敞口式离心喷嘴液膜动态填充及打开过程研究

Investigation on Dynamic Filling and Opening Process of Liquid Film in Open-End Swirl Injector

关键词:  离心喷嘴  液膜厚度  空心涡  数值模拟

Key words:  Swirl injector  Liquid film thickness  Air core  Numerical simulation

摘要:

为了揭示敞口式离心喷嘴液膜填充及打开过程，采用两相界面追踪方法VOF(volume of fluid)模拟了喷嘴内部及近喷口区域流动过程，计算得到的喷雾角和试验结果偏差不超过2%。计算结果表明:喷嘴内部填充过程中，自切向孔下游至喷嘴出口液膜厚度缓慢增加，在喷嘴出口处液膜厚度大幅度降低，呈非线性发展；相应地，切向孔截面空心涡经历了正方形-花瓣形-圆形的演化历程；喷口边缘处表面张力占主导，此时液膜较厚，因此液膜刚流出喷嘴时并没有立刻打开，而后变薄、失稳、脱落、破碎并部分聚合，随着时间推移，喷嘴出口液膜形态依次经历了铅笔形、洋葱形、郁金香形和完全发展形四种形态，与稳态下喷注压降改变时喷雾形态变化相一致。

Abstract:

In order to deeply understand the dynamic filling and opening process of the liquid film in an open-end swirl injector，a numerical simulation of the internal and external flow process of the nozzle was carried out using the VOF(Volume of fluid)interface tracking method. The relative error of spray angle between the numerical simulation and experiment were less than 2%. During the filling process，the liquid film thickness in the injector shows a nonlinear tendency in general. The liquid film thickness increases from the tangential inlet to the exit while it decreases sharply at the exit of the injector. Correspondingly the vortex shape in the tangential inlet surface derives from square to petal and then circle. As the surface tension dominates at the injector exit，the liquid film is rather thick so it does not open as soon as it leaves. On the one hand，the thick liquid film experiences thinning，instability，shedding，breaking and coalescing during the opening process. On the other hand，the liquid film at the outlet of the injector experiences distorted pencil shaped stage，onion shaped stage，tulip shaped stage and fully developed stage in turn，which are consistent with the spray pattern at steady state under different injection pressure drop.