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

CBET-0754812概述流体力学研究的一个主要成果是对流量和压降（功率要求）之间关系的定量理解。虽然这样的关系是很好地理解牛顿流体的第一原理，这是很难的情况下，粘弹性，聚合物流的研究，在这项合作研究。这一领域的重大进展无疑将对构成美国制造业经济重要组成部分的聚合物加工操作和聚合物基产品的基于知识的设计产生显著影响。本研究的中心目标是发展的粘弹性聚合物溶液，反过来又决定其摩擦阻力行为的条件下，可以忽略不计的惯性的流动-微观结构耦合机制的定量理解。具体来说，PI计划一个高度集成的研究计划，将利用最近开发的多尺度（微观宏观）和连续级计算工具内的PI？研究组研究了摩擦阻力增强（FRE）的有趣现象，其中当粘弹性聚合物溶液通过可变管道的流速超过临界值时，压降突然增加。取决于流动几何形状，该压降饱和的值大大超过相同粘度的牛顿液体。虽然自20世纪60年代以来，FRE已被实验所知，但它尚未基于第一原理进行解释，这主要是由于与使用现实模型模拟多维和/或时间相关的粘弹性流动相关联的计算瓶颈。已经提出了两个假设来解释FRE，即应力-构象滞后（归因于当弹性聚合物溶液进行收缩/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不稳定性引起的非线性流动转变。两者都将在这些研究中受到严格的检验。本研究将开发急需的大规模多尺度或“微观-宏观”模拟，将连续级有限元或光谱求解器与随机微分方程的快速积分器集成，以描述聚合物构型的演变。这将需要有效的并行算法来跟踪非线性流动过渡的惯性，粘弹性流和它们的使用，以了解弹性引起的流动修改摩擦阻力的影响。这两个项目负责人拥有互补的专门知识，是开展这些工作的理想场所。NSF支持的TLSAMP，管道工程多样性计划和GEM将用于确保非洲裔美国人，西班牙裔美国人，美国土著人和女学生的参与。 将开发互联网就绪的教学模块，以加强复杂流体、科学计算等更广泛领域的课程，并在现有的NSF-REU计划中重点关注复杂流体动力学。PI还将利用各自机构的广泛外展基础设施，让K-12教师和高中学生参与研究计划。

CBET-0754812SureshkumarOne 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 as studied in this collaborative study. 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.