Idealized simulations of turbulence advected by surface waves: Implications for interpreting turbulence measurements in shallow water

在浅水区，如内陆架、海湾和河口，湍流测量通常使用固定传感器。在这些环境中普遍存在的表面波混淆了湍流测量，因为波轨道速度通常比湍流波动大两个数量级，并且它们还平流湍流涡流被平流通过传感器。湍流通量的测量通常是有偏见的波速和频谱是难以解释的，因为能量分布在频率空间不同，比湍流时，平流单独的电流。拟合频谱形状的频谱来估计湍流通量，湍流动能和湍流长度尺度的方法目前仅限于波轨道速度小于或等于current.In这项研究中，一系列理想化的模拟将进行开发适合的情况下，波轨道速度超过电流的频谱拟合方法。理论和半经验的湍流波数谱从文献中，以及从高分辨率的湍流模拟领域将被转换为频谱，将观察到，如果涡平流通过一个固定位置的传感器的波和电流。初步理想化的模拟一维平流的各向同性湍流和各向异性边界层湍流单色波提供了一个框架，用于合成拟议的模拟，以及测量和方法在文献中，在重要的无量纲参数，涉及平流湍流波平流电流。理想化的模拟将扩展到二维（波浪的水平和垂直平流）和三维（波浪与水流成一定角度传播），以及内大陆架典型的窄带和宽带波浪条件。模拟结果将与PI先前收集的现有实验室和现场测量结果进行比较，以评估波浪下方湍流模型谱（为稳定流中的湍流而开发）的有效性，可能为波流边界层提供新的见解。理想化模拟的结果，沿着与现有的实验室和现场测量，将被用来开发新的工具，采用频谱拟合估计湍流参数和它们的不确定性从固定传感器测量时，波轨道速度超过电流。然而，这些测量结果可能难以解释。拟议的工作将提高对波浪轨道速度超过海流时在波浪下进行湍流测量所涉及的问题的理解，并开发在这些条件下估计湍流参数及其不确定性的方法，这对研究一系列浅水环境的物理和化学的科学家很有价值。在理想化模拟的背景下，以前的工作的合成将有助于指导从固定传感器在波浪环境中的湍流测量的分析。网站上提供的理想化模拟结果库将使科学家能够将他们的测量放在广泛的参数空间中，而无需重复模拟本身。用于执行理想化模拟和应用本研究开发的新方法的Matlab脚本也将在项目网站上提供。这笔赠款将为一名早期职业科学家提供工资支持和计算机工作站。

In shallow water such as the inner shelf, bays, and estuaries, turbulence measurements are often made with fixed sensors. Surface waves, which are ubiquitous in these environments, confound turbulence measurement because wave orbital velocities are typically two orders of magnitude larger than turbulent fluctuations and they also advect turbulent eddies are advected past sensors. Turbulent flux measurements are usually biased by wave velocities and spectra are difficult to interpret because energy is distributed differently in frequency space than when turbulence is advected by a current alone. Methods that fit spectral shapes to frequency spectra to estimate turbulent fluxes, turbulent kinetic energy, and turbulent length scales are presently limited to conditions where wave orbital velocities are less than or equal to currents.In this study a series of idealized simulations will be performed to develop spectral fitting methods suitable for situations where wave orbital velocities exceed currents. Theoretical and semi-empirical turbulence wavenumber spectra from the literature, as well as fields from high resolution simulations of turbulence will be converted to frequency spectra that would be observed if the eddies were advected past a fixed location sensor by waves and a current. Preliminary idealized simulations of 1D advection of isotropic turbulence and anisotropic boundary-layer turbulence by monochromatic waves provide a framework for synthesizing the proposed simulations, as well as measurements and methods in the literature, in terms of important dimensionless parameters that relate advection of turbulence by waves to advection by currents. Idealized simulations will be extended to 2D (horizontal and vertical advection by waves) and 3D (waves propagating at an angle to the current), and to narrow- and broad-banded wave conditions typical of those on the inner shelf. Simulation results will be compared with existing laboratory and field measurements collected previously by the PI to assess the validity of model spectra (which were developed for turbulence in steady flows) for turbulence beneath waves, potentially providing new insights into wave-current boundary layers. The results of idealized simulations, along with the existing laboratory and field measurements, will be used to develop new tools that employ spectral fitting to estimate turbulence parameters and their uncertainties from fixed sensor measurements when wave orbital velocities exceed currents.Broader ImpactsThere has been much interest recently in measuring turbulent momentum and scalar fluxes beneath surface waves using fixed location sensors; however, these measurements can be difficult to interpret. The proposed work will improve understanding of the issues involved with making turbulence measurements beneath waves when wave orbital velocities exceed currents, and develop methods for estimating turbulence parameters and their uncertainties in these conditions that will be valuable to scientists studying the physics and chemistry of a range of shallow water environments. The synthesis of previous work in the context of idealized simulations will help guide the analysis of turbulence measurements from fixed sensors in wavy environments. A library of idealized simulation results, available on a website, will allow scientists to put their measurements in the context of a broad parameter space without repeating the simulations themselves. Matlab scripts for performing idealized simulations and applying new methods developed in this study will also be made available on the project website. This grant will provide salary support and a computer workstation for one early career scientist.