The turbulence cascade in the near wake of a square prism
The turbulence cascade in the near wake of a square prism
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DOI：
10.1017/jfm.2017.390
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发表时间：
2017-07
影响因子：
3.7
通讯作者：
F. A. Portela;G. Papadakis;J. C. Vassilicos
中科院分区：
文献类型：
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作者：
F. A. Portela;G. Papadakis;J. C. Vassilicos
本文采用Kármán-Howarth-Monin-Hill方程，研究了雷诺数Re=3900$时，方柱产生的非均匀各向异性近场湍流尾流中心线上的湍流级联。这是完全广义的逐尺度能量平衡，与卡门-豪沃思方程不同，它不需要均匀性或各向同性假设。我们的数据是从直接数值模拟中获得的，因此使我们能够访问涉及这种能量平衡的所有过程。存在一个显着的长度尺度范围内的取向平均的非线性尺度间传输速率是近似恒定的和负的，表明平均向前湍流级联。这种平均级联由在不同尺度空间方向上共存的正向和反向级联行为组成。随着距离棱镜的增加，但在近场的尾流，方向平均的非线性尺度间传输速率往往近似等于减去湍流耗散率，即使所有的不稳定性相关的能量过程中的规模的规模的能量平衡是显着的，如果不是同样重要。我们还发现定义良好的近$-5/3$的能量谱在流向方向，特别是在中心线的位置，逆级联行为发生流向取向的长度尺度。
We present a study of the turbulence cascade on the centreline of an inhomogeneous and anisotropic near-field turbulent wake generated by a square prism at a Reynolds number of $Re=3900$ using the Kármán–Howarth–Monin–Hill equation. This is the fully generalised scale-by-scale energy balance which, unlike the Kármán–Howarth equation, does not require homogeneity or isotropy assumptions. Our data are obtained from a direct numerical simulation and therefore enable us to access all of the processes involved in this energy balance. A significant range of length scales exists where the orientation-averaged nonlinear interscale transfer rate is approximately constant and negative, indicating a forward turbulence cascade on average. This average cascade consists of coexisting forward and inverse cascade behaviours in different scale-space orientations. With increasing distance from the prism but within the near field of the wake, the orientation-averaged nonlinear interscale transfer rate tends to be approximately equal to minus the turbulence dissipation rate even though all of the inhomogeneity-related energy processes in the scale-by-scale energy balance are significant, if not equally important. We also find well-defined near $-5/3$ energy spectra in the streamwise direction, in particular at a centreline position where the inverse cascade behaviour occurs for streamwise oriented length scales.