On the Many Faces of Transition
On the Many Faces of Transition
复制标题
DOI：
10.1007/978-1-4899-5579-1_1
复制
发表时间：
1969
期刊：
影响因子：
--
通讯作者：
M. Morkovin
中科院分区：
文献类型：
--
作者：
M. Morkovin
对于给定的剪切层几何形状，高雷诺数湍流具有强大的、稳定的、几乎普遍的特征，这些特征与流动中的大量自由度有关。这些特征包括一系列占主导地位的能量运动的尺度，一系列的操作强度水平，以及平均三维相位关系，这些都以某种方式确保了自我再生过程的维持。在寻求一种理性的方法来处理令人困惑的各种过渡行为时，（参考文献1），作者阐明了许多通向湍流的不稳定路径是可以接受的，它们的有效性取决于给定的机制是否提供了自我再生所需的适当尺度、强度水平和三维相位关系。概念上的教训来自于最近完成的关于向湍流转捩的文献的批判性调查，并提出了许多适用于亚音速的统一的计算方法。特别是，线性放大，非线性限制，和二次不稳定诱导的非定常非线性效应的作用进行了讨论。这些机制说明了一些过渡流，包括那些存在粗糙度和流向涡。对最近过渡问题研究所提出的快过渡还是慢过渡的问题作出了澄清。(Ref. 2）最后，提出了导致过渡的线性和非线性过程的整体模型。
For a given shear-layer geometry the high-Reynolds-numbers turbulent flows possess strong, stable in-the-large, nearly universal features associated with the large number of degrees of freedom in the flows. These features include a range of scales of dominant energetic motion, a range of operating intensity levels, and average three-dimensional phase relations which, together, somehow insure the maintenance of a self-regenerative process. In seeking a rational approach to the bewildering variety of transitional behavior (Ref. 1), the author conjectures that many instability paths to turbulence are admissible and that their effectiveness hinges on whether the given mechanism supplies the proper scales, intensity level, and 3D phase relations needed for self-regeneration.Conceptual lessons are drawn from a recently completed critical survey of the literature on transition to turbulence, and a number of unifying conjectures are advanced for subsonic speeds. In particular, the roles of linear amplification, nonlinear limiting, and secondary instability inducted by unsteady nonlinear effects are discussed. These mechanisms are illustrated for a number of transitional flows, including those in presence of roughness and streamwise vorticity. A clarification is advanced for the question of fast versus slow transition raised at the recent Institute on Transition. (Ref. 2) Finally, an overall model of the linear and nonlinear processes leading to transition is proposed.