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<專題討論>2019/4/16(二)13:10綜合大樓2樓48218教室演講 : 苗君易 特聘教授 (成功大學航太系)

張貼者:2019年4月11日 上午2:48Dabby Lu
講題: On the blunt body drag
摘要: Aerodynamic flow around a blunt body is featured with flow separation taking place on its contoured surface where the adverse pressure gradient is in effect.  For such a flow, the aerodynamic drag is dominated by the form drag which is basically determined by the extent of the flow separation region.  In the sub-critical range, which can be described in terms of Reynolds number based on the characteristic length of the blunt body and the incoming freestream velocity, the drag coefficient of the blunt body stays almost constant.  This signifies that the phenomenon of flow separation, or the extent of the flow separation region noted, is not sensitive to the Reynolds number.  Nevertheless, as the Reynolds number is further increased and falls in the critical regime, a drastic reduction in drag coefficient is discerned.  This pronounced transition in drag is known as the drag crisis.  Physically, this phenomenon is involved with the development of laminar separation bubbles on the contoured surface, followed by turbulent reattachment, then turbulent separation further downstream.  As a result, the extent of the flow separation region is much reduced. Meanwhile, flow in the critical regime is characterized as highly unsteady, even non-stationary, which is intimately linked with the development of the laminar separation bubbles.
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Dabby Lu,
2019年4月11日 上午2:48
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