A Study on Peening by Submerged Ultra-High-Speed Water-Jets

Abstract

To clarify cavitation behaviours of submerged high-speed water-jets, systematic experimental studies were carried out by using a flow visualization technique. The cavitation behaviours were studied for both the free jet and the impinging jet at various stand-off distances x from the outlet edge of the nozzle. Effects of the injection pressure P ₁ and the nozzle structure on the behaviours were also examined. The behaviours of the jets are largely dominated by explosive cavity clouds and by remarkably developed vortex cavitation. Therefore the structure of the submerged jet differs from that of jet in still air. The distribution of impulsive pressure P _sh , which is measured by pressure sensitive films, clearly shows the existence of two pressure peaks along the jet. At the stand-off distance where P _sh shows the “1st peak,” the impinging jet results in the severe erosion on the ambient solid surfaces. Because of this, the performance of cutting- or drilling- fabrications is considered to be remarkably improved when jet impinging is conducted at x ₁ of the “1st peak.” On the other hand, at x ₂ of the “2nd peak” downstream from the “1st peak,” numerous pressure pulses are produced on the solid surfaces, but mass loss due to cavitation erosion is barely detected. Clearly, x ₂ of the “2nd peak” is believed to be suitable for precise peening fabrications.