Spreading, pinching, and coalescence: the Ohnesorge units.
Spreading, pinching, and coalescence: the Ohnesorge units.
复制标题
展开、收缩和合并：Ohnesorge 单位。
作者：
M. Fardin;M. Hautefeuille;V. Sharma
了解液滴扩散、挤压和聚并的运动学和动力学对于包括喷涂、印刷、涂层、点胶、乳化和雾化在内的各种应用至关重要。因此，实验研究可视化和表征液滴在基底上扩散的尺寸随时间的增加，或聚结液滴之间的液体桥，或液滴形成过程中捏颈半径的减小。即使对于牛顿流体，惯性、粘性和毛细应力的相互作用也会导致许多标度定律，其中有三种极限自相似情况：粘-惯性（VI）、粘-毛细（VC）和惯性-毛细（IC）。虽然实验是作为量纲分析方法的例子，但缺乏精确的预因子、过渡和缩放指数的值或估计，给定量分析和材料表征带来了困难。在本教程的回顾中，我们重新分析和总结了一套详细的具有里程碑意义的已发表的关于牛顿流体的实验研究。我们表明，超越VI、VC和IC单位，支持由所有三种材料特性（粘度、表面张力和密度）决定的固有时间尺度和长度尺度，创造了一个互补的系统，我们称之为Ohnesorge单位。我们发现，尽管在拓扑特征、时间尺度和材料特性上存在很大差异，但对Ohnesorge单元中扩散、挤压和凝聚滴的分析导致了实验数据集的显著崩溃，突出了这些流中显示的共享和普遍特征。
Understanding the kinematics and dynamics of spreading, pinching, and coalescence of drops is critically important for a diverse range of applications involving spraying, printing, coating, dispensing, emulsification, and atomization. Hence experimental studies visualize and characterize the increase in size over time for drops spreading over substrates, or liquid bridges between coalescing drops, or the decrease in the radius of pinching necks during drop formation. Even for Newtonian fluids, the interplay of inertial, viscous, and capillary stresses can lead to a number of scaling laws, with three limiting self-similar cases: visco-inertial (VI), visco-capillary (VC) and inertio-capillary (IC). Though experiments are presented as examples of the methods of dimensional analysis, the lack of precise values or estimates for pre-factors, transitions, and scaling exponents presents difficulties for quantitative analysis and material characterization. In this tutorial review, we reanalyze and summarize an elaborate set of landmark published experimental studies on a wide range of Newtonian fluids. We show that moving beyond VI, VC, and IC units in favor of intrinsic timescale and lengthscale determined by all three material properties (viscosity, surface tension and density), creates a complementary system that we call the Ohnesorge units. We find that in spite of large differences in topological features, timescales, and material properties, the analysis of spreading, pinching and coalescing drops in the Ohnesorge units results in a remarkable collapse of the experimental datasets, highlighting the shared and universal features displayed in such flows.