Observations on Cavitation Bubble Collapse

Abstract

Experimental observations are made on collapsing cavitation bubbles. Bubbles generated by two different methods are studied. The first method consists of bubble generation and collapse by flow over a submerged body. This work is done in the High-Speed Water Tunnel of the Hydrodynamics Laboratory. Existing photographic equipment and experimental techniques are employed. The second method consists of bubble generation and collapse by variation of the hydrostatic pressure. Much improved time and space resolution of the collapse is obtained in the latter case by design and construction of a high-speed photographic system. Bubble collapse pictures are taken at 10^5 frames per sec and an effective exposure time of 5 x 10^(-8) sec. A magnification of eight diameters fro.m object to image is attained. This equipment reveals new details of cavitation bubble collapse. Numerical solutions of the spherical bubble collapse equations are compared with experimental results. A consistently longer collapse time is observed in all cases. Observed bubble asymmetries are shown to be caused by pressure gradients. A large degree of coupling 1s shown to exist between the radial motion and the translational motion of the bubble centroid. Bubble collapse is observed to be much less stable than bubble growth.