We demonstrate via direct numerical simulations that a periodic, oscillating mean flow spontaneously develops from turbulently generated internal waves. We consider a minimal physical model where the fluid self-organizes in a convective layer adjacent to a stably stratified one. Internal waves are excited by turbulent convective motions, then nonlinearly interact to produce a mean flow reversing on timescales much longer than the waves’ period. Our results demonstrate for the first time that the three-scale dynamics due to convection, waves, and mean flow is generic and hence can occur in many astrophysical and geophysical fluids. We discuss efforts to reproduce the mean flow in reduced models, where the turbulence is bypassed. We demonstrate that wave intermittency, resulting from the chaotic nature of convection, plays a key role in the mean-flow dynamics, which thus cannot be captured using only second-order statistics of the turbulent motions.

中文翻译：

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混乱无序：湍流生成的内部波产生缓慢反转的平均流

通过直接数值模拟，我们证明了湍流产生的内波会自发地产生周期性的振荡平均流量。我们考虑一种最小的物理模型，其中流体在与稳定分层的层相邻的对流层中自组织。内部波被湍流的对流运动激发，然后非线性相互作用以产生平均时间反转的平均流，该时间流比波浪的周期长得多。我们的结果首次证明了由于对流，波浪和平均流引起的三尺度动力学是通用的，因此可能发生在许多天体和地球物理流体中。我们讨论了在绕过湍流的简化模型中重现平均流量的工作。我们证明了由于对流的混乱性质导致的波间歇性，