Large eddy simulation study of the airflow characteristics in a human whole-lung airway model

Abstract

Studying airflow characteristics in the human respiratory system is important for understanding the properties of the aerosol transport and deposition. This study first constructed a human whole-lung airway model (WLAM) with random features extending from the mouth to the 13th generation bronchus. The large eddy simulation method is utilized to investigate the features of both the averaged airflow fields and flow unsteadiness under inspiratory flow rates of 15 and 30 l/min, respectively. The results reveal the following novel findings: (1) secondary flow strength is not monotonically changing throughout the respiratory tract, depending on the local flow state and geometry, which allows for strong secondary flow motion even in the G13 bronchial airway. (2) In the upper airway, the peak distribution of turbulent kinetic energy (TKE) is due to in-plane secondary flow shear and longitudinal flow shear; local kinetic energy plays a vital role in the persistence of unsteadiness throughout the bronchial tree, which allows instability to still exist even in the bronchial airway with low Reynolds number. (3) TI is more dependent on the local flow state and geometric structure than TKE. These findings indicate that secondary flow and airflow unsteadiness in the thin bronchial airway are far stronger than previously reported and cannot be neglected. Therefore, further studies should investigate airflow unsteadiness in the thin bronchial airway using a suitable WLAM instead of a segmented bronchial airway model.