The organized flow structure of an oscillating bubble plume

Abstract

The detailed experimental investigation of an oscillating bubble plume created in a quasi‐two‐dimensional bubble column is reported for low void fraction and millimeter bubbles. The plume exhibits periodic oscillations and generates large‐scale coherent structures in the liquid. The local and transient hydrodynamics of this bubbly flow was investigated with particle‐image velocimetry (PIV) in the liquid phase and via optical fiber probe and the shadowgraph technique in the gas phase. First, long time averaging is performed (over a large number of plume oscillation periods). Thus, horizontal profiles of gas fraction and of horizontal and vertical components of mean and root mean square velocities in both phases can be examined. Then fluctuations of liquid velocities are studied, in terms of probability density function (indicating organized and random fluctuations), and in terms of phase‐averaged components. Finally, proper orthogonal decomposition is applied to PIV data to extract coherent structure contributions more efficiently.