Transient airflow structures and particle transport in a sequentially branching lung airway model

TLDR

The study aims to provide basic physical insight into aerosol transport relevant for dosimetry, health‑effect studies, and drug aerosol delivery. The authors used a validated finite‑volume CFD model (CFX4.3 with custom FORTRAN) to simulate oscillatory laminar 3‑D flow and micron‑particle transport in triple bifurcations of generations 3–6 under normal breathing and high‑frequency ventilation, examining flow structures, particle motion, Womersley number, geometry, secondary flow, and pressure drops. For low Womersley numbers, peak velocity profiles match steady‑state but off‑peak acceleration/deceleration differ, while particle motion largely mirrors steady‑state behavior; nevertheless, vortical structures cause preferential particle concentration during both inhalation and exhalation, with more complex patterns during expiration.

Abstract

Considering oscillatory laminar incompressible three-dimensional flow in triple planar and nonplanar bifurcations representing generations three to six of the human respiratory system, air flow fields and micron-particle transport have been simulated under normal breathing and high-frequency ventilation (HFV) conditions. A finite-volume code (CFX4.3 from AEA Technology, Pittsburgh, PA) and its user-enhanced FORTRAN programs were validated with experimental velocity data points for a single bifurcation. The airflow structures and micron-particle motion in the triple bifurcations were analyzed for a representative normal breathing cycle as well as HFV condition. While both the peak inspiratory and expiratory velocity profiles for the low Womersley case (α=0.93) agree well with those of instantaneously equivalent steady-state cases, some differences can be observed between flow acceleration and deceleration at off-peak periods or near flow reversal, especially during inspiratory flow. Similarly, the basic features of instantaneous particle motion closely resemble the steady-state case at equivalent inlet Reynolds numbers. The preferential concentration of particles caused by the coherent vortical structures was found in both inhalation and exhalation; however, it is more complicated during expiration. The effects of Womersley number and non-planar geometries as well as the variations in secondary flow intensity plus pressure drops across various bifurcations under normal breathing and HFV conditions were analyzed as well. This work may elucidate basic physical insight of aerosol transport relevant in dosimetry-and-health-effect studies as well as for drug aerosol delivery analyses.