The structure and control of a turbulent reattaching flow
The structure and control of a turbulent reattaching flow
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DOI：
10.1017/s0022112095003259
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发表时间：
1995-09
影响因子：
3.7
通讯作者：
L. Sigurdson
中科院分区：
文献类型：
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作者：
L. Sigurdson
实验研究了周期性速度扰动对与自由流同轴排列的圆柱体锐缘钝面下游分离泡的影响。速度波动是由位于气缸内的声学驱动器和位于固定分离线下游的小周向间隙产生的，以允许与外部流连通。当在低于自由剪切层的初始Kelvin-Helmholtz频率的频率下强制流动，并且与气泡高度相当的相关涡流波长时，可以显著地修改流动。再附着长度、气泡高度、分离压力和面部平均压力均降低。使用烟丝技术获得的流动照片上的大型结构的影响进行了研究。强迫增加了前缘附近的卷吸。结果表明，剪切层再附着前的末级涡是流动结构的重要组成部分。有两种不同的不稳定性：Kelvin-Helmholtz不稳定性的自由剪切层和“脱落”型不稳定性的整个气泡。前者由剪切层涡量与其自身的相互作用组成，后者由其由于壁的存在而产生的图像组成。为了确定最佳的强迫频率，提出了一种方法的频率缩放相关的数据为各种气泡，并支持与卡门涡脱落的类比。
An experimental study was made of the effect of a periodic velocity perturbation on the separation bubble downstream of the sharp-edged blunt face of a circular cylinder aligned coaxially with the free stream. Velocity fluctuations were produced with an acoustic driver located within the cylinder and a small circumferential gap located immediately downstream of the fixed separation line to allow communication with the external flow. The flow could be considerably modified when forced at frequencies lower than the initial Kelvin-Helmholtz frequencies of the free shear layer, and with associated vortex wavelengths comparable to the bubble height. Reattachment length, bubble height, pressure at separation, and average pressure on the face were all reduced. The effects on the large-scale structures were studied using flow photographs obtained by the smoke-wire technique. The forcing increased the entrainment near the leading edge. It was concluded that the final vortex of the shear layer before reattachment is an important element of the flow structure. There are two different instabilities involved: the Kelvin-Helmholtz instability of the free shear layer and the ‘shedding’-type instability of the entire bubble. The former consists of an interaction of the shear layer vorticity with itself, the latter with its images that result because of the presence of a wall. In order to determine the optimum forcing frequency, a method of frequency scaling is proposed which correlates data for a variety of bubbles and supports an analogy with Kármán vortex shedding.