キャビテーション壊食量の推定法

第2報: 気泡群崩壊による衝撃力頻度分布計測の信頼性評価

抄録

The objective of this study is to develop a procedure of predicting the cavitation erosion intensity. To this end, it is necessary to estimate impulsive forces caused by collapse of cavity bubbles. In the first report the authors measured cumulative events of impulsive forces by collapse of cavity bubbles on a two-dimensional foil with a piezoelectric sensor. In this paper the authors measured the cumulative events again with three sensors of different kind to verify the results reported in the first report. The measurements by the three different sensors agreed well with each other. Among these sensors, the PVDF sensor was practical and suitable for the authors' purpose. In addition, collapse of cavitation bubble clusters was observed with a digital high-speed video camera synchronized with the signal of impulsive force sensors. Duration of collapse was the order of 100 microseconds, which was far slower than that of an impulsive force that was around 5 microseconds. According to theoretical calculations the impulsive pressure is generated when the whole cloud cavity collapses completely. But in this observation the peaks of impulsive force did not meet the instant of final collapse, but occurred some 10 to some 100 microseconds earlier than the final collapse. These results suggest that an impulsive force may not be caused by the global collapse of a bubble cluster but by the collapse of a part of cloud cavity.