A STREAMWISE-CONSTANT MODEL OF TURBULENT PIPE FLOW
A STREAMWISE-CONSTANT MODEL OF TURBULENT PIPE FLOW
复制标题
湍流管流的流化常数模型
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
B. McKeon
中科院分区：
文献类型：
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作者：
J. Bourguignon;B. McKeon
提出了一种流向常数模型，研究了管道流动过渡过程中平均流量变化的基本机理。该模型受到两种不同类型的强迫：通过流函数的确定性形式的轴动量方程的简单强迫和流函数方程的随机强迫。使用单个强迫动量平衡方程，我们表明速度剖面的形状对强迫剖面的变化具有鲁棒性，并且需要线性非正态和非线性效应来捕获与过渡到湍流相关的平均流量的变化。该模型的特别简单的形式允许通过检查方程直接研究动量传递。由我们的模型产生的管道横截面上的高低速条纹分布与在管道流动过渡中泡发结构尾缘附近的速度场中观察到的分布非常相似。在随机强迫下，该模型表现出一个准周期的自我维持循环，其特征是“流向恒定的泡芙”的产生和随后的衰减，之所以这样称呼，是因为它们的速度场的时间演化与在以体速度运动的参照系中与三维泡芙相关的速度场投影之间的良好一致性。我们确定，流动动力学对产生近壁流向涡的再生机制相对不敏感，因此，使用小的、非结构化的背景扰动来再生流向涡，以取代来自流动的自然反馈，足以捕捉到高速和低速条纹的形成及其分离，从而导致湍流管道流动的速度剖面特征变钝。我们提出一个“准自我维持过程”来描述这些机制。
A streamwise-constant model is presented to investigate the basic mechanisms responsible for the change in mean flow occuring during pipe flow transition. The model is subject to two different types of forcing: a simple forcing of the axial momentum equation via a deterministic form for the streamfunction and a stochastic forcing of the streamfunction equation. Using a single forced momentum balance equation, we show that the shape of the velocity profile is robust to changes in the forcing profile and that both linear non-normal and nonlinear effects are required to capture the change in mean flow associated with transition to turbulence. The particularly simple form of the model allows for the study of the momentum transfer directly by inspection of the equations. The distribution of the high- and low-speed streaks over the cross-section of the pipe produced by our model is remarkably similar to one observed in the velocity field near the trailing edge of the puff structures present in pipe flow transition. Under stochastic forcing, the model exhibits a quasi-periodic self-sustaining cycle characterized by the creation and subsequent decay of “streamwise-constant puffs,” so-called due to the good agreement between the temporal evolution of their velocity field and the projection of the velocity field associated with three-dimensional puffs in a frame of reference moving at the bulk velocity. We establish that the flow dynamics are relatively insensitive to the regeneration mechanisms invoked to produce near-wall streamwise vortices, such that using small, unstructured background disturbances to regenerate the streamwise vortices in place of the natural feedback from the flow is sufficient to capture the formation of the high- and low-speed streaks and their segregation leading to the blunting of the velocity profile characteristic of turbulent pipe flow. We propose a “quasi self-sustaining process” to describe these mechanisms.
影响因子：
3.7
作者：
McKeon, B. J.;Sharma, A. S.
通讯作者：
Sharma, A. S.