レーザー誘起クラウドキャビテーションの非定常挙動と衝撃波の発生・伝播の同時観測実験

抄録

It is well known that cloud cavitation exhibits unsteady behavior characterized by repetitive processes of growth and collapse, which are associated with the generation of shock waves. The destructive power of cloud cavitation has been recognized and utilized in various fields. However, the involved processes―such as generation, growth, collapse, rebound, emission of shock waves, and their propagation―have not been thoroughly explored experimentally due to their extremely small temporal and spatial scales. In this study, we simultaneously observe the unsteady behavior of cavitation clouds induced by submerged water-jet injection and phenomena related to shock waves. Specifically, we have developed a simultaneous observation system using the shadowgraph and Schlieren methods, where two high-speed cameras operating at a shutter speed of 450,000 frames per second are arranged orthogonally to capture these unsteady phenomena. Our experimental findings clarify that the cloud has a high-void region known as the “nucleus of the cloud” and a low-void region. The nucleus of the cloud exhibits unsteady behavior, and a shock wave is emitted associated with its collapse. Finally, based on 100 repeated experiments, we suggest that the shock wave forms simultaneously with the cloud’s collapse and propagates faster than the sonic speed of water.