Turbulence Modulation Induced by Bubble-Liquid Mutual Interaction in an Oscillating-Grid Turbulence

Turbulence modulation induced by bubble swarms was experimentally investigated. Homogeneous isotropic turbulence is formed by using an oscillating grid in a cylindrical acrylic vessel. The bubble size and generation frequency are completely controlled using a bubble generator. A bubble swarm is generated at a frequency of 4 Hz and consists of 19 bubbles of 2.8 mm in equivalent diameter. The liquid phase velocities were measured via two LDA (Laser Doppler Anemometer). Turbulence intensity, spatial correlation and integral scale were evaluated from the LDA data obtained by the two spatially-separate-point measurement. The turbulence intensity dramatically changed by adding bubble swarms. The original isotropic turbulence was modulated to the anisotropic turbulence by the mutual interaction between bubble swarms and ambient isotropic turbulence. The turbulence modulation was also confirmed by the integral scale.