Large-scale coherent structures in the wake of axisymmetric bodies
Large-scale coherent structures in the wake of axisymmetric bodies
复制标题
DOI：
10.1017/s0022112079001841
复制
发表时间：
1979-07
影响因子：
3.7
通讯作者：
H. Fuchs;E. Mercker;U. Michel
中科院分区：
文献类型：
--
作者：
H. Fuchs;E. Mercker;U. Michel
采用热线探针和传声器探头分别放置在与圆盘对称轴垂直的3和9个圆盘直径的下游平面上，研究了通过圆盘的非定常流场。脉动速度和压力信号连续地受到大尺度相干运动的支配，这些运动将尾流作为一个整体包裹起来。这表明窄带两点空间相关可以作为描述基本随机信号的空间相干性和相位特性的实验工具。圆盘的轴对称边界条件所施加的特殊对称性使大尺度流动现象能够分解为相对简单的基本结构或模态。由此产生的方位角成分根据其各自的幅度和单独的功率谱进行量化。通过将目前的结果与早期射流研究中发现的某些显著不同的特征进行比较，证明了该方法在大尺度范围内揭示湍流特征的能力：m = 1和m = 2模态在尾迹中明显占主导地位，而m = 0和m = 1模态在相关的Strouhal数范围内在射流中占主导地位。这些大规模的连贯结构不仅仅是一种有趣的流动现象；它们必须在刚性流动边界上有巨大的反作用力（特别是如果这些边界允许振动响应），并且可能产生特定的反馈机制。为研究大尺度流动现象而提出的分析技术，在不以某种方式人为激励或强迫的情况下，消除了湍流信号中的部分随机性。也不需要对自然发生的波动进行有条件的采样。该方法也适用于除严格轴对称流外的其他流态。
The unsteady flow past a circular disk is studied with hot-wire and microphone probes positioned in planes normal to the axis of symmetry at 3 and 9 disk diameters down-stream. Both the fluctuating velocity and pressure signals are shown to be continuously dominated by large-scale coherent motions enveloping the wake flow as a whole. This suggests narrowband two-point space correlations as an experimental tool for describing spatial coherence and phase characteristics of the basically random signals. The specific symmetry imposed by the axisymmetric boundary conditions of the disk enables a decomposition of the large-scale flow phenomena into relatively simple elementary structures or modes. The resulting azimuthal constituents are quantified in terms of their respective magnitudes and individual power spectra. The capability of the approach to uncover characteristic features of turbulence as far as its large-scale domain is concerned is demonstrated by a comparison of the present results with certain remarkably different features found in earlier jet flow investigations: the m = 1 and m = 2 modes are found to clearly dominate in wakes whereas the m = 0 and m = 1 modes were dominant in jets in a relevant range of Strouhal numbers. These large-scale coherent structures are more than just an interesting flow phenomenon; they must have a tremendou back-reaction on rigid flow boundaries (particularly if these allow a vibrational response) and may give rise to specific feedback mechanisms. The analysing technique proposed for studying large-scale flow phenomena injets and wakes removes part of the randomness in the turbulent signals without artificially exciting or forcing them in one way or another. No conditional sampling of the naturally occurring fluctuations is required, either. The method may be applicable to other than strictly axisymmetric flow configurations, too.