3D Hydrodynamics in the Upper Human Bronchial Tree: Interplay between Geometry and Flow Distribution

Uniform flow distribution in a symmetric volume can be realized through a symmetric branched tree. It is shown however, by 3D numerical simulation of the Navier-Stokes equations, that the flow partitioning can be highly sensitive to deviations from exact symmetry if inertial effects are present. The flow asymmetry is quantified and found to depend on the Reynolds number. Moreover, for a given Reynolds number, we show that the flow distribution depends on the aspect ratio of the branching elements as well as their angular arrangement. Our results indicate that physiological variability should be severely restricted in order to ensure adequate fluid distribution through a tree. Time-dependant simulations have also been performed and have shown that inspiration and expiration flows are both subject to inertial effects but with completely different velocities structures.