GENERATION MECHANISM OF UNIDIRECTIONAL FLOW IN OSCILLATORY FLOW OF AVIAN LUNG

摘要

It is widely known that a unidirectional flow is generated in the avian lung during a breathing process. Though the unidirectional flow should be caused by a kind of an aerodynamic valve, its generation mechanism is not fully understood. In the present study, therefore, the oscillatory flow field in a right-angle branched tube, that was a bifurcation model of the avian trachea, was visualized and analyzed both experimentally and numerically to reveal the mechanisms of the unidirectional flow. The experimental results showed that a separation vortex observed at the entrance of a side-daughter tube played an important role for generation of the unidirectional net flow. The connective inertia was also suggested to be important in the process. From the numerical simulation, the details of the flow mechanism were revealed. The inertia force was found to drive the unidirectional flow during the whole period of oscillation. A good correlation was found between the pressure drop in the branched tube due to the separation vortex and the induced velocity of the unidirectional flow.