Quantitative visualization of swirl and cloud bubbles in Taylor–Couette flow

Abstract

We develop a novel method to study the gas phase features in a bubbly Taylor-Couette flow when bubbles are arranged as elevated toroidal strings. The fl ow is recorded in the front view plane with a highspeed camera for a Reynolds number of 1500 and a global void fraction of 0.14 %. An image processing algorithm is developed to discriminate bubbles accumulated in clouds near the inner cylinder (cloud bubbles) from bubbles trapped in the bulk flow by vortices (swirl bubbles). The analysis of the preferential positions, azimuthal velocities, and equivalent void fraction of clouds and swirl bubbles separately provides a new insight into the dynamics of the bubble's entrapment.

Defect-mediated turbulence in bubbly Taylor-Couette flow

“…In our study, we investigate higher Reynolds numbers and higher air injection rates than in Murai et al (2008) [8]. Unlike in Murai et al (2008) [8], Yoshida et al (2009) [13], Van Ruymbeke et al (2017) [15], Murai et al (2018) [14] for whom bubbles were preferentially entrapped in the outflow region, in the present study, the geometry of the gap implies preferential capture of the bubbles in the vortices (larger η value). This can potentially make a difference in the bubbly patterns development and defects occurrence.…”

“…With the occurrence of a propagative azimuthal wave, there is a preferential accumulation of the bubbles at the crest of the wave, leading to a nonhomogenous distribution of bubbles in the azimuthal direction [10,15]. This is visible by the alternance with time of regions of higher intensity at the crest and lower intensity at the trough (holes) in a same bright pattern.…”

“…In Van Ruymbeke et al (2017) [15], based on visualizations of the bubbly pattern, the contribution of cloud bubbles (entrapped in the outflow jet) was discriminated from the contribution of vortices (swirl bubbles). The analysis of preferential positions, azimuthal velocities, and equivalent 034302-2 void fraction, of these two kinds of bubbles separately, gave a new insight into the dynamics of the bubble's entrapment for a toroidal arrangement of the Taylor vortices.…”

Air cavities at the inner cylinder of turbulent Taylor–Couette flow

“…van den Berg et al (2007van den Berg et al ( , 2005, Chouippe et al (2014), Climent et al (2007), Djeridi et al (2004), van Gils et al (2013, Murai et al (2005Murai et al ( , 2008, Ndongo Fokoua et al (2015), Sugiyama et al (2008), Verschoof et al (2016). At lower Reynolds numbers, small bubbles do not only beautifully visualize Taylor rolls and other vortical structures in the flow (van Ruymbeke et al 2017), they also decrease the drag by destroying the momentum transport in these vortices (Spandan et al 2016). At higher Reynolds numbers, in which the drag and shear rates are high, a small percentage of large bubbles has a tremendous effect on the global drag, e.g.…”

Affecting drag in turbulent Talor-Couette flow

“…[9, 11, 97, 115-117, 126, 141, 142, 177, 210]. At lower Reynolds numbers, small bubbles do not only beautifully visualize Taylor rolls and other vortical structures in the flow [114], they also decrease the drag by destroying the momentum transport in these vortices [112]. At higher Reynolds numbers, in which the drag and shear rates are high, a small percentage of large bubbles has a tremendous effect on the global drag, e.g.…”