Fujioka H, Oka K, Tanishita K
Department of System Design Engineering, KEIO University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, 223, Japan.
J Biomech Eng. 2001 Apr;123(2):145-53. doi: 10.1115/1.1352735.
Axial gas transport due to the interaction between radial mixing and radially nonuniform axial velocities is responsible for gas transport in thick airways during High-frequency oscillatory ventilation (HFO). Because the airways can be characterized by a bifurcating tube network, the secondary flow in the curved portion of a bifurcating tube contributes to cross-stream mixing. In this study the oscillatory flow and concentration fields through a single symmetrical airway bifurcating tube model were numerically analyzed by solving three-dimensional Navier-Stokes and mass concentration equations with the SIMPLER algorithm. The simulation conditions were for a Womersley number, alpha = 9.1 and Reynolds numbers in the parent tube between 200 and 1000, corresponding to Dn2/alpha 4 in the curved portion between 2 and 80, where Dn is Dean number. For comparison with the results from the bifurcating tube, we calculated the velocity and concentration fields for fully developed oscillatory flow through a curved tube with a curvature rate of 1/10, which is identical to the curved portion of the bifurcating tube. For Dn2/alpha 4 < or = 10 in the curved portion of the bifurcating tube, the flow divider and area changes dominate the axial gas transport, because the effective diffusivity is greater than in either a straight or curved tube, in spite of low secondary velocities. However, for Dn2/alpha 4 > or = 20, the gas transport characteristics in a bifurcation are similar to a curved tube because of the significant effect of secondary flow.
在高频振荡通气（HFO）过程中，由于径向混合与径向不均匀轴向速度之间的相互作用而产生的轴向气体传输，是粗气道中气体传输的原因。由于气道可以用分叉管网来表征，分叉管弯曲部分的二次流有助于横向混合。在本研究中，通过使用SIMPLER算法求解三维纳维-斯托克斯方程和质量浓度方程，对通过单个对称气道分叉管模型的振荡流场和浓度场进行了数值分析。模拟条件为沃默斯利数α = 9.1，母管中的雷诺数在200至1000之间，对应于弯曲部分的Dn2/α4在2至80之间，其中Dn为迪恩数。为了与分叉管的结果进行比较，我们计算了通过曲率率为1/10的弯曲管的充分发展振荡流的速度场和浓度场，该弯曲管与分叉管的弯曲部分相同。在分叉管弯曲部分，当Dn2/α4≤10时，分流器和面积变化主导轴向气体传输，因为尽管二次速度较低，但有效扩散率大于直管或弯曲管中的有效扩散率。然而，当Dn2/α4≥20时，由于二次流的显著影响，分叉处的气体传输特性类似于弯曲管。
