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摘要:
已有的研究证实，在均匀各向同性湍流中速度梯度张量（VGT）演化的无量纲时间是当地Kolmogorov时间。本文使用大涡模拟的方法，计算了一个雷诺数7 000的槽道流场，以到壁面的无量纲距离的大小将流场分为不同区间，使用当地Kolmogorov时间对不同区间的应变率张量的拉格朗日时间自相关函数进行无量纲化。发现不同区间自相关函数的下降曲线不完全重合：在对数区中不同区间自相关函数的下降曲线基本重合，但在靠近壁面的黏性底层和过渡层中则无此现象。因此，当地Kolmogorov时间不是槽道中速度梯度张量演化的普适无量纲时间。
Abstract:It is confirmed that the dimensionless time for evolution of velocity gradient tensor (VGT) is local Kolmogorov time scale in homogeneous isotropic turbulence. The channel flow at Reynolds number 7 000 was calculated using large-eddy simulation in this paper. The flow field was divided into different regions according to the size of the dimensionless distance to the wall and the auto-correlation functions of different regions were normalized by local Kolmogorov time scale. The decline curves of auto-correlation functions in different regions were found not really the same. In logarithmic layer, the decline curves of auto-correlation functions in different regions almost overlapped, while the similar phenomenon did not exist in viscous bottom layer near the wall and buffer layer. The results show that local Kolmogorov time scale is not the universal dimensionless time of evolution of VGT in channel flow.
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Key words:
- turbulence /
- channel flow /
- large-eddy simulation /
- strain-rate tensor /
- Lagrangian auto-correlation
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图 1 52＜y+＜400时应变率张量自相关函数下降曲线
Figure 1. Decline curves of auto-correlation function of strain-rate tensor in 52 < y+ < 400 region
图 2 0＜y+＜52时应变率张量自相关函数下降曲线
Figure 2. Decline curves of auto-correlation function of strain-rate tensor in 0 < y+ < 52 region
图 3 52＜y+＜66区间不同无量纲方式对比
Figure 3. Comparison among different dimensionless patterns in 52 < y+ < 66 region
表 1 统计使用的子区间
Table 1. Information about statistical subregions
序号 y+范围 粒子样本数 1 0~4 100 680 2 8~12 19 116 3 16~20 16 501 4 24~28 13 596 5 32~36 13 365 6 40~44 12 072 7 48~52 11 663 8 52~66 29 073 9 80~94 22 411 10 108~122 20 331 11 136~150 19 610 12 164~178 16 608 13 288~312 18 123 14 376~400 40 832 
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