When: Nov 07 2019 @ 3:00 PM
Where: 205 Krieger Hall
205 Krieger Hall

“Novel Passive and Active Approaches to Fluid Friction Reduction using Polymers & Plastrons”

Presented by Professor Gareth H. McKinley
Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering
Massachusetts Institute of Technology
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 actually be reduced in the presence of a SH coating on the wall.
Gareth H. McKinley is the School of Engineering Professor of Teaching Innovation within the Department of Mechanical Engineering at MIT. He received his BA and M.Eng. degrees from the University of Cambridge and his Ph.D (1991) from the Chemical Engineering department at MIT. He taught in the Division of Engineering and Applied Sciences at Harvard from 1991-1997 and was an NSF Presidential Faculty Fellow from 1995-1997. He won the Annual Award of the British Society of Rheology in 1995 and the Frenkiel Award from the APS Division of Fluid Dynamics in 2001. He served as Executive Editor of the Journal of Non-Newtonian Fluid Mechanics from 2001 to 2009 and as Associate Editor of Journal of Fluid Mechanics from 2007-2009. He most recently served as the Associate Dept. Head for Research of the Mechanical Engineering Department at MIT from 2008-2013. He is also a co-founder of Cambridge Polymer Group. His research interests include extensional rheology of complex fluids, non-Newtonian fluid dynamics, microrheology & microfluidics, field-responsive fluids, super-hydrophobicity, wetting of nanostructured surfaces and the development of nanocomposite materials. He is the author of over 280 technical publications and was one of the winners of the 2007 Publication Award of the Society of Rheology. He is a Fellow of the American Physical Society. He was the recipient of the 2013 Bingham Medal of the Society of Rheology and in 2014 he was awarded the Gold Medal of the British Society of Rheology. He served as President of the Society from 2015-201 and is also the past chair of the US National Committee of Theoretical and Applied Mechanics (USNC/TAM). In 2019 he was elected to the National Academy of Engineering and also inducted as a Fellow of the Royal Society of London.