超声悬浮乙醇液滴气动破碎特性研究

采用超声波悬浮液滴的方式，选取直径分别为1.0mm、1.5mm和2.0mm的乙醇液滴为研究对象，在韦伯数We=15~90的范围内，对其在脉冲气流中的破碎特性进行了实验研究。利用高速摄像机拍摄破碎现象，分析了液滴的破碎模式与运动特性。研究结果表明，随着韦伯数的增加，液滴先后产生袋状破碎、袋状/蕊心破碎、羽状/液膜稀释破碎。三种不同的破碎模式本质上都是袋状破碎——边缘袋状破碎与核心袋状破碎，低We数下主要为核心袋状破碎，高We数下主要为边缘袋状破碎。We数越大，破碎形成的袋直径越小，数量越多，破碎越剧烈。初始直径增大会使液滴转变破碎模式的临界We数增大。脉冲气流中乙醇液滴的迎风面运动遵循匀加速规律，其无量纲位移以We-1/2的比例缩小后是无量纲时间的简单二次函数。液滴在横向的扩散过程分为两个阶段，一个是惯性控制阶段，另一个是毛细效应阶段。

Study on the aerodynamic breakup characteristics of ultrasound levitated ethanol droplets

Abstract: The breakup characteristics of the acoustic levitated ethanol droplet when exposed into an impulse jet flow were experimentally investigated with the droplet three diameter of 1.0mm, 1.5mm and 2.0mm and the Weber number varied from 15 to 90. The breakup phenomenon was recorded with a high speed camera, the breakup and motion characteristics were analyzed. Results show that with the increase of Weber number, the droplets are broken in bag-, bag-stamen- and plume/sheet-thinning breakup mode successively. The essence of these three breakup modes is bag breakup, i.e., rim bag and core bag. The core bag breakup dominates the breakup mode at low Weber numbers, while the rim bag breakup is dominant at high Weber numbers. With the increase of Weber number, the opening diameter of bag decreases, and the number of bags increases, the more violent the breakup is. The increase of droplet diameter leads to the increase of critical Weber number. The movement of the windward side of the droplet follows constant acceleration rule, the dimensionless displacement after scaled by We-1/2 is a simple quadratic function of dimensionless time. The spreading of the droplet at the cross direction consists of two stages, one is inertia controlled followed by the other a capillary effects dominant one.