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arXiv 2002.08784physics.flu-dynnlin.CD
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旋转turbulence中的相变和磁通环亚稳态

Phase transitions and flux-loop metastable states in rotating turbulence

P. Clark Di Leoni, A. Alexakis, L. Biferale, M. Buzzicotti

摘要:

通过使用高达512 × 512 × 32768网格点的记录分辨率的直接数值模拟,我们发现在旋转湍流中存在一种新的亚稳态的平衡态。我们通过改变旋转速率(与罗斯比数的倒数$Ro$成比例)和无量纲纵横比$λ=H/L$来扫描相空间,其中$L$和$H$分别是垂直和平行于旋转方向的域的大小。我们证明了三个湍流相的存在。对于小的$Ro$,但有限的$λ$,我们有一个分裂级联注入的能量被转移到大规模和小规模。对于大的$λ$和有限的$Ro$,没有逆级联,能量仅在傅立叶空间中向前传递。令人惊讶的是,在这两个制度之间,第三阶段是观察到这里首次报告。因此,对于$Ro$和$λ$的某些间隔,能量不再以任意大的尺度积累,而是停止在某些特征性的中间长度尺度,然后在傅立叶空间中向前重新分布,导致通量环机制,其中流动不平衡,净通量消失,异手性和同手性子通量不消失。该系统的进一步特征是亚稳态和临界慢化的存在,解释了为什么以前的实验和数值模拟无法检测到这种现象,需要极长的观察时间和巨大的计算资源。

英文摘要:

By using direct numerical simulations of up to a record resolution of 512x512x32768 grid points we discover the existence of a new metastable out-of-equilibrium state in rotating turbulence. We scan the phase space by varying both the rotation rate (proportional to the inverse of the Rossby number, $Ro$) and the dimensionless aspect ratio, $λ=H/L$, where $L$ and $H$ are the sizes of the domain perpendicular and parallel to the direction of rotation, respectively. We show the existence of three turbulent phases. For small $Ro$ but finite $λ$, we have a split cascade where the injected energy is transferred to both large and small scales. For large $λ$ and finite $Ro$ there is no inverse cascade and the energy is transferred forward in Fourier space only. Surprisingly, between these two regimes, a third phase is observed as reported here for the first time. Consequently, for certain intervals of $Ro$ and $λ$, energy is no longer accumulated at arbitrarily large scales, rather it stops at some characteristic intermediate length-scales from where it is then redistributed forward in Fourier space, leading to a flux-loop mechanism where the flow is out of equilibrium with vanishing net flux, and non-vanishing heterochiral and homochiral sub-fluxes. The system is further characterized by the presence of metastability and critical slowing down, explaining why previous experiments and numerical simulations were not able to detect this phenomenon, requiring extremely long observation time and huge computational resources.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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