Initial Analysis on the Effect of High-low Altitude Jet Stream on Heavy Precipitation in Guangxi

By using the routine observation data,a heavy precipitation process which happened in Guangxi on May 27,2006 was analyzed.The results that this heavy precipitation occurred in the common coordination weather system which included the high-altitude trough,the shear line and the ground cold front.The ascent branch of subtropical longitude circle circulation and the polar front jet stream longitude circle circulation had the important role for the formation of rainstorm area.The coupling effect of southerly jet,low-altitude westerly jet and high-altitude westerly jet in the boundary layer was the important reason of rainstorm occurrence.

EXPERIMENTAL INVESTIGATIONS ON DIFFUSION CHARACTERISTICS OF HIGH CONCENTRATION JETS IN ENVIRONMENTAL CURRENTS

By means of flow visualization and quantitative measurement, the diffusion pattern and concentration distribution characteristics of high concentration jets vertically discharged into shallow moving waterbody were experimentally investigated in water channel. The interactions between the high concentration jets and environmental flow conditions were analysed, and the formulae of impinging point coordinate and transverse spread angle are gained from data analysis. Experimental results indicate that the jets show complicated flow patterns and diffusion characteristics in near region, which are different from common submerged jets, and spread downstream in the manner of density currents.

Rock Breaking Performance of a Pick Assisted by High-pressure Water Jet under Different Configuration Modes

In the process of rock breaking, the conical pick bears great cutting force and wear, as a result, high-pressure water jet technology is used to assist with cutting. However, the effect of the water jet position has not been studied for rock breaking using a pick. Therefore, the models of rock breaking with different configuration modes of the water jet are established based on SPH combined with FEM. The effect of the water jet pressure, distance between the jet and the pick bit, and cutting depth on the rock breaking performance as well as a comparison of the tension and compression stress are studied via simulation; the simulation results are verified by experiments. The numerical and experimental results indicate that the decrease in the rates of the pick force obviously increases from 25 MPa to 40 MPa, but slowly after 40 MPa, and the optimal distance between the jet and the pick bit is 2 mm under the JFP and JSP modes. The JCP mode is proved the best, followed by the modes of JRP and JFP, and the worst mode is JSP. The decrease in the rates of the pick force of the JCP, JRP, JFP, and JSP modes are up to 30.96%, 28.96%, 33.46%, 28.17%, and 25.42%, respectively, in experiment. Moreover, the JSP mode can be regarded as a special JFP model when the distance between the pick-tip and the jet impact point is 0 mm. This paper has a dominant capability in introducing new numerical and experimental method for the study of rock breaking assisted by water jet and electing the best water jet position from four different configuration modes.

Numerical analysis on coal-breaking process under high pressure water jet

Based on the theory of nonlinear dynamic finite element,the control equation ofcoal and water jet was acquired in the coal breaking process under a water jet.The calculationmodel of coal breaking under a water jet was established;the fluid-structure couplingof water jet and coal was implemented by penalty function and convection calculation.The dynamic process of coal breaking under a water jet was simulated and analyzed bycombining the united fracture criteria of the maximum tensile strain and the maximal shearstrain in the two cases of damage to coal and damage failure to coal.

OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system

This paper used optical emission spectroscopy （OES） to study the gas phase in high power DC arc plasma jet chemical vapour deposition （CVD） during diamond films growth processes. The results show that all the deposition parameters （methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar） could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Research on Properties of Woven Fabrics Treated by High Pressure Water Jet

The paper introduces a new technique for the treatment of the woven fabrics. Sprayed by high pressure water jet, the appearance, handle and stiffness of the fabric are improved. Other properties of the high pressure water treated fabrics like drape coefficient, air permeability, tenacity are also presented.

High Speed Observation of Periodic Cavity Behavior in a Convergent-Divergent Nozzle for Cavitating Water Jet

Cloud cavitation shows an unsteady periodic tendency under a certain flow condition. In a cavitating water jet flow with cavitation clouds, the cavities or the clouds produce high impact at their collapse. In order to make clear a mechanism of the periodic cavity behavior, we experimentally examine the behavior in a transparent cylindrical convergent-divergent nozzle using a high-speed video camera. An effect of upstream pressure fluctuation due to a plunger pump is investigated from a viewpoint of unsteady behavior in a cavitating water jet. As a result, it is found that the cavitating flow has two kinds of oscillation patterns in the cavity length (cavitation cloud region). One is due to the upstream pressure fluctuation caused by the plunger pump. The other is much shorter periodic motion related to the characteristic oscillation of cavitation clouds accompanied with the shrinking (reentrant), growing and shedding motion of the clouds.

Shock oscillation in highly underexpanded jets

The oscillatory motions of shocks in highly underexpanded jets with nozzle pressure ratios of 5.60, 7.47, 9.34, and11.21 are quantitatively studied by using large eddy simulation. Two types of shock oscillations are observed： one is the Mach disk oscillation in the streamwise direction and the other is the shock oscillation in the radial direction. It is found that the Mach disk moves quickly in the middle of the oscillatory region but slowly at the top or bottom boundaries. The oscillation cycles of Mach disk are the same for different cases, and are all dominated by an axisymmetric mode of 5.298 k Hz. For the oscillation in the radial direction, the shocks oscillate more toward the jet centerline but less in the jet shear layer, and the oscillation magnitude is an increasing function of screech amplitude. The cycles of the radial shock oscillation switch randomly between the two screech frequencies for the first two cases. However, the oscillation periodicity is more complex for the jets with high nozzle pressure ratios of 9.34 and 11.21 than for the jets with the low nozzle pressure ratios of 5.6 and 7.47. In addition, the shock oscillation characteristics are also captured by coarse mesh and Smagorinsky model,but the coarse mesh tends to predict a slower and weaker shock oscillation.

Correlation analysis of five factors influencing minute volume during high frequency jet ventilation on lung modal: a laboratory study

Five factors influencing minute volume during high frequency jet ventilation were studied on lung modal by stepwise regression analysis. Among these factors, driving pressure is of the greatest dominance. Others are inspiratory and expiratory time ratio, tube diameter, frequency of ventilation and needle distanee, in the order of their impact. A formula was also developed for predicting the parameters.The result is quite satisfactory.

Diagnosis of gas phase near the substrate surface in diamond film deposition by high-power DC arc plasma jet CVD

Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.

Time Characterization of High Density Gas Jet from a Pulsed Supersonic Nozzle via Laser Produced Plasma

A high-density gas jet supersonic nozzle is reported in this paper. The jitter and actuation time of the nozzle is determined by the pin discharge and laser spark radiation respectively. The jitter time of the nozzle is within 10μs with the backing pressure as high as 25 bar. With a nanosecond laser pulse focused on the gas jet about 1 mm below the nozzle, the actuation time is calculated to be about 15 ms by detecting the laser produced spark radiation, which reveals the existence of the gas jet and the relative gas density evolving with time. Consequently the gas density is estimated to be well above 10^19 cm^-3, compared with theoretical simulations from the nozzle parameters.

Large Eddy Simulation of the Particle Coagulation in High Concentration Particle-Laden Planar Jet Flow

Particle coagulation by Brownian motion is an important but difficult research topic.When particle volume concentration is larger than 0.1%,the classic SMOLUCHOWSKI equation is not applicative anymore.The high concentration coagulation,with HEINE＇s correction,source terms for the Taylor-series expansion method of moments（TEMOM） are firstly driven in this paper.Ultra-fine particle（d0？100 mm） with initial volume fraction f？1% coagulation in a planar jet turbulence flow is simulated via the large eddy simulation（LES）.The instantaneous and time-averaged particle distributions and the high concentration enhancement are given out.The particle number concentration distribution results show that the coagulation is more intense comparing to dilute case in previous research,especially near the nozzle exit.After jet flow is fully developed,the effect is much more obvious at the region between vortexes.The time-averaged γ（the high concentration enhance factor） distributes sharply and symmetrically about the jet centerline at the upstream,but becomes broad and flat at downstream where the cross-stream averaged γ fluctuates drastically.As a new attempt,this paper shows Brownian coagulation with high concentration also can be calculated via TEMOM appropriately,and the coagulation at the region between vortexes is about 1.38 times intensive of the dilute result calculated by the classic Smoluchowski theory.

High Pressure Water-Jet Technology for the Surface Treatment of Al-Si Alloys and Repercussion on Tribological Properties

Recent developments in high pressure water-jet technology have brought the process to the forefront as a means of surface treatment. Water jet technology offers cleaning, cutting, processing as well as potential refinement of surface properties. By adapting the process parameters the surface characteristics can be changed while the profile remains the same. In the present study, water-jet technology was used for the surface treatment of Al-Si alloy to investigate its effect on tribological properties. Dry sliding wear behavior was investigated against AISI 52100 bearing steel ball using a reciprocating ball-on-flat configuration. Optical microscopy examination reveals that ploughing of grains, transgranular and intergranular propagation of cracks;are the mechanisms by which material is removed during water jet treatment. While, on the other hand, SEM observation of the wear track reveals that plastic deformation and delamination are the dominant wear mechanism during the wear process. Water jet treatment was compared to hot isostatic pressing in terms of its effects on wear resistance and surface porosity of Al-Si alloy. It was found that, hot isostatic pressing reduces the total amount of porosity at the expanse of hardness while water jet treatment produces a compressed surface having higher hardness and compressive residual stress, which ultimately increases wear resistance.

嵌岩低桩承台锁口钢管桩围堰设计与施工技术

昌九高铁扬子洲赣江公铁大桥西支主桥为(48+144+320+144+48)m无砟轨道钢箱桁组合梁斜拉桥。桥塔墩位于通航河道内,桥位处河床覆盖层浅,基岩强度高,基础由大直径钻孔桩和矩形嵌岩低桩承台组成,承台采用锁口钢管桩围堰施工方案。G33号主墩围堰平面设计尺寸54.56 m×28.52 m,锁口钢管桩采用Q345B材质∅1020 mm螺旋钢管,长28 m,钢管桩之间采用C-T形锁扣连接;围堰设置4层内支撑,单层内支撑设3道对撑,内支撑四角设型钢斜撑;基底设置混凝土垫层参与围堰结构受力。围堰采用XR360旋挖钻机在岩层中引孔,孔内换填细砂后插打钢管桩,钢管桩壁内、外两侧换填砂采用高压旋喷注浆加固。围堰设置智能化监测系统,对围堰受力、变形等进行实时动态监控。实践证明,该桥围堰结构安全可靠、止水效果良好、施工快捷高效。

Emission of High Energy during Super-Compressibility of Supersonic Jets

New source of light emission of high energy is found due to arising of instability in supersonic jets. These phenomena are observed in gas jets flowing from the nozzle with a central cone. It leads to high accelerations of the molecules, ions and elementary particles. The emission spectra of the jets are obtained. Decoding of the spectra allowed us to define inverted population of rotational and vibrational levels, electrons temperature, rotational and vibrational temperatures for molecular ions. Internal energy decreasing provides the instability and gas volume decreasing due to internal forces;super-compressibility is result of it;its produce high density of light energy emission in various continuous media.

基于5 kHz平面激光诱导荧光的射流火焰局部熄火时空特性分析

基于高频光学测量手段研究射流火焰局部熄火的分布特性,对于分析燃烧场不稳定性机理有重要意义。建立5 kHz的平面激光诱导荧光测量系统,对高速射流火焰开展实验研究,并获得火焰结构的动态发展过程;将双边滤波、竖直滑窗局部自适应阈值等图像处理方法引入平面激光诱导荧光图像的预处理,在局部断裂结构数量特征的基础上,提取局部断裂结构长度和空间位置等特征;基于上述特征深入解析局部熄火的时空分布特性,进一步完善高频平面激光诱导荧光诊断与分析方法。研究表明:双边滤波算法处理后,图像峰值信噪比为34.3 dB,结构相似度为0.93,噪声水平显著降低,获得了较好的去噪效果;使用竖直滑窗局部自适应方法进行图像分割的F1分数达到93.30%;断裂结构累计数量随时间线性增加,当射流马赫数由0.5增至1.6时,单侧图像断裂结构的每秒累计数量从790.7增至9 217.2,并且局部熄火频率与射流马赫数呈指数关系;断裂结构主要分布区域为火焰臂及上侧中央燃料区。本研究进一步拓展了高频平面激光诱导荧光技术的应用能力,证明了高频平面激光诱导荧光技术用于局部熄火时空分布特性研究的可行性。

MILD粉体燃烧技术研究进展与关键问题分析

MILD燃烧是一种在中度或极度低氧环境下发生的温和燃烧模式,兼具高燃烧热利用率和极低NOx排放的优势,国际燃烧领域认为它是拥有巨大应用潜力的清洁燃烧技术之一。自1990年左右开展相关研究以来,对于实现气体燃料的MILD燃烧的相关技术已相对成熟,而关于煤粉和生物质等固体燃料的MILD燃烧机制和实现条件的研究仍相对缺乏。基于高动量氧化剂射流来实现内部再循环,不再需要外部高温预热来建立MILD燃烧,极大拓宽了MILD燃烧的应用范围。从颗粒弥散、受热、着火、燃烧、污染物等方面概述了MILD粉体燃料燃烧的基础特性,由于颗粒的不均匀弥散和反应,煤粉等碳基固体燃料的MILD燃烧进程较气体燃料更复杂。高速射流MILD燃烧在增加点火延迟的同时也扩展了点火区和反应区,需要对燃烧各阶段的特征和机理开展系统研究。介绍了固体燃料MILD燃烧理论设计和装备研发领域所取得的研究成果,建议通过高精度数值模拟,改进现有燃煤锅炉燃烧器、调节工艺参数以匹配MILD燃烧模式,增加焦炭颗粒的停留时间以提高燃烬率,提高燃烧稳定性并抑制包括细颗粒物在内的各类污染物排放。基于互联能源系统的整体方法,推进MILD燃烧与各类新型燃烧技术的耦合研究,尤其加强煤粉、生物质与氢、氨等可燃气体共燃特性研究,助力能源转型。探究粉体MILD燃烧中的湍流两相流特征、湍流相间传热作用以及湍流-化学耦合作用是加深对粉体MILD燃烧理解的关键,涉及多变量分析和高精度模拟,是未来研究的重点和难点。

浅埋偏压黄土隧道地表旋喷桩加固工艺参数研究

在黄土隧道修建过程中,其洞口段因浅埋偏压、围岩软弱破碎等通常需要进行加固处理。地表旋喷桩法具有适用范围广、加固效果好等优点,被广泛应用于隧道浅埋偏压段软弱围岩地表加固工程。以浅埋偏压黄土隧道进口段初期支护侵限为研究背景,介绍了现场地表旋喷桩加固的施工过程;建立了侵限段三维加固模型并分析了地表旋喷桩加固前后的变形控制效果,说明了处治措施的合理性;对比分析了现场监控量测结果,验证了数值模拟的准确性;开展了地表旋喷桩的工艺设计参数优化分析。结果表明:由于偏压作用,地表最大沉降值偏离隧道中心线,且拱顶中心线处沉降>右拱肩处沉降>左拱肩处沉降;施加地表旋喷桩对于减小地表沉降十分有效,地表最大沉降值减小了45.5%;采用地表旋喷桩加固处理后,拱顶处加固效果最为显著,较加固前沉降减小了57.9%,同时加固后左、右拱肩沉降差值减小了17.4%;建议隧道浅埋偏压段地表旋喷桩加固工艺设计参数:桩直径为0.4~0.6 m、桩间距为1.2 m、横向加固范围为1.5~2倍洞径、竖向加固范围为洞身两侧旋喷桩与隧道拱底平齐。

高超声速大动压下整流罩分离测力风洞试验

针对高超声速试验模型整体式整流罩的反推火箭拔罩分离问题,开展了反推火箭喷流模拟方法和风洞测力试验装置设计研究,试验模拟了马赫数5、动压33 kPa时整流罩反推喷流干扰效应和分离距离影响,获得了反推喷流和分离距离影响下的整流罩气动特性。试验研究表明:反推火箭拔罩分离过程中,喷流干扰作用主导了整流罩的气动特性,使得法向力系数、轴向力系数和俯仰力矩系数分别出现了44.5%、32.4%和198.6%的最大变化量;在负迎角下,整流罩压心前移显著,使得静稳定设计的整流罩呈现出静不稳定性,不利于整流罩安全分离;分离距离越大,分离距离变化对整流罩气动特性的影响越弱;将分离初始迎角限定为小的正迎角,整流罩在分离过程中容易保持姿态稳定,有利于整流罩安全分离。