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...     

双股燃气射流在充液室内扩展特性的实验研究

为了探索高温高压双股燃气射流在整装式液体工质中的扩展特性,设计了五级圆柱渐扩型观察室和圆柱型观察室,借助数字高速录像系统,观察了双股燃气射流在充液室中的扩展过程,对比了不同的观察室边界以及不同的参数条件对双股燃气射流扩展过程的影响。实验结果表明,圆柱渐扩型观察室结构更有助于改善气液的掺混特性,通过参数的合理匹配可以一定程度上控制双股燃气射流在三维充液室中的扩展过程。     

圆柱形充液室中4股贴壁燃气射流扩展特性的实验研究

为了探索高温高压周向均布4股贴壁燃气射流在受限空间中的扩展特性,设计了贴壁燃气射流在圆柱形充液室内扩展的实验装置,借助数字高速录像系统,观察了4股贴壁燃气射流在充液室中的扩展过程,发现由Kelvin-Helmholtz不稳定性引起的表面不规则一直存在于整个射流扩展过程;通过处理拍摄记录的射流扩展序列图,获得不同时刻射流扩展的轴向和径向位移; 对比了不同破膜喷射压力和喷孔结构参数对4股贴壁燃气射流扩展过程的影响。实验结果表明:喷孔面积越大,贴壁射流初期轴向扩展速度越大,但由于径向扩展达到交汇的时间较早,湍流掺混和干涉强烈,衰减也越快;破膜喷射压力越高,射流径向扩展到达交汇的时间越短; 破膜喷射压力从12 MPa升高到20 MPa,射流轴向扩展速度大幅增加,气液湍流掺混效应增强。     

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。     

等离子射流与渐扩边界中液体工质相互作用特性的模拟实验

为了探索整装式液体工质电热化学炮中药室边界形状对燃烧控制的影响,采用数字高速录像系统对等离子体射流在液体工质中的扩展过程进行了测试,研究了不同放电电压、不同喷嘴直径、不同渐扩边界结构下等离子射流与液体工质的相互作用特性.获得了等离子射流在液体工质中扩展形态的时间序列图,处理出不同工况下Taylor空腔扩展的轴向位移与时...     

燃烧轻气炮多级渐扩型燃烧室流场特性数值研究

为了分析多级渐扩型燃烧室结构对燃烧轻气炮氢氧燃烧特性的影响, 通过计算流体力学方法, 分别对采用传统圆柱型燃烧室和多级渐扩型燃烧室的燃烧轻气炮氢氧燃烧发射过程进行数值模拟。对比结果表明, 多级渐扩型燃烧室结构能够明显地减小燃烧室压力波动幅度, 提高氢氧燃烧稳定性; 多级渐扩型燃烧室内形成回流区, 可以减小气流轴向运动速度; 火焰扩展形态与渐扩型结构相吻合, 燃烧反应区表面变化平稳; 多级渐扩型燃烧室结构对氢氧火焰传播过程和压力波动现象有着重要影响。     

可压缩旋转气体中超空化射流的热稳定性

液体射流热稳定性研究是对射流稳定性问题的更深层次的探讨,可以进一步加深对液体射流分裂与雾化机理的认识,具有重要的学术意义和工程应用价值. 基于射流稳定性理论,在同时考虑射流周围气体旋转、射流和周围气体可压缩性以及射流液体中含空化气泡的条件下,建立了描述可压缩旋转气体中超空化射流热稳定性的数学模型,并对数学模型及其求解方法进行了验证分析;在此基础上,分析了液体射流表面与周围气体间温差及射流内部温度梯度同时作用下对射流稳定性的影响;并进一步探讨了超空化射流的热稳定性. 结果表明,射流表面扰动波的最大扰动增长率、最不稳定频率以及最大扰动波数皆随气液温差的增大呈近似线性增大趋势;射流内部温度梯度的存在使得气液温差对射流的失稳作用更加显著;射流内部温度梯度会抑制超空化对射流稳定性的影响,但气液温差会在一定程度上促进超空化对射流的失稳作用.      

高速气流中横向液体射流雾化研究进展

在涡轮燃烧室和以液态碳氢燃料为工质的超燃冲压发动机中,高速气流中横向液体射流雾化是一个重要而复杂的过程.雾化过程进行的好坏直接关系到燃料的掺混和燃烧,进而影响发动机的性能. 针对高速气流中横向射流雾化的特点,对现阶段的实验和数值模拟研究进展进行了综述.实验方面结合国内外现状,阐明了一次、二次雾化的机理和雾化过程中的波现象,对穿透深度的确定方法及其影响因素进行了概括总结,分析了气液混合区的结构性质, 并列举和分析了常用的测量手段.数值模型研究介绍了现阶段的一次雾化和二次雾化常用的计算模型.最后提出了存在的问题和未来的研究方向.      

注塑成型喷射现象数值模拟及机理分析

喷射是熔体充填过程中一种特殊流动形态,也是注塑成型的不良现象,为了预测射流长度、形态演化,揭示喷射的产生机理,建立了粘性、非等温的熔体三维流动模型,构造了熔体流动前沿演化的输运方程。用有限体积法离散控制方程,提出了压强与速度及速度与温度的两重解耦合方案,开发了模拟程序,分析了模拟成型过程中粘性力、惯性力、速度、温度、压力等物理量的大小及变化规律。基于模拟结果分析了粘性力、惯性力的大小对喷射的影响,发现:当惯性力大于粘性力时产生喷射现象,随着粘性力增大,射流变为蛇形流;射流长度依赖于注射速度,速度越大,射流越长,熔体温度对射流长度基本没有影响。此外,实验结果表明,注塑成型喷射现象数值模拟及机理分析方法可以较好地预测射流长度、蛇形流的形态以及蛇形流中、后端摆动幅度。     

圆环旋转粘性液膜射流三维不稳定性研究

利用线性稳定性理论进行了射流液体粘性对圆环旋转液膜射流稳定性影响的研究,推导出了三维扰动下具有固体旋涡型速度分布的圆环旋转粘性液膜射流的色散方程;在此基础上进行了类反对称模式与类对称模式下的圆环旋转粘性液膜射流的三维不稳定性分析。研究结果表明,在类反对称模式下,液体粘性超过一定值后,射流最大扰动增长率随液体粘性的增加而迅速减小;轴对称模态的射流特征频率产生一个突降变化;随液体粘性增加,轴对称模态不稳定波数范围减小,非轴对称模态不稳定波数范围呈现出先减小后增大趋势。在类对称模式下,液体粘性对射流最大扰动增长率的影响主要体现在对非轴对称模态的影响上;液体粘性只在粘性较大时才会对非轴对称模态射流特征频率产生一定影响;液体粘性超过一定值后,轴对称模态与非轴对称模态的不稳定波数范围都会快速下降。     

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.     

Study on Expansion Characteristic of Twin Combustion Gas Jets in Five-Stage Cylindrical Stepped-wall Observation Chamber

The five-stage cylindrical stepped-wall observation chamber is designed to investigate the method of controlling the interior ballistic stability in bulk-loaded propellant guns. The expansion and mixing process of twin combustion gas jets in liquid is studied by means of high speed photographic system. The influence of multiple parameters on jet expansion shape is discussed. Based on the experiment, the three-dimensional mathematics model is established to simulate the expansion process of twin gas jets in liquid. The pressure, density, temperature, velocity contours and evolutionary process of vortices are obtained. Results show that vortices behind the corner of the steps are formed due to the inducing effect of steps. The jets can expand along the axial and radial direction simultaneously, weakening the Kelvin-Helmholtz instability. The numerical simulation results of axial expansion displacement are in good agreement with the experimental data.     

轻型火箭发射噪声场的分布特性

为了解小火箭发射噪声特性及其在喷口外围的声压场分布规律,针对燃气射流产生噪声问题进行了实验研究和数值计算。讨论了超声速射流噪声的3个主要成分(湍流混合噪声、啸音和宽带激波相关噪声)及相关特点,指出它们产生的根本原因是湍流射流的速度扰动。通过分析不同实验测点的射流噪声声压级峰值,得到了燃气射流噪声在轴向和径向上的分布规律,即随着离喷口距离的增大,轴向噪声的衰减程度大于径向。在实验基础上,利用大涡模拟与FW-H(Ffowcs Williams-Hawkings)声学比拟相结合的方法对燃气射流噪声的声学特性进行计算。结果表明,此方法获得的计算结果与实验结果吻合较好,可为进一步研究射流噪声控制提供参考。     

水下超声速气体射流回击现象的实验研究

对水下超声速气体射流的动力学行为进行了实验研究.通过流动可视化揭示了回击现象的演化过程,利用探针排获得了射流近场区的脉动压力分布,实验结果表明:在超声速喷管出口两倍直径处,射流形貌的变化导致气体中出现了大幅值压力脉冲.通过流场可视化与压力测量的同步校验,证实了喷口端面处回击事件与流场气相区中压力脉动之间相关性.     

The Effect of Splitting Timing on Mixing in a Jet with Double Injections

We present large-eddy simulation (LES) of a high-pressure gas jet that is injecting into a quiescent inert environment. The injection is through a nozzle with a diameter of 1.35 mm. Four injection strategies are considered in which the results of a single continuous injection case are compared with those of double injection cases with different injection splitting timing. In all double injection cases, the injection pulsing interval is kept the same, and the total injected mass is equal to that of the single injection case. On the other hand, the splitting timing is varied to investigate the effects of various injection splitting strategies on the mixture formation and the penetration length of the jet. Results show that the jet penetration length is not so sensitive to the splitting timing whereas the mixing quality can significantly change as a result of shifting the onset of injection splitting toward the end of injection. Especially, it is found that by adopting a post-injection strategy where a single injection splits into the main injection and late small injection near the end of injection period the mixing between the injected gas and ambient air is significantly improved. This trend is not as obvious when the injection splitting timing shifts toward the beginning or even in the middle of injection period. The increase of entrainment in the tail of each injection is one of the underlying physics in the mixing improvement in double injection cases. In addition to that, splitting a single injection into two smaller injections increases the surrounding area of the jet and also stretches it along the axial direction. It can potentially increase the mixing of injected gas with the ambient air.