Rheology and fluid dynamics of surfactant solutions with flow-induced structure

表面活性剂是由水溶性的头部和排斥水的油性尾部组成的分子。由于这种双重性质，溶解在水中的表面活性剂形成称为胶束的组合体，其中油性尾部形成中心，与周围的水分子通过水偏好的头部基团分开。胶束表面活性剂溶液用于从石油和天然气工业中的压裂液到化学加工工业中的传热液到各种个人护理和清洁产品的广泛应用。在流动过程中，形成细长的“蠕虫状”胶束的表面活性剂溶液经历一个过程，其中单个胶束联合收割机结合形成大得多的集合体。这些被称为流动诱导结构，并可能对溶液的流动特性产生显著影响。这些结构在蠕虫状胶束溶液的湍流中形成，导致用于泵送流体的能量成本的显著降低。尽管这些所谓的减阻表面活性剂体系的应用越来越频繁，但这种结构形成现象仍然知之甚少。 这项工作将推进预测蠕虫状胶束溶液流动行为的数学模型的发展，并使用这些模型来理解为什么它们在降低流动过程中的能耗方面如此有效。 该项目还将包括一个重要的外联部分：在服务研习课程中，工程系本科生将开发基于项目的流体力学课程，然后去男孩和女孩俱乐部与来自服务不足的少数民族人口的孩子分享这些课程。该项目的长期目标是（1）开发自我模型，组装复杂的流体，如胶束溶液，其在流体动力学分析中可计算处理，以及（2）使用这些模型来生成对这类流体在工程应用的流动特性中的行为的洞察和预测。这项工作将进一步发展最近提出的微观力学本构模型称为反应杆模型，把它更坚实的物理基础，并进行广泛的比较实验数据。它还将分析在一个圆形的Couette装置，其中许多有趣的功能的表面活性剂溶液中的流动诱导结构的流体的流动。最后，它将阐明湍流之间的相互作用，流动诱导的结构和减阻使用模型的计算。将与聚合物溶液的结果进行比较，以揭示聚合物和表面活性剂溶液中湍流减阻之间的差异。此外，还将模拟结果与实验观察到的表面活性剂溶液湍流特征进行比较。流动诱导结构的形成在复杂流体中很普遍，这项工作迈出了分析这些材料的流体动力学的第一步，从而对它们迷人行为的起源和后果有了新的见解。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Surfactants are molecules comprised of a head that is water soluble bonded to an oily tail that repels water. Because of this dual nature, surfactants dissolved in water form assemblages called micelles, in which the oily tails form the center, separated from the surrounding water molecules by the water-preferring head groups. Micellar surfactant solutions are used in a wide range of applications from fracking fluids in the oil and gas industry to heat-transfer fluids in the chemical process industries to various personal care and cleaning products. During flow, surfactant solutions that form long thin "wormlike" micelles undergo a process where individual micelles combine to form much larger assemblages. These are called flow-induced structures and can have dramatic effects on the flow properties of the solution. These structures form in turbulent flow of wormlike micelle solutions leading to substantial reduction in the energy cost for pumping the fluid. Despite the increasingly frequent application of these so-called drag-reducing surfactant systems, this structure-formation phenomenon remains poorly understood. This work will advance the development of mathematical models for predicting the flow behavior of wormlike micelle solutions and use these models to understand why they are so effective in reducing energy consumption in flow processes. The project will also involve a substantial outreach component: in a service-learning course, undergraduate engineering students will develop project-based lessons in fluid mechanics and then go out to the Boys and Girls Clubs to share these with kids from underserved minority populations.The long-term aim underlying this project is (1) development of models for self-assembling complex fluids like micellar solutions that areas computationally tractable for fluid dynamics analyses, and (2) use of these models to generate insights and predictions into the behavior of this class of fluids in flows characteristic of engineering applications. The work will further develop a recently-proposed micromechanical constitutive model called the reactive rod model, putting it firmer physical ground and making extensive comparisons to experimental data. It will also analyze the flow of an structure-forming fluid in a circular Couette device, where many of the interesting features of flow-induced structure in surfactant solutions have been studied experimentally. Finally, it will elucidate the interaction between turbulence, flow-induced structure and drag reduction using computations with the model. Comparisons with results for polymer solutions will be made, to uncover differences between turbulent drag reduction in polymer and surfactant solutions. Furthermore, comparisons of simulation results with experimentally observed features of turbulence in surfactant solutions will be made. Flow-induced structure formation is widespread in complex fluids and this work takes first steps into analysis of the fluid dynamics of these materials and thus toward new insights into the origins and consequences of their fascinating behavior.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.