Giant drag reduction on Leidenfrost spheres evaluated from extended free-fall trajectories

Aditya Jetly, Ivan U. Vakarelski*, Ziqiang Yang, Sigurdur T. Thoroddsen

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Scopus citations

Abstract

Vapor layer sustained on the surface of a heated sphere, by the means of the Leidenfrost effect, can dramatically reduce the hydrodynamic drag on a sphere due to an early drag crisis transition. Here we investigate the vapor layer effect on the free fall of heated metallic spheres in a fluorocarbon liquid, FC-72 (perfluorohexane), employing two tall liquid tanks: a 3 m tall 14 cm wide tank and a 2 m tall 20 × 20 cm cross-section tank with a heater device. These tanks are significantly larger than the tanks used in prior studies. We use high-speed video camera recordings to track extended fall trajectories and to compare the drag on room-temperature no-vapor-layer spheres to that of heated Leidenfrost vapor-layer spheres. Analysis of the extended free-fall trajectories and acceleration, based on the sphere dynamic equation of motion, enables the accurate evaluation of the vapor-layers-induced drag reduction, without the need for extrapolation. We demonstrate that the drag on the Leidenfrost sphere in FC-72, can be as low as CD = 0.04 ± 0.01, or an order of magnitude lower than the values for the no vapor layer spheres in the subcritical Reynolds number range. This drag reduction extends into the supercritical Reynolds number range. The analysis method developed herein, to describe the sphere trajectories, can be applied in other related studies. Results of this study are expected to stimulate the development on energy saving drag-reduction technologies based on lubricating gas layers.

Original languageEnglish (US)
Pages (from-to)181-188
Number of pages8
JournalExperimental Thermal and Fluid Science
Volume102
DOIs
StatePublished - Apr 2019

Bibliographical note

Publisher Copyright:
© 2018

Keywords

  • Drag crisis
  • Drag reduction
  • Leidenfrost effect
  • Vapor layer

ASJC Scopus subject areas

  • General Chemical Engineering
  • Mechanical Engineering
  • Aerospace Engineering
  • Fluid Flow and Transfer Processes
  • Nuclear Energy and Engineering

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