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.

本文采用大涡模拟对非稳态呼吸过程下上呼吸道的气流场进行了预测。几何模型是通过将流行的基于铸型的口喉模型与用喇叭形导管建模的气管支气管气道相结合来创建的。通过正弦位移几何模型的底面来模拟呼吸过程。通过商业CFD软件Converge，采用动态亚网格尺度模型的大涡模拟对湍流进行建模。本研究发现：（1）考虑到肺扩张，口腔内的次级涡流比在口腔入口处设置准稳态吸气流量要复杂得多；(2)相同雷诺数下，加速和减速吸气相气管内次级涡的性质无明显差异；(3) 相同雷诺数下，在加速呼气阶段的反向咽射流和再循环区比减速呼气阶段不稳定得多。我们得出结论，气流结构的特性受呼吸模式的影响很大，应该进行更多的研究，特别是呼气阶段的气流结构，以进一步了解流场的特性。