertainties in this relationship. Additionally, we highlight the significance of diabatic processes in COL deepening, addressing their misrepresentation in reanalysis and emphasizing the need for more observational and modelling studies to refine the energetic framework.

Investigating the mechanism of flow of transonic compact crossover tandem diffuser

Dealing with high transonic airflow at the outlet of a mixed-flow impeller is a challenging issue in research on the design of efficient and compact diffusers. A low aspect ratio and an adverse pressure gradient in the passage of the diffuser can lead to flow separation on the hub side of the bend and the suction side of the aft blade. Tandem blading can be used to attain flow control through an appropriate relative circumferential tandem position (λ). However, a comprehensive understanding of flow in a compact crossover tandem diffuser (CTD) requires further investigation. This study provides a detailed analysis of the mechanism of flow in a compact crossover baseline tandem diffuser (CBTD) as well as the influence of different values of λ on the structure of flow of the CTD. The findings show that the CBTD can suppress secondary flow separation on the hub side of the bend by reasonably distributing the radial load. We also found that a value of λ of 75% can delay the point of separation on the suction side of the aft blade over a wide range of spans, where this inhibits the corner separation vortex and improves the structure of flow and performance of the diffuser. We also preliminarily explore the impacts of excitation of full-span jet intensities with different values of λ on the corner separation vortex on the suction side of the aft blade and offer guidance for the design of a compact and efficient CTD.

Effects of mixture initial conditions on deflagration to detonation transition enhanced by transverse jets

To explore the effects of mixture initial conditions on the deflagration to detonation transition (DDT) enhanced by transverse jets, numerical studies were conducted on the flame acceleration of H2/Air mixture under different initial conditions, including initial pressure, temperature, and equivalence ratio. The results indicate significant differences in flame acceleration processes under different initial pressures (0.05, 0.1, 0.15, and 0.2 MPa). Changes in jet intensity and combustion rate induced by variations in mixture initial pressure collectively influence the flame acceleration process, but the impact of jet intensity is more significant. However, effective coupling between transverse wave propagation and flame acceleration is also crucial for the DDT process. Changes in mixture initial temperature (300, 350, 400, and 450 K) and equivalence ratio (0.8, 1.0, 1.2, and 1.4) have negligible impact on jet intensity. The variation trend of flame velocity under different initial temperatures or equivalence ratios is consistent, but the detonation initiation performance is slightly different. As the initial temperature increases, the DDT distance and DDT time are shortened. With an increasing equivalence ratio, the DDT distance and DDT time initially decrease and then increase, reaching the shortest at slightly rich fuel conditions.

Did steam boost the height and growth rate of the giant Hunga eruption plume?

The eruption of Hunga volcano on 15 January 2022 produced a higher plume and faster-growing umbrella cloud than has ever been previously recorded. The plume height exceeded 58 km, and the umbrella grew to 450 km in diameter within 50 min. Assuming an umbrella thickness of 10 km, this growth rate implied an average volume injection rate into the umbrella of 330–500 km3 s−1. Conventional relationships between plume height, umbrella-growth rate, and mass eruption rate suggest that this period of activity should have injected a few to several cubic kilometers of rock particles (tephra) into the plume. Yet tephra fall deposits on neighboring islands are only a few centimeters thick and can be reproduced using ash transport simulations with only 0.1–0.2 km3 erupted volume (dense-rock equivalent). How could such a powerful eruption contain so little tephra? Here, we propose that seawater mixing at the vent boosted the plume height and umbrella growth rate. Using the one-dimensional (1-D) steady plume model Plumeria, we find that a plume fed by ~90% water vapor at a temperature of 100 °C (referred to here as steam) could have exceeded 50 km height while keeping the injection rate of solids low enough to be consistent with Hunga’s modest tephra-fall deposit volume. Steam is envisaged to rise from intense phreatomagmatic jets or pyroclastic density currents entering the ocean. Overall, the height and expansion rate of Hunga’s giant plume is consistent with the total mass of fall deposits plus underwater density current deposits, even though most of the erupted mass decoupled from the high plume. This example represents a class of high (> 10 km), ash-poor, steam-driven plumes, that also includes Kīlauea (2020) and Fukutoku-oka-no-ba (2021). Their height is driven by heat flux following well-established relations; however, most of the heat is contained in steam rather than particles. As a result, the heights of these water-rich plumes do not follow well-known relations with the mass eruption rate of tephra.

Effect of impinging jet on rapid cooling of a miniature Joule-Thomson cryocooler: Experimental study of operating conditions

A miniature open-cycle Joule-Thomson (J-T) cryocooler possesses excellent potential for rapid cooling from ambient temperature to about 100 K within seconds. In this rapid cooling process, the interplay of the heat transfer process between the cryogenic fluid and the cold plate plays a crucial role, in addition to the J-T effect and the energy recovery within the heat exchanger of the cryocooler. The phase state of the impinging jet is determined by the jet temperature and has different heat transfer mechanism. To investigate this impinging jet behavior separately, an experimental system for the rapid cooling J-T cryocooler was set up and the jet temperature was measured besides other important parameters. The operating conditions, including the cylinder pressure, cylinder volume, ambient temperature, and the refrigerant, were studied orthogonal. It was observed that argon, compared to nitrogen, can be more rapidly throttled into its two-phase region within a second. However, nitrogen will perform better than argon in terms of cool-down time. This is attributed to the temperature difference between the jet and the cold plate, which significantly influences the boiling mode of the two-phase jet, and in turn affects the cryocooler's cooling rate. Nevertheless, due to the smaller heat transfer intensity of single-phase jet, the cool-down time of nitrogen deteriorates quickly at high ambient temperatures. Experimental results also revealed that the cooling rate of the cryocooler still can be enhanced even if cylinder pressure beyond its saturation curve, caused by the dynamic cooling process and the pressure drop within the finned tube.

Cu-based nano-multilayer film produced by HiPIMS for antimicrobial properties and its application in photodetector

This paper reports on the use of high-power impulse magnetron sputtering to deposit Cu-based nano-multilayer films (CuZrTiAl) on Si wafers and AISI 304 stainless steel. Co-sputtering can be performed using multiple simultaneous targets to decrease the cost of manufacturing alloy targets at industrial scales. Co-sputtering mode allows variations in the power supplied to the various targets to control the intensity of the plasma jets and thereby tailor the composition of the deposited films. Our primary aim in this study was to elucidate the effects of Al target power (from 0.3 to 1.3 kW) on the structure and antibacterial properties of the resulting coatings. Varying the Al target power was shown to alter the chemical composition, layer thickness, and structure. EPMA results revealed that increasing the power from 0.3 to 1.3 kW caused a monotonic increase in Al content from 6.1 to 18.3 at%. Dark-field TEM images revealed that decreasing the period thickness from 8.6 to 4.6 nm caused the ultra-thin film Cu to transform into a single isolated nano-crystal, which facilitated the release of Cu ions to improve antibacterial effects (from 84 % to 99 % for Escherichia coli). This study also demonstrated the recycling of the proposed Cu-based nanoscale multilayer films to fabricate metal-doped ZnO nanowires for use in photodetectors. The photodetector achieved a photocurrent-to-dark-current ratio of 150 when using an LED light source with a wavelength of 365 nm.

Study on the Influence of a Powered Nacelle on the Wake Vortex Characteristics of Wide-Body Aircraft

The aircraft wake vortex is an important factor affecting flight safety; as an important part of the aircraft, the powered nacelle will inevitably have an important impact on the aircraft wake vortex, so it is of great practical significance to research it. The present study focused on the numerical simulation of the wake flow of large aircraft (as the front aircraft) and the comparative analysis of the influence of engine jets on the wake flow. In order to meet the accuracy requirements and control the consumption of computing resources, LES and RANS methods were compared, and the RANS method was finally selected for subsequent calculation. The dynamic effect of jet flow was simulated by simplifying the boundary conditions of the inlet fan and outlet bypass as the mass flow boundary condition. The simulation results showed that the engine nacelle will have a significant impact on the morphology of the aircraft wake flow (position and strength of the main vortex in the wake flow system), which is caused by the vortices formed under the shear flow and separated flow of the nacelle. However, the nacelle will not significantly change the total strength of the wake vortex (half-plane circulation). The engine jet intensity causes additional turbulent mixing, which will accelerate the fusion of the nacelle vortex and ultimately change the intensity ratio of the inner wing vortex and the wingtip vortex, affecting the trajectory of the wake of the mean vortex. The study provides a corresponding reference for the following research on a wake vortex by a powered nacelle.

Study on the Characteristics of Low-level Jets in Short-term Heavy Rainfall under the Influence of Northeast Cold Vortex in Shenyang Based on Wind Profile Radar

To enhance the understanding of the mechanisms behind heavy rainstorms influenced by the northeast cold vortex in Shenyang, we analyzed the intensity, height, and index of low-level jets during short-term heavy rainfall events from May to September between 2017 and 2021. The findings are as follows: (1) The maximum wind speed below 2 km generally follows a normal distribution, with low-level jets already present prior to approximately 30% of the heavy rainfall events. The maximum wind speed at corresponding percentiles shows a slight increase as the rainstorm approaches. However, the frequency of low-level jets decreases, and wind speeds significantly drop during the rainstorm. (2) The height distribution of low-level jets increases with altitude, reaching its lowest point 2 to 3 hours before the onset of heavy rainfall. At this time, low-level jets exhibit their strongest and most vigorous development. Combined with the warm, moist air from the southwest providing moisture and thermal energy, these conditions can trigger the onset of heavy rainstorms. (3) The hourly distribution of the low-level jet index (I) remains relatively consistent leading up to a rainstorm. As the rainstorm nears, wind speeds decrease, and the minimum height of low-level jets rises, resulting in a decrease in the low-level jet index (I).