Experimental and Numerical Investigation of the Threedimensional Flow at Expiration in the Upper Human Airways

This study presents a comparison of numerical and experimental results of the steady flow field in the left main-bronchus of the upper human airways during exhalation. Stereo-particle-image velocimetry measurements were performed in multiple parallel measurement planes for a Reynolds number of Re_D = 700 based on the hydraulic diameter of the trachea to determine the highly three-dimensional flow in a realistic transparent silicone lung model. The numerical analysis is based on a Lattice-Boltzmann method. The results for the absolute velocity and the out-of-plane velocity component show a good agreement and emphasize the three-dimensionality of the flow. Two fluid jets, originating from two principal sub-bronchi, predominate the flow in the investigated bronchus. The vortical structures consisting of two pairs of counterrotating vortices are not generated by the curvature of the main-bronchus or the sub-bronchi but are caused by the merging of the flows and the redirection of the jets. Further downstream in the bronchus, the secondary flow structures vanish in the streamwise direction such that no spiral-like flow enters the trachea