Investigation of the effects of turbulent flow on energy and mass transfer close to solid surfaces

湍流是工业和环境中最常见的流体流动类型，也是物理学中尚未解决的问题之一。它混合和分散能量或质量（如化学物质或颗粒）的能力在日常应用中起着关键作用，如石油和天然气管道中的流动，工业反应堆中的流动，混合，加热或冷却，以及大气和海洋中的流动。该项目的目标是利用先进的计算技术了解湍流中通常观察到的流动特征对能量和质量输运的影响。这项研究的结果可能会导致有效的能源管理，有效的设计工业设备的传热和传质发生，以及更好的预测和控制污染物扩散。通过该项目产生的数据库将提供给科学界，通过该项目产生的模拟数据将用于开发可用于K-12科学演示的湍流弥散动画。发展综合湍流输运理论的中心问题是预测湍流粘度的空间变化，分子弥散对湍流输运的影响，以及相干速度结构对输运性质的影响。本文的主要假设是，从动量传递预测标量传递失败的原因是只有部分速度结构参与了壁面附近的湍流传递，而参与传递的尺度范围取决于分子的色散效应。要回答的主要问题是，在湍流输运中，超大尺度运动（称为VLSM）的作用是什么，以及分子扩散和对流之间的相互作用如何影响各向异性湍流中粒子的混合或分离。提出的方法是使用拉格朗日方法进行计算分析，它可以研究几个数量级的流体（例如，液态金属、气体、制冷剂和电化学流体），从而可以处理传统方法在当前超级计算机上通常不可行的情况。预期的结果可能导致紊流输送预测和控制的综合模型的发展。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Turbulence is the most common type of fluid flow in both the industry and the environment, while it is still one of the unsolved problems in physics. Its ability to mix and disperse energy or mass (like chemicals or particles) plays a key role in every day applications, like flows in oil and gas pipelines, in industrial reactors, in mixing, in heating or cooling, as well as in the atmosphere and in oceans. The goal of this project is to understand the effects of flow features that are commonly observed in turbulent flow on the transport of energy and mass using advanced computational techniques. The findings of this research could lead to efficient energy management, efficient design of industrial equipment where heat and mass transfer take place, and better prediction and control of pollutant dispersion. The database generated through this project will become available to the scientific community, and simulation data generated through this project will be used to develop animations of turbulent dispersion that can be used in K-12 science demonstrations.Central concerns for the development of a comprehensive turbulent transport theory have been the prediction of the spatial variation of turbulent viscosity, the effect of molecular dispersion on turbulent transport, and the effect of coherent velocity structures on the transport properties. The main hypothesis here is that the reason for the failure in predicting scalar transfer from momentum transfer is that only some of the velocity structures participate in turbulent transfer close to a wall, and the range of scales that participate in the transfer depends on molecular dispersion effects. Main questions to be answered are what is the role the very large scales of motion (known as VLSM) in turbulent transport, and how the interplay between molecular diffusion and convection affects mixing or separation of particles in anisotropic turbulence. The proposed approach is to use computations with Lagrangian methods for analysis, which afford the study of a range of fluids that span several orders of Prandtl number in magnitude (e.g., liquid metals, gases, refrigerants, and electrochemical fluids) making it possible to handle cases where conventional methods are often not feasible with the current supercomputers. Expected results could lead to the development of a comprehensive model for the prediction and control of turbulent transport.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.