Collaborative Research: Understanding pressure drop-flow rate relationships in inertialess viscoelastic flows: effects of flow instability and stress-conformation hysteresis

合作研究：了解无惯性粘弹性流中的压降-流速关系：流动不稳定性和应力构象滞后的影响

• 批准号: 0755269
• 负责人: Bamin Khomami
• 金额: $ 19.11万
• 依托单位: University of Tennessee Knoxville
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-15 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0755269&HistoricalAwards=false
• 关键词: Collaborative; Research; Understanding; pressure; drop

CBET-0755269KhomamiOne principal output of fluid mechanics research is the quantitative understanding of the relationship between flow rate and pressure drops (power requirements). While such relationships are well understood from first principles for Newtonian flows, it is hardly the case for viscoelastic, polymeric flows. Significant advances in this area will undoubtedly have pronounced impact on knowledge-based design of polymer processing operations and polymer-based products that constitute a significant portion of the U.S. manufacturing economy. The central goal of this research is the development of a quantitative understanding of the flow-microstructure coupling mechanisms in viscoelastic polymer solutions that in turn determine their friction drag behavior under conditions of negligible inertia. Specifically, the PIs plan a highly integrated research program that will leverage from recently developed multiscale (micro-macro) and continuum-level computational tools within the PIs' groups to investigate the intriguing phenomenon of friction resistance enhancement (FRE), where the pressure drop increases abruptly as the flow rate of a viscoelastic polymer solution through variable conduit, exceeds a critical value. Depending on the flow geometry, this pressure drop saturates at a value that greatly exceeds that for a Newtonian liquid of identical viscosity. While FRE has been known experimentally since the 1960s, it has not been explained based on first principles primarily due to the computational bottlenecks associated with the simulation of multi-dimensional and/or time-dependent viscoelastic flows using realistic models. Two hypotheses have been put forward to explain FRE, namely stress-conformation hysteresis (attributed to the inherent asymmetry in molecular unraveling and relaxation when an elastic polymer solution is subjected to contraction/expansion) and nonlinear flow transitions caused by a series of purely elastic flow instabilities. Both will be put to rigorous test in these studies. This study will develop much needed large-scale multiscale or 'micro-macro' simulations, integrating continuum-level finite element or spectral solvers with fast integrators of stochastic differential equations to describe the evolution of polymer configuration. This will require efficient parallel algorithms to track nonlinear flow transitions in inertialess, viscoelastic flows and their use to understand the effect of elastically-induced flow modifications on friction drag. The two PIs share complementary expertise and are ideally placed to undertake these efforts. NSF-supported TLSAMP, Pipeline Engineering Diversity Program and GEM will be used to ensure participation of African-American, Hispanic-American, Native-American and female students. Internet-ready instruction modules will be developed for enhancing curriculum in the broader areas of complex fluids, scientific computing and within an existing NSF-REU program that focuses on complex fluids dynamics. The PIs will also use the extensive outreach infrastructure at their respective institutions to involve K-12 teachers and high school students in the research program.

CBET-0755269Khomami 流体力学研究的一个主要成果是对流量和压降（功率需求）之间关系的定量理解。虽然从牛顿流的第一原理中可以很好地理解这种关系，但对于粘弹性聚合物流来说却很难理解。这一领域的重大进步无疑将对聚合物加工操作和基于聚合物的产品的基于知识的设计产生显着影响，这些产品构成了美国制造业经济的重要组成部分。这项研究的中心目标是定量理解粘弹性聚合物溶液中的流动-微观结构耦合机制，进而决定其在惯性可忽略不计的条件下的摩擦阻力行为。具体来说，PI 计划了一个高度集成的研究项目，该项目将利用 PI 小组内最近开发的多尺度（微观-宏观）和连续体级计算工具来研究摩擦阻力增强 (FRE) 的有趣现象，其中压力下降当粘弹性聚合物溶液通过可变导管的流速超过临界值时突然增加。根据流动几何形状，该压降的饱和值大大超过相同粘度的牛顿液体的压降。虽然 FRE 自 20 世纪 60 年代以来就已通过实验为人所知，但它尚未根据第一原理进行解释，这主要是由于与使用现实模型模拟多维和/或瞬态粘弹性流相关的计算瓶颈。人们提出了两个假设来解释FRE，即应力构象滞后（归因于弹性聚合物溶液收缩/膨胀时分子解开和松弛的固有不对称性）和由一系列纯弹性流动引起的非线性流动转变不稳定。两者都将在这些研究中接受严格的测试。这项研究将开发急需的大规模多尺度或“微观-宏观”模拟，将连续体级有限元或谱求解器与随机微分方程的快速积分器相集成，以描述聚合物构型的演变。这将需要高效的并行算法来跟踪无惯性粘弹性流中的非线性流动转变，并使用它们来了解弹性引起的流动修改对摩擦阻力的影响。两位 PI 拥有互补的专业知识，并且非常适合开展这些工作。 NSF 支持的 TLSAMP、管道工程多样性计划和 GEM 将用于确保非裔美国人、西班牙裔美国人、美国原住民和女学生的参与。 将开发可上网的教学模块，以增强复杂流体、科学计算等更广泛领域的课程，以及现有 NSF-REU 项目（重点关注复杂流体动力学）的课程。 PI 还将利用各自机构广泛的外展基础设施，让 K-12 教师和高中生参与研究项目。