Steady inspiratory flow in planar and non-planar models of human bronchial airways

Swirling flow associated with non-planar arterial geometry encourages interest in flow in larger human bronchial airways. where bifurcations are planar but consecutive bifurcation planes rotate by an angle (phi) of ca. 90degrees. Steady 'inspiratory' flow has been investigated in a two-generation symmetrically bifurcating human bronchial airway model by studying reddening by acid vapour of a litmus-containing coating as an approximate indicator of relative local wall shear (S-w). The inlet tube Reynolds number (Re-it) was 600 or 1800; the branching angle (theta) was 32.5degrees at first generation and 32.5degrees or 55 at second generation; phi was 0degrees or 90degrees between first and second generations: second-generation daughter tube volume flow rates were the same. With (phi) = 0degrees, S-w distribution between second-generation daughters was non-uniform. With phi = 90degrees, S-w distribution between second-generation daughters was uniform and flows were swirling with pitch lambda. With phi = 90degrees and Re-it given, increase of theta reduced lambda and increased S-w. With phi = 90 and theta given, increase of Re-it reduced lambda. Inspiratory flow in larger human bronchial airways is expected to be asymmetric and swirling, with implications for all transport processes including those of particles. The study may have implications for the design of general piping systems.