The generation of large-scale flows by stochastically excited internal gravity waves remains largely unexplored despite numerous applications in geophysical and astrophysical contexts. Here, we investigate this problem experimentally in a cylindrical annulus geometry. Our working fluid is made of two layers. In the top, fresh water layer, turbulence is generated by 12 jets with an oscillating flow rate. Those turbulent fluctuations impinge the interface with the bottom, linearly stratified, salt water layer, where they excite internal gravity waves which propagate, damp viscously, and generate a mean azimuthal flow. The jet structure, wave spectra, and mean-flow properties are addressed using particle image velocimetry. Our measurements validate quantitatively the transfer of momentum from the waves to the mean flow through the wave associated Reynolds stress, as previously validated for a monochromatic forcing. In addition, wave energy decays through time, likely because of the mixing at the interface between the two layers, and the driven mean flow accordingly decreases and eventually vanishes. This has up to now prevented the observation of quasibiennial-oscillation-like reversals in our system.

中文翻译：

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由湍流产生的内部重力波驱动的大规模流动

尽管在地球物理和天体物理环境中有许多应用，但由随机激发的内部重力波产生的大规模流动在很大程度上仍未得到探索。在这里，我们在圆柱环几何中通过实验研究这个问题。我们的工作液由两层组成。在顶部的淡水层中，湍流是由 12 个具有振荡流速的射流产生的。这些湍流波动撞击底部线性分层咸水层的界面，在那里它们激发内部重力波，这些波传播、粘性阻尼并产生平均方位角流。射流结构、波谱和平均流特性使用粒子图像测速法解决。我们的测量定量地验证了从波浪到平均流的动量通过与波相关的雷诺应力的转移，如先前针对单色强迫验证的那样。此外，波能随时间衰减，这可能是由于两层之间的界面处的混合，驱动的平均流相应地减少并最终消失。到目前为止，这已经阻止了在我们的系统中观察到类似两年一次的振荡逆转。