Abstract
Turbulence modification in the presence of bubbles was investigated by time-series measurements using a high-time resolution PIV. The experiments were carried out in a fully-developed vertical pipe with upflow of water at the Reynolds number of 9700 and the void fraction of 0.5%. The two-dimensional flow structure in the vicinity of bubbles was measured by a high-time resolution PIV with fluorescent tracer particles and bubbles shapes and positions were obtained by using a shadow imaging technique. It is observed that turbulence production was rapidly decreased and dissipation rate was enhanced in a whole region. A strong vorticity region was generated in front of bubbles, on the other hand, vorticities behind bubbles show larger values and exist longer in center of pipe than near the wall.
