Ill 



Discussion 



G. CHAHINE and D. H. FRUMAN 



The question of whether polymer solutions 

 affect cavitation inception through changes of the 

 flow structure or through the inhibition of biobble 

 growth has been the subject of much controversy. 

 In this excellent paper the authors seem to adhere 

 to the first school of thought and disregard the 

 second. We think that there is ample evidence of 

 the profound flow changes introduced by the ejected 

 polymers to support, at least partially, their 

 contention. However, evidence also exists showing 

 that the onset of acoustically generated cavitation 

 is delayed by the presence of minute amounts of 

 polymers and asbestos fibers [Hoyt (1977)]. also, 

 in investigating the behavior of spark -generated 

 bubbles in the vicinity of a solid wall , the dis- 

 cussers have observed significant changes being 

 promoted by the presence of the polymers. 



Figure 1 shows the geometric dimensions that 

 have been considered in the analysis of the bubble 

 behavior. The displacement of point A, where the 

 re-entering jet originates , divided by the maximum 

 lateral dimension of the bubble, R^max' ^^ plotted 

 in Figure 2 as a function of the dimensionless time 

 parameter, t/tp, and the parameter, n , which is the 

 ratio between R^jnax ^""^ ^' ^^^ distance between the 

 center of the spherical initial bubble and the wall. 

 As shown, the polymer solution has a retarding 



effect on the re-entering jet. This effect in- 

 creases with increasing r\ [Chahine and Frunian 

 (1979)]. Together with results shown in Hoyt, 

 our data further confirm that, in the absence of 

 flow, bubble behavior is affected by the intrinsic 

 properties of dilute polymer solutions. 



Ba 





A^' 



^ 



;s3o— oo"i: 



-^ 



»- 



.0.5 



RUN 



A PY59 

 APY71 

 • PY68 

 OPY64 



0.50 

 0.56 

 1.39 

 1.25 



LIQUID 



DISTILLED WATER 

 POLYOX 250 PPIVIW 



DISTILLED WATER 



R. 



FIGURE 1 



FIGURE 2 



REFERENCES 



Hoyt, J. W., (1977). Cavitation in Polymer Solu- 

 tions and Fiber Suspensions. Cavitation and Poly- 

 phase Flow Forum, ASME. 



Chahine, G. L., and D. H. Fruman (1979). Dilute 

 Polymer Solution Effects on Bubble Growth and Col- 

 lapse. Physios of Fluids. 



