根據衛生署調查台灣約有200萬的氣喘人口，也就是說有將近十分之ㄧ的台灣人患有氣喘。人類肺部的呼吸道是由許多微小支氣管組成(如同網路)，系統越接近終端其呼吸道就越細且分支增加。為解決呼吸道相關疾病，了解氣體在分歧管中之流動情形是一重要之工作。計算流體力學近年來已廣泛應用在醫學工程上，例如人體血管流及氣管流的模擬等。本文利用FLUENT商業軟體探討人體肺部在穩態吸氣模式下雷諾數範圍從200-2000，模擬三維二級、三級與四級分歧管之流場現象。SIMPLEC是被採用來求解不可壓縮流三維尤拉/納維史托克方程式及能量方程式。除了上述數值法外，本研究也採用Roe通量差分分離法求解可壓縮流。為探討上述方法之精確性，將求解噴嘴及分歧管無黏性流場和圓管黏性層流場，並與相關解析解比較。最後利用FLUENT軟體求解分歧管黏性層流場，並將二級與三級分歧管流場的解與相關文獻比較。此計算結果發現如速度分佈、流量分佈、壓差與二次流等，會受雷諾數、歧管曲率、彎管流效應、歧管脊處和歧管上游及不同的入流邊界條件皆會影響分歧管的流場狀態。此外，每個接合處皆會影響到下一級歧管的流場狀態，而採用均勻入流邊界，所得之壓力係數會比其他入流邊界條件來的高。
關鍵字：分歧管、二次流、歧管曲率、彎管流效應

According to the investigation of the Department of Health, approximately 2,000,000 people have asthma and it is about 10 percent of the populations in Taiwan. The human lung airways are composed of many bronchial. When the system close to the terminal, the airway becomes smaller and the branches increase. To solve the disease related to the respiratory system, understanding the gas behavior in bifurcating tube is an important work. In recent years, the computational fluid dynamics is widely applied in the biomechanical engineering, such as numerical simulation of coronary artery flow and human pulmonary artery flow. On this study, the FLUENT commercial software is used to investigate the inspiratory steady flow Reynolds number is about 200-2000 in the second, third, fourth generation bifurcation tubes. SIMPLEC algorithm is adopted to solve the incompressible three-dimensional Euler/Navier-Stokes equation and energy equation. Besides the above numerical simulations, Roe flux-splitting method is also utilized to study the compressible flow. To evaluate this approach, the inviscid nozzle and bifurcating tubes flow and viscous pipe flow are solved and the numerical results are compared with the related analytical solutions. Finally, the FLUENT code is used to simulation second-generation and third-generation bifurcation tubes flow, and the results are compare with the solutions in the other literature. From these results such as velocity distribution, mass flow rate distribution and secondary flow phenomena, the Reynolds number, Dean flow effect, carina ridge effect, upstream flow field and different boundary inlet condition will affect bifurcation tubes flows. Also, each junction will affect the flow field of next bronchial, and the pressure coefficient which is obtained by using the uniform inlet flow condition is high than that of other inlet boundary treatment.
Keywords:bifurcation tubes, secondary flow, bifurcation tubes curvature, Dean flow effect

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