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arXiv 2109.00489physics.flu-dyn
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线性动力学能量级联模型的时空统计特性

Space-time statistics of a linear dynamical energy cascade model

Gabriel B. Apolinário, Laurent Chevillard

摘要:

在Apolinário \emph{et al}(J. Stat. Phys. \textbf{186},15(2022))。这个偏微分方程,随机搅拌的强迫项,这是光滑的空间和三角洲相关的时间,被证明在无限时间收敛到一个状态的有限方差,没有援助的粘度。此外,其解的空间轮廓变得粗糙,具有与分数高斯场相同的规律性。在这里,我们专注于时间的行为,并得出明确的渐近预测的关联函数的时间,这个解决方案,并观察到他们的规律性是不受影响的空间规律性的问题,只有在时间的搅拌贡献的相关性。我们还表明,在时间的解决方案的相关性取决于位置,相反,在固定的时间在空间中的相关性。然后,我们调查的影响,这是相关的时间上的空间和时间统计的这个方程的强迫。在这种情况下,虽然对于小的相关时间的均匀的空间统计的白色的时间的情况下被恢复,对于大的相关时间的均匀性被打破,并在速度分布中观察到的系统的原点周围的浓度。换句话说,这个分数速度场是Kolmogorov在1941年提出的自相似速度场通过线性动力学模型在一维中的表示,但仅在固定时间,对于δ相关强迫,在这种情况下,空间统计是均匀和粗糙的,正如湍流速度场所期望的那样。然而,湍流时间的规律性并没有被这个模型捕获。

英文摘要:

A linear dynamical model for the development of the turbulent energy cascade was introduced in Apolinário \emph{et al} (J. Stat. Phys. \textbf{186}, 15 (2022)). This partial differential equation, randomly stirred by a forcing term which is smooth in space and delta-correlated in time, was shown to converge at infinite time towards a state of finite variance, without the aid of viscosity. Furthermore, the spatial profile of its solution gets rough, with the same regularity as a fractional Gaussian field. We here focus on the temporal behavior and derive explicit asymptotic predictions for the correlation function in time of this solution and observe that their regularity is not influenced by the spatial regularity of the problem, only by the correlation in time of the stirring contribution. We also show that the correlation in time of the solution depends on the position, contrary to its correlation in space at fixed times. We then investigate the influence of a forcing which is correlated in time on the spatial and time statistics of this equation. In this situation, while for small correlation times the homogeneous spatial statistics of the white-in-time case are recovered, for large correlation times homogeneity is broken, and a concentration around the origin of the system is observed in the velocity profiles. In other words, this fractional velocity field is a representation in one-dimension, through a linear dynamical model, of the self-similar velocity fields proposed by Kolmogorov in 1941, but only at fixed times, for a delta-correlated forcing, in which case the spatial statistics is homogeneous and rough, as expected of a turbulent velocity field. The regularity in time of turbulence, however, is not captured by this model.

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