為治療氣喘，探討氣管內的流場現是不容分辯且無爭議的。此方面研究大致上可分為數值模擬、理論分析及實驗操作。本文中使用計算流體力學之方法，探討暫態下空氣流經氣喘患者下呼吸道分歧管之行為。首先，使用設計軟體CATIA建立下呼吸道氣管模型(分歧管)，再將此模型匯入Ansys FLUENT 13.0軟體於流場區域內建立非結構四面體網格。在此商用軟體Ansys FLUENT 13.0被用來計算進行三維不可壓縮流。為提升計算效率，本研究使用多核心個人電腦進行平行運算。為評估上述相關程式及求解方法之正確性，首先探討典型分歧管穩態層流與暫態層流之流場現象，並將計算答案結果與相關文獻之結果做比對，接著進行氣喘患者下呼吸道分歧管之穩態與暫態層流計算。由計算結果可觀察出口端、分歧管管身部分及入口端等區域之速度分佈現象。除了探討二次流、渦流及穩態、暫態各時間下不同入口條件導致之差異等物理現象外，也可分析氣喘患者與健康狀態正常下一般分歧管流之差異。

Due to the prosper of petrochemical industry, therefore, people are suffering from the respiratory diseases such asthma. The air pollution problems become serious. In order effectively treat asthmatic disease, investigation of flow phenomena in bifurcating airway is imperative and meaningful. In this topic, the research approaches were put divide into numerical simulation, theoretical analysis and experiment respectively. By using the computational fluid dynamics (CFD )in both two- and three-dimensional bifurcating tube models. The flow phenomena of air on passing through the lower bifurcating airway in asthmatics was investigated , The commercial software CATIA is adopted to construct the model of bifurcate airway. Then these data were exported into Ansys FLUENT software to generate unstructured meshes. Finally Ansys FLUENT is utilized to complete the dimensional unsteady incompressible flow numerical modeling. For promoting the computational efficiency, those cases are operated on a personal computer with multiple cores. To evaluate the above-mentioned numerical approach and related programs, the steady laminar flow and unsteady laminar flow passing through a normal bifurcating airway were studied . Then, the steady / transient flow passing through an asthmatic bifurcating airway were studied, the numerical results were compared with those data in the related papers. From the velocity distributions on branch part of airway ,on the inlet and outlet planes, the flow behavior are observed. And the secondary flow and vortex flow were observed and the physical behavior for the steady and transient flows at different time and inlet condition were studied, the difference between typical case and asthmatic bifurcating airway flows can be compared.

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