Sub-Hinze Scale Bubble Production in Turbulent Bubble Break-Up

Abstract

We study bubble break-up in homogeneous and isotropic turbulence by direct numerical simulations of the two-phase incompressible Navier-Stokes equations. We create the turbulence by forcing in physical space and introduce the bubble once a statistically stationary state is reached. We perform a large ensemble of simulations to investigate the effect of the Weber number (the ratio of turbulent and surface tension forces) on bubble break-up dynamics and statistics, including the child bubble size distribution, and discuss the numerical requirements to obtain results independent of grid size. We characterize the critical Weber number below which no break-up occurs and the associated Hinze scale dh. At Weber number close to stable conditions (initial bubble sizes d0 ≈ dh), we observe binary and tertiary break-ups, leading to bubbles mostly between 0.5dh and dh, a signature of a production process local in scale. For large Weber numbers (d0 > 3dh), we observe the creation of a wide range of bubble radii, with numerous child bubbles between 0.1dh and 03.dh, an order of magnitude smaller than the parent bubble. The separation of scales between the parent and child bubble is a signature of a production process non-local in scale. The formation mechanism of these sub-Hinze scale bubbles relates to rapid large deformation and successive break-ups: the first break-up in a sequence leaves highly deformed bubbles which will break again, without recovering a spherical shape and creating an array of much smaller bubbles. We discuss the application of this scenario to the production of sub-Hinze bubbles under breaking waves.

Department(s)

Mechanical and Aerospace Engineering

Comments

National Science Foundation, Grant 1548562

Keywords and Phrases

bubble dynamics; multiphase flow

International Standard Serial Number (ISSN)

0022-1120; 1469-7645

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2021 Cambridge University Press, All rights reserved.

Publication Date

25 Jun 2021

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