High-speed Submerged Water Jet Research Articles

Marked Effects of Ambient Pressure on Impinging Erosion Induced by High-Speed Submerged Water Jets.

In order to extend the working range of high-speed submerged water jets and to improve its accuracy confidence, the jet working characteristics are studied under the condition of widely varying ambient pressures P2. The erosion tests were systematically carried out by using aluminum-alloy specimens, and the aspects of the cavitation clouds around the jets were simultaneously observed. Clearly, the pressure P2 drastically affects the aspects of cavitation and its occurrence region. With increasing P2, the length of the cavitating jet decreases, so that the standoff distance, where the most severe erosion appears, shifs upstream. In short, the intensity and the distribution of the impulsive pressures induced by the cavitating jets also drastically change with P2. The impinging erosion characteristics are also sensitive to the standoff distance and the injection time.

Jet Structure Analyses on High-Speed Submerged Water Jets through Cavitation Noises.

In order to establish a useful monitoring method for predicting the erosion induced by high-speed submerged water jets, we attempt to clarify the relation between the jet-structure and the cavitation noise arising around the free jets, by using two hydrophones, and also analyze the AE characteristics of the impulsive pressures induced by cavitation on the specimen of the impinging jets. It is found that the energies of high-frequency components in the jets change markedly with the injection pressure and the standoff distance. It is found that the AE characteristics are closely related to the impinging erosion.

Development of Erosion in High-Speed Submerged Water Jets.

High-Speed submerged water jets have two characteristic peaks with respect to the stand-off distance, in the same manner as high-speed water jets in air. In order to clarify the behavior of the impulsive pressures at these two peaks, we systematically carried out erosion tests using an aluminum-alloy specimen in a wide range of the injection pressure P1 from 10 to 70 MPa, and microscopically observed the eroded surfaces by SEM. We find that the mass loss rate Δm^^· at the 1st peak is decidedly due to the water-column impact, so that it is very sensitive to the injection pressure P1, while Δm^^· at the 2nd peak is due to the shock pressures of cavitation bubble collapse, so that it is not necessarily sensitive to P1. We also indicate that the form and the speed of erosion change markedly with the differences in the jet structure with the stand-off distance x/D.

Cavitation Noise Characteristics around High-Speed Submerged Water Jets.

In order to clarify structures of high-speed submerged water jets and to predict the jet working capacity, we systematically measured the cavitation noise around the jets using a hydrophone, for several nozzles. The power spectra and the rms values of the cavitation noise are carefully analyzed. Clearly, cavitation noise created by the jets is related to the behavior of cavitation bubble clouds, and the cavitation noise characteristics are markedly changed with the injection pressure and nozzle geometry.

30 画像の積層化立体表示による高速水中水噴流の非定常挙動の解明

30 画像の積層化立体表示による高速水中水噴流の非定常挙動の解明

Unsteady Behavior on High-Speed Submerged Water-Jets and Mechanism of Impinging Erosion.

Unsteady Behavior on High-Speed Submerged Water-Jets and Mechanism of Impinging Erosion.

The Suitable Region of High-Speed Submerged Water-Jets for Cutting and Peening.

In order to establish techniques of cutting, drilling, peening and flushing by high-speed submerged water-jets, we systematically observe the eroded surface on aluminum-alloy test-pieces in relation to the aspects of cavitating jets, especially for the impinging jet through lucite-test-pieces, for several types of nozzles. The impulsive pressures induced by the impinging jets are also measured by means of pressure-sensitive film. It is concluded that the erosion characteristics are quite different in two regions differentiated by the standoff distance. Cylindrical, small and deep pits occur in one of the regions, while small lots of plastic deformations occur in the other region. The former is suitable for cutting, while the latter is for peening.

High-Speed Observation of Ultra high-Speed Cavitating Submerged Water Jets.

This paper aims to clarify peculiar phenomena arising around a ultra high-speed submerged water jet accompanied by very severe cavitation. By means of a flow visualization technique with a xenon flash light, three kinds of water jets are carefully observed, and the spatial distributions of cavitation-pressure pulses around the jets are also measured with pressure-sensitive film. The effects of the working pressure and the shape of nozzles are clarified systematically. Thus, the characteristics and the structures of ultra high-speed cavitating submerged water jets are clearly shown.