Abstract In this study, the unsteady airflow field in a realistic model of human upper airways during the breathing cycle and the fibrous particle transport and deposition were investigated using the CFD method. An anatomically realistic model of airway passage including vestibule to the end of the trachea was constructed from the CT images of a 24-year-old healthy woman. Several user-defined functions (UDFs) were developed and incorporated into the discrete phase model (DPM) of ANSYS Fluent code and were used for the evaluation of ellipsoidal particle motion in transient airflows. The developed UDF was used to solve the coupled translational and rotational equations of motion of ellipsoidal fibers and to analyze their dispersion and deposition in the upper airways. The total and regional depositions for a range of fiber sizes were evaluated. The transient particle deposition fraction was compared with those obtained for the equivalent steady flow condition. In addition, the fraction of ellipsoidal fibers that penetrate the lower respiratory tract under cyclic breathing was calculated and compared with the steady flow simulation. The presented results showed that the steady simulation with an appropriate equivalent airflow rate can predict the total fibrous particle deposition during cyclic breathing with reasonable accuracy. The steady simulations, however, cannot properly predict the regional particle deposition under transient flows. In particular, the comparison between steady and transient penetration fraction reveals that the steady breathing model fails to accurately predict the penetration fraction of ellipsoidal fibers into the lower respiratory tract.

中文翻译：

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人体上呼吸道模型中气流和纤维颗粒的瞬态数值模拟

摘要 在这项研究中，使用 CFD 方法研究了呼吸循环期间人体上呼吸道的真实模型中的不稳定气流场以及纤维颗粒的传输和沉积。根据一名 24 岁健康女性的 CT 图像构建了包括前庭到气管末端的气道通道的解剖学逼真模型。开发了多个用户定义函数 (UDF) 并将其合并到 ANSYS Fluent 代码的离散相位模型 (DPM) 中，并用于评估瞬态气流中的椭球粒子运动。开发的 UDF 用于求解椭圆纤维运动的耦合平移和旋转方程，并分析它们在上呼吸道的分散和沉积。评估了一系列纤维尺寸的总沉积和区域沉积。将瞬态颗粒沉积分数与等效稳定流动条件下获得的分数进行比较。此外，计算了在循环呼吸下穿透下呼吸道的椭圆形纤维的分数，并与稳态流动模拟进行了比较。所呈现的结果表明，具有适当等效气流速率的稳定模拟可以以合理的准确度预测循环呼吸期间的总纤维颗粒沉积。然而，稳态模拟不能正确预测瞬态流下的区域颗粒沉积。特别是，稳态和瞬态穿透分数的比较表明，稳态呼吸模型无法准确预测椭圆形纤维进入下呼吸道的穿透分数。