Observations and Particle-based Simulation of Air-entrainment around a Surface Piercing Cylinder

Flow and air-entrainment around a surface piercing circular cylinder has been investigated experimentally and numerically. In water tunnel experiments, high speed video observations were made for surface piercing flow around a circular cylinder of 150 mm in diameter. Surface pressure measurements were also carried out at nine points around the cylinder. Flow velocity was from 1.5 to 3.0 m/s. The high-speed video observations showed that a pair of air pocket was formed on the side of the cylinder, and bubbles entrained into the air-pockets are shed downstream. The depth of the air-pocket fluctuated in a frequency range lower than the typical Karman vortex frequency. For numerical study, unsteady motion of air-entrainment process was simulated by an MPS method with some corrections to pressure calculation. The MPS calculation reproduced the dynamics of the air-pockets on the side of the cylinder. The time-variation of the predicted air-pocked depth also showed low-frequency fluctuations as observed in the experiment.