Magnetic fluid film enables almost complete drag reduction across laminar and turbulent flow regimes
L.M. Stancanelli (Swiss Federal Institute for Forest, Snow and Landscape Research WSL, ETH Zürich, TU Delft - Rivers, Ports, Waterways and Dredging Engineering)
Eleonora Secchi (ETH Zürich)
Markus Holzner (Swiss Federal Institute for Forest, Snow and Landscape Research WSL, BOKU-University of Natural Resources and Life Sciences, Eawag - Swiss Federal Institute of Aquatic Science and Technology)
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Abstract
In the race to curb energy and oil consumption, zeroing of wall frictional forces is highly desirable. The turbulent skin friction drag at the solid/liquid interface is responsible for substantial energy losses when conveying liquids through hydraulic networks, contributing approximately 10% to the global electric energy consumption. Despite extensive research, efficient drag reduction strategies effectively applicable in different flow regimes are still unavailable. Here, we use a wall-attached magnetic fluid film to achieve a wall drag reduction of up to 90% in channel flow. Using optical measurements supported by modelling, we find that the strong damping of wall friction emerges from the co-existence of slip and waviness at the coating interface, and the latter is a key factor to obtain almost complete wall drag reduction across laminar and turbulent flow regimes. Our magnetic fluid film is promising and ready to be applied in energy-saving and antifouling strategies in fluid transport and medical devices.
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