Numerical study of flow and thermal characteristics of pulsed impinging jet on a dimpled surface

This research comprehensively investigates the flow and thermal characteristics of a pulsating impinging jet over a dimpled surface.It analyzes the impact of key parameters(e.g.,inlet velocity pulsation functions,pulsation frequency,amplitude,dimple pitch,dimple depth,Reynolds number)on flow patterns and heat transfer.Validated computational fluid dynamics and the Re-normalization group turbulence model are employed to accurately simulate complex turbulent flow behavior.Local and average heat transfer coefficients are calculated and compared to steady impingement cases,revealing the potential benefits of pulsation for heat transfer enhancement.The study also examines how pulsation-induced flow modulation and thermal mixing affect heat transfer mechanisms.Results indicate that combining fluctuating flow with a dimpled surface can improve heat transfer rates.In summary,increasing pulsation amplitude consistently enhances heat transfer,while the effect of frequency varies between impinging and wall jet zones.

A comparative study for the impact performance of shaped charge JET on UHPC targets

With the development of two-stage munitions(a precursor shaped charge(SC)and a following kinetic energy projectile)to attack the hard concrete targets,as well as the increasing applications of ultra-high performance concrete(UHPC)in both civil and military protective structures,a comparative study on the impact performance of SC formed jet on UHPC target is performed experimentally and numerically at present.Firstly,a series of jet penetration/perforation test on the UHPC,45# steel and UHPC/45# steel composite targets are conducted.By assessing the penetration depth and borehole(crater and tunnel)diameter,the influences of target material and configuration as well as the standoff distance of SC on the impact performance of jet are experimentally discussed.Then,by adopting the 2 D multi-material Arbitrary Lagrange-Euler(ALE)algorithm,Fluid-Structure Interaction(FSI)method and erosion algorithm implemented in the finite element code LS-DYNA,the formation and impact performance of jet in the present test are well reproduced.Finally,based on the validated numerical algorithms,constitutive models and the corresponding parameters,the influences of target material(UHPC,NSC and 45# steel),standoff distance,target configuration(stacked and spaced)and weight efficiency on the impact performance of jet are further discussed.The derived conclusions could provide helpful references for evaluating the ballistic performance of jet and designing the protective structures.

Study on the characteristics of interaction flowfields induced by supersonic jet on a revolution body

The paper focuses on the triple jets interaction with a hypersonic external flow on a revolution body. The experimental model is a ogive-cylinder body with three supersonic nozzles, which are aligned along the flow direction. The freestream Mach numbers are 5 and 6. The spatial and surface flow characteristics are illustrated by the schlieren photographs and the typical pressure distribution. The results show that there are multi-wave system, separation, reattachment, multi-peak pressure, high-pressure and low-pressure zone boundaries obvious distinction in tri-jets interference flowfield. The present paper also analyzes how do the pressure ratio, the angle of attack, and Mach number effect on tri-jets interaction characteristics.

Impact of the Western Pacific Tropical Easterly Jet on Tropical Cyclone Genesis Frequency over the Western North Pacific

Although it is well known that the tropical easterly jet(TEJ)has a significant impact on summer weather and climate over India and Africa,whether the TEJ exerts an important impact on tropical cyclone(TC)activity over the western North Pacific(WNP)remains unknown.In this study,we examined the impact of the TEJ on the interannual variability of TC genesis frequency over the WNP in the TC season(June-September)during 1980-2020.The results show a significant positive correlation between TC genesis frequency over the WNP and the jet intensity in the entrance region of the TEJ over the tropical western Pacific(in brief WP_TEJ),with a correlation coefficient as high as 0.66.The intensified WP_TEJ results in strong ageostrophic northerly winds in the entrance region and thus upper-level divergence to the north of the jet axis over the main TC genesis region in the WNP.This would lead to an increase in upward motion in the troposphere with enhanced low-level convergence,which are the most important factors to the increases in low-level vorticity,mid-level humidity and low-level eddy kinetic energy,and the decreases in sea level pressure and vertical wind shear in the region.All these changes are favorable for TC genesis over the WNP and vice versa.Further analyses indicate that the interannual variability of the WP_TEJ intensity is likely to be linked to the local diabatic heating over the Indian Ocean-western Pacific and the central Pacific El Ni?o-Southern Oscillation.

Effect of An Atmospheric Plasma Jet on the Differentiation of Melanoblast Progenitor

Objective Melanoblasts are the cell source of regeneration for pigment restoration.The ability to differentiate into mature melanocytes is the essential feature of melanoblasts in depigmentation diseases.Cold atmospheric plasma is an ionized gas with near-room temperature and highly reactive species that has been shown to induce stem cell differentiation.The aim of the study was to explore the effect of cold atmospheric plasma on the differentiation of melanoblast progenitor cells.Methods In this study,melanoblasts were exposed to the plasma jet and the cell morphology was observed.The cell cycle and cell proliferation were detected.Furthermore,the cell immunofluorescence and the detection of melanin particle and nitric oxide were carried out to investigate the differentiation of melanoblast progenitor cells.Results Cells that were treated with the plasma had longer and more synaptic structures,and the G1 phase of cell cycle was prolonged in the treated group.More melanin synthesis-related proteins and melanin particles were produced after plasma treatment.Nitric oxide was one of the active components generated by the plasma jet,and the nitric oxide content in the cell culture medium of the treated group increased.Conclusion These results indicate that an increase in nitric oxide production caused by a plasma jet can promote cell differentiation.The application of plasma provides an innovative strategy for the treatment of depigmentation diseases.

Numerical study of the effect of coflow argon jet on a laminar argon thermal plasma jet

The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.

Studies of flow field characteristics during the impact of a gaseous jet on liquid–water column

Both experimental and numerical studies were presented on the flow field characteristics in the process of gaseous jet impinging on liquid–water column. The effects of the impinging process on the working performance of rocket engine were also analyzed. The experimental results showed that the liquid–water had better flame and smoke dissipation effect in the process of gaseous jet impinging on liquid–water column. However, the interaction between the gaseous jet and the liquid–water column resulted in two pressure oscillations with large amplitude appearing in the combustion chamber of the rocket engine with instantaneous pressure increased by 17.73% and 17.93%, respectively. To analyze the phenomena, a new computational method was proposed by coupling the governing equations of the MIXTURE model with the phase change equations of water and the combustion equation of propellant. Numerical simulations were carried out on the generation of gas, the accelerate gas flow, and the mutual interaction between gaseous jet and liquid–water column.Numerical simulations showed that a cavity would be formed in the liquid–water column when gaseous jet impinged on the liquid–water column. The development speed of the cavity increased obviously after each pressure oscillation. In the initial stage of impingement, the gaseous jet was blocked due to the inertia effect of high-density water, and a large amount of gas gathered in the area between the nozzle throat and the gas–liquid interface. The shock wave was formed in the nozzle expansion section. Under the dual action of the reverse pressure wave and the continuously ejected high-temperature gas upstream, the shock wave moved repeatedly in the nozzle expansion section, which led to the flow of gas in the combustion chamber being blocked, released, re-blocked, and re-released. This was also the main reason for the pressure oscillations in the combustion chamber.

The Effect of the Subtropical Jet on the Rainfall over Southern China in January 2008

ABSTRACT The third precipitation episode of China＇s great snowstorms of 2008 was analyzed using station observations and ECMWF six-hourly data. The variation of the shape of the upper-level subtropical jet played an important role in the rainfall over south- ern China. With the eastward movement of the trough, the jet shape changed from two straight jets to a tilting jet over China and then it moved southward. With these variations, the south-north movement of ascending flow and precipitation area over southern China occurred.

Effects of single synthetic jet on turbulent boundary layer

The turbulent boundary layer(TBL)is actively controlled by the synthetic jet generated from a circular hole.According to the datasets of velocity fields acquired by a time-resolved particle image velocimetry(TR-PIV)system,the average drag reduction rate of 6.2%in the downstream direction of the hole is obtained with control.The results of phase averaging show that the synthetic jet generates one vortex pair each period and the consequent vortex evolves into hairpin vortex in the environment with free-stream,while the reverse vortex decays rapidly.From the statistical average,it can be found that a low-speed streak is generated downstream.Induced by the two vortex legs,the fluid under them converges to the middle.The drag reduction effect produced by the synthetic jet is local,and it reaches a maximum value at x^(+)=400,where the drag reduction rate reaches about 12.2%.After the extraction of coherent structure from the spatial two-point correlation analysis,it can be seen that the synthetic jet suppresses the streamwise scale and wall–normal scale of the large scale coherent structure,and slightly weakens the spanwise motion to achieve the effect of drag reduction.

The Effect of the Propeller Jet on Pile Groups

The objective of this study is to determine the effect of jet propeller on the damage of berthing structures combined of armoured slope with pile groups. For this purpose, scour measurements were performed for four types berthing structures, which were armoured slope with tandem arrangements of piles for two and three piles and with side by side arrangements of piles for two and three piles. The effect of gap between piles on damage was investigated. The damage level induced by propeller jet between piles was determined. The gaps were 1, 2, 3, and 4 times the pile diameter. Three different values of Rpm （690, 820, and 950） were chosen for the tests. The diameter of circular piles is 40 mm. The slope ratio was 1/3 and the diameter of propeller was 10 cm.

Effect of wall jet on the bubble dynamics near arigid wall

The bubble dynamic near a rigid wall with a wall jet was investigated by codynamics(CFD)method with the volume of fluid(VOF)model,which had been validated by vious experimental data.The effects of different velocities of the wall jet and ditances on the bubble dynamics were studied.The results show that the bubble is squjet due to more force added on the bubble.When the velocity of the wall jet increa,the wall anthe pressure along the wall at collapse time increase because of the extra push indAs the stand-off distance increases,the pressure along the wall first increases then decrethe distance from the bubble to the wall increases.

Effects of Vortex Generator Jet on Corner Separation/Stall in High-Turning Compressor Cascade

The effects of the vortex generator jet(VGJ)attached at the endwall on the corner separation/stall control are investigated by numerical simulation in a high-turning linear compressor cascade. The results show that the corner separation could be reduced significantly, which results in a wider operation range as well as a more uniform exit flow angle and total pressure profile. At the near-stall operation point, the maximum relative reduction of the total pressure loss is up to 32.5%,, whereas the jet mass ratio is less than 0.4%,. Based on the analysis of the detailed flow structure, three principal effects of the VGJ on the endwall cross flow and corner separation are identified. One is to increase the tangential velocity component opposite to cross flow, thus inhibiting the endwall secondary flow near the jet exit. The second is to suppress the pitchwise extension of the passage vortex as an air fence. The third is to sweep the low energy fluids towards the mainstream on the up-washed side and to transport the mainstream fluids to the endwall to reenergize the boundary layer on the down-washed side.

The impacts of the East Asian subtropical westerly jet on weather extremes over China in early and late summer

Summer weather extremes(e.g.,heavy rainfall,heat waves)in China have been linked to anomalies of summer monsoon circulations.The East Asian subtropical westerly jet(EASWJ),an important component of the summer monsoon circulations,was investigated to elucidate the dynamical linkages between its intraseasonal variations and local weather extremes.Based on EOF analysis,the dominant mode of the EASWJ in early summer is characterized by anomalous westerlies centered over North China and anomalous easterlies centered over the south of Japan.This mode is conducive to the occurrence of precipitation extremes over Central and North China and humid heat extremes over most areas of China except Northwest and Northeast China.The centers of the dominant mode of the EASWJ in late summer extend more to the west and north than in early summer,and induce anomalous weather extremes in the corresponding areas.The dominant mode of the EASWJ in late summer is characterized by anomalous westerlies centered over the south of Lake Baikal and anomalous easterlies centered over Central China,which is favorable for the occurrence of precipitation extremes over northern and southern China and humid heat extremes over most areas of China except parts of southern China and northern Xinjiang Province.The variability of the EASWJ can influence precipitation and humid heat extremes by driving anomalous vertical motion and water vapor transport over the corresponding areas in early and late summer.

Study on influence of characteristics of air-supply jet on drain-contamination efficiency and air quality in heading

Based on the theory of air supply jet, the conception and theory of the air quality and the drain contamination efficiency, the results achieved by comparing the circular cross section wall jet with the plane wall jet were following: firstly, within the limitation of the ventilation distance at the tunnel heading in a coal mine, there were a better air quality and a higher efficiency of drain contamination with application of the plane wall jet ventilation. Secondly, there was a advantage to improve the air quality of the workers breathing area with mounting the air supply outlet on the top but not on the side of the tunnel heading.

The Influence of Modulated Slotted Synthetic Jet on the Bypass of Hump

This paper deals with the influence of phase modulated synthetic jet on the aerodynamics of the hump in a closed test section Of the Eiffel-type wind tunnel. Three experimental methods of measurement techniques of this phenomenon were used： the pressure profile using the Kiel total pressure probe, the velocity profile using the CTA （constant temperature anemometry） probe and the visualization of the flow field using the hot film and the thermo camera, The experimental results with and without the influence of the synthetic jet were compared, as well the impact of the phase shift of the neighbouring synthetic jets. As a reference case, the flow around the hump without the influence of the synthetic jet was selected. The results of the measurement are presented in figures and compared.

Investigation of hydroxyl-terminated polybutadiene propellant breaking characteristics and mechanism impacted by submerged cavitation water jet

A submerged cavitation water jet(SCWJ)is an effective method to recycle solid propellant from obsolete solid engines by the breaking method.Solid propellant's breaking modes and mechanical process under SCWJ impact are unclear.This study aims to understand those impact breaking mechanisms.The hydroxyl-terminated polybutadiene(HTPB)propellant was chosen as the research material,and a self-designed test system was used to conduct impact tests at four different working pressures.The high-speed camera characterized crack propagation,and the DIC method calculated strain change during the impact process.Besides,micro and macro fracture morphologies were characterized by scanning electron microscope(SEM)and computed tomography(CT)scanning.The results reveal that the compressive strain concentration region locates right below the nozzle,and the shear strain region distributes symmetrically with the jet axis,which increases to 4% at first 16th ms,the compressive strain rises to 2% and 6% in the axial and transverse direction,respectively.The two tensile cracks formed first at the compression strain concentrate region,and there generate many shear cracks around the tensile cracks,and those shear cracks that develop and aggregate cause the cracks to become wider and cut through the tensile cracks,forming the tensile-shear cracks and the impact parts eventually fail.The HTPB propellant forms a breaking hole shaped conical after impact 10 s.The mass loss increases by 17 times at maximum,with the working pressure increasing by three times.Meanwhile,the damage value of the breaking hole remaining on the surface increases by 7.8 times while 2.9 times in the depth of the breaking hole.The breaking efficiency is closely affected by working pressures.The failure modes of HTPB impacted by SCWJ are classified as tensile crack-dominated and tensile-shear crack-dominated damage mechanisms.

Interdecadal variability of summer precipitation in the Three River Source Region: Influences of SST and zonal shifts of the East Asian subtropical westerly jet

Summer precipitation in the Three Rivers Source Region(TRSR)of China is vital for the headwaters of the Yellow,Yangtze,and Lancang rivers and exhibits significant interdecadal variability.This study investigates the influence of the East Asian westerly jet(EAWJ)on TRSR rainfall.A strong correlation is found between TRSR summer precipitation and the Jet Zonal Position Index(JZPI)of the EAWJ from 1961 to 2019(R=0.619,p<0.01).During periods when a positive JZPI indicates a westward shift in the EAWJ,enhanced water vapor anomalies,warmer air,and low-level convergence anomalies contribute to increased TRSR summer precipitation.Using empirical orthogonal function and regression analyses,this research identifies the influence of large-scale circulation anomalies associated with the Atlantic–Eurasian teleconnection(AEA)from the North Atlantic(NA).The interdecadal variability between the NA and central tropical Pacific(CTP)significantly affects TRSR precipitation.This influence is mediated through the AEA via a Rossby wave train extending eastward along the EAWJ,and another south of 45°N.Moreover,the NA–CTP Opposite Phase Index(OPI),which quantifies the difference between the summer mean sea surface temperatures of the NA and the CTP,is identified as a critical factor in modulating the strength of this teleconnection and influencing the zonal position of the EAWJ.

The medium-temperature dependence of jet transport coefficient in high-energy nucleus-nucleus collisions

The medium-temperature T dependence of the jet transport coefficient̂q was studied via the nuclear modification factor RAA(p_(T))and elliptical flow parameter v_(2)(p_(T))for large transverse momentum p_(T) hadrons in high-energy nucleus-nucleus collisions.Within a next-to-leading-order perturbative QCD parton model for hard scatterings with modified fragmentation functions due to jet quenching controlled by q,we check the suppression and azimuthal anisotropy for large p_(T) hadrons,and extract q by global fits to RAA(pT)and v_(2)(pT)data in A+A collisions at RHIC and LHC,respectively.The numerical results from the best fits show that q∕T^(3) goes down with local medium-temperature T in the parton jet trajectory.Compared with the case of a constant q∕T^(3),the going-down T dependence of q∕T^(3) makes a hard parton jet to lose more energy near T_(c) and therefore strengthens the azimuthal anisotropy for large pT hadrons.As a result,v_(2)(p_(T))for large pT hadrons was enhanced by approximately 10%to better fit the data at RHIC/LHC.Considering the first-order phase transition from QGP to the hadron phase and the additional energy loss in the hadron phase,v_(2)(p_(T))is again enhanced by 5-10%at RHIC/LHC.

A novel approach of jet polishing for interior surface of small-grooved components using three developed setups

It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm.Traditional polishing methods are disabled to polish the component,meanwhile keeping the structure intact.To overcome this challenge,small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer.A novel approach to multi-phase jet(MPJ)polishing is proposed,utilizing a self-developed polisher that incorporates solid,liquid,and gas phases.In contrast,abrasive air jet(AAJ)polishing is recommended,employing a customized polisher that combines solid and gas phases.After jet polishing,surface roughness(Sa)on the interior surface of grooves decreases from pristine 8.596μm to 0.701μm and 0.336μm via AAJ polishing and MPJ polishing,respectively,and Sa reduces 92%and 96%,correspondingly.Furthermore,a formula defining the relationship between linear energy density and unit defect volume has been developed.The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm^(-1)to 0.22 J mm^(-1).The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones.Computational fluid dynamics simulation results reveal that material is removed by shear stress,and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove,resulting in uniform material removal.This is in good agreement with the experimental results.The novel proposed setups,approach,and findings provide new insights into manufacturing complex-structured components,polishing the small-grooved structure,and keeping it unbroken.

Jets,Accretion and Spin in Supermassive Black Holes

The theoretical model suggests that relativistic jets of active galactic nuclei(AGNs)rely on the black hole spin and/or accretion.We study the relationship between jet,accretion,and spin using supermassive black hole samples with reliable spin of black holes.Our results are as follows:(1)There is a weak correlation between radio luminosity and the spin of the black hole for our sample,which may imply that the jet of the supermassive black hole in our sample depends on the other physical parameters besides black hole spins,such as accretion disk luminosity.(2)The jet power of a supermassive black hole can be explained by the hybrid model with magnetic field of corona.(3)There is a significant correlation between radio-loudness and black hole spin for our sample.These sources with high radio-loudness tend to have high black hole spins.These results provide observational evidence that the black hole spin may explain the bimodal phenomena of radio-loud and radio-quiet AGNs.