사각덕트형 분지관의 유량분배에 대한 수치해석 인자의 영향에 관한 연구
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As a duct system consists channels which convey fluid to necessary places, it is necessary to design a duct system in order to get the exact amount of flow rates at each channel. On the stage of designing, an analytical device is needed to predict the flow rates at the duct outlet. A commercial program STAR-CD for analysis of fluid flow by CFD enables us to predict the fluid flow conveniently. However the computed results can be different depending on user's method depends on pre-processing on the program such as boundary conditions, mesh creation and other input data. Therefore, this study compares flow rates at the outlet, obtained experimental measurement and numerical computation, and then it presents appropriate pre-processing necessary for the flow analysis. Flow distributions in a rectangular duct with two branch ducts are measured at inlets and outlets, respectively, by 5W argon LDV system. The experiment data and numerical analysis show us that the distribution ratios are almost invariant to Reynolds number. There are less than 4% differences between them. Since computations by the distributed and uniform inlet boundary conditions are shown small differences between them, it is assumed that the uniform flow velocity at inlet can be applied to analysis of numerical computation of fluid flow. The outlet condition with zero velocity gradient proved to be inapplicable to the case in which the turbulent flow is not fully developed. It is assumed, therefore, that the numerical analysis with the total environmental pressure condition would be appropriate for boundary condition at outlet of duct system. While increasing the grid density enhances reliability in the numerical analysis, it takes more computational time accordingly. In addtion, it is recommended that user should decide the grid size from wall within the y+ value range of the dimensionless normal distance. The numerical analysis by standard model, RNG model, Chen's model for the turbulent flow shows at most 0.2% differences among them. However, numerical analysis by RNG model and Chen's model for the turbulent model causes a sharp increase in repetitive frequency in the numerical analysis for the same grid. Therefore, the standard model is assumed to be appropriate for the turbulent model unless the fluid flow is in a complicated form of the system.