Extreme velocity gradients in turbulent flows
Extreme velocity gradients in turbulent flows
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DOI：
10.1088/1367-2630/ab0756
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发表时间：
2019-04-04
影响因子：
3.3
通讯作者：
Yeung, P. K.
中科院分区：
文献类型：
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作者：
Buaria, Dhawal;Pumir, Alain;Yeung, P. K.
完全湍流的特征是间歇性地形成非常局部化和强烈的速度梯度。这些梯度可以比它们的典型值大几个数量级，并导致湍流的许多独特性质。使用具有前所未有的小尺度分辨率的Navier-Stokes方程的直接数值模拟，我们在由泰勒尺度雷诺数参数化的湍流强度的显著范围内表征了这种极端事件值得注意的是，我们发现最强的速度梯度以经验方式缩放为τ（-1）（K）R-λ（β），其中β近似为0.775 ± 0.025，其中T-K是柯尔莫哥洛夫时间尺度（其倒数T-K（-1）是速度梯度波动的均方根）。此外，我们观察到在非常小的距离r上的速度增量，
Fully turbulent flows are characterized by intermittent formation of very localized and intense velocity gradients. These gradients can be orders of magnitude larger than their typical value and lead to many unique properties of turbulence. Using direct numerical simulations of the Navier-Stokes equations with unprecedented small-scale resolution, we characterize such extreme events over a significant range of turbulence intensities, parameterized by the Taylor-scale Reynolds number (R-lambda).Remarkably, we find the strongest velocity gradients to empirically scale as tau(-1)(K) R-lambda(beta), with beta approximate to 0.775 + 0.025, where T-K is the Kolmogorov time scale (with its inverse, T-K(-1), being the rms of velocity gradient fluctuations). Additionally, we observe velocity increments across very small distances r