Simulation and Modeling of the Decay of Anisotropic Turbulence

大量的工业和环境过程涉及其运动是湍流的流体。 该项目涉及这些混沌，不稳定和三维流体运动的准确统计预测和建模。 重点是模拟和建模的湍流返回到各向同性的过程，这在过去一直抵制建模的努力。返回到各向同性的过程显着影响近壁湍流，管道流动，大气和海洋的热量和质量传递过程，如CO2吸收，热交换器的性能，翼尖涡，和主机的重要和目前很难模拟湍流的情况。关于结构的信息（即底层涡旋的形状）被假设为控制返回各向同性过程。 为了确定由于结构的贡献，大区域直接数值模拟（DNS）的返回各向同性均匀各向异性湍流。 各向异性是由五个基本不同的平均应变和壁产生的。 每一种都会产生非常不同的湍流结构。 将表征雷诺数、初始长度尺度和初始结构（通过两点相关性参数化）对返回各向同性过程的影响，并用于校准定向涡流湍流模型。 定向涡流碰撞模型在开源CFD程序OpenFoam中实现，使其易于为科学界所用。 这种开源实现将允许其他人在他们选择的任何复杂配置中快速测试模型的准确性。智力价值：这项工作将显着提高我们目前的理解湍流结构如何影响其非线性演化。 预计定向涡碰撞模型将是第一个能够准确预测各种不同情况下返回各向同性过程的湍流模型。 此外，本文的工作也将为其他包含湍流结构的湍流模型提供重要的参考。 更广泛的影响： 湍流模型是大多数计算流体动力学（CFD）模拟的必要组成部分。 具有定量预测精度的模型可以从根本上改变CFD作为设计和预测工具的实用性。该项目将为这一领域的研究人员提供一个由规范湍流组成的高质量数据库。 该项目中的一些超级计算任务可以并且将由本科研究人员在针对女性和少数民族的夏季REU体验期间执行。 这项工作将通过我们的地方公共广播附属机构WFCR向公众传播。

A very large number of industrial and environmental processes involve fluids whose motion is turbulent. This project involves the accurate statistical prediction and modeling of these chaotic, unsteady, and three-dimensional fluid motions. The focus is on simulating and then modeling the turbulent return-to-isotropy process which has resisted modeling efforts in the past.The return-to-isotropy process significantly influences near wall turbulence, duct flows, atmospheric and oceanic heat and mass transfer processes like CO2 absorption, heat exchanger performance, wing tip vortices, and a host of important and currently poorly modeled turbulent flow situations. Information about the structure (i.e. the shape of the underlying eddies) is hypothesized to control the return-to-isotropy process. In order to determine the contribution due to structure, large domain direct numerical simulations (DNS) of return-to-isotropy in homogeneous anisotropic turbulence are performed. Anisotropy is generated by five fundamentally different mean strains and by walls. Each produces very different turbulent structures. The influence on the return-to-isotropy process of the Reynolds number, initial length scale, and initial structure (parameterized by the two-point correlations) will be characterized and used to calibrate the oriented-eddy turbulence model. The oriented-eddy collision model is implemented in the open source CFD program, OpenFoam making it easily available to the scientific community. This open source implementation will allow others to rapidly test the accuracy of the model in any complex configuration of their choosing. Intellectual Merit: This work will significantly enhance our current understanding of how turbulence structure influences its nonlinear evolution. It is anticipated that the oriented-eddy collision model will be the first turbulence model capable of predicting the return-to-isotropy process accurately for a wide variety of different scenarios. In addition, this work will provide critical information for other turbulence models which incorporate turbulence structure. Broader Impacts: Turbulence models are a necessary component of most computational fluid dynamics (CFD) simulations. Models with quantitative predictive accuracy could radically transform the utility of CFD as a design and prediction tool. This project will provide researchers in this field with a high quality database consisting of canonical turbulent flows. Some of the supercomputing tasks in this project can, and will, be performed by undergraduate researchers during summer REU experiences that target women and minorities. This work will be disseminated to the general public via WFCR, our local public radio affiliate.