平面液体层碎裂过程实验研究

Experimental Investigation on Break-Up Process of Planar Liquid Jet Film

小宽厚比喷嘴喷射出的平面水膜进入静止空气中,在不同气流流速环境下对水膜碎裂过程进行了实验研究。结果表明,静止空气中的水膜表面波呈现对称波形,射流的碎裂长度随雷诺数的增大而增大,喷射压力对射流碎裂长度没有直接影响。空气助力作用使平面射流表面波的上、下气液交界面出现相位差。水膜的碎裂长度随空气助力气流速度的增大而减小;空气助力对于低雷诺数水膜射流具有很强的促进碎裂作用,所以会极大地改善低雷诺数射流的一次雾化效果。随着水流雷诺数的提高,空气助力作用对水膜碎裂长度的影响大为减弱;即使在高速助力空气的作用下,水膜仍长期保持较稳定的射流流态,没有出现明显的水膜撕裂现象。说明在小宽厚比喷嘴的瑞利(Rayleigh)模式射流中,高雷诺数射流是水膜的稳定因素。与气液流速比、气流马赫数等无量纲参数相比,液体喷射的雷诺数是射流碎裂的主要影响因素。

Planar water film was jetted into a stationary air medium with unequal velocity air streams on both sides from a small aspect ratio nozzle. The break-up process of planar water jet film was experimentally studied. Results show that the waveform of water film surface wave is symmetrical, and the length of break-up water jet segment is longer along with the liquid jet Reynolds number increases. Jet pressure has no direct influence on break-up length. Phase difference between upper and bottom gas-liquid interface of planar jet film is formed by air assistant. The length of water film break-up segment decreases along with air stream velocity increases. This indicates that air assistant may strongly promote break-up of water jet with lower Reynolds number. The effect of air assistant on water film break-up length is weak for water jet with larger Reynolds number. Liquid film remains stable for long time, and liquid film rip phenomenon did not appear even for high velocity air assistant. It is presented that high Reynolds number of liquid jet is a stable factor for Rayleigh mode jet from small aspect ration nozzle. Comparing with some dimensionless parameters, such as gas-liquid velocities ratio and Mach number, Reynolds number is a main influence factor for liquid jet break-up process.