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The impact of steady streaming and conditional turbulence on gas transport during high-frequency ventilation
Theoretical and Computational Fluid Dynamics ( IF 2.2 ) Pub Date : 2021-02-15 , DOI: 10.1007/s00162-020-00559-3
Chinthaka Jacob 1 , David G Tingay 2, 3 , Justin S Leontini 1
Affiliation  

High-frequency ventilation is a type of mechanical ventilation therapy applied on patients with damaged or delicate lungs. However, the transport of oxygen down, and carbon dioxide up, the airway is governed by subtle transport processes which hitherto have been difficult to quantify. We investigate one of these mechanisms in detail, nonlinear mean streaming, and the impact of the onset of turbulence on this streaming, via direct numerical simulations of a model 1:2 bifurcating pipe. This geometry is investigated as a minimal unit of the fractal structure of the airway. We first quantify the amount of gas recirculated via mean streaming by measuring the recirculating flux in both the upper and lower branches of the bifurcation. For conditions modeling the trachea-to-bronchi bifurcation of an infant, we find the recirculating flux is of the order of 3–5% of the peak flux . We also show that for conditions modeling the upper generations, the mean recirculation regions extend a significant distance away from the bifurcation, certainly far enough to recirculate gas between generations. We show that this mean streaming flow is driven by the formation of longitudinal vortices in the flow leaving the bifurcation. Second, we show that conditional turbulence arises in the upper generations of the airway. This turbulence appears only in the flow leaving the bifurcation, and at a point in the cycle centered around the maximum instantaneous flow rate. We hypothesize that its appearance is due to an instability of the longitudinal-vortices structure.



中文翻译:

高频通气过程中稳定流动和条件湍流对气体传输的影响

高频通气是一种机械通气疗法,适用于肺部受损或脆弱的患者。然而,氧气向下输送和二氧化碳向上输送,气道受到迄今为止难以量化的微妙输送过程的控制。我们通过模型 1:2 分叉管的直接数值模拟,详细研究了其中一种机制,非线性平均流,以及湍流开始对该流的影响。这种几何形状被研究为气道分形结构的最小单位。我们首先通过测量分叉上部和下部分支中的再循环通量来量化通过平均流再循环的气体量。对于模拟婴儿气管到支气管分叉的条件,我们发现循环通量约为峰值通量的 3-5%。我们还表明,对于模拟上一代的条件,平均再循环区域从分叉处延伸了相当长的距离,当然足以在几代之间再循环气体。我们表明,这种平均流动流动是由在离开分叉处的流动中形成纵向涡流驱动的。其次,我们表明条件性湍流出现在气道的上一代。这种湍流只出现在离开分叉处的流动中,并且出现在循环中以最大瞬时流量为中心的点上。我们假设它的出现是由于纵向涡流结构的不稳定性。平均再循环区域从分叉处延伸了相当长的距离,当然足够远,可以在几代人之间再循环气体。我们表明,这种平均流动流动是由在离开分叉处的流动中形成纵向涡流驱动的。其次,我们表明条件性湍流出现在气道的上一代。这种湍流只出现在离开分叉处的流动中,并且出现在循环中以最大瞬时流量为中心的点上。我们假设它的出现是由于纵向涡流结构的不稳定性。平均再循环区域从分叉处延伸了相当长的距离,当然足够远,可以在几代人之间再循环气体。我们表明,这种平均流动流动是由在离开分叉处的流动中形成纵向涡流驱动的。其次,我们表明条件性湍流出现在气道的上一代。这种湍流只出现在离开分叉处的流动中,并且出现在循环中以最大瞬时流量为中心的点上。我们假设它的出现是由于纵向涡流结构的不稳定性。我们表明,这种平均流动流动是由在离开分叉处的流动中形成纵向涡流驱动的。其次,我们表明条件性湍流出现在气道的上一代。这种湍流只出现在离开分叉处的流动中,并且出现在循环中以最大瞬时流量为中心的点上。我们假设它的出现是由于纵向涡流结构的不稳定性。我们表明,这种平均流动流动是由在离开分叉处的流动中形成纵向涡流驱动的。其次,我们表明条件性湍流出现在气道的上一代。这种湍流只出现在离开分叉处的流动中,并且出现在循环中以最大瞬时流量为中心的点上。我们假设它的出现是由于纵向涡流结构的不稳定性。

更新日期:2021-02-15
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