单液滴撞击液膜的颈部射流模拟及机理分析

DNS Analysis of Neck Jetting Flow Dynamics After Single Drop Impacting Onto a Preexisting Liquid Film

本文采用DNS耦合ACLS方法对喷雾中常见的单液滴撞击水平液膜现象进行二维的数值模拟,通过撞击后形态演变及内部场信息对比,重点分析颈部射流的形成机理,随后将研究对象拓展到倾斜液膜。本文验证了ACLS方法的准确性,成功捕捉到液膜倾角对空气卷吸现象的促进作用。研究表明,局部压差是液滴撞击水平液膜后产生颈部射流的直接原因,而对于撞击倾斜液膜的案例,前后两端颈部射流成因不同:前端射流由局部压差产生而后端射流随着液膜倾斜角的增大,旋涡机理的影响比重逐渐增强,两者处于共存竞争关系。

The present paper performs 2D numerical simulations for single drop impacting onto a flat film, ubiquitous in spray utilizations, using DNS coupling with ACLS method. We analysis the liquid topology evolution and internal field information after impacts, highlighting the mechanisms of jetting flow in neck regions, and then extend the methodology to inclined cases. The adopted ACLS method is validated to be accurate with perfect mass conservation. The inclined angle is observed to positively affect the cavitation near gas-liquid interface. Further researches show that pressure gradient is the direct force for jetting flow in flat cases. But the dominant mechanisms for front and back neck regions in inclined cases are different, i.e., pressure gradient is still the leading reason in the front while the vorticity becomes more important in the back for inclined cases. These two mechanisms are coexisting and competitive.