高马赫数下激波液滴相互作用的数值模拟研究

本文采用守恒清晰界面多相流数值方法模拟了超声速和高超声速环境下三维液滴的推进、变形和破碎演化过程.数值模拟结果与实验数据的一致性表明了本文所用数值方法和计算程序的准确性, 而网格无关性研究验证了采用的网格分辨率可以捕捉流场和界面的主要特征. 模拟结果验证了高韦伯数下液滴变形破碎过程所遵循的剪切诱导剥离(SIE)破碎机制, 其包含液滴的扁平化和剪切剥离两个主要特征. 而最近发现的SIE破碎机制下的循环破碎机制也在本文得到了验证, 即主液滴从球形液滴破碎为小液滴会经历多个循环重复的破碎阶段, 高韦伯数下液滴的破碎并非一次性剪切剥离的结果, 而是会发生逐层的剪切剥离和破碎. 本文还研究了马赫数对激波冲击液滴加速变形过程的影响. 结果表明, 高韦伯数下不同马赫数的液滴破碎过程具有高度一致性, 并遵循统一的SIE破碎机制.通过对液滴质心位移、速度、加速度和拽力系数的量化统计揭示其运动过程中的统一加速规律. 在激波的驱动下, 液滴并非以一个恒定的加速度做加速运动.在扁平化不明显的前期, 液滴以一个恒定的加速度做加速运动.随着液滴扁平化的发生, 迎风面积的增加导致拽力系数的增大, 进而导致液滴加速度的不断增大. 

NUMERICAL INVESTIGATION OF SHOCK-DROPLET INTERACTION WITH HIGH-MACH NUMBERS

In order to reveal the evolution of droplet propulsion, deformation, and fragmentation in supersonic and hypersonic environment, a conservative sharp-interface multiphase method is used to simulate the shock-droplet interaction with high-Mach and extremely high-Mach numbers. The numerical results are in good agreement with the experimental results, which indicates the accuracy of the numerical method and the corresponding computer code. The grid independence study demonstrates that the grid resolution used in this paper can capture the main features of the flow field and interface. The numerical results verify the shear-induced entrainment (SIE) breaking mechanism followed by the droplet deformation and fragmentation under high-Weber number, including two main features, i.e. the flattening of droplets and the shearing of the sheet at the droplet equator. The recently discovered recurrent breakup mechanism under the SIE mechanism has also been verified in this paper. The initial spherical-droplet is deformed, and breaks into smaller sub-droplets via recurrent rupture stages. And the fragmentation of droplets for high-Weber number is indeed not the result of one single shearing process, but rather occurs recurrently. The effect of the Mach number on the shock-droplet interaction is also investigated here. Our results indicate that the droplet fragmentation process for different Mach numbers is highly analogous, following the general SIE mechanism. The time evolution of the dimensionless center-of-mass drift, velocity, acceleration, and drag coefficient reveal the unified acceleration tendency for droplet under shock impact. In addition, the droplet does not propel with a constant acceleration rate for the whole stage. Instead, when the flattening effect is absent in early stage, the droplet accelerates at a constant acceleration. As the flattening occurs, the increase of the upwind area leads to an increase in the drag coefficient, which in turn increases acceleration rate of the droplet movement.