Behaviour of small regions of different gases carried in accelerated gas flows
Behaviour of small regions of different gases carried in accelerated gas flows
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DOI：
10.1017/s0022112060001419
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发表时间：
1960-02
影响因子：
3.7
通讯作者：
G. Rudinger;L. M. Somers
中科院分区：
文献类型：
--
作者：
G. Rudinger;L. M. Somers
流动中密度与周围气体不同的小区域并不完全遵循后者的加速运动，而是根据其密度小于或大于主流的密度而移动得更快或更慢。这种行为不能通过将气体“气泡”视为相同密度的假设固体颗粒来定量解释，因为气泡不能相对于周围气体移动而不转化为吸收相对运动的部分能量的涡流。为了说明加速效应，将激波管中已知压力波后面的流速与火花放电产生的气泡的观测速度进行比较。波对这种气泡的位移超过流量元件的位移20%以上，但气泡密度是未知的。如果火花放电被另一种气体的小射流所取代，压力波会切断这一射流的一部分，这一部分就代表了一个已知密度的气泡。一个理论的发展，允许计算这样的气泡加速度的响应。气泡速度与周围气体速度之比取决于两种气体的密度比和气泡的形状，但不取决于加速度。实验结果与H2，他，和SF6气泡在空气中，由不同强度的冲击波加速，并同意与理论预测。无论加速度是由非定常流中的压力波产生还是由定常流中的流线曲率产生，结果都适用。实验观察的各个方面进行了讨论。
Small regions in a flow where the density is different from that of the surrounding gas do not exactly follow accelerated motions of the latter, but move faster or slower depending on whether their density is smaller or larger than that of the main flow. This behaviour cannot be quantitatively explained by treating a gas ‘bubble’ as a hypothetical solid particle of the same density, because a gas bubble cannot move relative to the surrounding gas without being transformed into a vortex which absorbs part of the energy of the relative motion. To illustrate the acceleration effect, the flow velocity behind known pressure waves in a shock tube is compared with the observed velocity of a bubble produced by a spark discharge. The displacement of such a bubble by a wave exceeds that of a flow element by more than 20%, but the bubble density is not known. If the spark discharge is replaced by a small jet of another gas, a pressure wave cuts off a section of this jet which then represents a bubble of known density. A theory is developed which permits computing the response of such bubbles to accelerations. The ratio of the bubble velocity to the velocity of the surrounding gas depends on the density ratio for the two gases and on the shape of the bubble, but not on the acceleration. Experimental results with H2, He, and SF6 bubbles in air, accelerated by shock waves of various strength, are presented and agree well with the theoretical predictions. The results apply regardless of whether accelerations are produced by pressure waves in a non-steady flow or by curvature of streamlines in a steady flow. Various aspects of the experimental observations are discussed.