Air flow and particle deposition patterns in bronchial airway bifurcations: The effect of different CFD models and bifurcation geometries

The simulation of the experimentally observed inhomogeneity of particle deposition within human airway bifurcations requires the application of numerical methods for the solution of the equations governing the air flow and the motion of particles entrained in the airstream. In this paper, the effects of different computational fluid dynamics (CFD) models and airway bifurcation geometries on the resulting air flow fields and related particle deposition patterns are discussed. First, two different numerical approaches for the solution of the Navier-Stokes equations are compared with each other. In our earlier model (Model I), the three-dimensional air velocity field is calculated with a finite difference code, while the FIRE(R) finite volume CFD program package is employed in our more recent approach (Model II). The particle deposition parts are similar for both CFD models: trajectories of aerosol particles are simulated under the action of inertial impaction, gravitational settling, Brownian motion, and interception, utilizing Monte Carlo techniques. Second, the effect of two different airway bifurcation geometries on the resulting flow and deposition patterns are investigated here. A bifurcation model with a narrow central bifurcation zone (narrow bifurcation model) is compared with a smooth, physiologically realistic bifurcation (PRE) model. For this comparison, flow and deposition patterns are computed by applying our finite volume approach (Model II).