多液滴同步冲击液膜时中间薄膜射流形成机理与动力学特征

采用耦合水平集-流体体积（coupled level set and volume of fluid）方法结合高斯随机分布扰动对多液滴同步冲击平面液膜飞溅过程进行了三维数值模拟，通过分析压力、速度等细微场量分布，揭示了中间薄膜射流的生成、破碎以及后期柱状射流的形成机理。此外，讨论了Weber数、液膜厚度、液滴间距对薄膜射流高度的作用规律。结果表明，在液相加入高斯分布扰动后可以充分反映液滴冲击飞溅特征；相邻液滴颈部区域射流接触后，接触区压力梯度骤然升高，与流体运动间断共同作用下形成向上运动的薄膜射流，随后在流体不稳定性与气相涡流作用下发生破碎；薄膜射流高度随Weber数和液膜厚度升高而增大，液滴间距减小时，射流高度增大。

Central sheet formation mechanism and dynamic characteristics in simultaneous impact of multiple droplets on liquid film

This study employed the method of coupled level set and volume of fluid (CLSVOF) to simulate simultaneous impact of multiple droplets on a liquid film three-dimensionally, and focused on the splashing process with the implement of Gaussian distribution to generate perturbation on liquid phase. The formation and break-up mechanisms of the central sheet and the formation mechanism of the column jet were revealed through analyzing pressure and velocity distributions after impingement. The effects of impact Weber number, film thickness and droplet interval were discussed. It is shown that the splashing characteristics can be well predicted with the use of Gaussian distribution on liquid phase. After the neck-jet or crown liquid sheet contacting with each other, a great pressure gradient is produced in the contact region, which leads to production of the upward-moving central liquid sheet with the conjunct motivation of fluid kinematic discontinuity and breaks up under the effects of fluid instability and gas vortex. The central sheet height increases with increasing Weber number and film thickness, or with decreasing droplet interval.