Effect of Ventilation on the Velocity Decay of Cavitating Submerged Water Jet

High-speed water jet shows a peculiar processing property in cutting of submerged objects but its processing ability decreases quickly with the increase of standoff distance. Aiming at to improve the performance of submerged water jet an experiment investigation on the velocity distribution of cavitating submerged jet is carried out by PIV method where micro bubbles are used as flow tracers. Further, a sheathed orifice nozzle with ventilation hole is developed and the effect of air ventilation is investigated. The result reveals that the core velocity of no-ventilation cavitating jet is higher than ventilated ones near the sheath exit. However it becomes reverse at the downstream when x/d ≥ 40. The core velocity of ventilated jets decays much slowly compared to the case of no-ventilation jet. Air ventilation is demonstrated to be an effective way to enhance the perframnce of submerged water jets.