| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 87 === This study presents mainly an application of a control-volume- based finite-difference method to predict the diffusion of a heavy gas discharging into the turbulent atmosphere. The mathematical model employs a standard two-equation, and wall function to closure governing equations. An orthogonal , non-uniform , staggered grids are used for the estiblishment of mesh grids .
The parameters studied include the size of jet , the jet velocity of a heavy gas and height , position and numbers of the obstacles such as buildings. The numerical results show that the dimensionless velocity ratio has a strong influence on the fluid flow characteristics . As expected , an increase of the dimensionless velocity ratio enhances the concentration contours and spread, which also increases the recirculation region and the vortex strength behind the jet . In addition , the appearance of obstacles obviously decrease the downstream concentration . Decreasing the height of the obstacle or increasing the distance between the jet and the obstacle , the downstream concentration increases and diminishes the recirculation region due to an decrease of the obstructive effect .
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