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

表面活性剂是一种分子，它的头部是水溶性的，尾部是油性的，可以排斥水。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，其中油性尾部形成中心，与周围的水分子通过亲水的头基团分离。胶束表面活性剂溶液广泛应用于石油和天然气工业的压裂液，化学加工工业的传热液以及各种个人护理和清洁产品。在流动过程中，表面活性剂溶液会形成细长的“虫状”胶束，在此过程中，单个胶束结合形成更大的胶束。这些被称为流动诱导结构，可以对溶液的流动特性产生巨大的影响。这些结构在蠕虫状胶束溶液的湍流中形成，从而大大降低了泵送流体的能量成本。尽管这些所谓的减阻表面活性剂体系的应用越来越频繁，但对这种结构-形成现象的了解仍然很少。这项工作将促进预测虫状胶束溶液流动行为的数学模型的发展，并利用这些模型来理解为什么它们在减少流动过程中的能量消耗方面如此有效。该项目还将包括大量的外展内容：在服务学习课程中，本科工程专业学生将开发基于项目的流体力学课程，然后到男孩女孩俱乐部与来自服务不足的少数民族的孩子分享这些课程。该项目的长期目标是：(1)开发自组装复杂流体（如胶束溶液）的模型，这些模型在计算上易于进行流体动力学分析；(2)利用这些模型对这类流体在工程应用中流动特性的行为产生见解和预测。这项工作将进一步发展最近提出的微力学本构模型，称为反应棒模型，为其奠定更坚实的物理基础，并与实验数据进行广泛的比较。它还将分析形成结构的流体在圆形Couette装置中的流动，其中许多表面活性剂溶液中流动诱导结构的有趣特征已经在实验中进行了研究。最后，通过模型计算，阐明湍流、流致结构和减阻之间的相互作用。将与聚合物溶液的结果进行比较，以揭示聚合物溶液和表面活性剂溶液中湍流阻力减少的差异。此外，将模拟结果与实验观察到的表面活性剂溶液中的湍流特征进行比较。流动诱导的结构形成在复杂流体中很普遍，这项工作为分析这些材料的流体动力学迈出了第一步，从而对其迷人行为的起源和后果有了新的认识。该奖项反映了美国国家科学基金会的法定使命，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.