Dynamic structures of bubble-driven liquid flows in a cylindrical tank

Abstract

The spatial and temporal structures of turbulent water flows driven by air bubbles in a cylindrical tank were investigated. The time-resolved particle image velocimetry technique was adopted for quantitative visualization. Flow rates of compressed air were changed from 1 to 5 L/min at 0.5 MPa, and the corresponding range of bubble-based Reynolds number (Re) ranged from 8,300 to 21,100. The dynamics of flow structures was further investigated by the time-resolved proper orthogonal decomposition analysis technique. With increasing Re, mean velocity fields driven by the rising bubbles are almost same, but turbulence is dramatically enhanced. Both spatial and temporal modes were quite different with respect to the air flow rates. Three most dominant spatial structures are recirculating flow, bubble-induced motion, and sloshing of free surface, the bigger the latter the higher Re. We found the frequency of sloshing motion from flow visualization and the FFT analysis of temporal modes.

Shadow imaging in bubbly gas–liquid two-phase flow in porous structures

“…The flow structure in the vicinity of the bubble is determined by PIV with fluorescent particles, and the bubble deformation is observed from two angles using shadow imaging. Kim et al (2012) analyzed the spatial and temporal structure of air bubble-driven turbulent water flows in a cylindrical tank. They used a combination of volumetric illumination from the top and a vertical laser plane for PIV with fluorescent particles.…”