在试管中由水击形成的聚焦液体射流
A focused liquid jet formed by a water hammer in a test tube
摘要：
本文研究了由冲力引起的大加速度作用下试管内气液界面的运动。我们进行简单的实验，其中部分充满液体的管在重力作用下下落并撞击刚性地板。管内弯曲的气-液界面反转并最终形成细长射流（即所谓的聚焦射流）。在我们的实验中，出现了振动的界面或液体射流的速度的增量伴随着在液柱中的空化的发病。这些现象不能通过考虑经典势流分析中的压力脉冲来解释，经典势流分析没有考虑有限的声速以及相变。在这里，我们模拟这样的水锤事件作为一个一维的压力波传播和其相互作用的结果，通过声阻抗不匹配的边界。采用特征线法描述了压力波相互作用和空化现象。所提出的模型被发现，使我们能够捕捉液体射流的非定常功能。
英文摘要：
We investigate motion of a gas-liquid interface in a test tube induced by a large acceleration via impulsive force. We conduct simple experiments in which the tube partially filled with a liquid falls under gravity and impacts a rigid floor. A curved gas-liquid interface inside the tube reverses and eventually forms an elongated jet (i.e. the so-called a focused jet). In our experiments, there arises either vibration of the interface or increment in the velocity of a liquid jet accompanied by the onset of cavitation in the liquid column. These phenomena cannot be explained by considering pressure impulse in a classical potential flow analysis, which does not account for finite speeds of sound as well as phase change. Here we model such water-hammer events as a result of one-dimensional pressure wave propagation and its interaction with boundaries through acoustic impedance mismatching. The method of characteristics is applied to describe pressure wave interactions and the subsequent cavitation. The proposed model is found to allow us to capture the unsteady features of the liquid jet.
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