Methods of analysing and interpreting two-dimensional velocity field data in order to understand the scales of turbulence of bubbly two-phase flow were developed. Reynolds decomposition and large eddy simulation (LES) decompositions (low-pass filtering), in conjunction with proper orthogonal decomposition (POD) energy spectra analysis, as well as adjusted convective decomposition (constant convection velocity is gas bubble velocity) were applied to analyse the structure of turbulence. Particle image velocimetry was applied for velocity measurements. Decomposition analysis was performed for the local velocity around gas bubbles in a chosen region. Various decomposition methodologies were applied for interpretation of the results and it was found that the number of eddies revealed and vorticity magnitude varied with the decomposition method used. In particular, LES decomposition was found to perform better at showing smaller eddies. POD indicated the energy changes quantitatively through the spatial energy spectra, while the comparison of single-phase flow with bubbly two-phase flow offered an efficient way of decomposing the total velocity.

A combination of convective decomposition and POD was applied to the energy spectra level in order to obtain a novel view of the turbulence energy introduced by the gas bubbles.