Abstract:

Droplet breakup, as the secondary breakup phenomenon during liquid atomization, plays an important role in many fields, such as fuel combustion in internal combustion engines and spray cooling. Although droplet breakup in continuous flow has been well studied, the mechanism of droplet breakup in shear flow environment is still deficient in the reported related studies. In this paper, we investigated the droplet breakup characteristics in shear flow with medium shear effect by means of a high-speed camera observation system, combining with image processing and analyzing software such as Matlab and ImageJ. The experiments distinguished two different manifestations of bag-stamen breakup as mushroom bag-stamen breakup and cane bag-stamen breakup, whose main characteristics differences were reflected in the different position of the liquid stamen structure. Based on the experimental data, a prediction function of the degree of deformation applicable to the two manifestations of bag-stamen breakup was established, and the average relative error of the function was only 3.85% after verification of the experimental data. In addition, the study quantified the sub-droplet size distribution law of the two manifestations of bag-stamen breakup and analyzed and measured the effects of the hollow bag structure, bag-ring structure and stamen structure on the percentage of sub-droplet size in the bag-stamen breakup.

Key words: size distribution, turbulent flow, multiphase flow, droplet breakup, atomization

摘要：

液滴的破碎作为液体雾化过程中的二次破碎现象，在许多领域都起着重要作用，如内燃机燃料燃烧、喷雾冷却等。尽管均匀气流中的液滴破碎已有充分的研究，但已报道的相关研究中剪切气流环境下的液滴破碎机理仍存在不足。本文通过高速相机观测系统，结合Matlab以及ImageJ等图像处理分析软件，研究了中等剪切强度的剪切流中液滴的破碎特性。实验鉴定区分了两种不同表现形式的袋蕊破碎——蘑菇袋蕊破碎与手杖袋蕊破碎，其主要特征差异体现在液团花蕊结构位置不同。基于实验数据，建立了适用于两种袋蕊破碎的形变程度预测函数，经过实验数据的验证，函数的平均相对误差仅为3.85%。此外，研究量化了两种形式袋蕊破碎的子液滴尺寸分布规律并分析与测量了袋蕊破碎中空心袋结构、袋环结构和花蕊结构对破碎后子液滴尺寸占比的影响。

关键词: 粒度分布, 湍流, 多相流, 液滴破碎, 雾化