Time-resolved observations of pit formation and cloud behavior in cavitating jet

- Time-resolved observations of pits and cloud are carried out in cavitating jet.
- Pits are detected by thin gold-film sensor glued on wall.
- Cloud collapse is taken by axial imaging by time-difference shadowgraph.
- Local erosion rate is reproduced in pits growth rate and cloud collapse intensity
- Pits formation occurs at the instant of cloud collapse.

Time-resolved observations of pit formation and cloud structure in a cavitating jet are carried out to understand the erosion mechanism of a cavitating jet issuing from a converging and diverging nozzle in a still water environment. Pit formation is detected by a sensor made of gold film (0.2 μm in thickness) glued to a transparent glass plate, and the number and size of the pits are evaluated from digital image analysis. High-speed camera shadowgraph imaging allows observation of the cloud structure in the cavitating jet, which captures the cavitation cloud collapse combined with the time-difference analysis. The radial distribution of pits is in close agreement with the erosion depth distribution evaluated from the weight-loss profiles of an aluminum specimen in a cavitating jet. The pit distribution in the cloud collapse is well reproduced in the time-difference analysis. Furthermore, simultaneous observations of the pit and cloud structures show that pits are formed on the wall at the instant of cloud collapses during the periodic behavior of the cavitating jet.