Turbulent micro-structure in a bubbly channel flow

The objective of the present study is to elucidate the mechanism of interaction between global and local structure of turbulence, especially the influenced of inter-bubble spacing on the microscopic flow structure in bubbly flow. We explored the flow structure in the vicinity of the bubble in conjunction with bubble deformation by PIV/LIF and a shadow image technique respectively. The experiment consisted of a fully developed vertical upward channel flow with 0.5% and 1.0% void fraction. We used a small quantity of 3-Pentanol as surfactant to control the bubble diameter and number density of bubble. Our main conclusion is that not only the void fraction but also the distribution of the bubble diameter serves as characteristic spatial parameters of the turbulent structure of bubbly flow. Enstrophy contours characterizing turbulent modulation were derived from velocity data measured by PIV/LIF. The high intensity of enstrophy was distributed around the large bubble and in the narrow inter-bubble spacing. The spatial scale of enstrophy was almost the same as the vorticies induced by these large bubbles.