Turbulence in tidal flow over rough three-dimensional topography

这个项目研究了海洋内部的潮汐流，特别是水下山脉、海山和山脊附近的潮汐流，是如何导致湍流和其他复杂流动的产生的。这些水流使较重的、较冷的底部海水与较轻的、较温暖的海水混合在一起。该项目使用专门的高分辨率数值模拟来描述和预测理想锥形支架上的湍流运动。这些简化的几何图形被用来表示大致的水下地形，就像在海洋中发现的那样。所研究的水流及其产生的水温分布对天气和气候的形成起着重要作用。此外，它们还为海洋生物建立了环境，并确定了通常用于国防和海洋勘探的载人和无人潜航器所面临的条件。这个项目的结果将被科学界用于环境中精细尺度过程的观测及其在数值大尺度模型中的参数化。一名研究生和一名博士后研究员将获得资助，他们将在一个具有重大社会利益的问题的背景下接触海洋科学、流体力学和计算科学。海洋潮汐构成了一个巨大的能量库，可以转化为内部重力波和湍流。潮汐调制的水流在更大的范围内，名义上是二维的山脊、岛屿和海岬，会遇到淹没的、三维的、小尺度的1-10公里的地形特征。这些流动产生以振荡频率和高次谐波传播的内部重力波，以及瞬态下坡射流和背风波。产生的脱落涡相互作用，并与身体导致复杂的湍流运动。本项目将利用高分辨率模拟技术确定由三维特征周围流动形成的尾流涡（亚中尺度涡流）和非线性内波场的相对作用。本文将对低地形弗劳德数分层流态下陡坡（超临界坡）锥形障碍物进行高分辨率三维大涡模拟。模拟和分析的目的是描述和理解动力学作为以下非量纲参数的函数：平均和振荡速度分量的相对强度，流动偏移长度与特征沿流地形长度的比率，以及障碍物水平横截面的形状。在模拟中使用的简化设置将允许推进旋涡、尾迹和非线性内波近场的联合动力学知识，以及三维地形分层湍流的后果。初步结果表明，在多个垂直层中会产生相互作用的涡流、复杂的三维非线性内波场和湍流。

This project examines how tidal flows in the ocean interior, particularly near underwater mountains, seamounts and ridges, contribute to the generation of turbulent and other complex flows. These flows contribute to mixing of heavier, cold bottom waters with overlying lighter, warmer oceanic waters. The project uses specialized high resolution numerical simulations to describe and predict turbulent motions over idealized conical mounts. These simplified geometries are used to represent rough underwater topography, like that found in the oceans. The flows investigated, and the water temperature distribution they create, play an important role in setting weather and climate. Also, they establish the environment for marine life, and determine the conditions faced by manned and unmanned submerged vehicles, usually used for defense and ocean exploration. Results from this project will be utilized by the scientific community engaged to observations of fine-scale processes in the environment and their parameterization in numerical large-scale models. A graduate student and a postdoctoral researcher will be supported and they will gain exposure to ocean sciences, fluid mechanics, and computational science in the context of a problem of great societal interest. Ocean tides constitute a large reservoir of energy that can be converted to internal gravity waves and turbulence. Tidally modulated flows encounter submerged, three-dimensional (3D), small-scale topographic features of order 1-10 km within larger scale, nominally two-dimensional ridges, islands and headlands. These flows generate propagating internal gravity waves at the oscillation frequency and at higher harmonics, along with transient downslope jets and lee waves. The shed vortices generated interact among themselves and with the body leading to complex turbulent motions. This project will identify the relative roles of the wake vortices (sub-mesoscale eddies), formed by flow around the three-dimensional features, and the nonlinear internal wave field using high-resolution simulations. High-resolution 3D large eddy simulations (LES) of flow over a steep (supercritical slope) conical obstacle in the stratified flow regime of low topographic Froude number will be performed. The simulations and analyses aim to characterize and understand the dynamics as a function of the following non-dimensional parameters: the relative strength of mean and oscillating velocity components, the ratio of the flow excursion length to a characteristic along-flow topography length, and the shape of the horizontal cross-section of the obstacle. The simplified setting used in the simulations will allow to advance knowledge of the combined dynamics of the vortices, wake and the nonlinear internal-wave near field, and of the consequences for stratified turbulence at 3D topography. Preliminary results have shown the generation of interacting eddies, complex 3D nonlinear internal wave fields and turbulence occurring in multiple vertical layers.