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.
