Marginally turbulent flow in a square duct
Marginally turbulent flow in a square duct
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DOI：
10.1017/s0022112007007604
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发表时间：
2007-09
影响因子：
3.7
通讯作者：
M. Uhlmann;A. Pinelli;G. Kawahara;A. Sekimoto
中科院分区：
文献类型：
--
作者：
M. Uhlmann;A. Pinelli;G. Kawahara;A. Sekimoto
为了确定自持湍流的最低要求，对方形直管道内的湍流流动进行了直接数值模拟。据发现，湍流可以保持为约1100以上的整体雷诺数的值，对应于80的摩擦速度为基础的雷诺数。计算域的流向周期的最小值约为190壁单位，大致独立于雷诺数。我们提出了一个表征的流动状态在边缘雷诺数，这大大不同于完全湍流的一个：边缘状态呈现出四涡二次流结构交替的时间，而完全湍流的一个呈现通常的八涡模式。结果表明，在临界雷诺数范围内，缓冲层相干结构对普朗特第二类二次流的出现起着至关重要的作用。
A direct numerical simulation of turbulent flow in a straight square duct was performed in order to determine the minimal requirements for self-sustaining turbulence. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, corresponding to a friction-velocity-based Reynolds number of 80. The minimum value for the streamwise period of the computational domain is around 190 wall units, roughly independently of the Reynolds number. We present a characterization of the flow state at marginal Reynolds numbers which substantially differs from the fully turbulent one: the marginal state exhibits a four-vortex secondary flow structure alternating in time whereas the fully turbulent one presents the usual eight-vortex pattern. It is shown that in the regime of marginal Reynolds numbers buffer-layer coherent structures play a crucial role in the appearance of secondary flow of Prandtl's second kind.