Experimental and theoretical study on the break phenomenon of self-pulsation for liquid-centered swirl coaxial injectors

Abstract

Experimental observations together with theoretical analysis were conducted to investigate the break phenomenon and the corresponding mechanisms of self-pulsation for a liquid-centered swirl coaxial injector with recess number of RN=1. Instantaneous spray images were obtained based on background light imaging technology with a high-speed camera. By dynamic analysis of the flow process of the liquid sheet in the recess chamber, a 1D self-pulsation theoretical model was established, and the self-sustaining mechanisms of self-pulsation were analyzed in depth. The results show that the increase of the momentum flux ratio will lead to the occurrence of the break phenomenon of self-pulsation for the injector with a larger recess length, and the frequency and intensity of self-pulsation before and after the break phenomenon differ significantly. The flow dynamics in the recess chamber sequentially transform from a periodic expansion-dominated flow to a stable flow, and then develop to a periodic contraction-dominated flow during the break process of self-pulsation. With the occurrence of self-pulsation before the break phenomenon, the liquid sheet has little effect on the pressure disturbance in the recess chamber. In contrast, with the occurrence of self-pulsation after the break phenomenon, the pressure disturbance is obviously affected by the liquid sheet. Based on the theoretical analysis model of self-pulsation, the self-pulsation frequency can be predicted. Furthermore, the self-sustaining mechanism of self-pulsation before and after the break phenomenon is preliminarily confirmed. The energy transfer between the gas- and liquid-phase is an important factor for maintaining the self-pulsation process.

概要

目的

液体中心式气液同轴离心式喷嘴在一定条件下会出现自激振荡间断现象。本文旨在探讨自激振荡间断过程中缩进室内的液膜流动形态、压力振荡特性以及自激振荡自维持机理。

创新点

1. 通过测量喷嘴缩进室内部多点高频压力,分析压力扰动相位变换关系;2. 建立自激振荡理论模型,成功地模拟液膜微元流动过程。

方法

1. 通过实验分析,得到喷嘴缩进室内部液膜流动的变化形态,并对比自激振荡和稳态时缩进室内压力振荡关系(图6和7);2. 通过理论推导,构建液膜微元运动位置随时间的变化关系(公式(16)),并得到缩进室内压力和气/液动量随时间的变化关系(图12和13)。

结论

1. 气液动量通量比增加会使缩进较大的气液同轴离心式喷嘴出现自激振荡间断现象,并且间断前后自激振荡的频率和强度发生显著变化。2. 自激振荡间断现象发生时,缩进室内液膜流动模态依次由周期性扩张主导流动转变为稳定流动再转变为周期性收缩主导流动。3. 通过自激振荡理论模型,可以较好地预测自激振荡频率,气液两相的能量传递是维持自激振荡过程的重要因素。