Sedimenting Particulate Suspensions in Viscoelastic Fluids Under Shear

1337051PI：Shaqfeh刚性颗粒在粘弹性流体中的悬浮液在许多能源应用、材料设计应用和消费品应用中发挥着关键作用。例如，在石油钻探中，所谓的钻井泥浆是一种非常粘稠的粘弹性流体，设计用于在钻井过程中剪切变稀，但在停钻时变稠，以便岩屑能够保持悬浮。在一种被称为水力压裂(用于刺激石油和天然气生产的操作)的相关应用中，被称为支撑剂的固体悬浮液被用来通过将它们泵入油井来支撑裂缝打开。支撑剂的高质量性能要求放置在裂缝的深处，要求在流动过程中支撑多余的固体重量。通常使用的支撑剂输送液体是一种瓜尔胶聚合物水溶液，与硼酸根离子瞬间交联，因此具有很高的弹性。众所周知，颗粒在粘弹性流体中的沉积可能与在牛顿流体中观察到的完全不同，特别是在剪切作用下。例如，在非牛顿流体中，复杂的流变性导致沉积和剪切流动之间的非线性耦合，这在牛顿液体中找不到，这对上述钻井和水力压裂液的功能至关重要。在相关材料的应用中，特别是在与硅晶片蚀刻相关的应用中，从表面上清除颗粒物质通常通过称为漂洗的后处理来完成。最新的研究表明，即使在相同的粘度下，粘弹性溶液也比牛顿溶液成为更有效的清洗剂。同样，在这一应用中，流动的剪切流体中的弹性似乎以一种未知的方式变化，受重力作用的颗粒在与剪切流动方向垂直的方向上受到的力，从而产生了增强的提升力，以清洁表面。在这个项目中，研究小组将开发粘弹性流体中有限浓度颗粒悬浮的大规模计算机模拟。重点将集中在体力(即重力)作用下的颗粒以及垂直于重力的方向上的外加剪切流，目的是了解上述应用。计算机模拟将是独一无二的，它将非结构化的有限体积技术与弹性液体中的浸入边界技术相结合。在作者看来，这样的模拟是理解这些高度非平衡流动应用中的非线性物理，从而设计这些流体而不是根据历史先例开发它们的唯一已知方式。

1337051PI: ShaqfehSuspensions of rigid particles in viscoelastic fluids play key roles in many energy applications, materials design applications, and consumer product applications. For example, in oil drilling the so-called drilling mud is a very viscous, viscoelastic fluid designed to shear-thin during drilling, but thicken at stoppage so that the cuttings can remain suspended. In a related application known as hydraulic fracturing (an operation used to stimulate petroleum and gas production) suspensions of solids called proppant are used to prop open the fracture by pumping them into the well. Quality performance of the proppant demands placement deep into the fracture requiring that the excess weight of the solids be supported during the flow. A commonly used proppant-transport liquid is an aqueous guar polymer solution, transiently cross-linked with borate ion, such that it is highly elastic. It is well known that the sedimentation of particles in a viscoelastic fluid can be quite different from that which is observed in Newtonian fluids, especially under shear. For example, in a non-Newtonian liquid, the complex rheological properties induce a nonlinear coupling between the sedimentation and shear flow which is not found in Newtonian liquids and which is critical to the function of the aforementioned drilling and fracking fluids. In a related materials application, the cleaning of particulate matter from surfaces, particularly in applications associated with etching of silicon wafers is often done by a post processing known as rinse. Most recently, it has been shown that a viscoelastic solution becomes a far more effective rinse agent than a Newtonian solution, even at the same viscosity. Again, in this application, the elasticity in a flowing, sheared fluid seems to change, in a manner as yet unknown, the forces on particulates subject to gravity in directions orthogonal to the shear flow, creating thereby an enhanced lift force that cleans the surface. In this project, the research team will develop large scale, computer simulations of particle suspensions at finite concentration in viscoelastic fluids. The focus will be on particles acted on by a body force (i.e. gravity) as well as an applied shear flow in a direction orthogonal to gravity with the goal of understanding the applications described above. The computer simulations will be unique, first of their kind, combining unstructured, finite volume technology with immersed boundary techniques in elastic liquids. Such simulations are, in the authors view, the only known way to understand the nonlinear physics in these highly nonequilibrium flow applications and thus to engineer these fluids rather than develop them based on historical precedent.