decreasing , perhaps by one-half, the cavitation inception index in jets and 

 the flow over bodies reported by many workers (e.g., Ellis and coworkers, 

 Holl, Arndt and coworkers, Hoyt, van der Meulen; see van der Meulen 1974, 

 Gates 1977 for review). Despite the initial conclusions of Ellis (Ellis 

 et al. 1970) that bubble mechanics were not a factor in this suppression, 

 considerable uncertainty as to the basic cause of the effect remained. 



The Polymer Effect in Cavitation 



It is certainly fair to say that the presence of long-chain polymers 

 in dilute liquid solutions has had a vitalizing effect on liquid fluid 

 mechanics. The many reasons for this development are well covered by the 

 extensive review of Hoyt (1972). But, as sketched in the foregoing dis- 

 cussion, there is an additional unique effect of polymer solutions on cavi- 

 tation inception. Two kinds of flows have been extensively pursued, 

 cavitation inception on bodies (as discussed herein) and in jets. The 

 magnitude of the effect appears to be equivalent; we discuss only smooth 

 body inception in the following sections. 



It seems most natural in discussing these types of fluid to note the 

 appearance of particular phenomena with a characteristic time ratio, such 

 as the ratio of the time required for the fluid to move a certain length, 

 to a characteristic polymer molecular relaxation time. In fact such a 

 relation was used by Arndt (Arndt et al. 1976) to correlate such suppression 

 results, and it appeared to work best if a relevant boundary layer length 

 was used as the length parameter. At about the time of the 17th ATTC 

 conference (Morgan 1974) it was suggested by several workers including J.W. 

 Holl that, based on the appearance of the cavitation band at inception, 

 the polymer seemed to cause the interface to become turbulent with the 

 implication that transition had occurred. But this demonstration remained 

 for van der Meulen (1976) to carry out. He showed, by careful and ingeni- 

 ous adaptation of a schlieren-holographic technique, that the polymer fluid 

 appears to trigger a turbulent transition and that, on the hemispherical 

 body (for example) , this transition removed the laminar separation. Then 

 one would have, presumably, a situation rather similar to that of a body 



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