Experimental research on breakup of 2D power law liquid film

On account of limited knowledge of the breakup of power law liquid film, the process of its disintegration and atomization was studied by using a planar liquid film. A linear stability analysis was adopted to predict the breakup characteristics of the power law film. The predicting formulas of stripping breakup length and diameter of ligament were put forward presently. Through high-speed photography and laser light sheet illumination,different breakup characteristics of flat power law film under different conditions were derived. The characteristic dimension of breakup regimes were defined and extracted. The effects of several parameters(injection pressure,ambient pressure, nozzle structure and fluid property) on the stripping breakup length and spray angle were investigated. The results revealed that increasing both the velocity of liquid film and the ambient pressure facilitated the breakup of film, reduced the stripping breakup length and enlarged the spray angle in different extents. The comparison between theoretical and experimental results was conducted to validate the feasibility of the linear stability theory.

旋流作用下的液膜初始破碎可视化实验研究

利用背光照明和高速相机,对强剪切气动雾化喷嘴出口雾化进行了可视化实验研究,探究旋流中的液膜初始破碎特性及一二级旋流对液膜初始破碎的影响。唯象描述了液膜破碎过程和模式,并分析图像获得表征液膜初始破碎特性的物理量:液膜破碎长度和径向拍振频率。实验结果表明:旋流作用下液膜破碎主要为液袋破碎和液丝破碎模式,这与平面液膜相似,且受工况的影响规律也相同,但旋流作用使得破碎过程和模式叠加,更为复杂。液膜破碎长度主要由一级旋流决定,二级旋向的影响可忽略。径向拍振频率认为是由Kelvin-Helmholtz(KH)和Rayleigh-Taylor(RT)不稳定机理共同主导,且受一二级旋流共同影响;此外,在大气流流量时,同旋更有利液膜失稳破碎,即径向拍振频率更大,而小流量时反旋更利于破碎。进一步由实验数据得到拟合经验公式,两者吻合良好,且发现径向拍振频率可能与旋流数之间存在关联。最终认为旋流作用下液膜更易失稳破碎,且一级旋流决定了液膜初始破碎的基本形态,二级旋流起强化剪切和辅助作用。

航空发动机离心式喷嘴宏观喷雾特性

为探究航空发动机离心式喷嘴的喷雾宏观特性,通过将该喷嘴在高温高压定容弹中进行喷雾过程的实验,并结合阴影法与纹影法进行光学测量。首先以水作为射流工质,观察不同喷射压力下水进入大气环境中的雾化角变化,发现喷嘴结构对雾化角有着重要影响,最大雾化角与喷嘴出口的导流结构夹角相等。其次以正癸烷作为工质,通过不同环境压力和温度下的多组实验测量其它喷雾宏观特性如液膜破碎长度,结果表明在背压大于1.75MPa的工况下,该离心式喷嘴无法形成清晰稳定的锥形喷雾结构,此外还揭示了高背压加强了气动力而高环境温度减小了表面张力和粘性力,两者都起着促进雾化的作用。