Although bubble pinch-off is an archetype of a dynamical system evolving toward a singularity, it has always been described in idealized theoretical and experimental conditions. Here, we consider bubble pinch-off in a turbulent flow representative of natural conditions in the presence of strong and random perturbations, combining laboratory experiments, numerical simulations, and theoretical modeling. We show that the turbulence sets the initial conditions for pinch-off, namely the initial bubble shape and flow field, but after the pinch-off starts, the turbulent time at the neck scale becomes much slower than the pinching dynamics: The turbulence freezes. We show that the average neck size, d̅, can be described by d̅ ~ (t − t0)α, where t0 is the pinch-off or singularity time and α ≈ 0.5, in close agreement with the axisymmetric theory with no initial flow. While frozen, the turbulence can influence the pinch-off through the initial conditions. Neck shape oscillations described by a quasi-2-dimensional (quasi-2D) linear perturbation model are observed as are persistent eccentricities of the neck, which are related to the complex flow field induced by the deformed bubble shape. When turbulent stresses are less able to be counteracted by surface tension, a 3-dimensional (3D) kink-like structure develops in the neck, causing d̅ to escape its self-similar decrease. We identify the geometric controlling parameter that governs the appearance of these kink-like interfacial structures, which drive the collapse out of the self-similar route, governing both the likelihood of escaping the self-similar process and the time and length scale at which it occurs.
D. J. Ruth et al., "Bubble Pinch-Off in Turbulence," Proceedings of the National Academy of Sciences of the United States of America, vol. 116, no. 51, pp. 25412-25417, National Academy of Sciences, Dec 2019.
The definitive version is available at https://doi.org/10.1073/pnas.1909842116
Mechanical and Aerospace Engineering
Keywords and Phrases
Interface; Self-similarity; Singularity; Turbulence
International Standard Serial Number (ISSN)
Article - Journal
© 2019 The Authors, All rights reserved.
17 Dec 2019