Bubble transitions in strongly collapsed elastic tubes
Bubble transitions in strongly collapsed elastic tubes
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DOI：
10.1017/s0022112009007435
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发表时间：
2009-08
影响因子：
3.7
通讯作者：
A. Heap;A. Juel
中科院分区：
文献类型：
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作者：
A. Heap;A. Juel
在气道重新开放的台式模型中，实验研究了长气泡在强烈塌陷的充满流体的弹性管中稳定传播的选择。强塌陷的局部区域可能在肺中，因为塌陷的流体弹性不稳定性促进气道横截面的广泛变形超过相对壁接触点。我们发现，在这一点上发生了根本性的变化，在重新开放的机制。我们建立在最近的识别堆和Juel（物理流体，第20卷，2008年，文章编号081702）的三个不同的稳定传播的气泡（不对称，双尖和尖），连续选择增加值的毛细管数（钙，粘性比表面张力）在管最初崩溃的点以外的相对壁接触。不对称的气泡也观察到在较小的崩溃管的Ca值，我们表明，它分叉超临界从通常的抛物线尖端的气泡作为Ca的增加。我们还描述了不对称和双尖气泡，和双尖和尖气泡之间的不连续过渡的机制。特别是，我们发现，该管必须重新打开到一个临界高度的双头气泡被选中。双尖端气泡中的前体指状物的长度随着Ca而减小，并且当该长度小于指状物合并的点处的管的高度时，气泡失去对尖气泡的稳定性。与不对称和双头气泡相比，尖头气泡浸润管的最塌陷部分，以在低压下快速重新打开气道，并有可能减少通气引起的肺损伤。
The selection of long air bubbles propagating steadily in a strongly collapsed fluid-filled elastic tube is investigated experimentally in a benchtop model of airway reopening. Localized regions of strong collapse are likely in the lung, because collapsing fluid-elastic instabilities promote extensive deformation of the airway cross-section beyond the point of opposite wall contact. We find that radical changes in the reopening mechanics occur at this point. We build on the recent identification by Heap & Juel (Phys. Fluids, vol. 20, 2008, article no. 081702) of three different steadily propagating bubbles (asymmetric, double-tipped and pointed) that are selected successively for increasing values of the capillary number (Ca, ratio of viscous to surface tension forces) in tubes initially collapsed beyond the point of opposite wall contact. The asymmetric bubble is also observed in less collapsed tubes for small values of Ca, and we show that it bifurcates super-critically from the usual parabolic-tipped bubble as Ca increases. We also characterize the mechanisms underlying the discontinuous transitions between asymmetric and double-tipped bubbles, and double-tipped and pointed bubbles. In particular, we find that the tube must reopen to a critical height for double-tipped bubbles to be selected. The length of the precursor fingers in the double-tipped bubble decreases with Ca, and the bubble loses stability to pointed bubbles when this length is less than the height of the tube at the point where the fingers merge. By contrast with the asymmetric and double-tipped bubbles, the pointed bubble infiltrates the most collapsed part of the tube to yield the rapid reopening of the airway at low pressure, with the potential to reduce ventilation-induced lung damage.