Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 07, 2019 - November 08, 2019
The pressure measurement using a fiber optic prove hydrophone (FOPH) and the observation with a high-speed video camera have been conducted simultaneously to investigate the collapse of a laser-induced bubble near a rigid wall and the corresponding shockwave generation due to the bubble collapse. Prior to the experiment of the bubble collapse near a rigid wall, the experiment of a laser-induced bubble in infinite liquid has been conducted to check the applicability of the FOPH to the pressure measurement of shockwave generated by the bubble collapse. The directivity of FOPH is evaluated by controlling a directional angle to the spherical shockwave and a distance from a collapsing bubble. Although the peak value of the pressure decreased with an increase in the directional angle, only 5 % reduction of the peak value is confirmed in case of 20 degrees of the directional angle. The peak value of the shockwave decays in proportion to the -1th power of the distance, which shows the characteristic of a spherical wave propagation. In the experiment of the collapse of a laser-induced bubble near a rigid wall, the shockwave generated from a collapsing bubble have double peaks due to the micro-jet penetration and the bubble rebound. The first pressure peak corresponds to the micro-jet penetration and is proportional to the stand-off parameter from a wall and also correlates well with the water hummer pressure evaluated form the tip velocity of a micro jet measured by the high-speed observation.
