Lagrangian tracking of the wake vortices shedding from a wobbling bubble

Abstract

This study aims to elucidate the motion and the evolution of shedding vortices in the wake of a wobbling bubble based on experimental observation. Experimental observations of bubble wakes were conducted using Particle Image Velocimetry (PIV) for the ambient continuous phase and the backlight shadow imaging technique for the bubble. Vortices are detected and tracked in a Lagrangian framework based on the flow field in the vertical section. To investigate the three-dimensional structure of the flow field and to supplement the experimentally measured bubble sizes, bubbles with a diameter of 3–5 mm are numerically simulated, incorporating adaptive dynamic mesh refinement based on the bubble wake location. The study establishes a correlation between the transport velocity and swirling strength of wake vortices generated by wobbling bubbles and the bubble's parameters, facilitating more convenient predictions of wake behavior. The results indicate that the vortices trail the bubble at a transport velocity that is approximately 30 % of the bubbles’ velocity. During the vortex shedding process, the swirling strength of these vortices intensifies within a distance of 1.58 times the bubble radius and then decays with increasing distance from the bubble, following the formula of $1-\exp \left(-1.75/x\right)$.