基于扩展TAB模型的凝胶液滴二次雾化特性研究

Characteristics of Second Atomization for Gelled Droplet Based on Extended TAB Model

关键词:  凝胶液滴  二次雾化  TAB模型  初始破碎时间

Key words:  Gelled droplet  Secondary atomization  TAB model  Initial breakup time

摘要:

为初步研究幂率型凝胶液滴的二次雾化特性，将原始的Taylor-analogy-breakup(TAB)模型扩展并应用到幂率型凝胶颗粒中，采用四阶Runge-Kutta法对凝胶液滴的振荡方程和运动方程进行了数值求解，计算了不同空气动力和物性参数条件下的初始破碎时间和临界特征。结果表明:随着相对速度和液滴直径的增加，初始破碎时间迅速降低，然后保持稳定；随液/气密度比和表面张力系数增大，初始破碎时间呈线性增长趋势；初始破碎时间随稠度系数增大而增大，而当流动指数较小时初始破碎时间变化很小，流动指数超过0.6后初始破碎时间增长迅速，二者与相关实验比较存在一定误差；随Web数增大，液滴的振荡幅度变大，达到稳定后其无量纲变形系数就越大；凝胶液滴的稠度系数越高，临界Webc数越大，液滴二次雾化能力越低。流动指数小于0.6时，临界Webc数变化较小，而后其值则迅速上升。

Abstract:

In order to primarily study the characteristics of secondary atomization of gelled power-law droplet，the original Taylor-analogy-breakup(TAB) was extended and applied to the gelled power-law droplet. The equations of oscillation and motion of the gelled droplet was numerically solved using the fourth order Runge - Kutta method. Initial breakup time and critical characteristics were calculated under different aerodynamic and physical parameters. The relative results indicate that initial breakup time rapidly decreased with the increase of relative velocity and diameter of the droplet，and then remained stable. As the increase of liquid/gas density ratio and surface tension coefficient，a linear growth rate was revealed about the initial time. With the growing number of consistency index，initial breakup time increased. However，as the flow index was on the small side，the change of initial breakup time was small as well and grew fast when the flow index was in the excess of 0.6. There was a certain deviation in the comparison between both of them and the related experiment. Oscillation amplitude of the droplet became larger by promoting the Weber number，and also its dimensionless deformation coefficient was larger when the droplet became stable. Higher critical Weber number under higher consistency index of the gelled droplet resulted in lower ability of secondary atomization. The critical Weber number nearly stayed the same when flow index was lower than 0.6，but rose quickly while exceeded this number.