Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 11, 2020 - November 13, 2020
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. Prior to the experiment of the bubble collapse near a rigid wall, the experiment for the collapse of the laser-induced bubble in bulk water has been conducted to investigate the applicability of the FOPH to the pressure measurement of shockwaves. The directivity of FOPH and the distance attenuation of pressure waves have been evaluated by controlling a directional angle to the spherical shockwave and a distance from a collapsing bubble. In the experiment of the collapse of a laser-induced bubble near a rigid wall, the peak value of the shockwave decays in inverse proportion to the distance, which shows the characteristic of a spherical wave propagation. Also, the pressure generated at the bubble collapse site estimated by the pressure measurement with FOPH and the water hammer pressure estimated by using the jet velocity obtained from the high-speed images tend to increase in proportion to γ (γ = s/Rmax, where s is the distance between the boundary and the center of the bubble at the time of bubble generation and Rmax is the maximum bubble radius), in the range of 2.25 < γ < 4.56. The pressure measured with FOPH agrees well with the water hammer pressures at lower γ numbers of 2.25 and 2.81.
