Abstract
The objective of present study is to elucidate the mechanism of modification of turbulence structure in gas-liquid bubbly flow. The experiment consisted of a fully developed vertical upward pipe flow with 9700 of Reynolds number and less than 1.0% of void fraction. In order to obtain fundamental knowledge of the effects of void fraction and bubble diameter on modification of turbulence structure, we examine the interaction between vorticity field in the vicinity of bubbles and macro turbulence structure. We explored the two-dimensional flow structure in the vicinity of bubbles by applying PIV with fluorescent tracer particles, and also bubble shapes and positions were obtained by projecting shadow-image technique. It is suggested that the high concentrated bubbles in the vicinity of the wall make mean velocity profile flat. Fluctuation velocity and fluctuation vorticity intensity increased in the vicinity of the wall, although they decreased drastically in the middle channel region. Thus the turbulence reduction is remarkably occurred at the wide region of the pipe center.
