壁面运动与分叉结构对肺泡内混沌混合影响的研究OA

To investigate the effect of alveolar boundary conditions and alveolar duct bifurcation structures on chaotic mixing behavior of fluid within the pulmonary acinus,numerical simulations were conducted for both single-alveolus-alveolar duct models and multi-alveolus two-generation bifurcation models.By identifying critical points in the flow field and employing the dynamic mode decomposition(DMD)algorithm along with particle tracking techniques,Poincaré plot was constructed to analyze the chaotic dynamic characteristics of the system.The alveolar flow exhibits coexisting spiral and radial flows,with one saddle point and one focal point in the flow field.Poincaré plot reveals the existence of islands hindering mixing in the central alveolar region,surrounded by a chaotic region characterized by stretching and folding.Bidirectional particle exchange occurred between the alveolus and alveolar duct,forming annular strips encircling the islands.Although alveolar duct wall motion does not alter the overall chaotic structure,it has a certain influence on particle displacement and exchange volume.The presence of bifurcation structures reduces the number of islands and decreases particle exchange between alveoli and alveolar ducts.A decrease in Reynolds number will lead to the expansion of island regions and weakening of mixing.Furthermore,chaotic convection within the alveolus could drive particles to move toward the upstream inlet direction.