Novel Passive and Active Approaches to Fluid Drag Reduction using Polymers & Plastrons
MIE Distinguished Seminar
April 18, 2023
11:00 AM - 12:00 PM America/Chicago
842 W. Taylor St., Chicago, IL 60607
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Presenter: Gareth H. McKinley, PhD, Massachusetts Institute of Technology
Location: ERF 1043
Abstract: When a superhydrophobic (SH) textured surface is immersed in water it traps a thin shiny layer of air within the texture that is known as a plastron. Contact line pinning stabilizes this Cassie-Baxter state and the patches of air trapped in the texture can act as shear-free regions that locally lower the frictional dissipation. Recent developments of scalable manufacturing methods for producing robust SH surfaces open new possibilities for using these textures in drag reduction applications. We use a newly-developed bespoke Taylor-Couette (TC) apparatus to compare and contrast frictional drag reduction by dilute polymer solutions and superhydrophobic (SH) surfaces in turbulent flows for Reynolds numbers over a wide range (10,000 < Re < 100,000). By applying SH coatings to the inner rotating cylinder, we can evaluate the drag reducing performance and robustness of different textures and calculate the effective slip length in turbulent flow using a suitably-modified Prandtl-von Kármán (PvK) analysis. We also investigate how these plastrons can be partially stabilized against turbulent pressure fluctuations using active heating as well as chemical methods to locally regenerate vapor. Additionally, we can use our apparatus to revisit an alternative drag-reducing strategy using dilute solutions of various high molecular weight polymers. We show that natural polysaccharides derived from plant mucilage can be an inexpensive and effective alternative to costly synthetic polymers, whilst still approaching the same maximum drag reduction (MDR) asymptote. Finally, we explore combinations of these two complementary drag reduction methods – one arising from wall slip and the other due to changes in turbulence dynamics in the bulk flow – and find that the two effects are not always additive; interestingly, the effectiveness of polymer drag reduction can be enhanced or reduced in the presence of a SH coating on the wall.
Speaker Bio: Gareth H. McKinley FRS is the School of Engineering Professor of Teaching Innovation and former associate head and interim head of the Department of Mechanical Engineering at MIT. His research interests include extensional rheometry, microfluidic rheometry and non-Newtonian fluid dynamics. He is the author of more than 350 technical publications and has won the Publication Award of the Society of Rheology twice (2007; 2022) as well as the 2021 Walters Award from J. Non-Newtonian Fluid Mechanics. He was awarded the Bingham Medal of The Society of Rheology in 2013, the Gold Medal from the British Society of Rheology in 2014 and the G.I.Taylor Medal from the Society for Engineering Science (SES) in 2022. In 2019, he was elected to the National Academy of Engineering and also inducted as a Fellow of the Royal Society of London.
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