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Tidal power and turbulence: Unsteady hydrodynamics in 3D
Tidal power has huge potential as a source of predictable renewable energy in the UK, but the harsh operating environment increases the costs of manufacture and maintenance, and reduces the reliability of the resource. This talk will focus on the damage caused to turbines by surface waves and ocean turbulence, which often leads to overloading and premature failure of tidal devices.
A number of recent studies have shown that the low-order models used by industry to predict turbine load response to turbulence and waves are not capable of reproducing experimental results, even for very simple unsteady forcing. The cause of this discrepancy is that conventional low-order models are based on 2D strip-theory, which ignore any 3D effects on the unsteady hydrodynamics. 3D effects are in fact substantial in most tidal applications; the turbines themselves are highly 3D in shape (small aspect ratios and highly tapered), and the unsteady flow fields also have significant spatial variation. In this talk we will look at the impact of both of these 3D features on the unsteady loads experienced by tidal turbines.
Amanda Smyth is a Research Associate at Cambridge University Engineering Department, working in the Whittle Laboratory. She studied for a MEng in Mechanical Engineering at Imperial College London, after which she did her PhD at Cambridge University on "Three-Dimensional Unsteady Hydrodynamics of Tidal Turbines". Her work explores the limitations of using two-dimensional strip-theory methods for calculating the unsteady hydrodynamic loading experienced by tidal turbines, which are highly three-dimensional in shape. She is also working on developing turbine blades that are resistant to unsteady and turbulent flow, in order to increase the longevity and reliability of tidal devices.
On a wet day we need coats to keep dry, windscreen wipers to see and reservoirs to collect water and keep us alive. Our cars need oil to lubricate their engines, our ships need hulls that reduce drag and our planes need wings that limit ice formation. Nature has learnt to control water in a myriad of ways. The Lotus leaf cleanses itself of dust when it rains, a beetle in the desert collects drinking water from an early morning fog and some spiders walk on water. In all of these effects the unifying scientific principle is the control of the wettability of materials, often through the use of micro- and nano-scale topography to enhance the effect of surface chemistry. In this seminar I will outline recent examples of our research on smart surface-fluid interactions, including drag reduction and flow due to surface texture,1-4 interface localized liquid dielectrophoresis to create superspreading and dewetting,5-7 lubricant infused surfaces to remove pinning,8-10 and the Leidenfrost effect using turbine-like surfaces to create new types of heat engines and microfluidics.11-12
1. Busse, A. et al. Change in drag, apparent slip and optimum air layer thickness for laminar flow over an idealised superhydrophobic surface. J. Fluid Mech. 727, 488–508 (2013).
2. Brennan, J. C. et al. Flexible conformable hydrophobized surfaces for turbulent flow drag reduction. Sci. Reports 5, 10267 (2015).
3. McHale, G. in Non-wettable Surfaces Theory, Prep. Appl. (Ras, R. & Marmur, A.) (RSC, 2016).
4. Li, J. et al., Topological liquid diode. Science Advances 3, eaao3530 (2017).
5. Brown, C.V. et al. Voltage-programmable liquid optical interface. Nat. Photonics 3, 403–405 (2009).
6. McHale, G. et al. Voltage-induced spreading and superspreading of liquids. Nat. Commun. 4, 1605 (2013).
7. Edwards, A.M.J. et al. Not spreading in reverse: The dewetting of a liquid film into a single droplet. Sci. Adv. 2, e1600183 (2016).
8. Ruiz-Gutiérrez, É. et al., Energy invariance in capillary systems. Phys. Rev. Lett. 118, art. 218003 (2017).
9. Guan, J.H. et al., Drop transport and positioning on lubricant-impregnated surfaces. Soft Matter 12, 3404-3410 (2017).
10. Luo, J.T. et al., Slippery liquid-infused porous surfaces and droplet transportation by surface acoustic waves. Phys. Rev. Appl. 7, 014017 (2017).
11. Wells, G. G. et al., A sublimation heat engine. Nat. Commun. 6, 6390 (2015).
12. Dodd, L.E. et al., Low friction droplet transportation on a substrate with a selective Leidenfrost effect. ACS Appl. Mater. Interf. 8 22658–22663 (2016).
Acknowledgements The financial support of the UK Engineering & Physical Sciences Research Council (EPSRC) and Reece Innovation ltd is gratefully acknowledged. Many collaborators at Durham, Edinburgh, Nottingham Trent and Northumbria Universities were instrumental in the work described.
Biography. Glen McHale is a theoretical and experimental applied and materials physicist. At Northumbria University, he combines leading the Smart Materials & Surfaces laboratory with his role as Pro Vice-Chancellor for the Faculty of Engineering & Environment. His research considers the interaction of liquids with surfaces and has a particular focus on the use of surface texture/structure via microfabrication and materials methods, and the use of electric fields to control the wetting properties of surfaces. His work includes novel superhydrophobic surfaces, surfaces with drag reducing and slippery properties, and electrowetting/dielectrophoresis to control the wetting of surfaces. Glen has written invited “News and Views”, highlight, emerging area and review articles for a wide range of journals covering superhydrophobicity, dynamic wetting, liquid marbles and drag reduction. He has published over 170 refereed journal papers. He is a Fellow of the Institute of Physics, a Fellow of the RSA, a Senior Member of the IEEE, a member of the UK Engineering & Physical Sciences Research Council (EPSRC) Peer Review College, and he was a panel member for the "Electrical and Electronic Engineering, Metallurgy and Materials" unit of the last UK-wide national assessment of research (REF2014). Along with colleagues at Northumbria, Nottingham Trent and Oxford Universities, he has developed a public understanding of science exhibition, "Natures Raincoats" (www.naturesraincoats.com).