We investigate experimentally stratified turbulence forced by waves. Stratified turbulence is present in oceans and it is expected to be dominated by nonlinear interaction of internal gravity waves as described by the Garrett & Munk spectrum. In order to reach turbulent regimes dominated by stratification we use the Coriolis facility in Grenoble (France) which large size enables us to reach regimes with both low Froude number and large Reynolds number. Stratification is obtained by using vertically linearly varying salt concentration and we force large scale waves in a $6\times 6\times 1$ m${}^3$ domain. We perform time-resolved PIV to probe the space-time structure of the velocity field. We observe a wide band spectrum which is made of waves. Discrete modes are observed due to the square shape of the flow container as well as a continuum part which appears consistent with an axisymmetric superposition of random weakly nonlinear waves. Our observations support the interpretation of turbulence of a strongly stratified fluid as wave turbulence of internal waves although our spectrum is quite different from the Garrett & Munk spectrum. Weak turbulence proceeds down to a small cutoff length scale (the buoyancy wavelength) at which a transition to more strongly nonlinear turbulence is expected.

中文翻译：

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在科里奥利设施中产生内部重力波的弱非线性湍流

我们调查了波浪强迫的实验性分层湍流。分层湍流存在于海洋中，并且如Garrett＆Munk谱所描述的那样，预计它将以内部重力波的非线性相互作用为主导。为了达到以分层为主的动荡政权，我们使用位于法国格勒诺布尔的科里奥利设施，这种大型设施使我们能够达到低弗洛德数和大雷诺数的政权。通过使用垂直线性变化的盐浓度获得分层，并且我们将大波浪施加在$6\times 6\times \mathrm{1个}$ 米${}^3$域。我们执行时间分辨的PIV以探究速度场的时空结构。我们观察到由波组成的宽带频谱。由于流动容器的正方形以及连续部分而观察到离散模式，连续部分看起来与随机弱非线性波的轴对称叠加一致。我们的观察结果支持将强分层流体的湍流解释为内部波的湍流，尽管我们的谱与Garrett＆Munk谱完全不同。弱湍流会降到较小的截止长度尺度（浮力波长），在该尺度下会过渡到更强的非线性湍流。