韦伯数对紧耦合雾化喷嘴初始破碎模式的影响

为了获得韦伯数对紧耦合雾化喷嘴初始破碎模式的影响规律,利用流体体积函数(volume of fluid,VOF)模型对以水和空气为工质的典型紧耦合环缝型雾化喷嘴的初始破碎过程进行数值模拟,并利用高速摄影技术对数值模拟结果进行实验验证。重点分析韦伯数对紧耦合雾化初始破碎模式、初始破碎长度的影响,以及不同初始破碎模式的内在形成机制和特点。在液体雷诺数为4 500,气体动力韦伯数为70到18 650时,随韦伯数的增加,紧耦合雾化初始破碎模式由韦伯数为70的膜状破碎模式向韦伯数为330的振荡卷吸破碎模式转变,当韦伯数大于1 700时,紧耦合雾化的初始破碎模式转变为完全卷吸破碎模式,其中振荡卷吸破碎模式和典型金属雾化过程中的喷泉状破碎模式类似。初始破碎长度随韦伯数的增加逐渐减小,在韦伯数大于4 560后,基本维持恒定。喷嘴导液管底端存在的卷吸涡状结构会对初始破碎模式产生重要影响,涡状结构在完全卷吸破碎模式时最明显。

Effect of Weber Number on Primary Breakup Model of a Close Coupled Atomizing Nozzle

In order to obtain the effect of Weber number on the primary breakup mode of a close coupled atomizing nozzle, the numerical simulation with VOF model was used to investigate the primary breakup mode of the close coupled annular atomizing nozzle with water and air as working fluid. Experiments were performed by means of high-speed photography. The effect of Weber number on the primary breakup mode of the close coupled atomization and the primary breakup length was analyzed. The internal formation mechanism and characteristics of different primary breakup mode was also analyzed. When the liquid Reynolds number is 4 500 and the aerodynamic Weber number is from 70 to 18 650, the following conclusion could be obtained: With the increase of the Weber number, the primary breakup mode of the close coupled atomization is from the film breakup mode(We=70) to the oscillating entrainment breakup mode(We=330) which is similar to the fountain-like breakup mode in the typical metal atomization process. When the Weber number is above 1 700, the primary breakup mode changes to the full entrainment breakup mode. The initial breakup length decreases with the increase of the Weber number, and remains basically constant after the Weber number is above 4 560. The vortex structure existing at the bottom of the delivery tube has an important effect on the primary breakup mode. The full entrainment mode has the most obvious vortex structure.