Active turbulence from polymer additives: Theory, modeling and high fidelity simulations

复杂流体定义了在制药、食品、石油、生物工业中遇到的各种各样的流体。许多这些流体的流动方式挑战了工程师和科学家目前用于工程应用设计和优化以及理解物理现象的预测模型。例如，在液体中添加聚合物，这里感兴趣的复杂流体，可以减少管道中运输水或油时的阻力，但也可以增加微流体中的传热和混合。它可以在不可能形成乳液的条件下促进两种不混溶溶液之间的乳液形成，或者它可以控制喷雾中的液滴尺寸以改善农业灌溉或液体燃料喷射发动机中的燃烧。聚合物添加剂在上述一些应用中提供了很高的投资回报率，但是由于缺乏合理的理论理解，这些现象的建模或可预测性仍然很差。该项目的主要目标是开发高保真的预测计算模型，这将有利于处理复杂流体的大量行业。该项目还将包括一个教育部分，包括培训一名复杂流体动力学和数值模拟的研究生，以及开发用于湍流和计算流体动力学课程的开源工具。聚合物添加剂为研究复杂的能量传递提供了一个独特的窗口，涉及大尺度和小尺度之间，湍流和聚合物分子之间的直接和反向能量级联。聚合物添加剂已被确定为无惯性流中的弹性湍流、亚临界壁边界流中的弹性-惯性湍流和超临界壁边界流中的减阻直至称为最大减阻的渐近非层流状态的原因。这些国家都没有得到很好的理解。拟议的研究工作的目标是充分表征上述湍流状态的统计特性，研究在所有湍流状态下聚合物和流动之间的能量传递，以寻找普遍的特性，并利用该项目中获得的知识的累积总和，在非常低到大的雷诺数的非牛顿湍流的高保真度计算模型。用于支持该项目的数值模拟是为捕捉目标动力学而开发的最先进的粘弹直接数值模拟。该项目将创建一个独特而广泛的弹性和弹性惯性湍流数据库，该数据库将提供给科学界。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。

Complex fluids define a wide variety of fluids encountered in pharmaceutical, food, petroleum, biological industries. The manner in which many of these fluids flow challenges the predictive models currently used by engineers and scientists for the design and optimization of engineering applications and understanding of physical phenomena. For instance, the addition of polymers in a liquid, the complex fluid of interest here, can reduce drag when transporting water or oil in pipes, but also increase heat transfer and mixing in microfluidics. It can promote formation of emulsion between two immiscible solutions under conditions at which an emulsion is not otherwise possible, or it can control droplet sizes in spray to improve agricultural irrigation or combustion in liquid fuel injection engines. Polymer additives offer, and in some of the applications mentioned above, deliver large returns on investment, however the modeling or predictability of these phenomena remains poor owing to the absence of sound theoretical understanding. The main objective of this project is to develop high-fidelity predictive computational models that will benefit a large range of industries dealing with complex fluids. The project will also have an education component, encompassing training of a graduate student in complex fluid dynamics and numerical simulation, and the development of open-source tools used in turbulence and computational fluid dynamics courses.Polymer additives offer a unique window of investigation into complex energy transfers involving direct and inverse energy cascades between large and small scales, between turbulence and polymer molecules. Polymer additives have been identified as responsible for elastic turbulence in inertialess flows, elasto-inertial turbulence in subcritical wall-bounded flows and drag reduction in supercritical wall-bounded flows up to an asymptotic, non-laminar state called maximum drag reduction. None of these states are well understood. The objectives of the proposed research effort are to fully characterize the statistical properties of the above mentioned turbulent states, to investigate the energy transfer between polymers and flows in all turbulent states in search for universal properties and to leverage the cumulative sum of knowledge acquired within this project into high fidelity computational models of non-Newtonian turbulent flows at very low to large Reynolds numbers. The numerical simulations used to support this project are state-of-the-art viscoelastic direct numerical simulations developed to capture the targeted dynamics. This project will create a unique and extensive database of elastic and elasto-inertial turbulent flows which will be made available to the scientific community.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.