Abstract
Studies of flow through the human airway have shown that inhalation time (IT) and secondary flow structures can play important roles in particle deposition. However, the effects of varying IT in conjunction with the respiratory rate (RR) on airway flow remain unknown. Using three-dimensional numerical simulations of oscillatory flow through an idealized airway model (consisting of a mouth, glottis, trachea, and symmetric double bifurcation) at a trachea Reynolds number (Re) of 4200, we investigated how varying the ratio of IT to breathing time (BT) from 25% to 50% and RR from 10 breaths per minute (bpm) corresponding to a Womersley number (Wo) of 2.41 to 1000 bpm (Wo = 24.1) impacts airway flow characteristics. Irrespective of IT/BT, axial flow during inhalation at tracheal cross-sections was non-uniform for Wo = 2.41, as compared to centrally concentrated distribution for Wo = 24.1. For a given Wo and IT/BT, both axial and secondary (lateral) flow components unevenly split between left and right branches of a bifurcation. Irrespective of Wo, IT/BT and airway generation, lateral dispersion was a stronger transport mechanism than axial flow streaming. Discrepancy in the oscillatory flow relation Re/Wo2 = 2 L/D (L = stroke length; D = trachea diameter) was observed for IT/BT ≠ 50%, as L changed with IT/BT. We developed a modified dimensionless stroke length term including IT/BT. While viscous forces and convective acceleration were dominant for lower Wo, unsteady acceleration was dominant for higher Wo.
Highlights
Flow through the human airway is characterized by regions of flow separation and the formation of secondary flow structures [1,2]
In humans ranges between 10–15 breaths per minute, corresponding to a Womersley number (Wo) range of 2.41–2.95 based on the following relation: Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil
For a given Wo, the pressure drop remained almost the same in all inhalation time (IT)/breathing time (BT) ratios at peak inhalation, while the pressure drop increased with increasing IT/BT at peak exhalation
Summary
Flow through the human airway is characterized by regions of flow separation and the formation of secondary flow structures [1,2].
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