液体射流撞击液膜振荡行为的实验研究

Experimental Study on Oscillation Behavior of Liquid Sheet from Impinging Jets

关键词:  液体火箭发动机  液膜  撞击流  雾化  振荡

Key words:  Liquid rocket engine  Liquid sheet  Impinging jets  Atomization  Oscillation

摘要:

液体射流撞击过程是液体火箭发动机常见的高效雾化方式。为了进一步探究液体射流撞击雾化过程，采用高速摄像仪和图像处理技术对两股液体射流撞击液膜的振荡行为进行了实验研究, 考察了射流韦伯数（21≤We≤1356）和撞击角（2θ=60°，90°，120°）对液膜振荡的影响。结果表明，随着射流韦伯数增大（We>250），撞击液膜会从竖直稳定模式转变为振荡模式，促进液膜破裂和雾化。增大撞击角能加剧液膜振荡和增加雾化角。2θ=60°和90°的液膜振荡区间为250<We<400，2θ=120°的液膜振荡区间为We>250，无量纲振幅的时均极大值约为5。结果揭示了随着液体射流速度的增大，射流不稳定性的发展会引起撞击点的动量不平衡，进而形成液膜振荡。此外，液膜向下传播时与空气界面间的Kelvin-Helmholtz不稳定性也促进液膜振荡。

Abstract:

Impinging jets is a common method for efficient atomization of liquid rocket engines. To further elucidate the atomization process of liquid impinging jets, the oscillation behavior of liquid sheet formed by two impinging jets is experimentally studied by a high-speed camera and image processing method. Effects of the jet Weber number (21≤We≤1356) and impinging angle (2θ=60°, 90°, 120°) on the oscillation of liquid sheet are investigated. Results show that, as the jet Weber number increases (We>250), the liquid sheet transforms from a vertical stable pattern to an oscillation pattern, which promotes the breakup and atomization of the liquid sheet. An increase in the impinging angle can intensify the oscillation of liquid sheet and enlarge the atomizing angle. For 2θ=60° and 90°, the oscillation ranges of liquid sheet are 250<We<400, and for 2θ=120°, the oscillation range is We>250, and the time-averaged maximum value of normalized oscillation amplitude is about 5. Results reveal that as the liquid jet velocity increases, the development of jet instability causes the momentum imbalance of the impinging point, which consequently gives rise to the oscillation of liquid sheet. In addition, the Kelvin-Helmholtz instability between gas-liquid phases during the downstream propagation of liquid sheet also promotes the oscillation of the liquid sheet.