Effect of Coaxial Airstream on High-Pressure Submerged Water Jet

The effect of coaxial airstream on a high-pressure water jet is studied by measuring the stagnation pressure on the impinging target and by the optical observations of the water jets. The water jet is pressurized at 12.7 MPa and discharged into atmosphere and still water, which correspond to non-submerged and submerged water jets. The coaxial air is also pressurized at various pressure p_o/p_b = 1.0–3.0, where p_o and p_b are the stagnation air pressure and the atmospheric pressure. And the distance between the water jet nozzle and the normal target plate L divided by the nozzle diameter D is changed from 1.0 to 15. As a result, according to the optical observation for non-submerged case, the spreading angle of the non-submerged water jet is found to be the minimum angle in case of the coaxial air jet pressure ratio of 1.4. The recovery factor decreases both for the case of non-submerged and submerged one decrease as L/D increases. However, the recovery factor in case of submerged water jet is greatly increased by the coaxial airflow by 70% of that for no airstream. Comparison of the recovery factors between the case of submerged and non-submerged conditions reveals that the coaxial airstream seems to achieve the atmospheric environment for the submerged water jet, even in the submerged conditions.