On an eddy viscosity model for energetic deep-water surface gravity wave breaking
On an eddy viscosity model for energetic deep-water surface gravity wave breaking
复制标题
深水表面重力波破碎的涡粘模型
DOI：
10.1017/jfm.2021.863
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发表时间：
2021
影响因子：
3.7
通讯作者：
Khait A
中科院分区：
文献类型：
--
作者：
Khait A
我们提出了深水重力波破碎的基本物理过程的调查。我们的动机是找出导致涡动粘性破碎模型（EVBM）在预测强非线性波的表面高程的不足之处的根本原因。由于实验方法在提供高分辨率流动信息方面的局限性，我们提出了一种数值方法，通过开发EVBM封闭的独立的完全非线性准势（FNP）流动模型和耦合的FNP加Navier-Stokes流动模型。首先用调制不稳定性波列对数值模型进行了验证，然后用该模型模拟了一系列非破碎、中等破碎和强破碎条件下的宽带聚焦波列。对两种模式的数值解在地表高程和其他重要物理性质上的差异进行了系统的分析。结果发现，EVBM准确地预测的能量消耗的破碎和振幅谱的自由波的幅度，但未能准确捕捉破碎引起的相移。相移随破断强度的增加而增加，对于高波数分量尤其明显。这被确定为一个原因的上移的波的色散关系，这增加了大波数分量的频率。这种变化驱动大波数分量以几乎相同的速度传播，这明显高于线性色散水平。这抑制了谐波在焦点之后的瞬时色散传播，延长了聚焦波的寿命并扩展了其传播空间。
We present an investigation of the fundamental physical processes involved in deep-water gravity wave breaking. Our motivation is to identify the underlying reason causing the deficiency of the eddy viscosity breaking model (EVBM) in predicting surface elevation for strongly nonlinear waves. Owing to the limitation of experimental methods in the provision of high-resolution flow information, we propose a numerical methodology by developing an EVBM enclosed standalone fully nonlinear quasi-potential (FNP) flow model and a coupled FNP plus Navier–Stokes flow model. The numerical models were firstly verified with a wave train subject to modulational instability, then used to simulate a series of broad-banded focusing wave trains under non-, moderate- and strong-breaking conditions. A systematic analysis was carried out to investigate the discrepancies of numerical solutions produced by the two models in surface elevation and other important physical properties. It is found that EVBM predicts accurately the energy dissipated by breaking and the amplitude spectrum of free waves in terms of magnitude, but fails to capture accurately breaking induced phase shifting. The shift of phase grows with breaking intensity and is especially strong for high-wavenumber components. This is identified as a cause of the upshift of the wave dispersion relation, which increases the frequencies of large-wavenumber components. Such a variation drives large-wavenumber components to propagate at nearly the same speed, which is significantly higher than the linear dispersion levels. This suppresses the instant dispersive spreading of harmonics after the focal point, prolonging the lifespan of focused waves and expanding their propagation space.
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