背压对撞击式喷嘴雾化特性影响研究

Effects of Backpressure on Atomization Characteristics of Impinging Jet Injector

关键词:  撞击式喷嘴  射流  雾化特性  液膜  液滴  数值模拟

Key words:  Impinging jet injector  Jet  Atomization characteristics  Liquid film  Droplet  Numerical simulation

摘要:

为研究背压对撞击式喷嘴雾化特性的影响，将压力的变化等效为气体密度的变化，基于一种树形自适应加密算法，通过直接数值求解不可压Navier-Stokes方程组实现了不同背压条件下射流撞击雾化的数值模拟。首先将数值模拟结果与试验数据进行对比，验证数值模拟的有效性，在此基础上开展了高背压条件下雾化过程的数值模拟。结果表明，随着背压的提高，气动力相应增强，液膜的破碎更加剧烈，一次雾化区域的液滴数密度增大，雾场由稀疏向稠密发展；液膜在向下游运动过程中波动速度的幅值逐渐增大，并且随着背压的提高，液膜的波动由线性向非线性转变；背压增大导致破碎长度减小，经过参数修正得到了液膜破碎长度的经验公式，并与试验数据进行了对比；背压对液滴尺寸分布规律没有显著影响，但随着背压的提高，同一时刻大液滴所占的比例提高，整个雾场的Sauter平均直径有增加的趋势，当背压从0.1MPa增大到1MPa时，雾场的Sauter平均直径由155.5μm增大到166.9μm；背压增大，液滴粒径分布的均匀度指数减小，液滴尺寸分布更加不均匀。

Abstract:

To investigate the effects of backpressure on the atomization characteristics of impinging jet injector, variation of pressure was equivalent to the change of gas density. Based on tree-shaped adaptive mesh refinement algorithm, incompressible Navier-Stokes equations were directly solved to realize numerical simulation of impinging jet atomization. First, numerical results were validated by comparing with experimental data. On the basis of that, simulations of impinging jet atomization under high backpressures were carried out. The results revealed that with the increase of backpressure, aerodynamic force is enhanced accordingly. The breakup of liquid sheet becomes more severely, and the droplet density of primary atomization region increases at the same time. As a result, the atomization field develops from dilute to dense. The amplitude of fluctuating velocity component increases gradually when liquid sheet moves downstream. In addition, with the increase of backpressure the fluctuation develops from linear to nonlinear. The increase of backpressure leads to the decrease of breakup length of liquid sheet. Empirical correlation of breakup length of liquid sheet was obtained by parameter correction, and results from correlation were compared with experimental data. Backpressure has no significant effect on the droplet diameter distribution. However, with the increase of backpressure, the proportion of large droplets increase at the same time and Sauter mean diameter of the whole atomization field has the trend to increase. When the backpressure increases from 0.1MPa to 1MPa, Sauter mean diameter of the whole atomization field increases from 155.5μm to 166.9μm. In addition, with the increase of backpressure the homogeneous index of droplet diameter distribution decreases which implies that the distribution of droplet diameter becomes more uneven.