Effects of free-stream turbulence on surface pressure fluctuations in a separation bubble
Effects of free-stream turbulence on surface pressure fluctuations in a separation bubble
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DOI：
10.1017/s0022112096004594
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发表时间：
1997-04
影响因子：
3.7
通讯作者：
P. Saathoff;W. H. Melbourne
中科院分区：
文献类型：
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作者：
P. Saathoff;W. H. Melbourne
通过风洞实验研究了锐缘海崖体前缘压力脉动大的原因。用钝平板获得的测量结果表明，在距前缘约0.25XR的狭窄区域内出现非常低的压力，其中XR定义了从前缘到平均再附着位置的距离。这种现象在无扰动流和湍流中都有发生，尽管峰值压力波动的幅度随着湍流强度σu/u和湍流尺度LX的增加而增加。用高速电影摄影机进行的流动显示实验揭示了分离气泡中引起大的压力波动的过程。当接近气流中的扰动引起分离剪切层卷起，在表面附近产生强涡流时，就开始了这一过程。压力数据的条件采样被用来确定涡的展向长度。当剪切层卷起时，压力波动的展向相关性显著增加。相干测量表明，在分离泡的涡的展向长度是没有直接关系的纵向速度波动的自由流。
Wind-tunnel experiments were conducted to investigate the cause of large pressure fluctuations near leading edges of sharp-edged bluff bodies. Measurements obtained with a blunt flat plate showed that very low pressures occur in a narrow region located approximately 0.25XR from the leading edge, where XR defines the distance from the leading edge to the mean reattachment location. This phenomenon occurs in the undisturbed flow as well as turbulent flow, although the magnitude of peak pressure fluctuations increases with both turbulence intensity, σu/u, and turbulence scale, LX. Flow visualization experiments conducted with a high-speed cine-camera reveal the process that causes large pressure fluctuations in separation bubbles. This process is initiated when a perturbation in the approaching flow causes a roll-up of the separated shear layer, producing a strong vortex near the surface. Conditional sampling of pressure data was used to determine the spanwise length of the vortex. A significant increase in the spanwise correlation of pressure fluctuations occurs when the shear layer rolls up. Coherence measurements indicate that the spanwise length of vortices in the separation bubble is not directly related to longitudinal velocity fluctuations in the free-stream.