| Summary: | 碩士 === 國立臺北科技大學 === 車輛工程系所 === 96 === This study use the CFD-RC(Computation Fluid Dynamics Research Corporation) software to analyze the turbulent flow field behind a backward-facing step with of vertical wall mass bleed. The effect of sudden expansion ratio also included in this work. By changing the step heights, inlet flow rates and vertical mass injection rates, the corresponded reattachment points and recirculation regions were found and discussed. Using the previous reference works as a basic platform, then this work proceeds different parameter settings for further discussion. According to the analysis of the flow, the result shows that the reattachment length will increase with the increasing of the height of backward-facing step, inlet velocity and vertical mass injection, but the position of the reattachment point almost unchanged as the inlet Re is greater than 10000. The dependence of the three parameters influencing the position of the reattachment point is of the order as step height > inlet velocity > vertical mass injection. The vertical position of maximum turbulence intensity move toward the wall as the axial distance from the step increases, then it move apart from the wall as the axial distance is behind the reattachment point. The turbulence intensity in the recirculation zone is reduced as the vertical mass bleed increases. As the ratio of sudden expansion is 2, the reattachment point nearly exceeds the region of vertical mass bleed, and the flow field influenced by the vertical mass injection mainly locates in the range from 0.86 to 0.98 .
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