Numerical Simulations of Droplet Aerobreakup
Numerical Simulations of Droplet Aerobreakup
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DOI：
10.7907/z9kw5d09
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发表时间：
2014-11
期刊：
影响因子：
--
通讯作者：
J. C. Meng;T. Colonius
中科院分区：
文献类型：
--
作者：
J. C. Meng;T. Colonius
本论文旨在弥合液滴气泡状态知识中存在的一个空白，该知识与支配实验可观察到的液滴形态的基本流动物理有关。通过直接数值模拟激波后气流中水柱和水滴的气泡，研究了周围气流的行为，以深入了解水滴在剥离破碎过程中的变形和演化。可压缩的多组分Navier-Stokes方程使用多组分流程序--一种具有激波和界面捕捉的高精度结构化有限体积流求解器来求解。在对充气过程进行定性描述之后，与现有的实验数据进行了比较。在2D中，精确测量气缸在一定范围的入射激波马赫数范围内的质心加速度，可以表征非定常阻力系数。此外，来自粘性模拟的质量损失测量驳斥了一个著名的边界层剥离理论。给出了三维非轴对称气泡的数值模拟结果，重点描述了尾流区可观察到的复杂流动现象。随后对表面不稳定性的分析和流场的傅里叶分解揭示了不对称的方位调制和宽带不稳定的增长，导致尾流区退化为混沌流动。
The work presented in this thesis aims to bridge an existing gap in the state of droplet aerobreakup knowledge associated with the fundamental flow physics that govern the experimentally observable droplet morphologies. Using direct numerical simulations of the aerobreakup of water cylinders and droplets in the flow behind shock waves in air, we investigate the behavior of the surrounding gas flow to gain insight into the droplet’s deformation and evolution in the stripping breakup regime. The compressible multicomponent Navier-Stokes equations are solved using the Multicomponent Flow Code — a high-order accurate structured finite-volume flow solver with shock- and interface-capturing. Following qualitative descriptions of the aerobreakup process, comparisons are made with available experimental data. In 2D, accurate measurements of the cylinder’s center-of-mass acceleration across a range of incident shock Mach numbers allow characterization of the unsteady drag coefficient. Additionally, mass loss measurements from viscous simulations refute a well-known boundary layer stripping theory. The results of a 3D nonaxisymmetric aerobreakup simulation are presented with an emphasis on describing the intricate flow phenomena observable in the wake region. Subsequent analyses of the surface instabilities and a Fourier decomposition of the flow field reveal asymmetrical azimuthal modulations and broadband instability growth that result in the devolution of the wake region into chaotic flow.