NUMERICAL ANALYSIS OF OSCILLATORY FLOW AND GAS TRANSPORT THROUGH A BIFURCATING AIRWAY MODEL

The axial dispersion in the High-frequency oscillatory Ventilation (HFO) occurs due to the interaction between radial mixing and radially-nonuniform axial velocity profile. Since an aspect of the geometry of pulmonary airway is characterized by the curved portion in the pulmonary branch, the secondary flow in the airway plays the important role. Pedley and Kamm (1988) identified the significant effect of curvature on the gas dispersion, and discovered the conveetive resonance phenomena which gives a highly-peaked local maximum of axial gas transport, when the calculating circulation time of secondary flow becomes identical to the cycle period. Subsequently Sharp et.al. (1991) experimentally confirmed the presence of conveetive resonance in a fully developed oscillatory flow in a curved tube. However, the curved portion of pulmonary branch is not long enough to generate the fully developed flow. This leads to the necessity of study about. gas dispersion through a single bifurcating airway model. In the present study, oscillatory flow and gas transport of an incompressible, Newtonian fluid through a bifurcating airway model was numerically analyzed by solving the 3-dimensional Navier-Stokes equations. The employed model was based on Pedley's report(1977), which comprises the curvature ratio to be 1/8 and the angel formed between the two daughter tubes to be 70 degree, whose radius is taken to be 0.78 times of the parent tube. The purpose of this study is to get the basic knowledge of the secondary flow generation for various Reynolds number, the velocity field and the axial gas transport in sinusoidal oscillatory flow through the bifurcation.