Numerical Study on Mass Transport Enhancement in Oscillatory Flow of Avian Lung Model

Abstract

It is well known that the airflow in the gas exchange bronchi in avian lung has a unidirectional nature. Since the direction of the flow is against the blood flow, the gas exchange efficiency of avian respiration is higher than that of mammalian counterpart. To clarify flow phenomena in avian lungs, oscillatory flow fields and concentration fields in a right angle branched tube, model bifurcation of avian trachea, were numerically studied. The three-dimensional incompressible Navier-Stokes equations were solved by SIMPLE method, while the convection equation of concentration was solved by CIP method based on the results of flow simulation. The results showed that separation vortex observed at the entrance of a side-daughter tube during inspiration drove the unidirectional net flow from the side-daughter tube to the daughter tube. Due to the convective inertia, unidirectional net flow persisted even in the expiration. It was clearly shown that the unidirectional net flow strongly enhanced axial mass transport. The effect of constriction just upstream of the bifurcation was also studied and increase in the magnitude of unidirectional net flow was observed in the case with constriction.