Energy conservation in turbulent flows of complex and simple fluids: mechanisms and new approaches

复杂和简单流体湍流中的能量守恒：机制和新方法

• 批准号: RGPIN-2014-04903
• 负责人: Xi, Li
• 金额: $ 1.82万
• 依托单位: McMaster University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=707944
• 关键词: Energy; conservation; turbulent; flows; complex

When flow in a pipe or channel transitions from the laminar state to turbulence, its friction drag increases abruptly: i.e., energy dissipation is much higher in the latter. Turbulence, meanwhile, is ubiquitous in engineering applications; common examples include pipeline oil transferring, district heating/cooling systems, and the propulsion of ships, airplanes and vehicles. Techniques for turbulent drag reduction (DR) can therefore bring about massive benefit both economically (lower cost) and environmentally (less consumption of natural resources and less greenhouse gas emissions). Substantial DR - up to 80% - can be achieved by simply dissolving polymer additives into the fluid. Although polymers are not always permissible in practical applications, understanding of their DR effect will inspire new designs of flow-control techniques for reaching comparable levels of energy saving in simple fluids (without polymers). The most prominent problem in this area is the so-called maximum drag reduction (MDR): a universal asymptotic limit that bounds the level of DR reached by all different polymer solutions. Despite decades of research, MDR has remained the most important unsolved problem in the area of viscoelastic turbulence. Revealing its mechanism is not only of great fundamental interest, a clear picture of the dynamics in polymer solutions near the MDR regime is also pivotal for future developments in DR techniques in general. The proposed program focuses on the numerical computation of DR in turbulence, with a short-term goal set at the mechanism of MDR. The approaches we will take are inspired by a new conceptual framework proposed in our recent studies of simplified model flows. In addition to introducing a distinct perspective to MDR research, the framework also offers consistent explanations for all qualitative observations about MDR, showing great promise of guiding future research. Building on this progress, our plan divides into two directions: one aims at constructing a mechanistic depiction of MDR dynamics; the other focuses on validating our physical understanding in turbulence at realistic scales. Progress along this path will prepare us for our long-term goal: developing next-generation techniques for high levels of DR in simple Newtonian fluids. Polymers are insoluble, prohibited or undesirable in many situations; techniques for DR in simple fluids can thus reach a much broader range of applications. The level of energy saving achieved by existing techniques of such kind is however much lower than that of polymers. With better understanding of polymeric turbulence near MDR, new approaches can be envisioned in which the role of polymers is imitated so that turbulent dynamics can be tethered to MDR in the absence of these additives. Finally, the program is also designed with the training of highly qualified personnel (HQP) in mind. The proposed research breaks down into several projects for multiple students at both the graduate and undergraduate levels. Students working on these projects will build a solid background in fluid dynamics, polymer physics, rheology and applied mathematics. Meanwhile they will also receive systematic training in numerical computation and algorithm development. In addition to the academia, these skills are highly valued in a broad range of industrial sectors, especially the petroleum, chemical and manufacturing industries.

当管道或通道中的流动从层状状态转变为湍流时，其摩擦阻力突然增加：即，后者的能量耗散要高得多。同时，湍流在工程应用中无处不在；常见的例子包括管道油转移，区域供暖/冷却系统以及船舶，飞机和车辆的推进。因此，减少动荡阻力的技术（DR）可以在经济上（成本较低）和环境（较少的自然资源消耗和更少的温室气体排放）带来巨大的好处。通过简单地将聚合物添加剂溶解到流体中，可以实现大量DR-最高80％。尽管在实际应用中并不总是允许聚合物，但对其DR效应的理解将激发流动控制技术的新设计，以达到简单液体中（无聚合物）中可比节省能量的可比水平。 在该领域，最突出的问题是所谓的最大阻力减少（MDR）：一种通用的渐近限，它界定了所有不同聚合物溶液达到的DR水平。尽管进行了数十年的研究，但MDR仍然是粘弹性湍流领域中最重要的未解决问题。揭示其机制不仅具有极大的基本兴趣，还清楚地了解了MDR制度附近的聚合物解决方案中的动力学，这对于DR Technique的未来发展而言也至关重要。 所提出的程序着重于湍流中DR的数值计算，其短期目标设定为MDR机制。我们将采用的方法的灵感来自我们最近对简化模型流的研究中提出的新概念框架。除了对MDR研究介绍独特的观点外，该框架还为所有有关MDR的定性观察提供了一致的解释，这表明了指导未来研究的巨大希望。在这一进步的基础上，我们的计划分为两个方向：一个旨在构建MDR动力学的机械描述；另一个重点是验证我们在现实尺度下在湍流中的身体理解。 沿这条路的进步将为我们的长期目标做好准备：在简单的牛顿流体中为高水平的DR开发下一代技术。在许多情况下，聚合物是不溶性，禁止或不希望的。因此，简单流体中DR的技术可以达到更广泛的应用范围。然而，通过这种现有技术实现的节能水平远低于聚合物。有了更好地了解MDR附近的聚合物湍流，可以设想新的方法模仿聚合物的作用，以便在没有这些添加剂的情况下可以将湍流动力学束缚在MDR中。 最后，该计划还考虑了对高素质人员（HQP）的培训。拟议的研究将研究生和本科生的多个学生分为几个项目。从事这些项目的学生将在流体动力学，聚合物物理学，流变学和应用数学方面建立坚实的背景。同时，他们还将在数值计算和算法开发方面接受系统的培训。除学术界外，这些技能还高于广泛的工业领域，尤其是石油，化学和制造业。