Experimental and numerical investigation on inspiration and expiration flows in a three-generation human lung airway model at two flow rates

•The mainstream flow behaves as skewed, double-peaked and M-shaped patterns.•The secondary flow behaves as Dean-type two-vortex, four-vortex, six-vortex and eight-vortex patterns.•The respiratory flow patterns are heavily influenced by the combination of geometrical bifurcating/merging, local wall curvature, limited generation length and multi-generation interaction. The respiration flow pattern plays a key role in fluid flow, heat and mass transfer in human lung airway. To reveal the complex flow pattern within human lung multiple-generation airway, both the steady inspiration and expiration flows are comprehensively studied using laser Doppler velocimetry technique and computational fluid dynamics method for an idealized human tracheobronchial three-generation airway model at two flow rates, corresponding to an adult male breathing under light activity and moderate exercise conditions, respectively. The comparison of mainstream velocity between the measurements and simulations are generally good. Both of the inspiration and expiration flows are heavily influenced by the combination of geometrical bifurcating/merging, local wall curvature, limited generation length and multi-generation interaction. The mainstream flow is non-uniform and behaves as skewed, double-peaked and M-shaped patterns. The secondary flow is complex and characteristic of Dean-type two-vortex, four-vortex, six-vortex and eight-vortex patterns. This work is of scientific significance for a deep understanding of respiratory flow physics and of certain application values for clinical diagnosis and remedy of respiratory deceases.