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.

柴油荷电雾滴薄片剥离式破碎模型研究

燃油静电喷雾技术可以提高柴油的雾化性能，并能降低废气的排放。通过理论分析研究了柴油荷电雾滴薄片剥离式静电破碎，并采用已有试验结果进行验证。在考虑韦伯数和雷诺数影响下，通过瑞利极限分析了影响柴油雾滴破碎的主要影响因素，并计算了雾滴静电薄片剥离式破碎的临界荷质比，其临界荷质比的数量级约为10^-6～10^-5C／g，而在试验室获得的雾滴粒径范围内其荷质比式验值数量级为10^-6C／g。研究结果表明：在静电场作用下雾滴带有净电荷或者极化电荷，柴油雾滴以薄片剥离式破碎发生了瑞利破碎与泰勒破碎，试验数据与理论分析值较为接近，为柴油雾滴在低压下的静电破碎提供了有力依据。同时，柴油荷电雾滴发生破碎后其数密度大量增加，雾滴间产生聚并趋势，雾滴容易结并因而索太尔平均直径出现峰值，使雾滴粒径与荷电电压呈现非单调性曲线关系。

液体圆柱射流破碎过程的实验

采用高速摄像仪对圆柱射流的表面剥离现象和射流破碎长度进行了实验,在低速射流下,分析了Rayleigh模式下主液滴和卫星液滴形成过程及运动规律.随着射流速度的增大,射流表面开始出现了表面剥离小液滴.并发现存在一个临界雷诺数,当超过临界雷诺数时,射流表面出现表面剥离现象.通过对射流中表面剥离现象的实验和分析,给出了两种射流破碎长度随雷诺数变化规律和破碎长度拟合关系式.

数值分析喷水孔结构对水针断裂长度的影响

根据水刺加工工艺要求设计了圆锥圆柱型、流线型、圆柱圆锥型3种喷水孔结构。采用大型流体计算软件(CFD)模拟水流流过喷水孔内部的流体流动通道,在大气中形成动力水针过程,并依据数值模拟结果分析喷水孔结构对水针断裂长度的影响。经分析认为圆锥圆柱型喷水孔结构使水针表面易于发散形成水雾,水针断裂长度短;流线型喷水孔结构降低了流体流动通道对水流流动的扰动程度,水针断裂长度有所提高;而圆柱圆锥型喷水孔结构最利于水针保持柱状结构状态,水针断裂长度最长。