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

Abstract

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 (ϕ) of ca.90°. 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 (Sw). The inlet tube Reynolds number (Reit) was 600 or 1800; the branching angle (θ) was 32.5° at first generation and 32.5° or 55° at second generation; ϕ was 0° or 90° between first and second generations; second–generation daughter tube volume flow rates were the same. With ϕ = 0°, Sw distribution between second–generation daughters was non–uniform. With ϕ = 90°, Sw distribution between second–generation daughters was uniform and flows were swirling with pitch λ With ϕ = 90° and Reit given, increase of θ reduced λ and increased Sw. With ϕ = 90° and θ given, increase of Reit reduced λ 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.