Airflow analysis in the alveolar region using the lattice-Boltzmann method.

A validated lattice-Boltzmann code has been developed based on the Bhatnagar-Gross-Krook formulation to simulate and analyze transient laminar two-dimensional airflow in alveoli and bifurcating alveolated ducts with moving walls, representative of the human respiratory zone. A physically more realistic pressure boundary condition has been implemented, considering a physiological Reynolds number range, i.e., 0 < Re < 11, which covers the inhalation scenarios from resting mode to moderate exercise. Axial velocity contours, vortex propagation, and streamlines as well as mid-plane pressure variations in different alveolar geometries and shapes are illustrated and discussed. The results show that the influence of the geometric structure on the airflow fields in the human alveolar region is very important. Furthermore, the effect of a moving alveolus wall is significant, i.e., the vortices in the duct or alveolar sacs may change in size. In summary, for a given set of realistic inlet conditions, the airflow velocity and vortical flows are greatly dependent on the different alveolar sac shapes, local geometric structures, and sac expansion rates. The pressure distributions are less influenced by the alveolus shape and wall movement. The present results provide new physical insight and are important for the simulation of particle transport/deposition in the deep lung region.