牛顿流体液滴成形过程及断裂原因研究

Study on droplet formation process and breakage reason fora Newtonian fluid

利用高速摄影机对实验中液滴成形过程进行拍摄,获取一系列成形过程的瞬时图片。运用Fluent软件中VOF(Volume of fluid)方法,对低流量情况下毛细管末端液滴成形过程进行数值模拟,采用几何重构方法(Geometric reconstruction)对液滴成形的气液界面进行捕捉,并与高速摄影获得的成形实验结果比较,结果表明数值模拟结果与实验一致,表明数值模拟的可行性。在此基础上,计算出液滴整个成形过程中所受合力的变化,分析了成形过程液滴内部的压力,结果表明:液滴成形过程可分为成形、颈缩、断裂三个阶段;断裂阶段重力和表面张力将达到平衡,平衡之后重力占主导地位,微小的体积增量使得颈缩处急剧变细,液滴断裂;成形和颈缩阶段沿液滴中心线压力逐渐增大,断裂阶段颈缩处压力最大,达到360Pa。

The high-speed camera was used to record a series of forming process pictures in the experiment.The volume of fluid(VOF)method in fluent was used to simulate the droplet formation from the capillary at the low flow rate.The geometric reconstruction was used to capture the gas-liquid interface of droplet formation,and the numerical simulation results are in good agreement with the experimental resultsobtained by high-speed photography,which verifies the feasibility of numerical simulation.The change of the resultant force during the whole formation process was calculated,and the pressure inside the droplet was analyzed.The results show that the drop formation process is divided into three stages of formation,neck,and breakage and the pressure in the neck is the largest at the breakage stage.There is a balance between gravity and surface tension at the breakage stage.Then the gravity dominant,a small increase of volume causes the neck to shrink sharply and the droplets break.The pressure inside droplet gradually increases along the centerline of the droplet at the formation and neck stages.The pressure at neck reaches the maximum and is 360 Pa at the breakage stage.