Department of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran.
Department of Mechanical Engineering, Tarbiat Modares University, Tehran, Iran.
Respir Physiol Neurobiol. 2019 Aug;266:103-114. doi: 10.1016/j.resp.2019.04.012. Epub 2019 Apr 24.
The objective of this study is to assess tracheobronchial flow features with the cartilaginous rings during a light exercising. Tracheobronchial is part of human's body airway system that carries oxygen-rich air to human's lungs as well as takes carbon dioxide out of the human's lungs. Consequently, evaluation of the flow structures in tracheobronchial is important to support diagnosis of tracheal disorders. Computational Fluid Dynamics (CFD) allows evaluating effectiveness of tracheal cartilage rings in human body under different configurations. This study utilizes Large Eddy Simulation (LES) to model an anatomically-based human large conducting airway model with and without cartilaginous rings at the breathing conditions at Reynolds number of 5,176 in trachea region. It is observed that small recirculating areas shaped between rings cavities. While these recirculating areas are decaying, similar to periodic 2D-hills, the cartilaginous rings contribute to the construction of a vortical flow structure in the main flow. The separated vortically-shaped zone creates a wake in the flow and passes inside of the next ring cavity and disturb its boundary layer. At last, the small recirculation flow impinges onto tracheal wall. The outcome of this impinge flow is a latitudinal rotating flow perpendicular to the main flow in a cavity between the two cartilaginous rings crest which appear and disappear within a hundredth of a second. Kelvin-Helmholtz instability is observed in trachea caused by shear flow created behind of interaction between these flow structures near to tracheal wavy wall and main flow. A comparison of the results between a smooth wall model named simplified model and a rough wall model named modified model shows that these structures do not exist in simplified model, which is common in modeling tracheobronchial flow. This study proposes to consider macro surface roughness to account for the separating and rotating instantaneous flow structures. Finally, solving trachea airflow with its cartilages can become one of major issues in measuring the validity and capability of solving flow in developing types of sub-grid scale models as a turbulence studies benchmark.
本研究旨在评估在轻度运动时带有软骨环的气管支气管流特征。气管支气管是人体气道系统的一部分，它将富含氧气的空气输送到肺部，并将二氧化碳从肺部排出。因此，评估气管支气管内的流动结构对于支持气管疾病的诊断非常重要。计算流体动力学（CFD）允许在不同配置下评估人体气管软骨环的有效性。本研究利用大涡模拟（LES）在呼吸条件下对具有和不具有软骨环的解剖学基础人体大传导气道模型进行建模，在气管区域雷诺数为 5176 时。结果表明，在环腔之间形成了小的再循环区域。当这些再循环区域衰减时，类似于周期性的二维山丘，软骨环有助于在主流中构建涡流动结构。分离的涡状区域在流动中产生尾流，并穿过下一个环腔内部，干扰其边界层。最后，小的再循环流撞击到气管壁。这种撞击流的结果是在两个软骨环嵴之间的腔体内产生一个横向旋转流，垂直于主流，其在百分之一秒的时间内出现和消失。在气管中观察到由于剪切流引起的开尔文-亥姆霍兹不稳定性，这些流结构在气管波状壁附近与主流相互作用的后面产生。光滑壁模型（简化模型）和粗糙壁模型（改进模型）之间的结果比较表明，这些结构在简化模型中不存在，简化模型在模拟气管支气管流中很常见。本研究建议考虑宏观表面粗糙度来解释分离和旋转的瞬时流动结构。最后，解决带有软骨的气管气流问题可能成为测量开发类型的亚网格尺度模型中流场有效性和能力的主要问题之一，作为湍流研究的基准。
