高压旋转射流流动特性的实验研究

测量了叶轮导引高压射流喷嘴在不同叶轮螺旋倾角和喷嘴收缩角下高压水的喷射形状参数,通过分析给陋了此种射流的外边界曲线方程形式及射流扩散角与叶轮螺旋倾角、喷嘴收缩角的关系,最后对射流机理进行了探讨,并给出一种微团轨道模型研究方法。     

水中高压脉动气泡水射流形成机理及载荷特性研究

具有脉动特性的气泡(如水下爆炸气泡、螺旋桨空泡和气枪气泡)动力学行为很大程度上取决于其边界条件. 实验已证实,近自由液面气泡在坍塌过程中常常产生背离自由液面的水射流现象,而近刚性边界气泡在坍塌阶段产生朝向壁面的高速水射流,严重威胁水中结构的局部强度. 前人基于 Rayleigh-Plesset 气泡理论和 “Bjerknes” 力来预测气泡射流方向,然而理论方法难以透彻的揭示气泡射流的初生、发展和砰击过程中丰富的力学机理. 本文首先采用水下高压放电技术产生气泡,并通过高速摄影对不同边界条件下气泡的运动特性进行实验研究. 然后,采用边界积分法模拟气泡非球状坍塌过程. 研究表明,边界条件改变了气泡周围的流场压力梯度方向,进而影响气泡射流初生位置;射流在发展阶段,气泡附近流场的局部高压区和射流之间存在“正反馈效应”,从而揭示了气泡射流速度在短时间内即可增加到百米每秒的力学机理. 射流砰击会在流场中造成局部高压区,随着气泡回弹,射流速度和砰击压力逐渐减小. 本文还探讨了无量纲距离参数对气泡运动及射流砰击载荷的影响,旨为近场水下爆炸等相关领域提供参考.      

高压燃气射流在整装液体中扩展过程的实验和数值模拟

为研究高压燃气射流在整装液体中的扩展规律,探索提高射流稳定性的控制方法,设计了4级渐扩型圆柱观察室.采用高速录像系统,观察了燃气射流在液体模拟工质中扩展与掺混的过程,获得了射流扩展形态的序列照片,测量了Taylor空腔的扩展速度,对比了观察室内壁形状对射流扩展过程的影响.建立了二维轴对称气液两相湍流模型,模拟射流扩展过...     

水中高压脉动气泡水射流形成机理及载荷特性研究

具有脉动特性的气泡(如水下爆炸气泡、螺旋桨空泡和气枪气泡)动力学行为很大程度上取决于其边界条件.实验已证实,近自由液面气泡在坍塌过程中常常产生背离自由液面的水射流现象,而近刚性边界气泡在坍塌阶段产生朝向壁面的高速水射流,严重威胁水中结构的局部强度.前人基于Rayleigh-Plesset气泡理论和"Bjerknes"力来预测气泡射流方向,然而理论方法难以透彻的揭示气泡射流的初生、发展和砰击过程中丰富的力学机理.本文首先采用水下高压放电技术产生气泡,并通过高速摄影对不同边界条件下气泡的运动特性进行实验研究.然后,采用边界积分法模拟气泡非球状坍塌过程.研究表明,边界条件改变了气泡周围的流场压力梯度方向,进而影响气泡射流初生位置;射流在发展阶段,气泡附近流场的局部高压区和射流之间存在"正反馈效应",从而揭示了气泡射流速度在短时间内即可增加到百米每秒的力学机理.射流砰击会在流场中造成局部高压区,随着气泡回弹,射流速度和砰击压力逐渐减小.本文还探讨了无量纲距离参数对气泡运动及射流砰击载荷的影响,旨为近场水下爆炸等相关领域提供参考.     

激波冲击SF6重气泡引发射流的数值模拟

为深入研究重气泡内激波聚焦和射流生成的机理,采用高精度计算格式和高网格分辨率对马赫数为1.23的平面入射激波与SF₆重气泡的作用过程进行数值模拟,计算结果与文献中实验吻合较好。结果显示:入射激波在重气泡内首先在流向上汇聚形成上、下对称的高压区,随后,这对高压区在SF₆重气泡中心对称轴处再次碰撞,完成激波聚焦过程,并在气泡下游界面附近形成远大于初始压力和密度的局部高压高密度区,体现出SF₆重气泡极强的聚能效应;激波聚焦还引起气泡下游界面附近的涡量变化,涡对的旋转能够加速射流形成与发展。因此,SF₆重气泡下游界面附近的高压区和涡量分布对形成射流结构均有促进作用。     

电流动聚焦中非牛顿流体射流影响因素的实验研究

在一套流动聚焦装置上加载高压直流电场形成电流动聚焦,并开展了非牛顿流体带电射流的不稳定性特性实验研究。实验在自行设计的装置系统上完成,获得了电流动聚焦中非牛顿流体射流的流动状态,考察了不同控制参数下射流形态的变化。结果表明,由于非牛顿流体具有粘弹性,与牛顿流体相比,非牛顿流体带电射流体现了更复杂的流动特点。这些实验结果为我们理解复杂条件下非牛顿流体射流的流动机理提供了参考,也有助于深入的实验分析和理论研究奠定了基础。     

基于Fluent的超高压撞击流乳化喷嘴的优化分析

高压液体通过喷嘴加速,形成高速射流,与相反方向的另一股射流相互撞击,发生强烈的相互作用,产生强烈的径向和轴向湍流速度分量以及狭窄的高压高速湍流区,在此区域内,相间或液滴间的碰撞互磨产生的挤压力和剪切力使流体被细化。本文从液体连续相撞击流的两个特征：微观混合和压力波动入手,逐一分析了撞击速度与微观混合、压力波动的关系,得出了压力波动与撞击流速度乱U0成正比关系,微观混合与U^3 0成正比的规律。同时,用流体模拟软件Fluent对喷嘴的结构和尺寸进行优化,并得出最合理的喷嘴结构和尺寸。模拟认为：在相同压力下,采用矩形槽,出口孔径为0．2mm,槽的深度为0．27mm的结构时撞击速度达到最大,并通过实验验证了这一结论。     

高压泄爆导致的二次爆炸

基于计算结果和相关实验结果，通过理论分析，对高压泄爆导致的二次爆炸机理进行了系统的阐述。泄爆后，泄出的高压可燃气体在泄爆口附近形成可燃云团，由于欠膨胀，云团内存在稀疏波低压区和Mach干高压区。火焰射流泄出后，在一定条件下，可使Mach干高压区内的可燃云团爆炸式燃烧，压力迅速上升，以致产生二次爆炸。     

基于红外热像的自由剪切湍流被动标量高阶谱分析

利用红外热像仪对高压水射流进行了连续探测.对红外热像序列表征的标量脉动场进行双谱分析,检测湍射流的相干结构、射流不同截面内相干结构的尺度关联性以及射流不同发展阶段的特征尺度.研究表明,以红外热像为样本的全局自双谱表征了射流不同波段能分量对相干的贡献;按三列对图像采样的横断面局部互双谱给出了沿流向的大涡区、小涡区、以及各向同性湍流区的频率耦合特征;按三行对图像采样的纵向局部互双谱给出了射流的轴心线区、剪切层、空气湍流区大涡层和各向同性湍流层等各纵向断面的相干特征;通过红外热像序列的双谱分析,由流场相干结构的尺度关联性,得到了射流诱导的空气湍流场在不同发展阶段的特征尺度.     

射流对绕水翼云空化流动抑制机理研究

为理解绕水翼云空化流动的发展机理和探究水翼吸力面开孔射流的影响,采用密度修正的RNG k-ε湍流模型和Schnerr-Sauer空化模型对原始NACA66(mod)水翼和采用射流后的水翼的云空化非定常过程进行模拟和对比分析;采用在水翼吸力面近壁区设立监测线的方法对近壁区的流场进行监测,得到近壁区汽相体积分数、回射流速度、压力及压力梯度的时空分布云图;开展了云空化流场特性的涡动力学分析,进而分析水翼云空化的发生机理和射流抑制空化的抑制机理.结果表明:游离型空泡在下游溃灭时产生强烈的局部高压,其向上游传播导致前缘空穴的一次回缩,而空穴的二次回缩受回射流的影响.回射流的发展区域受限于较高的压力梯度,高的压力梯度一直存在,但回射流在一个周期内的首次出现需要时间的积累.在水翼吸力面射流使得射流孔附近压力升高,弥补了由于空化和绕流造成的压降,压力梯度增大,抗逆压能力增强,对回射流起到阻挡作用;另一方面,射流使得回射流区域面积和回射流的强度也有所减小,从而对云空化的发展起到抑制的效果.Q准则的涡结构云图相比于汽相体积分数云图能显示复杂的流动结构,前缘附着型空穴和尾缘游离型空穴内存在旋涡,回射流对空穴存在剪切作用造成空穴脱落.而射流对空穴和回射流的剪切和阻挡使云空化发展得到抑制.     

高速液体受限射流扩展形态研究

采用一种火药燃烧驱动液体喷射的新装置及其测试系统，研究受限空间中高速惰性液体射流的扩展结构。观察了环境反压、液体粘性、喷嘴结构等参量对射流扩展形态的影响，分析了射流雾化机理。研究结果对改进燃烧室设计及控制燃烧稳定性有一定的指导意义。     

Penetration height correlations for non-aerated and aerated transverse liquid jets in supersonic cross flow

Experimental results on the mixing of non-aerated and aerated transverse liquid jet in supersonic cross flow (M = 1.5) are presented in this paper. The goal of this study is to investigate the effect of the gas/liquid mass ratio on the penetration and atomization of an aerated liquid jet in high speed cross flow and to develop correlations for the penetration heights. High speed imaging system was used in this study for the visualization of the injection of aerated liquid jet. The results show the effect of jet/cross flow momentum flux ratio, the gas/liquid mass ratio and the Ohnesorge number on the penetration of aerated liquid jet in supersonic cross-flow. New correlations of the spray penetration height for the non-aerated liquid jet (GLR = 0) and the net gain in spray penetration height for the aerated liquid jet (GLR > 0) are presented.     

Three-ion model of EHD flows in the “wire-over-plane” electrode system

The results of numerical simulation of the complete system of electrohydrodynamic equations are presented for a dielectric liquid containing three kinds of ions, namely, two kinds arising owing to impurity molecule dissociation and the third kind arising owing to appearance of ions from liquid molecules with the electron-donor properties in near-electrode reactions. An analysis of the simulation results shows that a small jet of injected ions rapidly recombines with counterions under the conditions of weak injection; therefore, the jet of space charge differs significantly from the injected ion jet. This difference disappears under the conditions of strong injection. The flow structure is in the close correspondence with the results revealed experimentally.     

Effect of Nozzle Exit Turbulence on the Column Trajectory and Breakup Location of a Transverse Liquid Jet in a Gaseous Flow

This study examines the effect of fully developed turbulent flow at the exit of nozzle/injector on the trajectory and column breakup location of a liquid jet injected transverly into a gaseous crossflow. Liquid jet trajectory and column breakup for different nozzle geometries at different velocities of liquid jet and crossflow are analytically and experimentally Investigated. Shadowgraph imaging technique is used to determine the jet trajectory and breakup location of a transverse liquid jet in a uniform airflow. Particle image velocimetry (PIV) is used to measure the near-field velocity profile of a liquid jet discgarged into a quiescent atmosphere. The experimental results show a higher penetration and breakup height for the liquid jet ensuing from a nozzle with a smaller length to diameter ratio. This is due to the surface irregularities of the liquid column of a turbulent jet, which breaks up and consequently follows the cross airflow sooner. In order to capture the effect of turbulence, the analytical trajectory correlation developed in our previous studies is modified to account for the discharge coefficient of a nozzle. The discharge coefficient is estimated indirectly by comparing the liquid column trajectory predicted by the modified analytical correlation with that determined experimentally. The indirectly determined discharge coefficient is then used in the analytical correlation for predicting the breakup height of a transverse liquid jet. The results predicted using this approach are in good agreement with the experimental data of the present study at standard temperature and pressure (STP) test conditions.     

含能气体射流与液体相互作用的实验研究

为了研究整装式液体发射药的燃烧稳定性的控制方法,设计了点火喷射模拟装置及4种多级渐扩型观察室,利用数字高速摄像系统,观察含能气体射流在液体模拟工质中的扩展过程,并对实验中出现的喷孔壅塞现象进行了分析.结果表明:射流在渐扩型结构中扩展稳定,喷射压力、喷孔直径和渐扩结构对射流扩展形态和气液掺混过程有显著影响,通过合理调整这些参数,可以实现对射流扩展过程的有效控制;喷孔壅塞时射流扩展形态非对称,影响气液掺混,不利于控制射流的稳定性.     

Flow and breakup characteristics of elliptical liquid jets

This paper presents the results of an experimental study on liquid jets discharging from elliptical orifices into still ambient air. The experiments were conducted with a set of elliptical orifices of approximately same area of cross section but varying orifice aspect ratio using water and water–glycerol mixture as experimental fluids. The flow behavior of liquid jets was analyzed using their photographs captured by an imaging system. The measurements obtained for the elliptical liquid jets were compared with the circular liquid jets discharging from a circular orifice of the same area of cross section. Elliptical geometry of the orifice results in a flow process by which the emanating liquid jet periodically switches its major and minor axes as it flows downstream of the orifice. In this paper, we attempt to characterize the axis-switching process through its wavelength and amplitude. For a given elliptical orifice, the axis-switching process is dominantly seen in a particular range of flow conditions. The effects of the orifice aspect ratio and liquid viscosity on the axis-switching process are revealed through this study. The experimental results on jet breakup show that axis-switching process has a destabilizing effect on elliptical liquid jets within a particular range of flow conditions and it results in shorter breakup lengths compared to the circular jet. The extent to which axis-switching destabilizes the jet is dictated by the viscosity of liquid. An increase in orifice aspect ratio destabilizes elliptical liquid jets with low viscosity like water; however, this behavior seems to get obscured in water–glycerol mixture elliptical jets due to high viscosity.     

平面液体层碎裂过程实验研究

小宽厚比喷嘴喷射出的平面水膜进入静止空气中,在不同气流流速环境下对水膜碎裂过程进行了实验研究。结果表明,静止空气中的水膜表面波呈现对称波形,射流的碎裂长度随雷诺数的增大而增大,喷射压力对射流碎裂长度没有直接影响。空气助力作用使平面射流表面波的上、下气液交界面出现相位差。水膜的碎裂长度随空气助力气流速度的增大而减小;空气助力对于低雷诺数水膜射流具有很强的促进碎裂作用,所以会极大地改善低雷诺数射流的一次雾化效果。随着水流雷诺数的提高,空气助力作用对水膜碎裂长度的影响大为减弱;即使在高速助力空气的作用下,水膜仍长期保持较稳定的射流流态,没有出现明显的水膜撕裂现象。说明在小宽厚比喷嘴的瑞利(Rayleigh)模式射流中,高雷诺数射流是水膜的稳定因素。与气液流速比、气流马赫数等无量纲参数相比,液体喷射的雷诺数是射流碎裂的主要影响因素。     

同轴气流式液体射流分裂液滴粒径研究

针对同轴气流式液体射流分裂液滴粒径预测模型缺乏的现状,结合射流线性稳定性理论,建立了基于临界模数的同轴气流式黏性液体射流分裂液滴粒径表达式,在此基础上,分别研究了气流旋拧(气流同时存在轴向和周向运动)及流体物性(气体可压缩性、液体黏性、气液密度比和表面张力)对液滴粒径的影响规律.研究发现:周围气流轴向引射作用和同轴旋转...