Oscillation dynamics of a bubble rising in viscous liquid

Abstract

In the present work, we study the oscillation dynamics of 3 mm-diameter bubbles generated through an orifice submerged in viscous liquids. The viscosity of those liquids is varied to change the behavior of the rising bubble. The details of the rising motion and shape oscillation of the bubbles are measured using a combination of high speed, high-resolution imaging, and an accurate digital image processing technique. Direct Numerical Simulations that mimic the experimental conditions are also performed using a front-tracking technique, called the Local Front Reconstruction Method. The predictions of the bubble shape and rising velocity obtained by the numerical simulations show good agreement with the experimental results. Our experimental and numerical results show that the oscillation frequency and the damping rate at lower modes can be predicted using available theoretical models found in the literature. However, discrepancies arise between our results with the theoretical predictions at higher order oscillation modes. We conclude that the discrepancies are due to the influence of rising motion and the vortex wave, which is not considered in the theoretical models.

Hydrodynamic interaction of bubbles rising side-by-side in viscous liquids

“…The errors are in the order of 1%, except for the initial moment up to 10 ms, which is related to the detachment phase of the bubble. This has been demonstrated in a previous study (Kong et al 2019).…”

“…1 Features of the four possible modes corresponding to a setup, b bubble pair generated at two orifices and rising side-byside (scales are different), and c centres of mass and distances of two centres; the dimensionless distance of two centres is defined as S = 2s∕D eq consequence the behaviour of the rising bubble pair. To minimise the effect of preceding bubbles, a flow rate of 1 ml/min was chosen, based on earlier tests (Kong et al 2019).…”

“…The recorded images were processed using an in-house Matlab program. Details can be found in Kong et al (2019). The uncertainty in determining the bubble centre from the image processing is lower than 1% due to the high resolution.…”

“…To validate the data-processing method in the present study, DNS results were used as a well-defined case (Mirsandi et al 2018;Kong et al 2019), see Fig. 3.…”

“…Compared with deformed bubbles and spherical bubbles, deformable bubbles are less rigid. The bubbles will experience shape oscillations (Kong et al 2019) due to the wake behaviour. As shown in Fig.…”