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.

Three modes of a direct-current plasma jet operated underwater to degrade methylene blue

A direct-current air plasma jet operated underwater presents three stable modes including an intermittently-pulsed discharge, a periodically-pulsed discharge and a continuous discharge with increasing the power voltage. The three discharge modes have different appearances for the plasma plumes. Moreover, gap voltage-current characteristics indicate that the continuous discharge is in a normal glow regime. Spectral lines from reactive species（OH, N2, N2^＋, Hα,and O） have been revealed in the emission spectrum of the plasma jet operated underwater.Spectral intensities emitted from OH radical and oxygen atom increase with increasing the power voltage or the gas flow rate, indicating that reactive species are abundant. These reactive species cause the degradation of the methylene blue dye in solution. Effects of the experimental parameters such as the power voltage, the gas flow rate and the treatment time are investigated on the degradation efficiency. Results indicate that the degradation efficiency increases with increasing the power voltage, the gas flow rate or the treatment time. Compared with degradation in the intermittently-pulsed mode or the periodically-pulsed one, it is more efficient in the continuous mode, reaching 98% after 21 min treatment.

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

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。

波流共同作用下射流稀释特性的动量积分模拟研究

污水通常以射流的形式向海排放,其在海洋环境水体中的稀释过程是射流与波浪、潮流共同作用的结果。本文基于合理的假设条件,对射流运动的控制方程进行积分处理,结合波流环境下射流的结构特征,引入射流卷吸与拖曳力函数,结合必要的边界条件,形成封闭的控制方程组,建立波流环境下射流动量积分模型。通过与实验资料的对比分析可以看出,该模型可以准确模拟波流环境下射流在近区段的时均运动与稀释过程;相较于单一的横流作用,波流共同作用下射流对周边水体的影响范围更大,射流初始稀释能力更强。基于多个组次的动量积分模拟实验,通过无量纲分析与最小二乘拟合,建立了波流共同作用下射流轨迹中心线位置及最小稀释度的经验公式。相关成果可为排海污水环境影响评估提供快速、准确的分析手段。

混合流动控制对风机叶片气动特性的影响

针对风力机叶片失速会降低风力机输出功率的问题,文章首先基于Fluent软件建立了NREL Phase Ⅵ风力机气动特性分析模型,计算风速为13 m/s时风力机叶片截面压力系数及功率特性,并与风洞实验数据进行对比,验证风力机气动特性分析模型的准确性;然后,将主动射流和涡流发生器(VGs)耦合到风力机叶片上,发现随射流孔宽度和涡流发生器高度的增加,风力机功率均呈先增后减趋势;最后,建立混合流动控制的风力机气动分析模型,研究射流与VGs弦向间距及后缘VGs高度对风力机气动特性的影响。研究表明:当间距为0.3C(C为翼型弦长)时,风力机输出功率达到最高,相比于射流单一控制,增幅为6.61%;当后缘VGs高度为15 mm时,混合式流动控制的效果最佳,风机功率最高。

CH_(4)层流射流火焰燃烧特性及带电粒子浓度研究

为了研究天然气管道泄漏火灾形成射流火焰的燃烧特性,自主搭建了CH_(4)层流燃烧系统,通过对比不同尺寸喷嘴在0.48~0.72 L/min射流流量条件下火焰的响应特征,分析射流出口上方的火焰形态、温度及带电粒子浓度运移规律。结果表明:火焰喷嘴尺寸相同时,射流火焰的几何尺寸和测点平均温度均随射流流量的增加而增大,但不同喷嘴尺寸处的射流出口温度均随喷嘴流量的增加而降低。越靠近喷嘴区域,火焰根部离子电流值越大,但最大值不超过1.0μA,并且火焰轴向离子电流变化率随流量的增加而降低,火焰边缘处的离子电流值随测点与喷嘴之间的间距增大而减小。

Investigation of the Behavior of a Jet Issued into Two-Layer Density-Stratified Fluid

This study experimentally investigates a jet flow issued into a two-layer density-stratified fluid in a tank and the resultant mixing phenomena. The upper and lower fluids are water and a NaCl- water solution, respectively, with the lower fluid issued vertically upward from a circular nozzle mounted on the tank bottom. Experimental highlights of the jet behavior and mixing phenomena are classified into three patterns according to the jet Reynolds number and mass concentration of the NaCl-water solution. The internal density current clearly occurs along the density interface, and the maximum jet height is predicted by the Froude number defined by the density difference between the upper and lower fluids. The effect of fluid thickness on the maximum jet height is also clarified.

Behavior of near-field dilution of thermal buoyant jet discharged horizontally in compound open-channel

The RNG κ-ε model considering the buoyancy effect, which is solved by the hybrid finite analytic method, is used to simulate the mixture of the horizontal round thermal buoyant jet in compound open channel flow. The mixing features near the spout and flowing characteristic of the secondary currents are studied by numerical simulation. Meanwhile, （1） the distribution of the measured isovels for stream-wise velocity, （2） secondary currents, （3） the distribution of the measured isovels for temperature of typical cross-section near the spout, were obtained by the three-dimensional Micro ADV and the temperature measuring device. Compared with experimental data, the RNG κ-ε model based on buoyancy effect can preferably simulate the jet which performs the bifurcation phenomenon, jet reattachment （Conada effect） and beach secondary currents phenomenon with the effect of ambient flow, buoyancy, and secondary currents of compound section and so on.

Preparation and characterization of jet-electrodeposited nanocrystalline nickel coatings

Nanocrystalline nickel coatings were prepared by both direct current(DC) and pulse current(PC) jet-electrodeposition. The influences of current density and jet velocity on the surface morphology,microstructure and preferred orientation of the coatings obtained were investigated by SEM,TEM and XRD. It is found that the current density strongly affects the microstructure of the nickel coating. An increase of the DC current density results in a slight increase of the grain size and preferred orientation progressive evolution(i.e. from(111) to(200)),whereas an increase of the PC current density leads to a certain decrease of the grain size and preferred orientation change(i.e. from(111) to a strong(220)). Moreover,jet velocity shows no significant effect on the grain size and preferred orientation for the nanocrystalline coatings obtained in both DC and PC within the range of jet velocity studied.

Numerical Simulation of Jet Issuing Diagonally Upward into Density-Stratified Fluid in Cylindrical Tank

This study simulates the behavior of a jet issuing into a two-layer density-stratified fluid in a cylindrical tank and the resulting mixing phenomena. The upper and lower fluids are water and an aqueous solution of sodium chloride (NaCl), respectively, with the lower fluid issuing diagonally upward from a nozzle on the bottom of the tank. The angle between the centerline of the jet and the tank bottom is 60°. The phenomena when the Reynolds number Re of the jet is 475, 1426, and 2614 are simulated. The mass concentration of the aqueous solution of NaCl is 0.02. The simulation successfully grasps the jet behavior and the resulting mixing, which agree with the authors’ experimental results at the corresponding Re value. The secondary flows that appear in the horizontal cross-sections consist of a pair of vortices and flows along the tank wall. The secondary flow at the density interface represents the intrusion of an internal density current, which gives rise to mixing along the interface.

Behavior of a Jet Issuing Diagonally Upward into Two-Layer Density-Stratified Fluid in a Cylindrical Tank

This study is concerned with the experimental investigation of a jet issuing diagonally upward into a two-layer density-stratified fluid in a cylindrical tank and the resulting mixing phenomena. The upper and lower fluids are water and an aqueous solution of sodium chloride (NaCl), respectively, and the lower fluid issues from a nozzle on the bottom of the tank. The angle between the centerline of the jet and the bottom of the tank is 60o, and the mass concentration of the NaCl solution is 0.02. The investigation reveals that secondary flow is caused by the jet in the horizontal cross-sections of the tank and that it is composed of a pair of vortices. It confirms that the secondary flow at the density interface corresponds to an internal density current. The investigation also clarifies the effect of the Reynolds number of the jet on mixing between the lower and upper fluids.

Optical characterization of single-crystal diamond grown by DC arc plasma jet CVD

Optical centers of single-crystal diamond grown by DC arc plasma jet chemical vapor deposition(CVD) were examined using a low-temperature photoluminescence(PL) technique. The results show that most of the nitrogen-vacancy(NV) complexes are present as NV-centers, although some H2 and H3 centers and B-aggregates are also present in the single-crystal diamond because of nitrogen aggregation resulting from high N_2 incorporation and the high mobility of vacancies under growth temperatures of 950–1000°C. Furthermore, emissions of radiation-induced defects were also detected at 389, 467.5, 550, and 588.6 nm in the PL spectra. The reason for the formation of these radiation-induced defects is not clear. Although a Ni-based alloy was used during the diamond growth, Ni-related emissions were not detected in the PL spectra. In addition, the silicon-vacancy(Si-V)-related emission line at 737 nm, which has been observed in the spectra of many previously reported microwave plasma chemical vapor deposition(MPCVD) synthetic diamonds, was absent in the PL spectra of the single-crystal diamond prepared in this work. The high density of NV-centers, along with the absence of Ni-related defects and Si-V centers, makes the single-crystal diamond grown by DC arc plasma jet CVD a promising material for applications in quantum computing.

喷射电沉积电流密度对Ni/Co多层膜性能影响研究

金属多层膜因具有较高的硬度与良好的耐腐蚀性,有望成为性能更为优越的保护性镀层材料。采用喷射电沉积技术在304不锈钢基体上制备了不同电流密度下的Ni/Co多层膜,分别对其微观结构、显微硬度和耐腐蚀性能等方面展开了研究。结果表明:在较高电流密度下的喷射电沉积中,多层膜内主要存在面心立方结构和密排六方结构的晶体,且随着电流密度升高,Ni/Co多层膜表面微观形貌逐渐均匀完整,晶粒逐渐细化。当电沉积电流密度为80 A/dm2时,Ni/Co多层膜的自腐蚀电流密度为5.428×10-7 A/cm2,显微硬度为525.4HV,显示出优异的机械性能与抗腐蚀性能。

具有内外分段阳极结构的金属离子等离子体推进器的放电特性

金属离子等离子体推进器是一种通过烧蚀阴极金属材料,产生电离度高的金属离子等离子体,在Hump峰加速作用下从而定向喷射形成推力的推进器类型。文中提出了一种带有分段阳极结构的金属离子等离子体推进器(SA-MIPT),该结构由圆锥状阴极、圆筒状绝缘套桶以及圆环状分段阳极组成。基于该金属离子等离子体推进器,探究了峰值电压维持时间t1以及阳极吸收电子对金属等离子体的生成及喷射性能的影响。研究结果表明,当t1从0.4μs增大到1.2μs时,单脉冲放电中生成的等离子体的定向传播速度、离子电流幅值以及离子电流与阴极电流的比值Gr分别提高了1.7倍、18倍、15倍。此外,研究发现采用减小阳极裸露面积或者阳极侧串联电阻的方法,能够有效提高从推进器喷口喷射出去的等离子体射流的喷射性能。当内阳极宽度W从2 mm减小到0.1 mm时,放电生成的离子电流峰值以及对应的Gr值分别提高了2.41倍、2.66倍。当阳极宽度W=2mm不变,在内阳极侧串联1 MΩ电阻后,放电生成的离子电流峰值以及对应的Gr值分别提高了2.24倍、2.52倍。

An experimental and numerical approach-characterisation of power cartridge for water-jet application

Power Cartridges are pyrotechnic devices where hot combustion gases utilized to do mechanical work for disruption of suspected Improvised Explosive Devices(IEDs). It plays a vital role either in destroying the suspicious object or making them non-functional by generating the gas pressure on burning of propellant against the water column inside the barrel, Present work is focused on characterisation,numerical solution such as deformation; strain; stress using FEM(Finite Element Method), design qualification, performance and evaluation of power cartridge for disruptor application. Experimental trials for pressure-time(P-t) measurement in closed vessel(CV), various electrical parameters like all fire current(AFC), no fire current(NFC) and ignition delay have been measured. Further, mechanical properties for brass material have been determined. An attempt has been made to characterise the power cartridge by FEM and carrying out the experiments for water-jet application.

±800 kV混合直流输电工程用DC 80 kV SF_(6)/N_(2)等离子体喷射触发间隙研制

白鹤滩—江苏±800 kV混合直流输电工程在交流侧故障穿越过程中,为了限制柔直母线上过电压吸收冗余能量需要加装可控自恢复消能装置。为了实现可控自恢复消能装置的1 ms快速投入,需要研制DC 80 kV SF_(6)/N_(2)等离子体喷射触发间隙。根据工程需求,分析了工程应用条件,明确触发间隙关键技术要求。针对高性能触发的要求,提出了高压脉冲型等离子体双级接续触发方法,设计了同轴层压式产品化触发腔,搭建触发特性试验平台,开展触发性能试验研究,并提出通过监测触发过程中储能电容电压变化在线监测触发性能的方法,研究结果表明,最低可触发电压为50 kV,触发时延在0.3 ms以内,空载触发寿命为1800次。针对大直流通流及快速绝缘恢复的要求,依据横磁电极旋弧原理,完成自旋弧主电极设计,开展电场及旋弧仿真,设计搭建了通流及绝缘恢复试验回路开展试验研究,拍摄电弧运动。结果表明,电弧能够沿主电极边缘高速旋转,实现30kA/50ms通流后0.1s恢复耐受1.5倍额定电压、通流寿命50次。基于上述关键问题的解决,完成了双冗余等离子体喷射触发间隙本体及高电位测控的成套装置结构设计,研制了样机并通过了第三方性能试验验证,绝缘、触发和通流关键技术指标全面满足白江工程要求并将工程应用。

2000年8月南海中部与南部海洋温、盐与环流特征

根据 2 0 0 0年 8— 9月份南海中部与南部航次的温、盐资料 ,采用P 矢量诊断方法 ,结合ADCP测流资料和同期伪风应力资料以及TOPEX/Poseidon高度计资料 ,研究了 2 0 0 0年夏季风持续强迫之后南海大尺度环流与中尺度涡旋的空间结构。结果表明 ,南海夏季温度和盐度水平分布随深度有显著的变化 :中层 (2 5 0— 4 0 0m左右 )温、盐水平分布与其它各层的温度和盐度分布相比有很大的差异。用诊断方法计算得到的环流场与用TOPEX/Poseidon海面高度计资料计算得到的地转流场比较一致 ,即流场内部有多个中尺度的涡旋 ,主要有越南东南外海反气旋涡、中沙群岛东南反气旋涡以及南沙群岛东北角的气旋涡等 ,这说明南海中部与南部盛夏环流具有较强的地转分量和显著的多涡结构 ,并且这些中尺度涡在垂向上存在速度场的切变。

爆炸复合钢板界面射流熔化与凝固的研究

本文研究了奥氏体不锈钢 /普通低合金钢爆焊复合钢板界面熔区的形成。通过试验发现 ,爆炸时钢板碰撞形成的射流被截断的位置与铸态凝固组织存在的位置一致 ,说明界面熔区是由射流构成的。通过分析 ,射流熔化的原因并非仅仅来自绝热剪切 ,射流与基体的摩擦生热同样起着重要的作用。射流熔区的凝固组织对复合板质量影响较大 ;

波流环境中射流的大涡数值模拟

采用大涡模拟方法(LES)对波流环境中的垂向圆管射流进行了数值模拟。出口边界采用人工海绵层加零梯度条件以减小数值反射,且保证自由出流;入口边界分别采用线性叠加和非线性叠加的波流边界条件,通过与物理实验数据对比发现,采用非线性叠加的边界条件时模拟精度更高。数模结果表明,在波浪和水流共同作用下,射流体上部出现了较为明显的"水团"现象,射流平均速度矢量较纯流环境中更靠近底床,这与前期实验观察的结果一致。