Fluid Transient Phenomena Associated with Column Separation in the Return Line of a Hydraulic Machine Press

概要

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A generation mechanism has been developed to describe the surge pressures produced in the return line during the decompression cycle of a hydraulic machine press, and a mathematical model which is capable of predicting the pressures with a good degree accuracy suitable for practical usage has been produced. Experiments were carried out on a small model which is dynamically similar to a real machine in the 2000-ton (20-MN) class. The following three topics of industrial interest, relating to fluid transient phenomena, were mainly examined. (1) the pressure surge produced during the decompression process, (2) the duration of cavitation after column separation, and (3) the pressure surge at the collapse of the first cavity. Particular attention was paid to observing the mechanism of the appearance of gas bubbles near the downstream side of the valve, and of their growth and decay sequences. Values calculated from a proposed bubble model, in which the effects of gas (air) released from the liquid in the early stages of decompression and of surface tension due to minute gas bubbles were considered, were found to agree with measured results with an error of within 10% under ordinary operating conditions.
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