瞬态加速液柱的流体力学问题研究

Fluid mechanics in the transient acceleration of a liquid column

介绍了用激波和压缩气体加速液柱时的流体动力现象的实验研究,实验中采用了高速摄影技术。研究分为两部分:第一部分,液柱在被加速后在管内的气/液两相流的发展以及流出管外后喷雾流的形成,喷雾流自下而上产生;第二部分,气/液界面上的流体力学不稳定性,即Rayleigh Taylor(RT)不稳定性及Richt myer Meshkov(RM)不稳定性,液柱自上而下运动。实验发现,用此方法产生的喷雾具有流量大、射程远、覆盖面积大等特点。液柱在管内的加速过程中,上端面保持平面,下端面在经历了初始的不稳定性之后形成弹状流。在本实验的驱动压力及马赫数的范围内,RT和RM不稳定性的后期的发展过程比较接近,尽管两者的增长率不同。在RT不稳定性的初始阶段,高密度流体的尖钉先伸入低密度流体中;但是,在RM不稳定性的初始阶段,低密度的气泡先伸入高密度流体中。

This paper presents some new experimental results of using shock tubes to drive water spray with large flow rate. Highspeed photographywas extensively used in the experiments. Water columns were vertically accelerated upwards from shock tubes under four different kinds of operation conditions. It is found that the increase in the driving pressure will increase not only the velocity of the spray but also the amount of the liquid. It is also confirmed through the present study that (1) the rupture method of the diaphragm (dynamic or quasistatic) is not important in the spray generation; (2) The acceleration of liquid column before flowing out of the tube has a significant effect on the spray generation. Inspired by the above research, the RayleighTaylor (RT) and RichtmyerMeshkov (RM) instabilities at gas/liquid interfaces were also studied by accelerating liquid columns vertically downwards. It is found that in RT instability the coefficients of the mixing region αb= 0.0475 and αs/αb= 2.65, and in the RM instability, the width of the mixing region hi is time dependent with either a linear relationship hi ∝ t or a power law hi ∝ tθi, where θi >1. Surface tension σ and viscosity μ of the liquid affect the formation of the bubbles and spikes.