Flow structures and cavitation in submerged waterjet at high jet pressure

Complexity of the submerged waterjet driven by high pressure resides in the jet itself and ambient water as well. To explore the traits of the high-pressure submerged waterjet, an experimental study is carried out at jet pressures of 13, 16 and 18 MPa. The submerged waterjet flow is measured using particle image velocimetry in conjunction with seeded Rhodamine 6B fluorescence particles. Vorticity is calculated from velocity distribution. High-speed photography is utilized to capture the evolution of cavitation phenomenon near the nozzle. Pressure fluctuations excited in the water tank are acquired with miniature pressure transducers. At the three high jet pressures, submerged waterjet velocity attenuates remarkably along the streamwise direction, demonstrating substantial difference in comparison with low-pressure submerged waterjet. The semi-width of the waterjet stream increases downstream in a nearly linear manner. Pressure fluctuations in the water tank are featured by a wide frequency band within which low frequencies are most predominant. Meanwhile, relatively high frequencies are associated with cavitation evolution. Cavitation cloud development encompasses three distinct stages, namely cavitation cloud extending, cavitation cloud preserving and cavitation cloud shrinking. Of significance is the cavitation cloud profile, it is represented by disperse cavity elements at 13 MPa. And the coherence of the cavitation cloud, as well as cavitation area fraction, is enhanced as jet pressure increases.