Jet Length Research Articles

Research on structural parameter optimization of elliptical bipolar linear shaped charge based on machine learning

Numerical simulation based on SPH method, compared with laboratory experiments, using the grey correlation theory to analyze the correlation between the parameters of the elliptical bipolar linear shaped charge and the performance of the shaped charge jet. The structure of shaped charge is optimized by machine learning to obtain the optimal structural parameters, and it is compared with the rock crack development of shaped charge blasting in practical application. The results show that the structural parameters of the shaped charge have the same influence on the jet head velocity, and there are certain differences in the impact on the jet length. The fitted curve of the support vector machine (SVM) regression model based on the genetic algorithm (GA) is high prediction accurate. By comparing the optimization results with the actual engineering application of the shaped charge structure, the rock breaking effect has been significantly improved, which has important guiding significance for the actual engineering application.

Stepwise development of atmospheric pressure plasma jet driven by bursts of high-voltage nanosecond pulses at multi-tens MHz

This study employs the bursts of high-voltage nanosecond pulses at multi-tens MHz to drive the helium atmospheric pressure plasma jet. Such bursts are obtained by modulating a high-voltage nanosecond pulse based on the wave reflections in a coaxial cable. The development processes and mechanisms of the plasma jet are analyzed in detail based on the discharge waveforms, discharge images, gas temperature, electron density, and axial electric field. Because the time interval between adjacent pulses is much shorter than the characteristic plasma decay time, the discharge channel driven by the first pulse still has high residual electron density and conductivity when the second pulse arrives. The first discharge channel serves as an extension of the high-voltage electrode. In this case, the second discharge starts at the end of the first discharge channel and continues to propagate forward. Driven by the bursts of high-voltage nanosecond pulses, the stepwise propagation of a guided streamer along the plasma jet is observed. The characteristic of the stepwise development of the guided streamer is stable and repeatable under the same condition and does not change at different helium flow rates if the flow is laminar. Reducing the cable length results in a higher equivalent pulse frequency in the bursts and significantly increases the plasma jet length. However, an excessively high frequency will cause a rise in gas temperature and pressure fluctuation in helium flow, resulting in a reduction in the length of the laminar region and an unstable discharge.

Optimization of Spatial Parameters of a 2.45-GHz Atmospheric Pressure Cold Plasma Jet: Comparison Between Multiphysics Simulation and Experimental Results

In this article, the optimization of spatial parameters of a 2.45-GHz atmospheric pressure plasma jet (APPJ) at different operational parameters has been done. For this purpose, simulations and experiments have been carried out to investigate the spatial dimensions of the microwave cold plasma jet generated from the device. To achieve this, the plasma discharge behavior and jet formation have been studied at different working gas flow rates and input microwave power. The 3-D simulations have been carried out by using the plasma module and electromagnetic wave module of COMSOL Multiphysics v. 5.5. Experimental validation was achieved and simulated spatial dimensions of plasma jet showed good correspondence with the experimental results. Simulated variations of jet length and diameter with gas flow rate and applied power matched closely with experimental results. Intrinsic plasma parameters, such as electron temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{e}$ </tex-math></inline-formula> ) and number density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n_{e}$ </tex-math></inline-formula> ), were also obtained with the simulation model and compared with experimental findings based on optical emission spectroscopy (OES) results and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{e}$ </tex-math></inline-formula> values matched well in both cases.

Experimental Investigation on Ignition of Hyperburner Based on Gliding Arc Plasma Igniter Driven by Pressure Difference

The hyperburner is a key component of a TBCC engine, and its reliable ignition and stable operation are critical. The gliding arc plasma igniter driven by differential pressure has the technical advantages of low energy consumption and high jet temperature. In this paper, the electrical and flow characteristics of the gliding arc plasma igniter are studied, and the basic ignition experiment in the hyperburner is carried out. Electrical characteristic experiments show that the discharge duration, the evolution of the gliding arc and the fracture frequency are affected by the pressure difference between the inlet and outlet of the igniter (Δp). With the increase in Δp, the frequency of the trapezoidal envelope in the voltage and current waveforms increases, and the frequency of the evolution and fracture of the gliding arc increases. The continuous discharge time of the gliding arc decreases when Δp = 550 Torr. The flow characteristic experiments show that the velocity of the swirl sheath is increased and the protective effect on the gliding arc is enhanced with the increase in Δp. In the range of 20–550 Torr, the jet length first increases and then decreases with the increase in Δp. The jet length reaches a maximum of 31 mm at Δp = 50 Torr. Basic ignition experiments show that proper Δp can widen the lean ignition limit and shorten the ignition delay time. In the working conditions of this paper, the ignition effect is the best when Δp = 350 Torr, which can widen the lean ignition limit by 37.5% and shorten the ignition delay time by 17%. After increasing the oil–gas ratios, the combustion is more complete and the ignition delay time can be shortened by 93.1% at most.

Stratified micro-environments using a sidewall air supply: An experimental and simulation study

The idea of providing stratified micro-environments in a shared environment by utilizing a sidewall air supply is proposed, to provide different thermal comfort and air quality levels to satisfy individual needs at different occupied positions. Experimental cases with various supply air parameters and room layouts are conducted in a mock consultation room consisting of two face-to-face occupants. Further, parametric studies using computational fluid dynamics (CFD) are performed. Overall thermal sensation and local thermal comfort are both evaluated. Tracer gas (i.e., CO2) concentration distributions are investigated experimentally, while the air age is used as an indicator in CFD simulations. The results show that the proposed strategy simultaneously provides displacement ventilation (DV) and stratum ventilation (SV) in a shared environment, satisfying individual preferences and needs. The demarcation thermal length of the supply air jet between DV and SV is around 0.8 m. The normalized contaminant concentration at the breathing level is 0.00–0.30 with both table and floor contaminant sources. Better air quality is achieved in the area served by a higher thermal length. The local discomfort and “lock-up” effect under DV is reduced, by the interaction between the supply air jets, which is validated, as the partition impeding the interaction brings a significant influence. Short jet spacing of 0.75 m implies that multiple stratified micro-environments can be provided in a medium room, while a medium distance between the occupant and the supply air terminal (i.e., 1.7 m) is the most efficient in cooling and renewing the air age.

Study on optimization of jet forming of tandem shaped charge warhead

In order to greatly improve the length of shaped charge jet and optimize the jet forming performance, the forming process of a tandem shaped charge structure with reverse detonation mode was numerically simulated. The effects of the rear and front stage liner thickness on the jet length, jet head velocity, jet kinetic energy and energy conversion rate were analyzed respectively using LS-DYNA finite element analysis software. Then the optimal thickness of the front and rear stage liner of the tandem shaped charge structure was optimized, and the jet length was measured. Under the condition of charge diameter of 200 mm, when the liner thickness was 0.02CD (charge diameter) for K-charge and liner thickness was 0.25CD for the front stage warhead, the jet forming was stable and the length is the longest. After the two-stage warhead was detonated in reverse order (the initiation delay time was 220 μs), a tandem jet can be formed, and the effective jet length (excluding the pestle body) is 65 % higher than that of the later stage charge.

Experimental study on direct contact condensation of saturated steam at low mass flux in subcooled quiescent water

Abstract The phenomenon of saturated steam jet injection in subcooled quiescent water has many practical applications including in heat exchangers, steam jet pumps, steam dumping systems in nuclear plants, etc. The experimental setup is designed and fabricated indigenously to investigate this phenomenon at lower mass fluxes ∼120 and 150 kg/m2 s. The steam jet of conical shape has been observed for all the test conditions. The recorded axial temperature distribution showed that near the nozzle region, the temperature is governed by the saturated condition of steam while the later region is dependent on the water pool temperature. The maximum temperature is observed to be at the center of the jet. It has been found that the dimensionless penetration length of the steam jet in water is directly dependent on both the temperature of the water pool and the mass flux of steam. The dimensionless jet length has been found in the range ∼1.54–2.02 and 2.07–2.19 for mass fluxes ∼120 and 150 kg/m2 s, respectively. The average heat transfer coefficient has been found in the range ∼1.97–2.37 MW/m2 K.

Primary atomization of liquid-fuel jets in confined turbulent pipe-flows of air at elevated temperatures

The primary atomization of evaporating laminar liquid jets of either pure n-pentane or n-heptane injected continuously from a circular nozzle concentrically and axisymmetrically into high-temperature turbulent coflows of air in confined a pipe has been studied experimentally. Fuel-jet bulk velocities up to 2.7 m/s, air coflow bulk velocities up to 37 m/s and temperatures up to 1150 K were investigated within a 25 mm round pipe. In the near-field region of the injector nozzle, liquid fuel jets were formed whose length increased with the fuel injection velocity and decreased with the air velocity. Smaller droplets were formed at both higher fuel and air velocities. Droplet diameters within the range from 200 to 900 µm were measured, indicating the polydispersed nature of the fuel spray. The mean droplet diameter increased non-monotonically with increasing axial distance from the nozzle due to a complex competition between droplet coalescence and evaporation. No significant effect of the air inlet temperature was observed within the investigated range of conditions on the jet length and droplet size. However, smaller droplets were obtained in flows with lower turbulence intensities and longer longitudinal integral lengthscales. Analysis of the data reveals that the mean droplet diameters can be predicted by the empirical expression (dmean/djet) = 34 × 103 We∆1.29Re∆-3, independent of the two perforated plates selected and used in the present work. The resulting data can contribute towards a better understanding of interfacial dynamics, and the development and validation of advanced multiphase-flow and reacting-flow models.

Experimental and numerical investigation of jet performance based on Johnson-Cook model of liner material

A comparative study of the shaped jets of six liner materials, namely, copper, Cu–Zn alloy, Steel1006, high nitrogen steel, and two titanium alloys, was conducted to investigate the influence of the macroscopic mechanical properties of the materials on the jet's performance. The X-ray experiment of the jet was performed, and the numerical calculation of the jet formation was carried out by means of simulation based on the Johnson–Cook model. Copper, Cu–Zn alloy, and Steel1006 formed cohesive jets, whereas the jets of the three other materials had different degrees of radial dispersion. The penetration depth of the jet has a significant negative correlation with its radial dispersion degree. In the numerical calculation, the head shape of the jet under the Euler algorithm can be used to judge its cohesion. Arrowheads or rounded oval heads symbolize cohesive jets, whereas blunt or even mouth-forward “bowl-shaped” heads indicate jets with radial dispersion. The degree of dispersion is positively correlated with the degree of dullness of the jet head. Simulation results show that the influence of material melting temperature and thermal softening effect on jet velocity, length, and diameter is particularly evident, whereas the influence ability of yield strength and strain rate effect is always at a very low level. Materials with small shear modulus, high yield strength, and significant strain effects are more prone to forming non-cohesive jets, which was verified by the jet forming experiments of amorphous alloy with these material characteristics.

Effect of excitation Strouhal number on velocity field and mixing capability of acoustically excited dual jets

The present study experimentally investigated the effect of the excitation Strouhal number on the velocity field and mixing capability of excited dual jets. The dual jets were acoustically excited by a loudspeaker. The velocity pulsation at the jet exit was examined using a hotwire anemometer. The evolution process of the excited dual jets was captured using the smoke flow visualization technique. The jet spread width was measured from a long-exposure image by using the edge-detection method. The time-averaged velocity fields were measured using the particle image velocimetry (PIV) technique. The mixing capability was examined by tracer-gas concentration detection. Two characteristic flow modes, namely the bifurcated and parallel vortices, were classified in the domain of pulsation intensity and excitation Strouhal number. The excitation Strouhal number dominated the change in the characteristic flow modes. The leading vortices induced jet flow bifurcation in the bifurcated vortices mode, while the vortices broke up early in the parallel vortices mode. The recirculation region, merging length, combined length, jet spread, and later distribution of the dual jets excited in the bifurcated mode were larger than those in the parallel vortices mode. The tracer-gas value in the bifurcated vortices mode was smaller than that in the parallel vortices mode; therefore, the mixing capability in the bifurcated vortices mode was better than that in the parallel vortices mode. The unexcited and excited dual jets were compared to evaluate the effect of acoustic excitation on the flow and mixing characteristics.

Study on the variation rule of smoke back‐layering length of tunnel ceiling jet induced by strong fire plume

AbstractTunnel fire is a major research topic in tunnel safety. Because of the tunnel's narrow and enclosed structure, smoke movement plays an important role in the investigation of the tunnel fire. In this paper, the Froude similarity principle is used to study the variation rule of the smoke back‐layering length of tunnel ceiling jet induced by strong fire plume with different heat release rates, longitudinal ventilation velocities, and effective heights of fire source analyzed. It is found that the smoke back‐layering length of tunnel ceiling jet induced by strong fire plume increases with the increase of effective height of fire source and decreases with the increase of longitudinal ventilation velocity. When the heat release rate is relatively small (), the smoke back‐layering length of the tunnel ceiling jet induced by strong fire plume increases as the heat release rate increases. However, for the larger heat release rate (), the smoke back‐layering length of the tunnel ceiling jet induced by strong fire plume is mainly related to the longitudinal ventilation velocity. Based on Thomas's model and Li's model, by introducing the correction coefficient, correction formulas of the smoke back‐layering length of tunnel ceiling jet induced by strong fire plume changing with the effective height of fire source are proposed.

Gassing During Tapping of Silicon

During tapping of metal from silicon furnaces, a significant amount of gas is often released through the tap-hole. The gas is combustible, and a flame jet is created which poses a safety threat to operators. Due to the high temperatures involved, thermal NOx is also produced. This is a threat to the environment and the health of the operators. These phenomena, known as gassing, have been studied here by a mathematical model for reactive turbulent flows. The results show that the flame jet can extend several meters out from the tap-hole, and that the strength of the flame jet increases with the amount of gassing. The simulations also show that the NOx production increases with the amount of gas exiting the tap-hole, and that the thermal NOx formation does not substantially impact the length of the gas jet.

Simulation and application of post-combustion oxygen lance in a top-blown converter

ABSTRACT Flow field characteristics of conventional four-hole oxygen lance and single-flow post-combustion (PC) oxygen lance at steelmaking temperature are studied by numerical simulation, and the industrial trials are carried out in the 120 t top-blown converter to evaluate their metallurgical effects. The simulation results indicate that with the increase of ambient temperature, the potential core length of oxygen jet, jet velocity and radial width (jet diameter) increase. And the jet characteristics of PC oxygen lance are better than those of conventional lance in the radial and axial directions. The industrial trials show that, compared with the conventional lance, using the PC oxygen lance can shorten blowing time by 93 s, reduce actual oxygen consumption by 3.56 m3 t−1 and increase dephosphorization rate by 1.67%. Meanwhile, PC oxygen lance is better for slagging and solves the problem of splashing or drying caused by increasing the oxygen flow rate of the conventional lance.

Application of Effective Orifice Jet Length for Treating SST Effluent of STP by Hydrodynamic Cavitation

Advanced oxidation process in general and hydrodynamic cavitation, in particular, has emerged as a promising technology for the treatment of wastewater in the last few years as the process is energy-efficient and cost-effective. In this process, cavities are generated due to local pressure drops caused by constrictions. This work aimed to investigate the potential of hydrodynamic cavitation as a tertiary treatment to the secondary sedimentation tank effluent of a sewage treatment plant, with two laboratory-scale experimental setups having an orifice plate of a 1 mm diameter hole. The process dependency was estimated by optimizing inlet pressure (0.8 bar for setup I and 5 bar for setup II). Moreover, effective orifice jet length was varied to investigate the impact of fluid buoyancy force on expansion and collapse of a cavity on the chemical oxygen demand removal and disinfection. At L2 length (two-thirds of the original length), both setups can degrade the organic and inorganic pollutants to the maximum extent. With the optimum condition in setup II, maximum COD, TSS, and fecal coliform degradation were 80.47%, 62.83%, and 52.27%, respectively, compared to setup I.

Numerical Simulation of Orbit Controlled Hot-gas Lateral Jet of the triangular plate with rudder

Hypersonic interception weapons have high requirements for the efficiency and accuracy of the control system. As an effective control approach, the thermochemical non-equilibrium effect of jet flow must be considered in order to accurately predict the aerodynamic characteristic. At present, relevant researches are mostly focused on the low-flow rate hot jet, while numerical simulation and wind tunnel test studies on high-flow rate hot jet are rare. In this paper, the interaction flow field of the rail-controlled jet at the altitude of 60Km and 70Km has been simulated by solving the three-dimensional viscous fluid governing equations. The influence of the thermalchemical non-equilibrium effect of the jet interaction on the flow field characteristics and aerodynamic characteristics of the aircraft was analyzed. The primary results show that: (1) The flow fields of the cold-gas jet, frozen-gas jet and hot-gas jet have significant differences under the high-flow rate jet condition, which is mainly reflected the size and the pressure value of the separation region before the nozzle. The separation region length of the cold-gas jet is approximately twice that of the hot-gas jet and the length of the frozen-gas jet is between them; (2)Jet interaction will increase the surface pressure of the aircraft and reduce the skin-friction. When Ma=25, the aerodynamic interaction of hot jet is only about 30% of that of cold jet; (3) Jet interaction on aerodynamic characteristics increases with altitudes. With the increase of Mach number, the difference between the predicted results of hot jet and cold jet is enlarged because of the enhancement of the thermochemical non-equilibrium effect.

Unexpected stability of micrometer weakly viscoelastic jets

We study experimentally the stability of micrometer weakly viscoelastic jets produced with transonic flow focusing. Highly stable jets are formed when a low molecular weight polymer is added to water at a given low concentration, and the injected flow rate is reduced to its minimum value. In this case, the capillary instability is delayed, and the jet breakup occurs at distances from the ejector of the order of tens of thousands the jet diameter. The results indicate that the intense converging extensional flow in the ejection point builds up viscoelastic stress that does not relax in the jet even for times much longer than the polymer relaxation time. We hypothesize that the drag (shear) force exerted by the outer gas stream prevents the stress relaxation. It is also possible that partial polymer entanglement at the jet emission point contributes to this effect. We measure the jet length and the diameter at the ejector orifice and breakup point. The diameter takes values just above 2 μm at the breakup point regardless of the liquid flow rate and gas pressure.

Characterization of aerosol plumes from singing and playing wind instruments associated with the risk of airborne virus transmission.

The exhalation of aerosols during musical performances or rehearsals posed a risk of airborne virus transmission in the COVID‐19 pandemic. Previous research studied aerosol plumes by only focusing on one risk factor, either the source strength or convective transport capability. Furthermore, the source strength was characterized by the aerosol concentration and ignored the airflow rate needed for risk analysis in actual musical performances. This study characterizes aerosol plumes that account for both the source strength and convective transport capability by conducting experiments with 18 human subjects. The source strength was characterized by the source aerosol emission rate, defined as the source aerosol concentration multiplied by the source airflow rate (brass 383 particle/s, singing 408 particle/s, and woodwind 480 particle/s). The convective transport capability was characterized by the plume influence distance, defined as the sum of the horizontal jet length and horizontal instrument length (brass 0.6 m, singing 0.6 m and woodwind 0.8 m). Results indicate that woodwind instruments produced the highest risk with approximately 20% higher source aerosol emission rates and 30% higher plume influence distances compared with the average of the same risk indicators for singing and brass instruments. Interestingly, the clarinet performance produced moderate source aerosol concentrations at the instrument’s bell, but had the highest source aerosol emission rates due to high source airflow rates. Flute performance generated plumes with the lowest source aerosol emission rates but the highest plume influence distances due to the highest source airflow rate. Notably, these comprehensive results show that the source airflow is a critical component of the risk of airborne disease transmission. The effectiveness of masking and bell covering in reducing aerosol transmission is due to the mitigation of both source aerosol concentrations and plume influence distances. This study also found a musician who generated approximately five times more source aerosol concentrations than those of the other musicians who played the same instrument. Despite voice and brass instruments producing measurably lower average risk, it is possible to have an individual musician produce aerosol plumes with high source strength, resulting in enhanced transmission risk; however, our sample size was too small to make generalizable conclusions regarding the broad musician population.

Experimental study on steam plume shape characteristics for bevelled spray nozzles exhausting into quiescent water

Steam-water direct contact condensation phenomenon is being widely used in many industries including chemical, thermal and especially in nuclear industry due to its efficient heat and mass exchange capabilities. The present experimental study explores the underlying physics of the steam cavity/plume shapes by condensing supersonic steam exhausting from five different bevelled nozzles into quiescent water tank. Based on the high speed image capturing methodology, the effects of steam pressure, water temperature and nozzle exit inclination angle on the cavity shape characteristics have been studied. Existence of six different plume shapes (oscillatory, conical, expansion–contraction, double expansion contraction, cylindrical and divergent) have been identified. The results show that for a fixed nozzle geometry, with the increase in water temperature and steam pressure, the steam jet becomes lengthy. However, under the same steam pressure and water temperature conditions, the plume shortens with the increase in nozzle exit inclination angle. The dimensionless jet length has been found in the range of 1.26–5.64. Furthermore, it has been observed that steam plume exhausting from bevelled nozzle undergoes deflection from its nozzle symmetry axis possibly due to the pressure difference between upper and lower lip of nozzle. This deflection may either be upward oriented at high steam pressure or downward deflected at lower steam pressure. Additionally, on the basis of findings from 175 No’s of experiments, condensation regime maps have also been developed for bevelled spray nozzle.

Study on the Characteristics of Coherent Supersonic Jet with Superheated Steam

By establishing a mathematical model to simulate a mixed jet of oxygen and superheated steam from a coherent supersonic jet oxygen lance, we studied the effect of superheated steam on the fluid characteristics of the mixed jet. The model was initially verified through laboratory experiments prior to analyzing the fluid characteristics of the mixed jet in detail. These characteristics included the jet velocity, the temperature, the turbulent kinetic energy (TKE), and the mass distribution. The results showed that, at an ambient temperature of 1700 K, the jet velocity measured in the laboratory experiment was consistent with the fluid velocity obtained by numerical simulations, with an error of only 2.7%. In a high-temperature environment, the jet velocity of the mixed oxygen and superheated steam jet was increased, the TKE around the center jet was enhanced, the superheated steam exhibited an inhibitory effect on the combustion reaction of annular methane, and the potential core length of the coherent supersonic jet was reduced, which was conducive to methane combustion and delayed the reduction in the central jet velocity.

Investigation on the Cavity Backwater of Chute Aerators under Various Atmospheric Pressures

A chute aerator is a device that entrains air into water and protects against cavitation erosion. The state of the jet cavity determines the aerator efficiency under different flow conditions. In the case of a low Froude number and low velocity, backwater is generated in the jet cavity. In severe cases, this backwater blocks the air intake holes and affects air intake efficiency. With the development and construction of water conservancy projects, an increasing number of dams have been constructed at altitudes above 3000 m. The influence of cavity backwater depth at reduced atmospheric pressures is unknown and may increase the risk of high-speed aerated flows in high-altitude areas. In this study, the relevant parameters of backwater were measured at various atmospheric pressures, including the jet length, cavity subpressure, backwater depth, and net cavity length. The pressure difference of atmospheric pressure can range from 0 to 94 kPa. The test results indicate that a decrease in atmospheric pressure causes variations in the cavity subpressure. The absolute value of the difference between the inside and outside of the cavity decreases with a decrease in atmospheric pressure. An empirical formula for calculating the subpressure at different atmospheric pressures is proposed for PN &lt; 0.1. The air velocity in the ventilation shaft decreases with a decrease in atmospheric pressure. The effects of variation in the atmospheric pressure on jet length can be ignored because the variation in jet length with different atmospheric pressures was constant. Additionally, the influence of varying atmospheric pressure on the cavity backwater is evident. The backwater depth decreases with a decrease in atmospheric pressure. When the atmospheric pressure decreases from 96 to 6 kPa, the maximum reduction in backwater depth is over 50%. Atmospheric pressure is a parameter that affects cavity backwater. Based on the measured backwater depth data, an empirical formula for calculating the backwater depth at different atmospheric pressures is proposed. This indicates a relationship between the atmospheric pressure and backwater depth under different flow conditions. It was further found that the bottom cavity may require a larger air intake volume at low atmospheric pressures and that it is necessary to optimize the aerator and the ventilation system.