Effect of bubble deformability in turbulent bubbly upflow in a vertical channel

Abstract

As bubbles rising in a vertical channel with upflow become bigger, it is well known that the void fraction distribution changes in a fundamental way, from a wall peak for small bubbles to a maximum void fraction at the channel center for larger bubbles. Here, we use direct numerical simulations of buoyant bubbles in a turbulent flow to show that it is not the size of the bubbles that matters, but their deformability.

Dynamics of an initially spherical bubble rising in quiescent liquid

“…A remarkable set of papers 5,6,[13][14][15] study bubbly flows in which the interaction between the flow and a large number of bubbles is studied. In particular, turbulent flows can be significantly affected by bubbliness.…”

Direct Numerical Simulation of Turbulent Channel Flow with Deformed Bubbles

“…In the original MARS method, the surface tension forces (:F vi , the i-th components of surface tension force, i=1, 2,3) according to the CSF model, 6) are defined by the following equations:…”

“…Recently, DNS of the turbulent shear flows with deformability bubbles have been conducted by Kawamura and Kodama, 1) Lu et al, 2) and Lu and Tryggvason, 3) by means of the front-tracking method. These previous DNSs focused on interaction between turbulent structures near wall and bubbles to investigate friction drag reduction effects on the wall.…”

Numerical Study on Flow Structures and Heat Transfer Characteristics of Turbulent Bubbly Upflow in a Vertical Channel

“…Liu (1993) also found in the experiments of turbulent bubbly upflow in a vertical channel that the void fraction has peaks near the walls for the bubbles smaller than 5-6mm, while it has a peak in the core of the channel for the bubbles larger than 5-6mm. Lu & Tryggvason (2008) also showed in their direct numerical simulations of turbulent bubbly upflow in a vertical channel that nearly spherical bubbles tend to concentrate on the near-wall regions, while strongly deformable bubbles tend to be expelled from the near-wall regions. They also showed that the turbulence structures are changed by the motions of bubbles.…”

“…We utilize so-called 'minimal turbulent channel' in the present study. The simulations are performed on the domain of Lu & Tryggvason (2008). In the simulation of Lu & Tryggvason (2008), the constant pressure gradient to drive the flow was set so that the friction Reynolds number  Re was 127.2.…”