Relaminarization and Turbulence Suppression in Rotating Flows

旋流是一类重要的流动，因为它们与许多工业技术和过程相关，例如燃烧，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。旋流和旋转流表现出复杂的流动行为和相互作用。具体而言，已经观察到，涡旋和旋转湍流（无组织或混乱）可以发展出良好组织的流动特征，以至于它们可以被认为是层流（有组织的）。层流通常优于湍流，因为后者显示出更高的流动阻力，这反过来又增加了阻力和能量损失。该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，以及它如何导致流的重新组织。其目的是获得一个理解的物理机制嵌入在旋流和旋转流，并提高这些类型的流的预测能力。因此，这项研究的结果可能会影响在其过程中出现旋流和旋转流的关键行业，如石油和天然气，生物医学，能源收集和航空航天。此外，与牛津大学研究人员的这一合作项目增加了研究生培训的国际层面，并使继续努力促进本科生和高中生参与计算和实验室研究成为可能。本研究项目旨在研究旋转流中复杂的湍流物理。精心设计的实验结合高保真直接数值模拟正在被用来获得详细的了解正在进行的流动物理在很大范围内的这些参数。旋转管流中的整个反向过渡过程正在以前所未有的网格分辨率进行模拟，使研究人员能够捕捉到广泛的相关湍流尺度。国家的最先进的粒子图像测速仪和热线风速测量被用来表征非定常流的功能，并验证直接数值模拟。通过湍流预算的检查以及几种数据处理技术的应用，包括高阶谱分析和模态分解，将实验和模拟结果结合起来。具体而言，该研究项目正在研究远离壁的螺旋流结构如何与近壁结构相互作用，以减轻近壁湍流产生结构并使流动重新分层。此外，旋转流（层流和湍流）的稳定性特征和再层化过程之间的可能联系正在研究中。

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.