Ryoichiro Oshima

High-speed observation of ultrahigh-speed submerged water jets

Some peculiar phenomena occur around ultrahigh-speed submerged water jets accompanied by very severe cavitation erosion. Using the flow visualization technique with a xenon flash, the water jets were carefully observed, and the spatial distributions of highly erosive impulsive pressures around the jets were measured by means of a pressure-sensitive film technique. The effects of the injection pressure and the nozzle configuration are systematically clarified. Thus, the characteristics and structures of ultrahigh-speed submerged water jets are clearly shown.

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

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.

Characteristics of jet-turbo pumping systems.

Pumping system characteristics are surveyed theoretically and explored in tests under the condition of 60 kPa suction head to improve cavitation performance in a pumping system with two jet pumps and one turbo pump. One of the two jet pumps is connected to a suction pipe upstream from the turbo pump and the other one is to a delivery loop downstream. Also analytical and experimental studies are carried out on the relationship between pumping system efficiency and individual pump efficiency, using a pumping system with a jet pump connected to the suction pipe upstrean from a centrifugal pump.