两种喷嘴喷射性能的试验研究

为比较自激振荡脉冲喷嘴和连续射流喷嘴的喷射性能,利用自行搭建的喷嘴性能测试装置对两种喷嘴的喷射性能进行了试验研究,实测了不同压力下两种喷嘴的时均喷液量,分析了不同口径的连续射流喷嘴和自激脉冲喷嘴的喷射特性,主要探讨了连续射流喷嘴、自激喷头下喷嘴直径对喷嘴喷液性能的影响,并进行了两种射流打击油泥样本的对比试验．试验结果表明,时均喷液特性相似的连续射流和脉冲射流在冲击油泥样本时,相同时间下脉冲射流的冲击破坏范围要大于连续射流,根据试验中油泥的屈服破坏过程,确定了射流有效打击力的临界值,建立射流清洗油泥时有效射程的经验估算式．     

低压大流量自激脉冲空化射流试验研究

采用自行设计的自激脉冲空化射流喷嘴和试验测试系统进行了一系列低压大流量空化射流试验,得到了一组喷嘴结构参数,使得喷嘴在入口压力为0.95~1.13 MPa时能产生较为明显的脉冲效果。通过试验获得了随入口压力升高腔室内部流场变化规律,并对试验中喷嘴腔室内部压力突降现象进行分析。试验表明自激脉冲空化射流的打击力是连续射流的1.3~1.6倍。     

低压大流量自激脉冲空化射流试验研究EI北大核心CSCD

采用自行设计的自激脉冲空化射流喷嘴和试验测试系统进行了一系列低压大流量空化射流试验,得到了一组喷嘴结构参数,使得喷嘴在入口压力为0.95~1.13 MPa时能产生较为明显的脉冲效果。通过试验获得了随入口压力升高腔室内部流场变化规律,并对试验中喷嘴腔室内部压力突降现象进行分析。试验表明自激脉冲空化射流的打击力是连续射流的1.3~1.6倍。     

自激脉冲喷嘴装置试验研究

本文对自激脉冲射流喷嘴进行试验设计和数据分析,以自激频率、振幅以及打击力等作为响应函数,研究喷嘴结构与工作压力的配套关系。通过对自激频率和振幅的分析,揭示自激振荡腔内部周期性空化现象及其对自激脉冲形成的影响,从而从解释自激脉冲射流发生机理。根据试验数据,拟合打击力随参数变化的经验公式。最终得出工业应用中典型尺寸范围的自激脉冲喷嘴与自激频率及打击力的关系,为工业设计中的频域调制理论提供了试验数据。     

自激脉冲射流喷嘴参数对装置能耗影响分析

为揭示喷嘴各参数变化对低压大流量自激振荡脉冲射流装置能耗的影响,本文借助数值模拟的方式,对自激振荡脉冲射流喷嘴的能耗问题进行了探讨,根据各结构参数和运行参数变化对腔内速度矢量场、腔内空化区形状即压力场、以及脉冲射流频率影响的分析结果,得到了如下论断:在合适的工况下,上喷嘴入口速度的降低将同比例降低下喷嘴出口的能量输出,上喷嘴压力提高与下喷嘴射流动能的增加成三倍关系.经过与试验结果对照,验证了这一结论,这一结果对于优化设计自激振荡脉冲射流喷嘴,指导自激喷嘴工业化设计具有重要的价值.     

FC—72圆形射流冲击模拟电子芯片单相局部对流传热的实验研究

以最新微电子设备冷却剂ＦＣ－７２为工质，实验研究了自由和浸没情况下，圆形射流冲击５ｍｍ×５ｍｍ模拟电子芯片的局部对流换热情况。喷嘴直径ｄ＝０．９８７ｍｍ，Ｒｅ数范围为３４８８～４２６４４。测定了自由和侵没情况下驻点换热及换热系数的径向分布，讨论了雷诺数、喷嘴一传热面间距的影响。首次发现ＦＣ—７２自由射流在高Ｒｅ数下，随着喷射间距的增加，驻点换热得到加强，而浸没射流随喷射间距的增大，驻点换热出现非单调性变化；给出了喷射间距ｚ／ｄ＝４时驻点换热系数的关联式，并与其它工质的已有结果进行了比较；对换热系数径向分布的研究表明，与自由射流不同，浸没射流分布曲线上明显出现由层流向湍流过渡所引起的二次峰值。     

脉冲流冲击冷却换热的液晶显示实验研究

采用热色液晶定量测温技术对稳态及脉冲式空气-氮气圆形浸没射流冲击冷却换热进行了实验研究.脉冲射流的实验结果表明,对于喷嘴直径D=3 mm的情形,无论脉冲频率高低,均无强化换热效果;对于D=I0 mm的情形,在较高Re数时出现个别工况的驻点换热强化.脉冲射流表现出换热系数沿径向分布趋于均匀的特点.     

自激振荡脉冲喷嘴结构参数配比试验研究

结构参数对自激振荡脉冲射流冲击效果存在着很大的影响,本文通过理论推导得出了自激喷嘴固有频率定性分析公式,并通过对上喷嘴直径为8-12.5 mm的低压大流量自激振荡脉冲射流喷嘴的系统试验研究,得到了其结构参数的最佳配比关系,并与以往文献介绍的高压小流量自激振荡脉冲喷嘴优化的结构参数配比相比较,根据定性公式分析引发差异的原因,结果对自激振荡脉冲射流喷嘴结构的设计具有借鉴价值。     

蒸汽浸没射流凝结引起的冲击特性研究

本文在广泛的蒸汽压力和过冷水温度范围内,针对饱和蒸汽通过不同出口直径的喷嘴在过冷水中浸没射流凝结引起的压力冲击特性进行了实验研究,测量得到了不同轴向位置和径向位置的冲击压力,并分析了入口蒸汽压力,过冷水温度和喷嘴出口直径对冲击压力的影响规律。结果表明冲击压力主要受入口蒸汽压力和过冷水温度的影响;同时,当汽水参数以及无量纲轴向和径向距离相同时,不同出口直径的喷嘴对应的冲击压力变化很小,从而表明喷嘴出口直径对压力冲击影响很小。     

气固两相对撞流颗粒运动特性分析

本文采用PIV两相同时测量方法,对低载荷气固两相双喷嘴对置撞击射流中的颗粒运动特性进行了研究。实验中轴向射流出口雷诺数为Re=14500,喷嘴内径为d=10 mm,喷嘴间距为L/d=12;颗粒相采用平均直径为dp=100μm的实心玻璃微珠,圆管加速段中的颗粒质量载荷控制为1%~4%。研究结果表明,低载荷下撞击射流中的颗粒间碰撞可忽略,颗粒浓度在喷嘴附近达到峰值;惯性使得颗粒轴向速度在穿入到反向射流前缓慢衰减,之后迅速减小;颗粒在撞击区形成高湍动区域,进而强化了颗粒相的混合效应。     

常压微波等离子体炬的模拟及硫化氢处理

对常压微波等离子体炬装置及H2S废气的处理进行了研究。介绍了一种具有特殊喷嘴结构的微波等离子体炬装置,模拟了不同喷嘴结构下谐振腔中微波电场的强度及分布,在此基础上,进行了H2S废气处理的实验研究。结果表明:采用新型喷嘴结构在喷嘴尖端产生的电场强度和分布更利于等离子体炬的激发,微波功率为500 W时,喷嘴尖端处的电场强度在1.5×106 V/m以上,远大于氩气的击穿电场强度,能有效地激发等离子体炬;当H2S气体与Ar气体流量比为10∶90,总流量为1000mL/min,微波功率为1000 W时,H2S的转化率最大达91.32%;大气微波等离子体炬能有效地处理H2S废气。实验结果证明了模拟结果的正确性和装置的有效性。     

Investigating an annular nozzle on combustion products of hydrocarbon fuels

Full-scale and computational experiments were used to investigate the flows in the jet thrust unit with annular nozzle and deflector in the form of a spherical segment. The used working gas was the combustion products of air mixtures with acetylene, gas-phase aviation kerosene, and natural gas. Experimental studies were carried out in a hot-shot wind tunnel in the range of stagnation pressure from 0.48 to 2.05 MPa. The calculations for the cases of combustion products outflow in terrestrial and high altitude conditions were performed with the original computer program that used the Euler and Navier-Stokes systems supplemented by equations of chemical kinetics. It was found that the thrust of the jet module with an annular nozzle at high altitude almost twice exceeds the sound nozzle thrust, but is lesser (about 25 %) than the thrust of the ideal calculated Laval nozzle; the difference therewith decreases markedly with the decrease of flight altitude and stagnation pressure.     

微型超高压宝石喷嘴内部的空化与磨损

宝石喷嘴是影响超高压水射流切割系统工作效率的重要部件,而宝石内部的空化直接影响射流的形成,也是宝石磨损的重要原因之一。对400 MPa压力范围内宝石孔内部的空化两相流进行了数值模拟,阐述了射流在宝石内的形成过程,分析了长径比、压力和入口形状对宝石内空化的影响,并在相应压力下对宝石喷嘴的磨损进行了实验研究。结果表明:宝石内部的空化发展程度随着长径比的增大而减弱;在一定的长径比范围内,空化可以发展到喷嘴出口,并最终使射流的初始直径小于喷嘴直径,且在此条件下当压力升高时,射流的初始直径增大;良好的入口形线可以降低空化的发展程度;宝石入口的磨损较出口更显著,空蚀和高压水的冲蚀造成了宝石孔边缘形状的破坏,这种破坏随着压力的升高而加剧,选择合适的长径比是减少冲蚀磨损的有效途径。     

Utilization of ultrasound to enhance high-speed water jet effects

Continuous high-speed water jets are presently used in many industrial applications such as cutting of various materials, cleaning and removal of surface layers. However, there is still a need for further research to enhance the performance of pure water jets. An obvious method is to generate water jets at ultra-high pressures (currently up to 700 MPa). An alternate approach is to eliminate the need for such high pressures by pulsing of the jet. This follows from the fact that the impact pressure on a target generated by a slug of water is considerably higher than the stagnation pressure of a corresponding continuous jet. Ultrasonically forced modulation of a continuous stream of water represents the most promising method of pulsed jet generation because of its simplicity and practicality. A pulsed jet is generated by modulating a continuous stream of water by ultrasonic waves. A velocity transformer connected to a piezoelectric transducer is located axially inside a nozzle to induce longitudinal pulsations in the water. An extensive laboratory research program is in progress to understand the basic principles of the process and to optimize the nozzle design for several applications. The results reported in this paper show that the performance of such a pulsed jet is far superior to that of a continuous jet operating at the same parameters. Experimental results obtained with the ultrasonic vibration of a tip situated inside the nozzle indicate that using this technique one can achieve performance of the jet even order of magnitude higher in comparison to continuous jet at the same hydraulic parameters. Performance of ultrasonically modulated jets in cutting of various materials was tested in laboratory conditions. In this paper, results of measurement of dynamic pressure in the nozzle and force effects of modulated jets are presented together with results obtained in cutting of various materials using ultrasonically modulated water jets. The results are compared with those obtained with continuous jets at the same operating parameters. Potential of forced modulation of the jet in applications of cleaning, paint and coating removal from surfaces and concrete cutting in the process of repair of concrete structures is mentioned.     

围压条件下空化磨料射流的冲蚀特性与机制分析

 磨料射流在水利水电、石油工程和海洋资源开发等领域有着广泛的应用,研究射流的冲蚀特性和破坏物料机制对提高水射流利用效率具有重要意义。利用自行研制的实验装置,研究了围压条件下自振空化、文丘里和锥形3种喷嘴形成的磨料射流冲蚀特性,分析了空化磨料射流冲蚀物料的机制。结果表明：自振空化喷嘴和文丘里喷嘴的冲蚀效果优于锥形喷嘴,空化作用有助于提高磨料射流的冲蚀效果;磨料射流的冲蚀效率随围压的增大而降低,主要原因是围压对纯水射流和空化磨料射流的压力脉动和冲击力具有抑制作用。分析认为,空化磨料射流冲蚀破碎物料的机制主要包括冲蚀、气蚀和共混磨蚀3 种作用。     

引射式气动窗口的光束质量研究

 实验研究了引射式气动窗口喷流引射对输出光束质量的影响,给出了不同引射喷管喉道尺寸下,不同引射喷流滞止压力时的气动窗口光学特性参数,其中包括:Strehl强度比,波像差最大值,波阵面形状,均方根值以及调制传递函数。实验表明,除引射喷管喉道尺寸dH=2.5mm,引射喷流滞止压力为0.5MPa工况外,其它工况时喷流引射对输出光束质量影响很小。因此引射式气动窗口可以保证输出高质量的光束。     

DF/HF化学激光器HYLTE喷管的副喷管质量流量系数

 对DF/HF化学激光器HYLTE喷管的副喷管质量流量进行了数值和理论计算，得出入口滞止压力在0.01~0.4MPa之间、喉道半高度在0.1~0.9mm之间的喷管的氘气，氢气和氦气质量流量系数，总结出质量流量系数随入口滞止压力和喉道高度的变化规律，并给出拟合公式，为副喷管的设计提供依据。     

光谱方法研究大气压氩气等离子体喷枪的放电特性

利用同轴介质阻挡放电喷枪,通过氩气的流动在大气压空气中产生了均匀的等离子体羽。等离子体羽沿气流方向较为均匀,但在喷嘴处为白色且亮度较高,远离喷嘴处为蓝色,亮度较低。研究了等离子体羽长度与外加电压幅值、驱动频率和气体流速的关系,气流小于4 L·min-1时等离子羽的长度随气流的增大而增大,而当气流大于4 L·min-1时长度随气流的增大而减小。当气流保持恒定时,等离子体羽的长度随外加电压幅值或驱动频率的增大而增大。结合气体放电理论以及分析湍流和平流对放电的影响,对等离子体羽长度随实验参数的变化进行了定性解释。光学方法研究发现在外加电压正半周期等离子羽有一个发光脉冲,而负半周期没有发光信号。同轴介质阻挡放电正半周期有两个发光脉冲,负半周期有一个发光脉冲。通过对该N₂现象的分析,为等离子体羽的产生机制提供了一种可能的解释。采集了同轴介质阻挡放电和等离子体羽的发射光谱,研究发现除等离子体羽存在明显的OH和N₂的发射谱线外,其发射光谱没有明显差别。利用光学发射谱N+₂第一负带系,对等离子体羽转动温度进行了测量,发现转动温度沿远离喷嘴的方向逐渐降低,且转动温度随电压幅值的增大而增大。     

Influence of nozzle spacing and diameter on acoustic radiation from supersonic jets in closely spaced arrays

Acoustic emissions were characterized for fourteen, 8 × 8 arrays of axisymmetric supersonic jets experimentally. The nozzle diameters ranged from 3.2 mm (1/8 in.) to 6.4 mm (1/4 in.) and the hole-to-hole spacing (S) over hole diameter (d), or the S/d ratios ranged from 1.44 to 3. The arrays were tested at several net pressure ratios ranging from 2 to 24. It was found that up to a critical net pressure ratio, the arrays radiated ultrasonic frequencies. Beyond this critical net pressure ratio the characteristic frequency decreased to lie within the audible range. Frequency response plots of the sound pressure indicate a broadband frequency peak generated by the turbulent mixing noise of the jet. At lower net pressure ratio (NPR) values, this broadband peak is similar to a single jet within the jet array. However, as the NPR continues to increase this frequency peak shifts to lower values which are similar to a single jet with an equivalent exit area of the entire array. Dimensional analysis revealed that at a critical net pressure ratio a dramatic reduction in the characteristic Strouhal number occurred. A small increase in the characteristic acoustic pressure was also observed at net pressure ratios below the critical net pressure ratio and a larger increase was observed at higher net pressure ratios. The critical net pressure ratio appeared to be a linear function of S/d for the nozzle arrays. A linear curve fit was applied to the measured critical net pressure ratio and this was compared to a theoretical model prediction. The experimental results revealed that the critical net pressure ratio is well predicted by the models.