Estimation of the Shear Stress (WSS) at the Wall of Tracheal Bifurcation

The paper is concerned with experimental investigations and numerical simulations of airflow in a rigid model of human tracheal bifurcation during a respiratory cycle in the presence of cough. The main goal of the study is to calculate the velocity and tracheal wall shear stress (WSS) distributions under the time variation in the pressure difference. A sequence of inspiration-expiration of measured flow rates and pressure is used to calibrate the 3D unsteady numerical solutions for different imposed boundary conditions at the edges of the bifurcation. The experimental data are obtained using commercial medical devices: (i) a spirometer and (ii) a mechanical ventilator, respectively. CT images of the lung airways were used to reconstruct the tracheal test geometry by 3D printing techniques. Flow spectrum, vortical structures, and the wall stresses are analyzed for the computed cases. Four turbulence models (k − ɛ, k − ω SST, k − ɛ R, and LES) are compared, and all indicate an increase in peak WSS and vortex intensity during coughing versus normal expiration. The present work confirms the importance of CFD simulations to model and quantify airflow throughout the respiratory cycle. The paper proposes a method to calculate wall shear stress, one of the most relevant parameters for characterizing airway function and the mechanical response of tracheal endothelial cells.