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Bubble entrapment during sphere impact onto quiescent liquid surfaces

Published online by Cambridge University Press:  20 June 2011

J. O. MARSTON ,
I. U. VAKARELSKI  and
S. T. THORODDSEN
J. O. MARSTON*
Affiliation:
Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
I. U. VAKARELSKI
Affiliation:
Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
S. T. THORODDSEN
Affiliation:
Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Clean Combustion Research Centre, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
*
†Email address for correspondence: jeremy.marston@kaust.edu.sa
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Abstract

We report observations of air bubble entrapment when a solid sphere impacts a quiescent liquid surface. Using high-speed imaging, we show that a small amount of air is entrapped at the bottom tip of the impacting sphere. This phenomenon is examined across a broad range of impact Reynolds numbers, 0.2 ≤ Re = (DU0/νl) ≤ 1.2 × 105. Initially, a thin air pocket is formed due to the lubrication pressure in the air layer between the sphere and the liquid surface. As the liquid surface deforms, the liquid contacts the sphere at a finite radius, producing a thin sheet of air which usually contracts to a nearly hemispherical bubble at the bottom tip of the sphere depending on the impact parameters and liquid properties. When a bubble is formed, the final bubble size increases slightly with the sphere diameter, decreases with impact speed but appears independent of liquid viscosity. In contrast, for the largest viscosities tested herein, the entrapped air remains in the form of a sheet, which subsequently deforms upon close approach to the base of the tank. The initial contact diameter is found to conform to scalings based on the gas Reynolds number whilst the initial thickness of the air pocket or ‘dimple’ scales with a Stokes' number incorporating the influence of the air viscosity, sphere diameter and impact speed and liquid density.

JFM classification

Drops and Bubbles: Bubble dynamics Interfacial Flows (free surface): Contact lines Low-Reynolds-number flows: Lubrication theory
Type
Papers
Information
Journal of Fluid Mechanics , Volume 680 , 10 August 2011 , pp. 660 - 670
Copyright
Copyright © Cambridge University Press 2011

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