Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : November 12, 2022 - November 13, 2022
Two cavitation bubbles generated by laser irradiation in water generate microjets due to their mutual interference. The characteristics of microjets vary depending on the size and distance of the bubbles, as well as on the time difference between bubble generation and microjet generation. Therefore, the purpose of this study is to clarify the effect of the bubble generation time difference, T*D in dimensionless form, on the bubble motion and microjet by numerical calculations and experiments. Numerical calculations are performed using the boundary element method and the VOF method, both of which have conflicting characteristics, and two numerical methods are used for efficient analysis. In this study, cavitation bubbles are generated at the top and bottom, and the lower bubble that is generated first is bubble A, and the upper bubble that is generated after a delay is bubble B. When the distance between the bubbles and the bubble size ratio are kept constant and the bubble generation time difference is varied, it is found that there are three types of microjets generated in bubble A due to the mutual interference between the two cavitation bubbles. Upward microjets are generated in bubble A and penetrate upward when the bubble generation time difference is small. This occurs when the expansion of bubble A is slightly disturbed, causing the underside of bubble A to become concave. A downward microjet is generated in bubble A and penetrates downward when the bubble generation time difference is large. This is caused by the upper side of bubble A being pushed in due to the strong influence of the expansion of bubble B. When the bubble generation time difference is in the range of 0.16 ≤ T*D ≤ 0.20, bubble A is separated into two parts, resulting in the creation of upward and downward microjets. This is caused by the predominant horizontal nipping of bubble A.
