Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis
Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis
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气泡引起的湍流中的流动拓扑：直接数值模拟分析
DOI：
10.1017/jfm.2018.750
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发表时间：
2018
影响因子：
3.7
通讯作者：
N. Chakraborty
中科院分区：
文献类型：
--
作者：
J. Hasslberger;M. Klein;N. Chakraborty
本文详细研究了气泡诱导两相湍流中的流动拓扑。两个自由移动和变形的气泡，已被悬浮在液体水中的逆流条件下已被认为是这种分析。这里考虑的直接数值模拟数据是基于两相流控制方程的单流体制剂。为了研究相干结构的发展，进行了局部流拓扑分析。利用速度梯度张量的不变量，所有可能的小尺度流动结构可以分为两个节点和两个焦点拓扑不可压缩湍流。在气相中的焦点拓扑结构的体积分数始终高于在周围的液相。这一观察结果被认为与同时存在高流体速度和高界面曲率的区域的强涡量产生有关。取决于状态（稳定/层流或不稳定/湍流），与界面处的密度和粘度跃变相关的附加效应影响行为。分析还指出，一个特定的术语的涡量输运方程作为负责诱导的界面处的涡运动。除了已知的机制，这个术语，涉及表面张力和界面曲率梯度，代表了另一个潜在的湍流产生源，适合于进一步研究。
This paper presents a detailed investigation of flow topologies in bubble-induced two-phase turbulence. Two freely moving and deforming air bubbles that have been suspended in liquid water under counterflow conditions have been considered for this analysis. The direct numerical simulation data considered here are based on the one-fluid formulation of the two-phase flow governing equations. To study the development of coherent structures, a local flow topology analysis is performed. Using the invariants of the velocity gradient tensor, all possible small-scale flow structures can be categorized into two nodal and two focal topologies for incompressible turbulent flows. The volume fraction of focal topologies in the gaseous phase is consistently higher than in the surrounding liquid phase. This observation has been argued to be linked to a strong vorticity production at the regions of simultaneous high fluid velocity and high interface curvature. Depending on the regime (steady/laminar or unsteady/turbulent), additional effects related to the density and viscosity jump at the interface influence the behaviour. The analysis also points to a specific term of the vorticity transport equation as being responsible for the induction of vortical motion at the interface. Besides the known mechanisms, this term, related to surface tension and gradients of interface curvature, represents another potential source of turbulence production that lends itself to further investigation.
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DOI：
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