CAREER: Coupled Roughness/Pressure-Gradient Effects and Reducing the Complexity of Highly-Irregular Roughness in Wall Turbulence

摘要CBET-0644640K。伊利诺伊大学厄巴纳-香槟分校克里斯滕森的理论价值：人们已经对典型的光滑壁湍流进行了多年的研究，现在对其基本结构有了一个相对清晰的图景。然而，这些努力对技术相关流动的直接适用性仍然是未知的，这种流动通常发生在复杂的几何形状中，并存在多种非正则影响，如强烈的压力梯度和高度不规则的表面粗糙度。PI计划通过处理两个关键主题来扩大他在高度不规则表面粗糙度领域的AFOSR研究，这两个主题是在存在非正则影响的情况下推进与技术相关的湍流建模、预测和控制的科学。这项工作的大部分工作将涉及在沉积和有利压力梯度(FPG)条件下涡轮机叶片的粗糙度复制的共同影响下的湍流边界层的研究。PI已经在动量厚度雷诺数为3900和11000的零压力梯度条件下进行了详细的粒子动力学测量。PI计划在具有FPG条件的光滑和粗糙的墙壁上进行类似的测量。这项计划中的工作将解决这两种影响之间的协同在过渡和完全粗糙区域中是否相似，以及壁面相似性在FPG条件下是否有效。第二个研究领域将涉及设计高度不规则表面粗糙度的拓扑模型，特别是从损坏的涡轮叶片复制，使用仅具有最高能量拓扑尺度的适当正交分解(POD)。使用PIV在湍流通道流中复制和测试模型拓扑的短提取，以评估它们再现在实际表面上观察到的流动特征的能力。了解最大的粗糙度与更细的表面拓扑学相比的重要性等问题，将为设计更具代表性的模拟粗糙度拓扑提供“指导方针”，也将有助于将过去的模拟粗糙度研究与实际粗糙度上的流动联系起来。更广泛的影响：拟议努力的结果将对改进实际工程流量的建模和控制产生直接影响，其中许多对社会有相当大的影响(例如，提高运输系统的燃油效率，以减少石油消耗)。将进行大部分研究的学生将通过伊利诺伊大学现有的项目(Surge、Merge等)从代表性不足的群体中积极招募。并将在动荡和高级诊断学领域接受异常强大的教育。这一职业奖项的教育部分包括开发研究生级别的微型流体力学课程，以及修订研究生级别的流体力学实验方法课程，以包括微型测量方法。国际工程学院还计划建立一个流体和热学的学生研讨会系列，以促进工程学院具有相似研究兴趣的研究生的成长和合作。

AbstractCBET-0644640K. Christensen, University of Illinois Urbana-ChampaignIntellectual merit: Canonical smooth-wall turbulence has been studied for many years and a relatively clear picture of its underlying structure now exists. However, the direct applicability of these efforts to technologically relevant flows, which often occur in complex geometries and in the presence of multiple noncanonical influences, like strong pressure gradients and highly-irregular surface roughness, is still unknown. The PI plans to expand his AFOSR research in the area of highly-irregular surface roughness by tackling two crucial topics central to advancing the science of modeling, predicting and controlling technologically-relevant turbulent flows in the presence of noncanonical influences. The majority of this effort will involve the study of turbulent boundary layers under the coupled influence of roughness replicated from turbine blades damaged by deposition and favorable-pressure-gradient (FPG) conditions. The PI has already made detailed PIV measurements under zero-pressure-gradient (ZPG) conditions at momentum thickness Reynolds numbers of 3900 and 11000. The PI plans to make similar measurements over smooth and rough walls with FPG conditions. This planned effort will address whether synergy between the two influences is similar in the transitionally- and fully-rough regimes and if wall similarity is valid under FPG conditions.A second research area will involve the design of topological models for highly-irregular surface roughness, specifically replicated from damaged turbine blades, using proper orthogonal decomposition (POD) with only the most energetic topological scales. Short fetches of the model topologies will be replicated and tested in turbulent channel flow using PIV to assess their ability to reproduce the flow features observed over the actual surface. Understanding issues such as the importance of the largest roughness scales compared to the finer scales of the surface topology will provide "guidelines" for the design of more representative simulated roughness topologies and would also assist in relating past simulated roughness studies to flows over practical roughness. Broader Impacts: The results of the proposed effort will have a direct impact on improved modeling and control of practical engineering flows, many of which have considerable influence on society (increased fuel efficiency of transportation systems for reduced oil consumption, for example). The students who will perform the bulk of this research will be actively recruited from under-represented groups using established programs at the University of Illinois (SURGE, MERGE, etc.) and will receive an exceptionally strong education in the areas of turbulence and advanced diagnostics. The educational component of this CAREER award includes the development of a graduate-level microscale fluid mechanics course and the revision of a graduate-level experimental methods of fluid mechanics course to include microscale measurement methods. The PI also plans to establish a student seminar series in fluid and thermal science to foster the growth of and collaboration amongst graduate students in the College of Engineering with similar research interests.