当液体局部区域的压力下降并低于临界压力时，内部会发生空化现象并形成空泡。空泡是典型两相流动现象，其成核、生长、运动及溃灭不仅会改变液体的流动特性，还会对材料的表面造成空蚀损伤。研究空泡的动力学行为对于认识空化现象、探究空蚀破坏机理具有重要的意义。本文以空泡作为研究对象，结合数值计算和实验分析，对单空泡、多空泡系统的动力学行为进行了系统研究，并通过实验探究了空泡坍缩过程中可能存在的高能粒子发射现象。为了分析空泡的动力学行为，本文新建了可压缩两相介质流动过程的数值模型。针对粒子Level Set方法目前还存在的不足，新模型有目的性地进行了改进并提出了优化型粒子Level Set方法，该方法不仅重新定义了逃逸粒子修正Level Set函数场的流程，而且还实现了“越界”网格节点Level Set函数值的有效修正，显著提升了多相运动界面的追踪精度。此外，为了降低两相介质界面附近的数值振荡，新模型还对改进型虚拟流体方法进行了优化，并提出了基于线性插值方法的优化型界面条件处理方法。数值对比结果显示，与现有方法相比，新建数值模型在准确性和稳定性方面均表现出了明显的优势。近壁空泡和双空泡溃灭过程的数值计算结果显示，溃灭初始时刻空泡内外的巨大压力差会促使空泡在液体中形成一组稀疏波，此稀疏波经过反射所形成的反射稀疏波在传播过程中会减缓空泡泡壁运动速度的增加，破坏空泡泡壁运动速度分布的球对称性，是诱导空泡局部形成内凹并产生微射流的主要原因。超声多空泡系统声发射特征的实验研究表明，随着空泡平均距离的减小，多空泡系统的动力学过程会呈现出非常明显的非线性特征，即空泡之间的相互作用会显著增强；而当液体中加入一定量的十二烷基硫酸钠之后，非线性特征会迅速消失，即表面活性剂有效增大了空泡之间的平均距离，减弱了空泡之间的相互作用。空泡动力学理论分析结果显示，空泡之间的尺寸差异是空泡相互产生非线性影响的根本原因，且大空泡对小空泡动力学过程的非线性干扰要远大于小空泡对大空泡的影响。最后，本文研制了“受限”超声空化实验平台，并基于3He正比计数器搭建了中子探测系统。表面活性剂添加前后重水溶液的对比实验以及镉板阻挡实验均表明，中子探测系统在超声空化实验过程中捕捉到了氘氘热核聚变反应的标志性产物——中子，验证了空泡坍缩过程中其内部极端物理环境的存在。
When the pressure of the liquid drops below the vapor pressure, cavitation would develop and induce the generation of cavitation bubbles. The dynamics of cavitation bubble is a typical two phase flow phenomenon. Besides the adverse influence on the flow, the nucleation, growth, oscillation and the collapse of cavitation bubbles also take the resposiblity for cavitation erosion on the material surface. Therefore, it makes great sense to study the dynamics of the cavitation bubbles for improving the understanding of cavitaion and cavitation erosion. Accordingly, this thesis focuses on the dynamics of cavitation bubbles. Aside from experimental studies, numerical computations were also performed to investigate the dynamics of single cavitation bubble, as well as the cloud cavitation bubbles. Moreover, a series of experiments were specially conducted to study the possible emission of high energy paritcles during the implosion of cavitation bubbles.To achieve a numerical study on the dynamical behavior of cavitation bubbles, a compressible two-phase flow solver was established here. In order to make the capture of the moving interface more accurate and roubust, the particle level set method was carefully optimized in this thesis. On one hand, the optimized particle level method redefined the correction procedure to determine the final corrected level set value for each grid point; on the other hand, a sophisticated correction process was specially proposed to deal with those “mismatched” points. Aside from the optimized particle level set method, the modified ghost fulid method was also optimized to remove the possible development of numerical oscillation near the interface. The numerical examples reveal that the simulations accomplished with this new solver are quite accurate and robust.The numerical computations carried on the collapse of a single cavitation bubble near solid boundary and the collapse of two interacting cavitation bubbles show that the initial huge pressure difference across bubble interface would generate an expansion wave in the liquid at the beginning of the collapse. When this expansion wave hits the solid boundary or encouters with another expansion wave travelling in the liquid, it would become a rarefaction wave running toward the bubble. Both the velocity and the acceleration of the bubble interface gradually slow down in the wake of this rarefaction wave, which destroies the spherical distributation of the interfical velocity and finally lead to the generation of micro-jet. The experimental study on the acoustic noise emitted from the ultrasonic cavitation bubbles indicates that the nonlinear feature of the dynamics of cavitation bubbles would gradually increase with the enhancement of bubble-bubble interaction by decreasing the distance between bubbles, and that the addition of surface additive solute (sodium dodecyl sulfate) could substantially reduce the nonlinearity of the dynamics of cavitation bubbles by increasing the distance between bubbles. Calculations performed on the dynamics of two interacting spherical cavitation bubbles suggest that the size difference between the bubbles takes the most responsibility for the mutual nonlinear bubble-bubble interaction, and that the larger this size difference is, the stronger nonlinear influence the small bubble would suffer.Moreover, in order to study the high energy particles emitted from the imploding cavitation bubbles, the “confining” ultrasonic cavitation system, as well as the neutron detection system based on 3He proportional counter, was established in this thesis. The results of control experiments show that the neutron emission did happen in the cavitated heavy water solution containing sodium dodecyl sulfate, which indicated the existence of supercritically physical condition insdie the imploding cavitation bubbles.
