title: Sustained drag reduction in a turbulent flow using a low-temperature Leidenfrost surface.
abstract: Skin friction drag contributes a major portion of the total drag for small and large water vehicles at high Reynolds number (Re). One emerging approach to reducing drag is to use superhydrophobic surfaces to promote slip boundary conditions. However, the air layer or "plastron" trapped on submerged superhydrophobic surfaces often diminishes quickly under hydrostatic pressure and/or turbulent pressure fluctuations. We use active heating on a superhydrophobic surface to establish a stable vapor layer or "Leidenfrost" state at a relatively low superheat temperature. The continuous film of water vapor lubricates the interface, and the resulting slip boundary condition leads to skin friction drag reduction on the inner rotor of a custom Taylor-Couette apparatus. We find that skin friction can be reduced by 80 to 90% relative to an unheated superhydrophobic surface forRein the range 26,100 ≤Re≤ 52,000. We derive a boundary layer and slip theory to describe the hydrodynamics in the system and show that the plastron thickness ish= 44 ± 11 μm, in agreement with expectations for a Leidenfrost surface.
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Dhananjai
authors.initials: D
authors.lastname: Saranadhi
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Dayong
authors.initials: D
authors.lastname: Chen
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Kleingartner
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.; School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
authors.forename: Siddarth
authors.identifier: 0000-0003-4591-6090
authors.initials: S
authors.lastname: Srinivasan
authors.affiliation: Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Robert E
authors.identifier: 0000-0003-1085-7692
authors.initials: RE
authors.lastname: Cohen
authors.affiliation: Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Gareth H
authors.identifier: 0000-0001-8323-2779
authors.initials: GH
authors.lastname: McKinley
keywords: Skin friction drag; low-temperature Leidenfrost effect; slip boundary condition; superhydrophobic surface; sustained drag reduction; turbulent Taylor-Couette flow