空气指状流在弹性分支网络中的传播
The propagation of air fingers into an elastic branching network
AI总结：
本研究以弹性充液赫雷肖通道为气道再通模型，实验探究空气指状流在Y形分叉处的传播规律，揭示了初始塌陷程度、流速对传播稳定性及恢复特征尺度的调控机制。
摘要：
我们通过实验研究了空气指状流在充液弹性Hele-Shaw（赫雷肖）通道Y形分叉处的传播过程，以此作为气道再通的台式模型。通道的柔顺性由弹性上边界提供，我们可以设置通道塌陷的初始构型，并以恒定体积通量注入空气。实验中通常观察到空气指状流在主通道内稳定传播，在到达Y形分叉前会失去稳定状态，但随后会在子通道中恢复稳定。在初始塌陷程度较低时，尽管Y形通道不同区域的初始塌陷存在微小差异，子通道中稳定的指状流形态和气泡压力与主通道中的对应特征一致。然而，在初始塌陷程度较高、弹性片几乎接触通道底部边界的情况下，主通道中实验上无法区分的指状流，可能导致子通道出现多种再通状态。由于调控指状流传播的力学机制发生转变，子通道中恢复稳定传播的下游距离也会随注入流速和初始塌陷程度发生显著变化。我们发现，在低流速和/或低初始塌陷的黏性力与表面张力主导的区域，这种恢复的特征时间和长度尺度最大；而在高流速和/或高初始塌陷的弹性力与表面张力平衡的极限区域，这些特征量会逐渐减小并趋于恒定平台值。我们的研究结果表明，实际网络中的通道长度通常不足以维持稳定的传播状态。
英文摘要：
We study experimentally the propagation of an air finger through the Y-bifurcation of an elastic, liquid-filled Hele-Shaw channel, as a benchtop model of airway reopening. With channel compliance provided by an elastic upper boundary, we can impose collapsed channel configurations into which we inject air with constant volume-flux. We typically observe steady finger propagation in the main channel, which is lost ahead of the Y-bifurcation but subsequently recovered in the daughter channels. At low levels of initial collapse, steady finger shapes and bubble pressure in the daughter channels map onto those in the main channel, despite small differences in initial collapse in different parts of the Y-channel. However, at higher levels of initial collapse where the elastic sheet almost touches the bottom boundary of the channel, experimentally indistinguishable fingers in the main channel can lead to multiple states of reopening of the daughter channels. The downstream distance at which steady propagation is recovered in the daughter channels also varies considerably with injection flow rate and initial collapse because of a transition in the mechanics regulating finger propagation. We find that the characteristic time and length-scales of this recovery are largest in the regime where viscous and surface tension forces dominate at low flow rate and/or low initial collapse, and that they decrease towards a constant plateau reached in the limit where elastic and surface tension forces balance at high flow rate and/or high initial collapse. Our findings suggest that practical networks are unlikely to comprise long enough channels for steady state propagation to remain established.
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