Investigation and Control of the Combined Three Dimensional Organized Structures in Turbulent Wakes behind Bluff Bodies

研究了长径比为10的有限长圆柱体和薄圆盘在不同攻角下的非定常三维流动结构。利用FFT分析仪在频域确定了流动细节，在时间域采用锁相平均技术获得了湍流尾迹中大尺度有序结构的特征。从复杂的湍流尾迹流中提取了三种不同频率、不同特征的典型有序结构。结果表明：1.有限长圆柱体后的尾流通常由以下三种不同起源的大尺度组织涡结构组成：(1)低频分量(尖端分量)，它是从圆柱体尖端脱落的一对纵向涡流；(2)中频分量(中跨分量)，它是发夹型的组织涡，从圆柱体的中间跨度脱落；(3)…更多的高频成分(根成分)，它是从连杆的根部脱落的，与二维卡门旋涡非常相似。有限长圆柱体后的尾流不仅包括上述三种典型的有序涡结构，还包括具有中等特征和频率的各种类型的涡以及几乎随机构型的小旋涡。因此，圆柱后的湍流尾迹看起来是一种非常复杂的流动。带有纵向涡的薄圆盘后的尾迹流动是无失速条件下的典型涡旋特征，只显示了少量的有序结构。失速条件下典型的涡旋特征是环状涡的尾迹流，具有明显的有组织的流动结构和明确的频率。基于脱落环状涡高度的频率的Strouhal数在0.19-0.22之间。较少

The unsteady three dimensional flow structures behind a finite circular cylinder with an aspect ratio of 10 and a thin circular disc at various angles of attack have been investigated. The flow details in the frequency domain were determined using FFT analyzer and the features of large-scaled organized structures in the turbulent wakes were obtained with phase-locked averaging technique in the time domain. Three typical organized structures with different frequencies and different features were extracted from the complex turbulent wake flows. The results can be summarized as follows :1. The wake flows behind a finite circular cylinder typically consist of the following three large-scaled organized vortex structures with different origins, (1) low frequency component(tip component), which is a pair of longitudinal vortices shed from a tip of the cylinder, (2) mid-frequency component (mid-span component), which is hairpin typed organized vortices shed from a mid-span of the cylinder, (3) … More high frequency component (root component), which is shed from the root of the sylinder and quite similar to the two-dimensional Karman's vortices .2. The wake flow behind a finite circular cylinder consists of not only the typical three types of organized vortex structures described above but also various types of vortices with intermediate features and frequencies as well as small eddies with almost random configurations. Therefore, the turbulent wake behind a circular cylinder appears to be a very complicated flow at a glance.3. The wake flow behind a thin circular disc with longituninal vortices, which is a typical vortex features for unstalled conditions, indicates only a few organized structure. The wake flow with ring-type vortices, which is typical vortex features for stalled conditions, indicates a clear organized flow structures with well defined frequency. The Strouhal numbers of the frequency based on the height of the shed ring-type vortices are in the range from 0.19 to 0.22. Less