Void Fraction Measurement in the Boundary Layer of Training Ship Seiun-Maru

The full-scale experiment of microbubbles was performed using the training ship Seiun-Maru in 2001. The void fraction was successfully measured in the turbulent boundary layer under the bottom surface, using an optical void measurement device developed by the authors. The void distribution had a peak in the region 5–10mm from the hull surface. The device also could be used to measure the bubble size distribution. The number-averaged bubble diameter was about 0.5mm.