Kelvin-Helmholtz turbulence in complex environments

这个项目的重点是混合事件发生在剪切流接近边界和其他复杂的环境。例如，海洋表面附近的剪切驱动的混合事件将热量和CO2流入海洋内部。剪切驱动的混合事件的先前的研究已经假设该事件在空间和时间上是孤立的，即它开始于平滑的层流，并且远离任何边界或其他可能影响其演变的重要流动结构。这项研究将解决的影响，如海洋表面，底部，或其他附近的混合事件的空间接近的影响。主要的工具将是一系列的直接数值模拟剪切流的边界或其他流动结构足够接近的影响混合。研究结果将用于指导海洋表面附近和深海洋流（如密集溢流）中湍流通量的参数化。结果将有助于理解密集的底层流，表面混合层和参数化所产生的湍流。该项目将支持一名博士后和一名研究生。这两个年轻的科学家将学习和使用先进的数值模拟技能。此外，双方都将有机会参加研究航行，观察剪切驱动的湍流。开尔文-亥姆霍兹（KH）湍流是一种常见和有用的海洋湍流模型。它通常用于描述边界附近的湍流，例如，在近底重力流或在表面混合层的底部。虽然线性理论告诉我们，边界的接近可以影响的基本长度和时间尺度的KH波涛，鲜为人知的非线性演化和随后的混合的效果。例如，在赤道太平洋海面50米范围内观测到长度达300米的KH巨浪。在这些情况下，边界的接近可能对所产生的混合和海气性质的输送有很大的影响。在孤立的情况下，KH不稳定性通过一系列的二次不稳定性变成湍流.该顺序对初始剪切流的细节敏感，并且对最终实现的混合量具有很大影响。据推测，附近的边界将改变二次不稳定性的顺序，从而改变混合量。即使远离边界，例如在温跃层中，混合事件也会偶尔发生，因此可能会受到附近其他事件的影响。使用千万亿次机在UCAR，一系列的直接模拟将在边界和其他流动特征的存在下的KH事件。结果将被用来解释剪切驱动的混合事件在赤道海洋表面附近的观测，并扩大我们的KH不稳定机制的理解，因为它在整个ocean.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

This project focuses on mixing events that occur in sheared flows close to boundaries and in other complex environments. For example, shear-driven mixing events near the ocean surface flux heat and CO2 into the ocean interior. Previous studies of shear-driven mixing events have assumed that the event is isolated in space and time, i.e. it begins with smooth, laminar flow and is located far from any boundary or other significant flow structure that could impact its evolution. This research will address the effects of spatially proximate influences such as the ocean surface, the bottom, or another nearby mixing event. The main tool will be a sequence of direct numerical simulations of sheared flows with either a boundary or another flow structure close enough to influence the mixing. Results will be used to guide parameterization of turbulent fluxes near the ocean surface and in deep ocean currents such as dense overflows. The results will be useful in understanding dense bottom currents, surface mixed layers and in parameterizing the resulting turbulence. The project will support a postdoc and a graduate student. Both of these junior scientists will learn and use advanced numerical simulation skills. In addition, both will have the opportunity to take part in research cruises to observe shear-driven turbulence.The Kelvin-Helmholtz (KH) ansatz is a common and useful model for ocean turbulence. It is often used to describe turbulence near boundaries, e.g., in near-bottom gravity currents or at the base of a surface mixed layer. While linear theory tells us that boundary proximity can affect the basic length and time scales of KH billows, little is known of the effect on the nonlinear evolution and subsequent mixing. For example, KH billows with lengths up to 300m have been observed within 50m of the surface in the equatorial Pacific. In these cases, boundary proximity is likely to have a large effect on the resulting mixing and on air-sea property transports. In isolation, KH instability becomes turbulent via a well- explored sequence of secondary instabilities. This sequence is sensitive to the details of the initial shear flow, and it has a great influence on the amount of mixing that is ultimately achieved. It is hypothesized that a nearby boundary will alter the sequence of secondary instabilities and thereby change the amount of mixing. Even far from boundaries, e.g. in the thermocline, mixing events occur sporadically and may therefore feel the influence of other, nearby events. Using the petascale machines at UCAR, a sequence of direct simulations will be made of KH events in the presence of boundaries and other flow features. Results will be used to interpret observations of shear-driven mixing events near the surface in the equatorial oceans and to broaden our understanding of the KH instability mechanism as it operates throughout the ocean.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.