FRACTAL ANALYSIS AND NUMERICAL SIMULATION ON PULSATING FLOW PATTERNS IN A THREE-DIMENSIONAL BRONCHIAL TREE

The pulsating airflow through human bronchial tree is of great significance for understanding its function and morphology. Fractal theory and numerical simulation are applied in this paper to study the global and local flow characteristics in the bronchial tree under unstable conditions. First, the pulsating flow impedance of fractal bronchial tree is derived, and the structure of bronchial tree is optimized by minimizing flow impedance. It has been shown that the optimal structure depends on the physical law governing the airflow. The optimized diameter ratio between parent and daughter branches for pulsating flow is different from Murray’s law, and the fractal dimension for branch diameter lies in 2 and 3. Afterwards, the local pulsating flow field by three-dimensional (3D) numerical simulation on a symmetrical bronchial model is compared with the global flow characteristics by fractal analysis. The numerical results show that asymmetrical airflow characteristics can be found at high Reynolds number, and the velocity distribution of the main bronchus is more irregular and the turbulence phenomenon is more evident. This work can help to understand the association between function and structure of the bronchial tree, and it may shed light on the physical mechanisms and drugs targeting of pulmonary disease.