Investigation of airflow field in the upper airway under unsteady respiration pattern using large eddy simulation method.

In this paper, the airflow field in the upper airway under unsteady respiration process is predicted using large eddy simulation. The geometrical model is created by combining a popular cast-based mouth-throat model with tracheo-bronchial airways modeled with a trumpet-shaped conduit. The respiration process is simulated by sinusoidal displacing the bottom surface of the geometrical model. Large eddy simulation with dynamic sub-grid scale model is adopted for modeling the turbulent flow via a commercial CFD software, Converge. This study has found that (1) the secondary vortices in the mouth cavity are much more complex considering the lung expansion than setting the quasi-steady inspiration flow at the mouth-inlet; (2) the properties of secondary vortices in the trachea are not evidently different at the same Reynolds number at the accelerating and decelerating inspiration phases; (3) the reversed pharynx jet as well as recirculation zone is much unsteadier at the accelerating expiration phase than decelerating expiration phase for the same Reynolds number. We conclude that the properties of airflow structures are highly impacted by the respiration pattern and more investigations should be conducted, particularly, on the airflow structures during expiration phase for further understanding the properties of flow field.