Physical and Computational Concepts for Systematic Development of Drag Reducing Surfaces in Pipes

PI：禤浩焯，罗纳德提案编号：1335731拟议研究的主要目标是研究管流中湍流旋涡的结构，以开发适合于大型工程系统(如美国国家管网)实施的被动减阻面。尽管已经尝试了许多减阻策略来减少表面湍流引起的壁面摩擦，但很难找到一套明确的、无可争辩的原则来解释如何设计表面来减少表面摩擦阻力。已经成功的表面，如肋骨，是通过试验和错误的方法结合壁面湍流的最简单方面的知识来设计的，或者是通过仿生的方法复制生命形式使用的方法，如鲨鱼皮。然而，过去十年在理解造成摩擦应力的相干结构方面取得的进展，现在使人们有可能在触手可及的范围内采用系统的方法来减少阻力。在管流中过渡到湍流的问题是一个特别令人烦恼的问题，一个多世纪以来一直悬而未决。这些问题的答案似乎对减阻机构的发明至关重要，或者至少是非常有价值的，减阻机构通过抑制湍流的形成或减弱其强度来运作。其具体目标是研究雷诺数远高于较低临界值时管流向湍流的转变；研究导致加速湍流重新分层的涡流机制；以及发展大涡模拟方法，能够高保真地揭示高雷诺数时减阻面的影响。了解管流中湍流的起源将指导减阻剂的设计工作。解释重新分层流动行为背后的涡流机制将测试目前壁面湍流的物理模型，如发夹模型，并提供对一种形式的湍流行为的见解，以减少阻力。探索奇异摄动方法，用完全可分辨的近壁物理模拟高雷诺数流动的模型，可以提高我们模拟和模拟表面湍流的能力，包括复杂的减阻模式。克服动荡的摩擦消耗了美国国家能源预算中令人惊讶的一大部分。在美国全境输送石油和天然气的管道系统需要每年大约1新台币的能源支出的3%来泵送流体，相当于每年约300B美元，以克服管道中湍流造成的流动阻力。

PI: Adrian, Ronald Proposal Number: 1335731 The broad goal of the proposed research is to investigate the structure of turbulence eddies in pipe flows for the purpose of developing passive drag reducing surfaces suitable for implementation in large-scale engineering systems such as the U. S. national network of pipelines. Despite the many drag reducing strategies that have been tried to reduce wall friction caused by turbulent flow over surfaces, it is difficult to find any clear, undisputed set of principles that explains how one should design surfaces to reduce skin friction drag. The surfaces that have been successful, such as riblets, have been devised by trial and error methods coupled with the knowledge of the simplest aspects of wall turbulence, or by bio-mimetic approaches that copy methods used by life forms such as shark skin. However, progress over the past decade in understanding the coherent structures responsible for creating friction stresses now brings the possibility of a systematic approach to drag reduction within reach. The matter of transition to turbulent flow in pipe flow is an especially vexing question that has remained open for more that a century. The answers to these questions seem likely to be essential, or at the least very valuable, to the invention of drag reducing agencies that operate by inhibiting the formation of turbulence or diminishing its strength. The specific goals are to investigate the transition to turbulence in pipe flow at Reynolds numbers well above the lower critical value; to investigate the eddy mechanisms leading to re-laminarization of accelerating turbulent flows; and to develop large eddy simulation methods capable of revealing, with high fidelity, the effects of drag reducing surfaces at high Reynolds numbers.Intellectual Merit :The transition to turbulence in pipe flow is one of the longest standing mysteries in fluid mechanics. Understanding the origins of turbulence in pipe flow will guide efforts to design drag reducing agents. Explaining the eddy mechanisms underlying the behavior of relaminarizing flow will test current physical models of wall turbulence such as the hairpin packet paradigm, and also provide insights into a form of turbulence behavior that reduces drag. Exploring singular perturbation methods for devising models for simulating high Reynolds number flow with fully resolved near-wall physics may improve our ability to simulate and model turbulent flow over surfaces, including complex drag reducing patterns.Broader Impacts :Tools that will contribute to the eventual development of drag reducing methods for pipe flow would enable economically valuable energy savings. Overcoming turbulent friction consumes a surprisingly large fraction of the United States' national energy budget. The system of pipelines carrying oil and natural gas throughout the U. S. requires 3% of the roughly 1 T$ annual energy expenditure to pump the fluids, corresponding about 30B$ per annum to overcome the flow resistance due to turbulence in the pipes.