Journal
JOURNAL OF FLUID MECHANICS
Volume 912, Issue -, Pages -Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2020.1135
Keywords
computational methods; capillary waves; wave-structure interactions
Categories
Funding
- EPSRC [EP/N018176/1]
- Brown OVPR Seed Award
- UTRA Undergraduate Research program
- EPSRC [EP/N018176/1] Funding Source: UKRI
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This study investigates the phenomenon of a millimetre-size superhydrophobic sphere impacting on a quiescent bath, where it can be propelled back into the air while transferring energy to the fluid. Different physical parameters are explored to understand the dependence of rebound behavior, and various models are developed to explain the observed trends. The experiments, simulations, and models provide insights into the complex multi-scale system and reveal new phenomena at different ends of the Weber number spectrum.
A millimetre-size superhydrophobic sphere impacting on the free surface of a quiescent bath can be propelled back into the air by capillary effects and dynamic fluid forces, whilst transferring part of its energy to the fluid. We report the findings of a thorough investigation of this phenomenon, involving different approaches. Over the range from minimum impact velocities required to produce rebounds to impact velocities that cause the sinking of the solid sphere, we focus on the dependence of the coefficient of restitution, contact time and maximum surface deflection on the different physical parameters of the problem. Experiments, simulations and asymptotic analysis reveal trends in the rebound metrics, uncover new phenomena at both ends of the Weber number spectrum, and collapse the data. Direct numerical simulations using a pseudo-solid sphere successfully reproduce experimental data whilst also providing insight into flow quantities that are challenging to determine from experiments. A model based on matching the motion of a perfectly hydrophobic impactor to a linearised fluid free surface is validated against direct numerical simulations and used in the low-Weber-number regime. The hierarchical and cross-validated models in this study allow us to explore the entirety of our target parameter space within a challenging multi-scale system.
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