Relaminarization and Turbulence Suppression in Rotating Flows

旋流是一类重要的流动，因为它与许多工业技术和过程有关，如燃烧、热交换器、旋风分离和混合。为了设计下一代高效的汽车、飞机和能源系统，了解涡流和旋转对湍流的影响以更好地预测性能是很重要的。旋流和旋流表现出复杂的流动行为和相互作用。具体来说，已经观察到旋转和旋转湍流（无组织或混沌）可以发展出组织良好的流动特征，以至于可以认为它们是层流（有组织）。层流通常比湍流更受欢迎，因为后者表现出更高的流动阻力，从而增加阻力和能量损失。本研究项目的总体重点是研究旋转和旋流对流场特性的影响，以及它如何导致流动的重组。目的是了解旋涡和旋转流的物理机制，并提高对这些类型流的预测能力。因此，这项研究的结果可能会影响到一些关键行业，如石油和天然气、生物医学、能源收集和航空航天等行业，这些行业的过程中会出现漩涡和旋转流。此外，这个与牛津大学研究人员的合作项目为研究生的培训增加了一个国际维度，也使继续努力促进本科生和高中生参与计算和实验实验室研究。本研究项目旨在研究旋转流动中涉及的复杂湍流物理。精心设计的实验与高保真直接数值模拟相结合，在这些参数的大范围内获得持续流动物理的详细信息。以前所未有的网格分辨率模拟了旋转管道流动的整个反向转变过程，使研究人员能够捕捉到大范围的相关湍流尺度。采用最先进的粒子图像测速和热线风速测量来表征非定常流动特征并验证直接数值模拟。实验和模拟结果正在通过对湍流预算的检查以及几种数据简化技术的应用进行整合，包括高阶谱分析和模态分解。具体来说，该研究项目正在研究远离壁面的螺旋流结构如何与近壁面结构相互作用，以减轻近壁面湍流产生结构并对流动进行再分层。此外，正在研究旋转流（层流和湍流）的稳定性特征与再层化过程之间的可能联系。

Swirling flows are an important class of flows because of their relevance to many industrial technologies and processes, such as combustion, heat exchangers, cyclone separation, and mixing. In order to design the next generation of efficient cars, aircraft and energy systems, it is important to understand the effect of swirl and rotation on turbulent flows to better predict performance. Swirling and rotating flows display complicated flow behavior and interactions. Specifically, it has been observed that swirling and rotating turbulent flows (unorganized or chaotic) can develop well-organized flow features to the extent that they may be considered laminar (organized). Laminar flows are generally preferred over turbulent flows, because the latter display higher flow resistance that, in turn, increases drag and energy losses. The overall focus of this research project is to study the effect of rotation and swirl on the character of the flow field and how it can lead to a re-organization of the flow. The objectives are to gain an understanding of the physical mechanisms embedded within swirling and rotating flows and to improve prediction capabilities for these types of flows. Consequently, the results of this research could impact key industries where swirling and rotating flows appear in their processes, such as oil and gas, biomedical, energy harvesting, and aerospace. In addition, this collaborative project with researchers at Oxford University adds an international dimension to the training of graduate students and also enables continued efforts to promote undergraduate and high school student participation in computational and experimental laboratory research. This research project aims to examine the complex turbulent flow physics involved in rotating flows. Carefully designed experiments in conjunction with high-fidelity direct numerical simulations are being used to obtain detailed insight about the ongoing flow physics over a wide range of these parameters. The entire reverse transition process in rotating pipe flows is being simulated at an unprecedented grid resolution allowing the researchers to capture the wide range of relevant turbulent scales. State-of-the-art particle image velocimetry and hot-wire anemometry measurements are being employed to characterize the unsteady flow features and to validate the direct numerical simulations. The experimental and simulation results are being integrated through the examination of turbulence budgets as well as the application of several data reduction techniques, including higher-order spectral analysis and modal decomposition. Specifically, the research project is studying how helical flow structures far from the wall interact with the near wall structures to mitigate the near-wall turbulence producing structures and to act to relaminarize the flow. Moreover, possible connections between the stability characteristics of the rotating flow (both laminar and turbulent) and the relaminarization process are being examined.