反应性重气泡内激波聚焦引发射流与点火的机理研究

When planar shock wave interacts with reactive heavy gas bubble, the gas bubble can occur Richtmyer-Meshkov instability, which results in the instability and deformation of itself, meanwhile the transmitted shock wave can focus within the heavy gas bubble, and form a local region with high temperature and high pressure, which can induce the jet at the heavy gas bubble interface and ignite the combustible premixed gas within the gas bubble. The related study has important scientific and practical significances. However, the basic scientific problems such as jet induction and ignition by shock-focusing phenomenon are still not fully understood up to now. In this project, the mechanism of jet and ignition induced by shock-focusing phenomenon is deeply studied using Large-eddy simulation, combining with theoretical analysis and experimental verification. It includes the specific analysis of problems, such as shock-focusing, jet induction, three-dimensional structure evolution of jet, ignition, flame propagation, influnce of combustion on the gas bubble interface morphology and jet development. And the influence of initial conditions, such as shock strength and gas properties, is discussed. In addition, the emphasis is placed on the effect of the reflected shock wave on the distorted gas bubble. It is expected that the outcomes of this project can not only clarify the internal mechanism of jet and ignition induced by shock-focusing phenomenon, but aslo provide the theoretical fundaments and specific guidance for the rational use of shock-focusing phenomenon.

平面激波与反应性重气泡作用时，气泡界面会发生Richtmyer-Meshkov不稳定，导致其失稳变形，同时透射激波可在重气泡内发生聚焦，形成局部的高温高压区，从而在其界面处引发射流并可实现对气泡内可燃预混气的点火，相关研究具有重要的科学意义和应用价值，而其中涉及的射流引发和激波聚焦点火等基本科学问题至今未得到充分认识。本项目拟采用大涡模拟方法，结合理论分析和实验验证，对反应性重气泡内激波聚焦引发射流与点火的机理进行深入研究，具体分析激波聚焦、射流引发、射流三维空间结构演化、点火、火焰传播、燃烧过程对气泡界面形态和射流发展影响等诸方面的问题，并探讨激波强度、气体属性等初始条件的影响，重点考察反射激波对变形重气泡的作用。相关研究可以澄清激波聚焦引发射流与点火过程的内在机理，为在实际中合理利用激波聚焦现象提供理论基础和具体指导。

激波与不同密度气泡界面的相互作用蕴含了复杂的物理化学机制，因此，采用高精度数值格式对入射及反射激波分别与惰性气泡及火焰的作用过程进行了数值研究。本项目的主要结论是：.(1)入射激波在SF6重气泡内的聚焦过程分成两个阶段完成，气泡下游附近的高压区和涡量分布对形成射流均有促进作用。当改变激波反射距离后，适当的距离会使反射激波与气泡二次作用后在气泡左侧界面引发射流。.(2)强激波对Kr重气泡有更强的压缩与扰动作用，形成更强的涡，弯曲项和拉伸效应是流向涡形成的最主要来源。.(3)斜压项在火焰区内涡量变化中起主导，促进涡量生成。.(4)激波诱导火焰界面过程可促进未燃气与可燃气的混合，进而强化燃烧，但燃烧的增强却能抑制混合。越长的激波反射距离，流场黏性的影响越强，能抑制火焰界面的皱褶。.(5)激波强度和火焰尺寸增加均可在流场中引发爆轰，而爆轰可使火焰迅速膨胀，提高放热率，从而影响燃烧特性。.(6)波后火焰区内Okubo-Weiss函数积分量基本守恒，且波后火焰区的流动拓扑分类主要以焦点和鞍点为主。.(7)三维火焰在不同可压缩性区域内总体上受旋转控制；此外，Q-R平面的“泪珠状”分布表明反射激波后火焰区的湍流化程度较高，而 QS*-QW平面中的概率密度分布表明可压缩区具有更大的耗散。