Flow structure and particle transport in a triple bifurcation airway model

Considering steady laminar incompressible flow in a triple bifurcation, whi ch represents generations three to six of the human respiratory system, air flow fields and micron-particle transport have been simulated for several combinations of relatively high and low inlet Reynolds and Stokes numbers. While the upstream bifurcations are hardly affected by the third bifurcatio n, complex air and particle flow fields occur in the daughter tubes leading to the third dividers. Variations in Reynolds number, 500 less than or equ al to Re less than or equal to 2000, and Stokes number, 0.04 less than or e qual to St less than or equal to0.12, cause locally changing vortical air f lows as well as irregular particle motions. Preferential concentration of p articles can be induced by the secondary vortical flow in the tubes when th e inlet Reynolds number is high enough. The air and particle velocity profi les in the third daughter tubes are still quite different from those in the upstream tubes, which indicates that additional downstream effects are pos sible. This work may contribute to respiratory dose estimation in health ri sk assessment studies, as well as the analyses of drug aerosol delivery.