液体射流首次破碎的直接数值模拟及动力学过程分析 *

Direct Numerical Simulationand Dynamics Analysis ofPrimary Breakupin Liquid Jet

关键词:  首次破碎  气动作用  扰动  液丝  液滴  直接数值模拟

Key words:  Primary breakup  Dynamic interaction  Perturbation  Ligament  Droplet  Direct numeri. cal simulation

摘要:

为探究液体射流破碎的失稳和首次雾化过程，结合使用 VOF(Volume of Fluid)界面流模拟方法和有界压缩格式，对以 30m/s的速度进入静止空气的射流进行了直接数值模拟。计算捕捉到了射流破碎引起的液丝和液滴和复杂流场结构的演化过程，以供开展动力学特性研究。研究分析了射流头部和液柱核心的形态变化过程，考察了射流与周围空气两相之间的相互作用机理。分析指出射流前锋最先受到扰动，在空气动力作用下产生液丝和液滴，同时将扰动借助气相和液相两种介质向上游传递，对射流的破碎进程产生促进作用。随着射流失稳和破碎程度加深，流场高度紊乱，使得气液混合程度进一步提高。揭示了射流首次破碎时头部抽丝的动力学机制，以及液丝在周围气体影响下演变并产生液滴的若干机制。

Abstract:

In order to investigate the interfacial instability mechanism and primary atomization of liquid jet，direct numerical simulations coupled with VOF(Volume of Fluid)interface simulation method and bounded compression scheme were used to simulate the injection of liquid jet into still air at 30m/s. The simulation resultsshow that liquid ligaments and droplets are produced through jet breakup. And the evolutionary process of com.plex flow field structure is obtained for the study of the dynamic characteristics. The deformation of jet tip and jet core，and the liquid-gas aerodynamic interaction are analyzed. Impacted against the quiescent gas，the liquid jet head atomizes into ligaments and droplets by aerodynamic effect，which makes jet front the initial disturbed area.The perturbations are transferred to upstream through jet core and ambient gas，therefore promoting further atomi. zation. Along with the development of jet surface instability and atomization，the gas flow field becomes highly turbulent，which enhances the liquid-gas mixing. The dynamic mechanisms of liquid ligaments trigger from theliquid jet tip，deform by surrounding air，and pinch-off to produce droplets are revealed.