超声悬浮乙醇液滴气动变形与运动特性研究

Aerodynamic Deformation and Motion Characteristics of Ultrasound Levitated Ethanol Droplets

关键词:  超声悬浮  液滴  破碎模式  运动特性  扩散

Key words:  Ultrasonic levitation  Droplet  Breakup mode  Motion characteristic  Dispersion

摘要:

利用超声悬浮的方法为液滴提供静止、无接触初始条件，用高速摄影机拍摄液滴，研究不同直径乙醇液滴在Weber数5~90，脉冲气流冲击作用下的变形与运动特性。研究结果表明，随着韦伯数的增大，液滴先后产生常见的袋状破碎、袋状/蕊心破碎、羽状/液膜稀释破碎。不同破碎模式在本质上都是袋状破碎，包括边缘环袋破碎与液核多袋破碎。Weber数越大，边缘环袋破碎作用越弱，液核多袋破碎越占据主导地位。乙醇液滴的迎风面顶点纵向运动遵循匀加速规律，其无量纲位移与无量纲时间符合二次函数关系式。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；另一个是毛细效应控制阶段。液滴未破碎时，其横向扩展无量纲直径与上述无量纲位移符合二次函数关系式，而破碎后二次液滴的无量纲扩散直径与毛细时间则符合线性关系式。

Abstract:

The ultrasonic suspension method is used to provide static and non-contact initial conditions for the droplets， and the high-speed camera is used to photograph the droplets. The purpose of this paper is to study the deformation and motion characteristics of ethanol droplets with different diameters under the impact action in the range of Weber number 15 ~ 90. The results show that with the increase of Weber number， the common breakup modes， such as bag breaking， bag breaking / core breaking， pinnate / liquid film dilution breaking， are essentially bag like breaking （ edge ring bag breaking and liquid core multi bag breaking）. The larger we number is， the weaker the edge ring bag breaking is， and the more dominant liquid core bag breaking is. The results show that the longitudinal motion of the top of the windward side of the ethanol droplet follows the law of uniform acceleration， and its dimensionless displacement and dimensionless time conform to the quadratic function. There are two stages in the process of droplet diffusion， one is inertia control， the other is capillary effect control. When the droplet is not broken， the dimensionless diameter of its lateral expansion is in accordance with the quadratic function relation with the above dimensionless displacement， while the dimensionless diffusion diameter and capillary time of the secondary droplet after crushing conform to the linear relationship.