Abstract: In order to deeply understand mechanisms of spray column structure and process of atomization in direct injection，the vertical spray in quiescent gas is conducted based on the method of VOF(Volume of Fluid) and LES(large eddy simulation) method. The results of simulation are in good agreement with the experimental results. An umbrella-like head shape was formed after the spray injected into atmosphere by instability of Rayleigh-Taylor. Tip of edge was broken and generated ligaments at phase of spray thinner，droplets shed from ligament were distributed equidistantly with 0.1mm . Vortex was formed behind tip edge at the same time. The vortex interacts with liquid column and promotes shedding from liquid core surface. Surface of spray column appears fish scale because of Kelvin-Helmholtz(K-H) surface wave，it leads to spray column atomization，and wavelength becomes longer from 0.26mm to 0.78mm.

Key words: Rayleigh-Taylor(RT) instability；Spray column；Primary breakup；Volume of fluid；Atomization

摘要： 为深入了解直流喷射过程中射流柱的细部结构以及其脱落过程，利用LES结合VOF的方法，对静止大气中垂直射流现象进行模拟。模拟得到的液相喷雾结构和试验结果能够很好地吻合。通过计算观察得到射流柱进入到大气中后由于Rayleigh-Taylor(RT)不稳定性迅速形成伞状的头部，头部的边缘在不断变薄失稳的过程中脱落形成液带，液带脱落产生的液滴具有等距性，间距为0.106mm，并在伞状边缘的下方形成一个气涡，气涡与上游的射流柱相互作用，促进射流柱表面的脱落。射流柱表面由于Kelvin-Helmholtz(K-H)表面波的作用呈现鱼鳞状的结构，并导致射流柱整体断裂、破碎，其表面波波长由初始的0.26mm迅速增长到0.78mm。

关键词: RT不稳定性；射流柱；首次破碎；VOF；雾化