Turbulent Drag Reduction in Polymer Solutions: Studies of the Interaction of Viscoelasticity and Exact Coherent States

项目编号：CTS-0328325主要研究人员：迈克尔·D·格拉哈明斯：威斯康辛大学聚合物溶液中的减阻：粘弹性和精确相干态相互作用的研究通过添加少量非常大的聚合物分子，可以显著降低快速泵送液体所需的能量。这种“流变性减阻”现象已被广泛应用于减少管道中的能量损失，促进了减少船舶上方阻力的研究，最近还因其有可能显著提高所谓的区域供暖和冷却系统的效率而受到关注。在区域供暖和冷却系统中，冷水或热水在中心位置产生，并被泵送到周围地区的建筑中。然而，尽管它目前和潜在的广泛应用，这种现象背后的基本机制仍然不清楚。这项研究建立在最近发现的“精确相干态”--行波流动模式的基础上，这种流动模式是固体表面附近湍流有组织的流体运动的基础。这些有组织的运动或“相干结构”与流体所消耗的能量密切相关，因此精确的相干状态为更好地理解流变减阻提供了一个自然的起点。利用基于分子的聚合物溶液流动数学模型的计算，将阐明聚合物对这些状态的影响，并与实验观察到的结果进行比较。特别令人感兴趣的是所谓的最大减阻渐近线的起源，即通过实验观察到的聚合物添加剂可以实现的减阻量的上限。这项研究将提供多个层次的教育机会。参与的研究生将获得一个独特的多学科视角，结合聚合物物理、流变学、流体动力学和非线性动力学。本科生将参与一个涉及在大规模流动系统中实施减阻流体的实际问题的项目。通过这项研究获得的知识将导致合理设计流体和流动系统的原则，以最大限度地利用减阻添加剂。更广泛地说，这项研究将有助于深入了解湍流的相干结构，从而开发出节能的流量控制策略。

ABSTRACTPROPOSAL NO.: CTS-0328325PRINCIPAL INVESTIGATORS: MICHAEL D. GRAHAMINSTITUTION: UNIVERSITY OF WISCONSINTURBULENT DRAG REDUCTION IN POLYMER SOLUTIONS: STUDIES OF THE INTERACTION OF VISCOELASTICITY AND EXACT COHERENT STATESThe energy required to rapidly pump a liquid can be dramatically reduced by addition of a small quantity of very large polymer molecules. This "rheological drag reduction" phenomenon has found widespread application in reduction of energy losses in pipelines, has spurred research into reducing drag over ships and has recently gained attention for its potential to dramatically improve efficiency of so-called district heating and cooling systems, in which chilled or heated water is generated at a central location and pumped to buildings in the surrounding area. Despite its widespread current and potential applications, however, the fundamental mechanisms underlying this phenomenon remain unclear. This study builds on the recent discovery of "exact coherent states" -- traveling wave flow patterns that underlie the organized fluid motions of turbulence near solid surfaces. These organized motions, or "coherent structures" are closely associated with the energy consumed by the flow, so the exact coherent states provide a natural starting point for better understanding rheological drag reduction. Using computations with molecularly based mathematical models of the flow of polymer solutions, the effect of polymer on these states will be elucidated and compared with those observed experimentally. Of particular interest is the origin of the so-called "maximum drag reduction asymptote", the experimentally observed upper limit on the amount of drag reduction that can be achieved with polymer additives. This study will provide educational opportunities at a number of levels. The graduate students involved will gain a unique multidisciplinary perspective, combining polymer physics, rheology, fluid dynamics and nonlinear dynamics. Undergraduate students will participate in a project involving practical issues of implementing drag-reducing fluids in a large-scale flow system. The knowledge gained under this study will lead to principles for rational design of both fluids and flow systems to best take advantage of drag-reducing additives. More broadly, the study will enable development of energy saving flow control strategies by contributing to a firm understanding of the coherent structures of turbulence.