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

abstractcbet - 0644640 k。学术价值：典型的光滑壁湍流已经被研究了很多年，现在它的底层结构已经有了一个相对清晰的图像。然而，这些努力对技术相关流动的直接适用性仍然未知，这些流动通常发生在复杂的几何形状中，并且存在多种非规范影响，如强压力梯度和高度不规则的表面粗糙度。PI计划通过解决两个关键主题来扩展他在高度不规则表面粗糙度领域的AFOSR研究，这些主题对推进建模、预测和控制存在非典型影响的技术相关湍流的科学至关重要。这项工作的大部分将涉及研究湍流边界层在由沉积和有利压力梯度（FPG）条件损伤的涡轮叶片复制的粗糙度的耦合影响下。PI已经在动量厚度雷诺数为3900和11000的零压力梯度（ZPG）条件下进行了详细的PIV测量。PI计划在FPG条件下对光滑和粗糙的壁面进行类似的测量。这项计划的工作将解决两种影响之间的协同作用在过渡和完全粗糙状态下是否相似，以及在FPG条件下壁面相似性是否有效。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中复制，使用适当的正交分解（POD），只有最具能量的拓扑尺度。模型拓扑的简短提取将在湍流通道流动中进行复制和测试，使用PIV来评估它们重现实际表面观察到的流动特征的能力。理解诸如与表面拓扑的细尺度相比，最大粗糙度尺度的重要性等问题，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的流动联系起来。更广泛的影响：所提议的努力的结果将对实际工程流程的改进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）。参与本项研究的学生将积极地从代表性不足的群体中招募，使用伊利诺伊大学已建立的项目（SURGE， MERGE等），并将在湍流和高级诊断领域接受特别强的教育。该职业奖的教育内容包括开发研究生水平的微尺度流体力学课程，以及修改研究生水平的流体力学实验方法课程，使其包括微尺度测量方法。学院亦计划举办流体及热科学系列学生研讨会，以促进工程学院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.