Internal gravity wave radiation from a stratified turbulent wake
Internal gravity wave radiation from a stratified turbulent wake
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来自分层湍流尾流的内部重力波辐射
作者：
K. Rowe;P. Diamessis;Q. Zhou
通过一系列数值实验研究了线性分层流体中拖曳球湍流尾流辐射重力内波的近场能量和方向特性。对初始雷诺数Re\equiv UD/\unicode[STIX]{x1 D 708}\in \{5\times 10^{3}，10 ^{5}，4\times 10^{5}\}$和内部弗劳德数Fr\equiv 2U/ND\in \{4，16，64\}$进行了模拟，这些数值是使用基于体的尺度定义的：$D$，球体直径; $U$，拖曳速度;和$N$，Brunt-Väisälä频率。在整个尾流演化过程中，对随时间演化的尾流场快照进行采样。通过计算尾流随动椭圆柱体的总波功率，量化了内波辐射从尾流中提取的能量。辐射的总时间积分波能量被发现与$Re$增加和$Fr$减少。峰值辐射波功率发生在早期的时候，接近发病的浮力控制，并被发现是大约不变的幅度为$Re$的增加。对于所考虑的两个较高的Re，在较晚的时间，IGW继续被发射-占总辐射波能量的明显增加。最强大的IGW辐射出的尾流在一个广泛的角度为$Nt<10$，在20 ^{\circ }{-}70^{\circ }$的水平为$10\leqslant Nt\leqslant 25$，几乎平行于水平的后期在非平衡状态的尾流演变。内波辐射被发现是一个重要的汇后，唤醒动能$Nt=10$，这表明波辐射不能被忽视时，在地球物理和海洋工程应用中的分层湍流尾流建模。
The near-field energetics and directional properties of internal gravity waves (IGWs) radiated from the turbulent wake of a sphere towed through a linearly stratified fluid are investigated using a series numerical experiments. Simulations have been performed for an initial Reynolds number $Re\equiv UD/\unicode[STIX]{x1D708}\in \{5\times 10^{3},10^{5},4\times 10^{5}\}$ and internal Froude number $Fr\equiv 2U/ND\in \{4,16,64\}$, defined using body-based scales – $D$, the sphere diameter; $U$, the tow speed; and $N$, the Brunt–Väisälä frequency. Snapshots of temporally evolving wake flow fields are sampled over the full wake evolution. The energy extracted from the wake through internal wave radiation is quantified by computing the total wave power emitted through a wake-following elliptic cylinder. The total time-integrated wave energy radiated is found to increase with $Re$ and decrease with $Fr$. The peak radiated wave power occurs at early times, near to the onset of buoyancy control, and is found to be approximately unchanged in magnitude as $Re$ is increased. For the two higher $Re$ considered, at late times, IGWs continue to be emitted – accounting for a distinct increase in total radiated wave energy. The most powerful IGWs are radiated out of the wake at a wide range of angles for $Nt<10$, at $20^{\circ }{-}70^{\circ }$ to the horizontal for $10\leqslant Nt\leqslant 25$, and nearly parallel to the horizontal late in the non-equilibrium regime of wake evolution. Internal wave radiation is found to be an important sink for wake kinetic energy after $Nt=10$, suggesting wave radiation cannot be neglected when modelling stratified turbulent wakes in geophysical and ocean engineering applications.