Abstract：
To enhance the understanding of airflow characteristics in the human respiratory system, the expiratory airflow in a human respiratory tract model was simulated using large eddy simulation and dynamic mesh under different expiration conditions aligned with clinically measured data. The airflow unsteadiness was quantitatively assessed using power spectral density (PSD) and spectral entropy (SE). The following findings were obtained: (1) The airflow is highly turbulent in the mouth-pharynx region during expiration, with its dynamic characteristics being influenced by both the transient expiration flow pattern at mouth piece and the glottis motion. (2) PSD analysis reveals that the expiratory airflow is very unsteady, exhibiting a broad-band attenuation spectrum in the pharynx-trachea region. When only transient expiration or glottis motion is considered, the PSD spectrum changes slightly. When both are ignored, however, the change is significant, with the peak frequency reduced to 10% of the real expiration condition. (3) SE analysis indicates that the airflow transitions into turbulence in the trachea, and there may be multiple transitions in the region of soft palate. The transient expiration or glottis motion alone increases turbulence intensity by 2%-15%, while ignoring both reduces turbulence intensity by 10%-20%. This study implies that turbulence characteristics can be significantly different under different expiratory conditions, and therefore it is necessary to determine the expiratory flow characteristics using clinically measured expiratory data.
摘要：
为加强对人体呼吸系统气流特性的认识,使用大涡模拟和动态网格在与临床测量数据一致的不同呼气条件下模拟人体呼吸道模型中的呼气气流。使用功率谱密度（PSD）和谱熵（SE）定量评估气流不稳定。获得了以下发现:(1)呼气期间口咽区域气流高度湍流,其动态特性受口腔瞬时呼气流型和声门运动的影响。(2)PSD分析表明呼气气流非常不稳定，在咽气管区域表现出宽带衰减谱。当只考虑短暂的呼气或声门运动时，PSD光谱略有变化。当两者都被忽略时，然而,变化是重大的，峰值频率降低到实际呼气条件的10%。(3)SE分析表明气流在气管内转变为湍流,并且在软腭区域可能有多个过渡。仅短暂的呼气或声门运动会使湍流强度增加2％-15％，同时忽略两者，湍流强度降低10%-20%。这项研究表明，在不同的呼气条件下，湍流特性可能会有很大的不同。因此，有必要使用临床测量的呼气数据来确定呼气流量特性。
