Study on the influences of interaction behaviors between multiple combustion-gas jets on expansion characteristics of Taylor cavities

The purpose of this study is to investigate means of controlling the interior ballistic stability of a bulk-loaded propellant gun（BLPG）.Experiments on the interaction of twin combustion gas jets and liquid medium in a cylindrical stepped-wall combustion chamber are conducted in detail to obtain time series processes of jet expansion,and a numerical simulation under the same working conditions is also conducted to verify the reliability of the numerical method by comparing numerical results and experimental results.From this,numerical simulations on mutual interference and expansion characteristics of multiple combustion gas jets（four,six,and eight jets） in liquid medium are carried out,and the distribution characteristic of pressure,velocity,temperature,and evolutionary processes of Taylor cavities and streamlines of jet flow Held are obtained in detail.The results of numerical simulations show that when different numbers of combustion gas jets expand in liquid medium,there are two different types of vortices in the jet flow field,including corner vortices of liquid phase near the step and backflow vortices of gas phase within Taylor cavities.Because of these two types of vortices,the radial expansion characteristic of the jets is increased,while changing numbers of combustion gas jets can restrain Kelvin-Helmholtz instability to a certain degree in jet expansion processes,which can at last realize the goal of controlling the interior ballistic stability of a BLPG.The optimum method for both suppressing Kelvin-Helmholtz instability and promoting radial expansion of Taylor cavities can be determined by analyzing the change of characteristic parameters in a jet flow field.

Three-Di mensional Computations of Multiple TandemJets in Crossflow

The mixing and merging characteristics of multiple tandem jets in crossflow are investigated by use of the Computational Fluid Dynamics （CFD） code FI,UENT. The realizable k - ε model is employed for turbulent elosure of the Reynolds-averaged Navier-Stokes equations. Numerical experiments are performed for 1-, 2- and 4-jet groups, tbr jet-tocrossflow velocity ratios of R = 4.2 ～ 16.3. The computed velocity and scalar concentration field are in good agreement with experiments using Particle Image Velocimetry （PIV） and Laser Induced Fluorescence （LIF）, as well as previous work. The results show that the leading jet behavior is similar to a single free jet in crossflow, while all the downstream rear jets have less bent-over jet trajectories - suggesting a reduced ambient velocity for the rear jets. The concentration decay of the leading jet is greater than that of the rear jets. When normalized by appropriate crossflow momentum length scales, all jet trajectories follow a universal relation regardless of the sequential order of jet position and the nund）er of jets. Supported by the velocity and trajectory measurements, the averaged maximum effective crossflow velocity ratio is computed to be in the range of 0.39 to 0.47.

Analyzing of mixing performance determination factors for the structure of radial multiple jets-in-crossflow

The radial multiple jets-in-crossflow mixing structure(RMJCMS) is extensively used in industrial manufacture. In this research, the effects of thickness of injection ring on mixing performance and factors influencing the mixing performance of RMJCMS were discussed based on the results of computational fluid dynamics. The simulation results showed that the dimensionless mixing distance, with the increase of the thickness of injection ring, drops from 1.1 to 0.18 first and then increases to 0.27 while the uniformity of flux monotonously improves, manifesting that the consistency of flux is not the single element determining the mixing performance. Analyzing the simulation results, a conclusion was drawn that the consistency of flux, penetration mode and interaction among injection flows which can be altered by adjusting the thickness of injection ring, determine the mixing performance of RMJCMS jointly. That is to say, in RMJCMS an injection ring with a suitable thickness can realize the function of injection and rectification simultaneously, which not only improves the mixing performance but also reduces the complexity of RMJCMS as well.

Scour process caused by multiple subvertical non-crossing jets

The scour process induced by plunging jets is an important topic for hydraulic engineers. In recent decades, several researchers have developed new strategies and methodologies to control the scour morphology, including different jet arrangements and structures located in the stilling basin. It has been found that multiple jets can cause less scouring than single plunging jets. Based on this evidence, this study aimed to investigate the equilibrium morphology caused by multiple non-crossing jets. A dedicated laboratory model was built and experimental tests were carried out under different combinations of jet inclination angles, by varying the tailwater level and the virtual crossing point location, which was set below the original channel bed level. It was experimentally shown that the equilibrium scour morphology depends on the jet discharge, the differences in non-crossing jet inclination angles, the downstream water level, and the distance of the virtual crossing point from the original channel bed level. In particular, the last parameter was found to be one of the most influential parameters, because of the resulting flow patterns inside the water body. Furthermore, the analysis of experimental evidence allowed for a complete and detailed classification of the scour hole typologies. Three different scour typologies were distinguished and classified. Finally, based on previous studies, two novel re-lationships have been proposed to predict both the maximum scour depth and length within a large range of hydraulic and geometric parameters.

An experimental study on heat transfer process of multiple mist impinging jets

Mist jet impingement cooling is an enhanced heat transfer method widely used after the continuous galvanizing process. The key of a successful design and operation of the mist jet impingement cooling system lies in mastering heat transfer coefficients. The heat transfer coefficients of high temperature steel plates cooled with multiple mist impinging jets were experimentally investigated, and the effects of gas and water flow rates on heat transfer coefficients were studied. The test results illustrate that the gas flow rate has little effect on the mist heat transfer rate. It is also found that the water flow rate has a great impact on the heat transfer coefficient. When the water flow rate ranges from 0.96m3/h to 1.59 m3/h, an increase in the rate will produce a higher heat transfer coefficient with a maximum of 5650 W/（m2 · K）. Compared with the conventional gas jet cooling, the heat transfer coefficient of the mist jet cooling will be much higher, which can effectively strengthen the after-pot cooling.

Numerical Optimization of Pressure Force from Multiple Jets Impinging on a Moving Curved Surface for Industrial Drying Machines

Jet force on the surface is typical for impinging jets towards the surface and it is very important in drying applications for force-sensitive surfaces. The designer should optimize the design parameters of industrial drying equipment to achieve minimum pressure force between multiple jets and a moving curved surface. SST k-ω turbulence model is used to simulate a real geometry for industrial drying applications. The SST k-ω turbulence model succeeded with reasonable accuracy in reproducing the experimental results. The jet to surface distance, jet to jet spacing, jet inlet velocity, jet angle, and surface velocity are chosen as the design parameters. For the optimization of the impinging round jet, the pressure force coefficient on the moving curved surface is set as the objective function to be minimized. The SHERPA search algorithm is used to search for the optimal point from the weighted sum of all objectives method. One correlation is developed and validated for the pressure force coefficient. It is found that the pressure force coefficient is highly dependent on the nozzle to surface distance and jet angle but relatively insensitive to jet inlet velocity, jet to jet spacing, and surface velocity. The minimum pressure force coefficient correlates with a high value of nozzle to surface distance (tenfold diameter in this analysis) and a low value of the jet angle (40? in this analysis). The agreement in the prediction of the pressure force coefficient between the numerical simulation and developed correlation is found to be reasonable and all the data points deviate from the correlation approximately 8% on average.

Effect of CO_(2) Opposing Multiple Jets on Thermoacoustic Instability and NO_(x) Emissions in a Lean-Premixed Model Combustor

This paper experimentally studied the effect of CO_(2) opposing multiple jets on the thermoacoustic instability and NO_(x) emissions in a lean-premixed model combustor.The feasibility was verified from three variables:the CO_(2) jet flow rate,hole numbers,and hole diameters of the nozzles.Results indicate that the control effect of thermoacoustic instability and NO_x emissions show a reverse trend with the increase of open area ratio on the whole,and the optimal jet flow rate range is 1-4 L/min with CO_(2) opposing multiple jets.In this flow rate range,the amplitude and frequency of the dynamic pressure and heat release signals CH~* basically decrease as the CO_(2) flow rate increases,which avoids high-frequency and high-amplitude thermoacoustic instability.The amplitude-damped ratio of dynamic pressure and CH*can reach as high as 98.75% and 93.64% with an optimal open area ratio of 3.72%.NO_(x) emissions also decrease as the jet flow rate increases,and the maximum suppression ratio can reach 68.14%.Besides,the flame shape changes from a steep inverted "V" to a more flat "M",and the flame length will become shorter with CO_(2) opposing multiple jets.This research achieved the synchronous control of thermoacoustic instability and NO_(x) emissions,which could be a design reference for constructing a safer and cleaner combustor.

Transformation of single drop breakup from binary to ternary and multiple in turbulent jet flows

By releasing liquid drops in turbulent jet flows,we investigated the transformation of single drop breakup from binary to ternary and multiple.Silicone oil and deionized water were the dispersed phase and continuous phase,respectively.The probability of binary,ternary,and multiple breakup of oil drops in jet flows is a function of the jet Reynolds number.To address the underlying mechanisms of this transformation of drop breakup,we performed two-dimensional particle image velocimetry(PIV)experiments of single-phase jet flows.With the combination of drop breakup phenomenon and two-dimensional PIV results in a single-phase flow field,these transformation conditions can be estimated:the capillary number ranges from 0.17 to 0.27,and the Weber number ranges from 55 to 111.

The Acoustic Performance of 3D Printed Multiple Jet Nozzles with DifferentConfigurations

This work investigated multiple jet nozzles with various geometrical shape,number of exits,and material on reducing noise radiated from jet flows.Nozzles are categorized in two groups with few and many exit numbers,each with various exit shapes,slot and circular,and geometry.Firstly,nozzles are designed and then fabricated by a 3D printer,Form Labs,Form2USA,with polymeric resin.Also,the nozzle with the most noise reduction made of stainless steel.Noise and air thrust were measured at three air pressure gauges,3,5,7 BAR and directions from nozzle apex,30°,90°,135°.Nozzles with slot exit shape made of both plastic and stainless steel revealed the most noise reduction among all nozzles with few exit numbers,nearly 11–14 dB(A)and 11.5–15 dB(A),respectively.On average,slotted nozzle noise reduction was nearly 5–6 dB(A)more than finned nozzle.However,nozzles with more exit numbers,finned and finned-central exit,illustrated much more noise reduction than nozzles with few exit numbers,by almost 16–18 dB(A),they represented similar sound.All tested nozzles and open pipe demonstrated equal air thrust at each pressure gauges.The nozzles with slotted exit shape,either plastic or stainless steel,can provide reasonable noise reduction in comparison to other configuration with few exit numbers.In contrast,nozzles with more exit numbers demonstrated the most noise reduction.

Experimental investigation of crossflow characteristics in multi-jets system at small nozzle-to-plate spacing

To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures together with the distributions of the mean velocity components for Reynolds numbers (Re) ranging from 6 213 to 13 418,nozzle-to-plate spacing (H/D) varying from 0. 20 to1. 25,respectively. Results show that the crossflow configuration is significantly different from those of large nozzle-to-plate spacing. In addition,a turning point H/D=0.50 is revealed in the profile of the normalized maximum radial velocity which is associated with the heat transfer distribution on the impingement plate.

A BIOREACTOR FOR TWO-STAGE MULTIPLE SHOOT CULTURE OF CATHARANTHUS ROSEUS

A self made gas-liquid jet bioreactor in spray flow mode is used in the two-stage multiple shoot culture of C. roseus. The experimental results show that the gas-liquid jet bioreactor is suitable for the multiple shoot culture of C. roseus in two stages, and the multiple shoots of C. roseus reach as high as 35g(dry wt.) · L-1 of biomass content and as high as 1.18% (dry wt.) of total indole alkaloids.

Evolution of ionization waves in a multi-pulsed plasma jet:the role of memory charges

In this paper,we discuss the properties of ionization waves(IWs)in a multi-pulsed plasma jet while using the two-dimensional computational approach.The IWs are generated by application of three short negative pulses with a repetition frequency 12.5 MHz.The simulations are performed continuously during a single run while accounting for charges accumulated inside(surface charges)and outside(space charges)the tube.The plasma forming gas mixture(He/O2=99.8%/0.2%)is injected through the discharge tube into the surrounding humid air.We show that an IW can emerge from the tube exit at a pulse rising edge(as a negative IW)and at a falling edge of the same pulse(as a positive IW).It is demonstrated that remnants of the negative and positive charges play an essential role in the discharge evolution.The first pulse travels the shortest distance as it propagates through the initially non-ionized environment.The IWs developing during the second pulse essentially enlarge the plasma plume length.At the same time,the IWs generated by the third pulse eventually decay due to the remnants of charges accumulated during the previous pulses.Accumulated memory charges can lead to the IW extinction.

波流环境中多孔射流三维数值模拟

建立了波流环境中多孔射流的三维大涡数学模型,探讨了波流共同作用下多孔射流的扩散和稀释机制,分析了孔间距对双孔射流、射流与环境水体相互作用的影响,并给出了最优相对孔间距。模拟结果表明:在波谷相位时刻,由于横流与波浪相互作用强烈,流场内的三维涡旋结构丰富、尺度较大、数目众多,有利于射流与环境水体、射流与射流之间的掺混,这是波流环境比单一横流环境中多孔射流运动扩散效果更佳的主要原因;随着孔间距的增大,双孔射流之间的相互作用慢慢削弱,而射流与环境水体之间的相互作用却在不断增强;双孔射流在孔间距为7.0倍管口直径时扩散效果最好。

地面井分层卸压的煤系气合采原理及方式探讨

为了进一步认识制约煤系气合采的因素,提高煤系合层排采各产层的产气贡献,分别从动力、通道和气源条件出发,分析了煤系气合采的必备因素。基于改变地应力状态提高储层导流能力以及分层改变储层流体压力,满足多层合采动力条件的原理,提出了地面井分层卸压的煤系气合采方式。该方式通过在地面进行定向钻井,在目标储层中进行高压水射流作业,人工创造卸压空间(缝、槽、穴等),改变地应力状态,降低有效应力伤害,增加储层导流通道的数量和开度,提高目标储层压降传递速率。待储层压力降至符合煤系气合采动力条件时进行合层排采,从而提高煤系合采各产气层的产气贡献。相较于常规增产改造措施,此方式能够减少煤系气储层在有效应力作用下的储层伤害,且有助于提高储层压降传递效率,增强煤系气的解吸和扩散,降低多层煤系气合采过程中的层间干扰。在以上研究基础上,认为地面井分层卸压的合采方式主要适用于储层地应力大、产层间距小的煤系气储层,且有望在薄互层煤系气储层增产改造及层间干扰严重的叠合共生煤系储层开发领域进行应用推广。

NUMERICAL SIMULATION OF UNSTEADY-STATE UNDEREXPANDED JET USING DISCONTINUOUS GALERKIN FINITE ELEMENT METHOD

A discontinuous Galerkin finite element method （DG-FEM） is developed for solving the axisymmetric Euler equations based on two-dimensional conservation laws. The method is used to simulate the unsteady-state underexpanded axisymmetric jet. Several flow property distributions along the jet axis, including density, pres- sure and Mach number are obtained and the qualitative flowfield structures of interest are well captured using the proposed method, including shock waves, slipstreams, traveling vortex ring and multiple Mach disks. Two Mach disk locations agree well with computational and experimental measurement results. It indicates that the method is robust and efficient for solving the unsteady-state underexpanded axisymmetric jet.

Point-symmetry in SNR G1.9+0.3:A Supernova that Destroyed its Planetary Nebula Progenitor

I analyze a new X-ray image of the youngest supernova remnant(SNR)in the Galaxy,which is the type Ia SNR G1.9+0.3,and reveal a very clear point-symmetrical structure.Since explosion models of type Ia supernovae(SNe Ia)do not form such morphologies,the point-symmetrical morphology must come from the circumstellar material(CSM)into which the ejecta expands.The large-scale point-symmetry that I identify and the known substantial deceleration of the ejecta of SNR G1.9+0.3 suggest a relatively massive CSM of■1M⊙.I argue that the most likely explanation is the explosion of this SN Ia into a planetary nebula.The scenario that predicts a large fraction of SN Ia inside PNe(SNIPs)is the core degenerate scenario.Other SN Ia scenarios might lead to only a very small fraction of SNIPs or none at all.

NUMERICAL STUDY OF HYDRODYNAMICS OF MULTIPLE TANDEM JETS IN CROSS FLOW

The hydrodynamics of a single jet and four tandem jets in a cross flow are simulated by using the Computational Fluid Dynamics （CFD） software Fluent. The realizable model is used to close the Reynolds-Averaged equations. The flow characteristics of the jets, including the jet trajectory, the velocity field and the turbulent kinetic energy are obtained with various jet-to-cross flow velocity ratios in the range of 2.38-17.88. It is shown that a single jet penetrates slightly deeper than the first jet in a jet group at the same , although the difference decreases with the decrease of . It is also found that the way in which the velo-city decays along the centerline of the jet is similar for both a single jet and the first jet in a group, and the speed of the decay increases with the decrease of . The downstream jets in a group are found to behave differently due to the sheltering effect of the first jet in the group. Compared with the first jet, the downstream jets penetrate deeper into the cross flow, and the velocity decays more slowly. The circulation zone between the two upstream jets in the front is stronger than those formed between the downstream jets. The Turbulent Kinetic Energy （TKE） sees a distinct double-peak across the cross-sections close to each nozzle, with low values in the jet core and high values in the shear layers. The double-peak gradually vanishes, as the shear layers of the jet merge further away from the nozzle, where the TKE assumes peaks at the jet centerline.

Study on the flow field and concentration characteristics of the multiple tandem jets in crossflow

The characteristics of single and multiple tandem jets(n=2,3,4) in crossflow have been investigated using the realizable k-ε model.The results of this model agree well with experimental measurements using PIV(Particle Image Velocimetry) or LIF(Laser Induced Fluorescence).We analyzed the calculated results and obtained detailed properties of velocity and concentration of the multiple jets in the pre-merging and post-merging regions.When the velocity ratio is identical,the bending degree of the leading jet is greater than that of the rear jets.The last jet penetrates deeper as the jet number increases,and the shielding effect of the front jet declines with jet spacing increase.Interaction of the jet and crossflow induces formation and development of a counter-rotating vortex pair(CVP).CVP makes the distribution of concentration appear kidney-shaped(except in the merging region),and maximum concentration is at the center of the counter-rotating vortex.Concentration at the CVP center is 1.03-1.4 times that of the local jet trajectory.Post-merging velocity and concentration characteristics differ from those of the single jet because of the shielding effect and mixing of all jets.This paper presents a unified formula of trajectory,concentration half-width and trajectory dilution,by introducing a reduction factor.

Multiple equilibria of cross-equatorial Inertial jets

Based on the developed Anderson and Moore's theory about cross-equatorial inertial jets and a nonlinear equivalence shallow water model, new universal functions are determined by the characters of the vortical large-scale air flow (atmosphere) or ocean current (ocean) related to the jet, then the potential vorticity and energy conservation equations along the streamline in the cross-equatorial in-ertial jets can be obtained. Because the governing equations are nonlinear, some limited multiple equi-libria of cross-equatorial inertial jets may exist. According to the character of large-scale air flow or ocean current outside the jets, the existent criterion for multiple eqnilibria in cross-equatorial inertial jets is discussed, and two examples for multiple equilibia of nonlinear governing equations are given.

A HYBRID MODEL FOR SIMULATING VELOCITY FIELD OF A RIVER WITH COMPLEX GEOMETRY PLUNGED BY MULTIPLE JETS

A hybrid model that combines both physical and numerical models was employed to simulate the velocity field in a river area in complex geometry with multiple plunging jets. The simulation was based on experiments concerning energy dissipation and scour prevention at the Xiluodu Hydropower Station on the Yangtze River. The calculated results indicate that the complex geometry of the river area has a significant influence on the velocity field, especially on the circulation flow pattern at upstream and downstream of the plunging area and on the asymmetric characteristics of the spiral flow near both banks. The scour characteristics of the downstream river bed caused by the multiple jets were also predicted and analyzed according to the characteristics of the calculated velocity field. The good agreement between the simulated and experimental results indicates that the hybrid model can be used to effectively solve complicated 3-D problems with complex geometric and inlet conditions. Such problems may not easily be solved by using either a physical or a numerical model alone, and therefore the method presented in this article is considered to be a practical and effective way of dealing with this kind of problems.