Jets and Shock Waves from Cavitation 



Fig. 11 - Sequences taken at beginning, middle, and 

 end of a film at 5000 framies per second showing a 

 thin, high-velocity jet which has formed and hit be- 

 tween the first two frames of the last sequence 

 (actual size) 



a wall much as a massive but deformable missile ready to deliver a definite 

 impulse by virtue of its translational velocity. Concentration of this impulse 

 over a small area of the wall through the jet mechanism will depend critically 

 on a large number of factors, especially the location of stagnation points in the 

 flow and the flow velocity. Such dependence might well explain the observations 

 by Knapp (17) that cavitation damage in the vicinity of a re-entrant flow stagna- 

 tion point was extremely sensitive to flow velocity (he stated it varied as the 

 sixth power of the velocity). He and other investigators have also found that an 

 extremely small fraction of the bubbles present actually did damage. This 

 would fit in well with the ideas presented here. Of course it should be noted 

 that the possibility of damage by shock waves has not been ruled out, and the 

 mechanism considered here is offered in addition to and not in place of the 

 shock-wave hypothesis. However, shock wave generation is probably an infre- 

 quent event itself; and if only spherical collapses were effective, it would be 

 more infrequent still. 



In view of the many new qualitative observations and ideas it seemed most 

 desirable to construct new equipment at the California Institute of Technology in 

 which single bubbles could be generated and subjected to a known and repeatable 



147 



