BULK FLOW DISTRIBUTIONS THROUGH CASCADES OF UNIFORM BRANCHES (BRANCHING, KINEMATIC IRREVERSIBILITY, CONVECTIVE MIXING, OSCILLATING JET, VORTICITY)

An experimental study has been carried out to determine how laminar flow is distributed in branching networks. For low-pressure flows typical of the pulmonary airways, the partitioning of regional "inspiratory" flows in symmetric planar networks has been observed to deviate markedly from predicted distributions based on the concept of flow resistance. By contrast, "expiratory" flows are distributed uniformly among all the branches. A series of experiments has been performed to demonstrate that "inspiratory" flow distributions are determined largely by the axial velocity profile at the inlet and by the rate of convective mixing within branch segments joining adjacent bifurcations. These results have been incorporated into a proposed non-resistive model of regional flow regulation, based on changes in bronchial geometry.;These flow principles have been extended to include asymmetric branching models of pulmonary airways, using regional flow irreversibility as a quantitative index of the non-resistive component of flow partitioning. In auxiliary experiments an oscillating jet technique has been developed to estimate the rate of mixing produced by flow through a bifurcation. An empirical model utilizes both the skewness of the inlet axial velocity profile and downstream convective mixing to predict the degree of non-uniform flow splitting in symmetric networks.