School of Aerospace Engineering, Huazhong Science and Technology University, Wuhan, China.
Department of Engineering Mechanics, Shanghai Jiao Tong University, Shanghai, China.
Respir Physiol Neurobiol. 2020 Aug;279:103468. doi: 10.1016/j.resp.2020.103468. Epub 2020 Jun 4.
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.
本文采用大涡模拟方法预测非定常呼吸过程中上呼吸道的气流场。几何模型是通过将流行的基于铸模的口腔-喉咙模型与用喇叭形管道建模的气管-支气管气道组合而成。通过商用 CFD 软件 Converge 对几何模型的底面进行正弦位移来模拟呼吸过程。采用动态亚网格尺度模型的大涡模拟方法通过商用 CFD 软件 Converge 对湍流进行建模。本研究发现：（1）与在口腔入口处设置准稳态吸气流相比，考虑到肺部扩张，口腔内的二次涡更加复杂；（2）在相同雷诺数下，加速和减速吸气阶段的气管内二次涡的特性没有明显差异；（3）对于相同的雷诺数，加速呼气阶段的咽反流以及回流区比减速呼气阶段的更不稳定。我们得出结论，气流结构的特性受呼吸模式的影响很大，需要进一步进行更多的研究，特别是在呼气阶段的气流结构，以进一步了解流场的特性。
