Bulk Turbulence in Polymer Solutions: Beyond Friction Drag Reduction

主要研究者：Ouellette，Nicholas提案编号：1436423拟议研究的目标是探索在湍流中加入聚合物的影响。 当少量的添加剂，包括长链聚合物，表面活性剂或微气泡，被添加到湍流中时，流动的结构和动力学可能会发生显着变化。添加剂最著名的作用是减少表面摩擦阻力：少量的聚合物或表面活性剂可以减少湍流壁面流动中的阻力高达80%。经过多年的研究，科学界开始就这种减阻的基本物理学达成共识。然而，表面摩擦力仅仅是浸没在流体中的船舶或其他物体所经历的总流体阻力的一部分。边界层的分离和湍流尾流的动力学导致能量损失，该能量损失经常支配物体上的摩擦损失。了解添加剂如何影响这些其他类型的阻力，需要研究在添加剂存在的情况下，远离任何壁的整体湍流的变化。虽然它是已知的，整体湍流的变化与添加剂，目前的模型不能解释实验观察。这里提出的研究将通过详细的实验测量聚合物溶液中的整体湍流来解决这个差距。在教育和推广方面，将为本科生实验班开发一个基于非牛顿湍流的新模块。此外，PI还将制作有关研究成果的电影，在校内咖啡厅和YouTube上展示，并将通过当地的科学展计划参与K-12推广活动。该项目的主要目标是了解聚合物对湍流动力学的修改的哪些方面取决于壁的存在，哪些方面更具有普遍性。为了解决这个问题，能量注入，规模到规模的转移，和耗散率将被测量为聚合物浓度的函数，并修改湍流的衰减将进行研究。此外，将测量的空间结构的流动，以测试的共同假设，即聚合物相互作用，并抑制小尺度涡。实验测量将在拉格朗日框架中进行，使用拉格朗日粒子跟踪，其中使用多相机立体成像设置来跟踪小示踪粒子在三维和时间上的运动，因为它们被流平流。

PI: Ouellette, NicholasProposal Number: 1436423The goal of the proposed research is to explore the effects of adding polymers in the bulk of turbulent flows. When small amounts of additives, including long-chain polymers, surfactants, or microbubbles, are added to a turbulent flow, the structure and dynamics of the flow can change dramatically. The most celebrated effect of additives is skin-friction drag reduction: tiny amounts of polymers or surfactants can reduce the drag in a turbulent wall-bounded flow by up to 80%. After years of research, the scientific community is beginning to reach consensus on the fundamental physics of this drag reduction. Skin friction, however, is only a part of the total fluid drag experienced by ships or other objects immersed in a fluid. Separation of the boundary layer and the dynamics of turbulent wakes lead to energy losses that frequently dominate the frictional losses over the object. Understanding how additives affect these other types of drag requires the study of the modification of bulk turbulence, far from any walls, in the presence of additives. Although it is known that bulk turbulence does change with additives, current models cannot explain the experimental observations. The research proposed here will address this gap via detailed experimental measurements of bulk turbulence in polymer solutions. In terms of education and outreach, a new module for an undergraduate laboratory class based on non-Newtonian turbulence, will be developed. In addition, the PI will develop movies about the research results that will be displayed in an on-campus coffee shop and on YouTube, and will participate in K-12 outreach via a local science-fair program.The primary goal of the project is to understand what aspects of the modification of the turbulent dynamics by polymers is dependent on the presence of a wall, and what aspects are more universal. To address this question, the rates of energy injection, scale-to-scale transfer, and dissipation will be measured as a function of polymer concentration, and modification to the decay of turbulence will be studied. In addition, measurements will be made of the spatial structure of the flow, in order to test the common hypothesis that polymers interact with and suppress small-scale vorticity. The experimental measurements will be made in the Lagrangian framework, using Lagrangian particle tracking, where a multicamera stereoimaging setup is used to follow the motion of small tracer particles in three dimensions and in time as they are advected by the flow.