Internal wave attractors : from geometrical focusing to non-linear energy cascade and mixing
Internal wave attractors : from geometrical focusing to non-linear energy cascade and mixing
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内波吸引子：从几何聚焦到非线性能量级联和混合
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发表时间：
2016
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通讯作者：
C. Brouzet
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作者：
C. Brouzet
海洋动力学中最重要的一个问题与从大尺度到小尺度的能量级联及其对混合的贡献有关。内波吸引子可能是造成这种级联的可能机制之一。在这份手稿中，我们在充满线性分层流体的梯形测试罐中对内波吸引子进行了实验研究。在这样的几何结构中，波可以形成称为吸引子的闭环。我们证明吸引子的形成是纯线性的：因此通过波聚焦产生小尺度。发现吸引子特性仅取决于水箱的梯形几何形状。在海洋尺度上，我们表明吸引子很可能不稳定。事实上，内波吸引子容易出现三元共振不稳定性，它将能量从吸引子转移到一对次级波。这种不稳定性及其主要特征被描述为盆地几何形状的函数。对于长期实验，不稳定性会产生几对次级波，产生一系列三元相互作用，并将能量从大规模单色输入转移到多尺度内波运动。我们首次揭示了内波湍流的实验性令人信服的特征。除了这个级联之外，我们还有一个混合机制，它似乎独立于梯形几何形状，因此是通用的。本手稿是通过对分层流体中水平振荡物体的附加质量和波浪阻尼系数的研究完成的，并应用于潮汐转换。
A question of paramount importance in the dynamics of oceans is related to the energy cascade from large to small scales and its contribution to mixing. Internal wave attractors may be one of the possible mechanisms responsible for such a cascade. In this manuscript, we study experimentally internal wave attractors in a trapezoidal test tank filled with linearly stratified fluid. In such a geometry, the waves can form closed loops called attractors. We show that the attractor formation is purely linear: small scales are thus created by wave focusing. The attractor characteristics are found to only depend on the trapezoidal geometry of the tank. At the ocean scale, we show that attractors are very likely to be unstable. Indeed, internal wave attractors are prone to a triadic resonance instability, which transfers energy from the attractor to a pair of secondary waves. This instability and its main characteristics are described as a function of the geometry of the basin. For long-term experiments, the instability produces several pairs of secondary waves, creating a cascade of triadic interactions and transferring energy from large-scale monochromatic input to multi-scale internal-wave motion. We reveal, for the first time, experimental convincing signatures of internal wave turbulence. Beyond this cascade, we have a mixing regime, which appears to be independent of the trapezoidal geometry and, thus, universal. This manuscript is completed by a study on added mass and wave damping coefficient of bodies oscillating horizontally in a stratified fluid, with applications to tidal conversion.