Jets and Shock Waves from Cavitation 



REPLY TO DR. HICKLING 



It was not meant to imply that centers of high gas compression could not 

 occur in an asymmetric collapse. However, it seems reasonable that a given 

 cavity would not be as effective in this regard after being broken up into a num- 

 ber of smaller ones. 



Figure 4 was introduced to illustrate the fact that there can be shock waves 

 generated from more than one center during a bubble collapse. This is evident 

 from the two shock fronts in Fig. 4. These shocks were assumed to be formed 

 from liquid-liquid impact because of the evident failure of the bubble to collapse 

 completely. It should also be pointed out that light flashes are produced by a 

 liquid jet striking a solid surface.* The source of this light is still in question, 

 but even if it does come from gas compression, it is compression caused by an 

 impacting jet. 



I agree with Dr. Hickling that cavity collapse is a complicated process and 

 that there are several hydrodynamic effects involved in cavitation damage. I do 

 believe that sufficient evidence has been accumulated to show that jet impact is 

 a major cause of damage even if it is not the only one. 



REPLY TO D. C. GIBSON 



I particularly want to thank Mr. Gibson and Dr. Benjamin for their illus- 

 tration of the effectiveness of shock waves from bubble collapse in generating 

 new cavities. I have long felt that this might be an important mechanism in 

 cavitation hysteresis. My experience, especially in acoustically generated cavi- 

 tation, is that the presence of one cavitation cloud is very effective in starting 

 another, even at some distance away. I have also noticed secondary bubble for- 

 mation both from spark generated bubbles and bubbles originating from gas 

 nuclei in a varying pressure field. I agree completely with the explanation 

 given, especially since the effect also seems to exist with other than spark gen- 

 erated bubbles. 



*S.M. DeCorso and R.E. Kothmann, "Erosion by Liquid Impact," Symposium on 

 Erosion and Cavitation, ASTM STP 307, Am. Soc. Testing Materials, 1962; S.M. 

 DeCorso and R.E. Kothmann, "Characteristics of the Light Flash Produced 

 Upon Impact of a Liquid vv^ith a Surface," Materials Research and Standards, 

 Oct. 1965, pp. 525-528; J.H. Brunton, "High Speed Liquid Impact," Phil. Trans, 

 of the Royal Soc. of London, Ser. A, Vol. 260, pp. 79-85, July 1966. 



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