Transport and Deposition of Particles and Fibers in Human Tracheobronchial Tree

Abstract

Transport and deposition of ellipsoidal fibers in the human upper airways were analyzed using an asymmetric airway bifurcation model. The trachea and the first two generations (G0–G1) of the tracheobronchial tree were included in the study. The focus of the study was on prediction of transport and deposition of fibers and elongated particles. The laryngeal jet at the trachea entrance was modeled as an effective turbulence disturbance, and Reynolds stress transport turbulence model (RST) was used. For accurate modeling of the near wall airflow, the “two-layer zonal model” was used for boundary consideration, and the turbulence normal fluctuation close to wall is further corrected based on the “quadratic variation near wall model” (Tian and Ahmadi 2007). Lagrangian simulation of ellipsoidal fiber transport and deposition was developed where the coupled translational and rotational motions of the fibers were accounted for. The particle equations of motion included the hydrodynamic drag and torque, shear induced lift, gravitational sedimentation, and turbulence diffusion effects. The simulation results showed that the elongated fiber remained aligned with the main flow most of the time. On short duration occasions, the fibers rotated impulsively along their path. The fiber rotational motion was dependent on fiber geometry and the local flow shear. Fiber deposition pattern and deposition rate in the trachea and the first bifurcation were evaluated, and the results were compared with the experiments.