An experimental study of non-linear interaction of velocity fluctuations in the transition region of a two-dimensional wake
An experimental study of non-linear interaction of velocity fluctuations in the transition region of a two-dimensional wake
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DOI：
10.1017/s0022112070002124
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发表时间：
1970-12
影响因子：
3.7
通讯作者：
Hiroshi Sato
中科院分区：
文献类型：
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作者：
Hiroshi Sato
作为我们先前工作(Sato&Kuriki 1961)的扩展，我们对二维尾迹的层流-湍流转变进行了实验研究，重点研究了速度起伏的非线性相互作用。在自然跃迁中，由于不规则扰动的选择性放大，首先出现了正弦速度波动。当涨落的幅度变大时，会发生非线性相互作用：产生正弦涨落的高次谐波和缓慢的不规则涨落。向湍流的过渡是渐进的，没有突然的“崩溃”。当两个频率的声音(f1和f2)被引入到尾迹中时，会产生两个速度脉动。当幅度较小时，它们被独立放大。如果振幅超过某些值，就会发生相互作用，其中一个分量的增长会被另一个分量的存在所抑制。同时，f1−f2，2(F1−f2)…的频率波动和f1+f2，2(f1+f2)…都被生产出来。自然转变中缓慢、不规则波动的行为与F1−f2成分的行为非常相似。它们似乎是由相同的机制产生的。在尾迹的过渡区，速度涨落幅度的微小变化被抑制效应增强，频率的微小不规则性被f1−f2分量的产生放大。这是规则涨落随机化的两个基本过程，它们导致了湍流的发展。
As an extension of our previous work (Sato & Kuriki 1961), an experimental study was made on the laminar-turbulent transition of a two-dimensional wake, with emphasis on the non-linear interaction of velocity fluctuations. In the natural transition, a sinusoidal velocity fluctuation first appears as a result of the selective amplification of irregular disturbances. When the amplitude of the fluctuation becomes large, a non-linear interaction takes place: higher harmonics of the sinusoidal fluctuation and a slow, irregular fluctuation are generated. The transition into turbulence is gradual, and there are no abrupt ‘breakdowns’. When a sound with two frequencies (f1 and f2) is introduced into the wake, two velocity fluctuations are induced. They are amplified independently when amplitudes are small. If amplitudes exceed certain values, a mutual interaction takes place, and the growth of each component is suppressed by the presence of the other. At the same time, fluctuations with frequencies of f1 − f2, 2(f1 − f2) … and f1 + f2, 2(f1 + f2) … are produced. The behaviour of the slow, irregular fluctuation in the natural transition closely resembles that of the f1 − f2 component. They seem to be produced by the same mechanism. In the transition region of the wake, a small variation in the amplitude of velocity fluctuation is enhanced by the suppression effect, and a small irregularity in the frequency is amplified by the generation of the f1 − f2 component. These are two elementary processes of randomization of regular fluctuations, which lead to the development of turbulence.