壁面近傍での気泡崩壊時の二方向同時撮影画像と衝撃圧分布との関係

Abstract

The pressure measurement using a fiber optic prove hydrophone and simultaneous two-directional observation with a high-speed video camera have been conducted to investigate the collapse of a laser-induced bubble near a rigid wall and the corresponding shockwave generation. Pressure measurements at multiple locations near the rigid wall and observations of frontal and overhead views relate to the locations of pitting damage due to bubble collapse observed by Philipp and Lauterborn (J. Fluid Mech., 1998). In γ=s/Rmax≅1.5 where s is the distance between the bubble center and the wall surface and Rmax is the equivalent bubble radius at the maximum growth, the second bubble collapse occurs on the rigid wall: the overhead view reveals that the bubble collapses asymmetrically with a toroidal (ring) shape and bubble blobs remain at the bubble center and on both sides of the ring in the direction of laser injection. It is shown that the area of the bubble blobs on the ring correlates with the high pressure on the wall. This suggests that the collapse of these blobs leads to the high pressures and asymmetric pitting damages on the wall.