| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 100 === In recent years, the air pollution problem is getting more and more serious, and it causes many people to have on respiratory system disease (such as asthma). For effectively inhaling the medicinal preparations, the study of flow phenomena in bifurcating airway is important and meaningful. About this topic, the research approaches may divide into experiment, numerical simulation and theoretical analysis. By using the method of computational fluid dynamics, the behavior of air flow passing through the bifurcating airway in asthmatics is investigate in this thesis. First, the FLUENT software is utilized to compute the three-dimensional incompressible flow, then a self developed compressible flow code is used to steady the problem. Because the air flow is compressible and it is within the low Mach number flow regime in the majority of breathing conditions, a numerical approach and related program are developed in this thesis to solve the low-speed compressible flows. To investigate the flow in bifurcating airway, the CATIA software is adopted to construct the trachea model (bifurcating tube). Then an interface program is adopted, so that the CATIA software and homemade mesh-generation program are combined together to construct the unstructured tetrahedral meshes in the flow domain. On the above-mentioned meshes, a numerical approach is developed to solve the unsteady three-dimensional Navier-Stokes equations. This approach includes four-step Runge-Kutta time-integration scheme, Roe’s flux-difference splitting method and Modified Gauss-Seidel iterative method for solving the Rossow’s pressure correction equation. To promote the computational efficiency, it is operated on a personal computer with multiple cores. To evaluate the above-mentioned numerical approach and related program, the steady laminar flow passing through a typical bifurcating airway is studied first, and the computed results by using the present method and FLUENT code are compared with the related experimental data. Then, the steady laminar flow passing through an asthmatic bifurcating airway is studied, and the present solutions are compared with the results in the related paper. From the computed results, the velocity distributions on the inlet, outlet and branch part of airway are observed. Besides the secondary flow and vortex phenomena are investigated, the difference between normal and asthmatic airway flows are analyzed.
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