Laminar to Turbulent Transition in Pipe Flow: Effect of Dispersed Phase

主要研究者：Longmire，Ellen提案编号：1605719所提出的研究的目标是在实验和理论上探索在管道中的两相流的情况下从层流到湍流的转变。虽然许多先前的工作已经完成了单相流体的过渡，这个建议的主题是在很大程度上未被探索。所提出的工作将产生影响的理解过渡到湍流的基本概念时，两个阶段中的一个是分散在其他。这项工作的技术应用是重要的，最显着的是在3D打印和增材制造的过程中。最近的管流实验表明，当液体流包括不混溶液滴或刚性颗粒的第二相时，过渡的临界雷诺数可以被转移到显着较低的值或延迟到更高的值。移动的方向取决于离散相的体积分数以及管道与颗粒直径的比率。这些转变背后的物理机制尚不清楚。拟议的研究的目的是通过实验和分析来揭示和表征这些机制。假设存在至少两种机制：较大的液滴或颗粒可以促进由颗粒与周围流体速度之间的局部差异引起的不稳定性，并且较小的液滴或颗粒可以抑制较大尺度不稳定性和相干结构的生长或以其他方式破坏较大尺度不稳定性和相干结构。实验计划在一个透明的管道设施，其中临界雷诺数将被确定为液体/液体和液体/固体分散体。结果将进行分析，以确定时间演变的流量功能，合奏平均统计，并与过渡流结构的动态显着模式，并最终影响过渡的具体机制。拟议的教育活动包括本科生和研究生参与研究，与小学教师合作制定科学课程，以及积极指导女高中生和女大学生的外联活动，以促进科学和工程。

PI: Longmire, EllenProposal Number: 1605719The goal of the proposed research is to experimentally and theoretically explore the transition from laminar to turbulent flow in the case of two phase flow in a pipe. While a lot of prior work has been done on transition for single phase fluids, the theme of this proposal is largely unexplored. The proposed work will have an impact on understanding the fundamental notions in transition to turbulence when one of the two phases is dispersed in the other. The technological applications of this work are important, most notably in the process of 3D printing and in additive manufacturing.Recent experiments on pipe flows suggest that the critical Reynolds number for transition can either be shifted to significantly lower values or delayed to much higher values when a liquid flow includes a second phase of immiscible liquid drops or rigid particles. The direction of the shift depends on the volume fraction of the discrete phase as well as the ratio of pipe-to-particle diameter. The physical mechanisms behind these transition changes are unknown. The objective of the proposed research is to uncover and characterize these mechanisms through experimentation and analysis. It is hypothesized that at least two mechanisms are present: larger drops or particles can promote instabilities caused by local differences between the particle and surrounding fluid velocity, and smaller drops or particles can suppress growth of or otherwise disrupt larger scale instabilities and coherent structures. Experiments are planned in a transparent pipe facility where critical Reynolds number will be determined for liquid/liquid and liquid/solid dispersions. Results will be analyzed to determine time evolving flow features, ensemble averaged statistics, and dynamically significant modes associated with transitional flow structures, and ultimately the specific mechanisms affecting transition. The educational activities proposed include undergraduate and graduate student involvement in research, engagement with elementary school teachers to develop science curriculum, and outreach activities ranging from actively mentoring female high school and college students to meetings of the PI with members of Congress in order to promote science and engineering.