338 



pressure can excite cavitation inception. This fact 

 alone indicates that consideration should be given 

 to the details of the turbulent pressure field. 

 The available evidence indicates that two basic 

 factors related to the pressure field enter into 

 the scale effects. First, as the scale of the 

 flow increases, cavitation nuclei are relatively 

 more responsive to a wider range of pressure 

 fluctuations. Secondly, the available evidence 

 indicates that large deviations from the mean 

 pressure are more probable with increasing Reynolds 

 number. This would explain some of the observed 

 increases in cavitation index with physical scale. 

 In view of the almost total lack of information on 

 the statistics of turbulent pressure field (aside 

 from some correlation and spectral data) and the 

 potential importance of this knowledge to under- 

 standing cavitation, it is strongly recommended 

 that careful experiments be initiated to remedy the 

 situation. Such experiments have been proposed by 

 George (1974b, 1975). 



Direct application of the pressure field informa- 

 tion to cavitation is unfortunately clouded by gas 

 content effects which also increase the cavitation 

 index with increasing exposure time. The fact that 

 a reasonably precise scaling law for cavitation 

 noise has not yet been found (perhaps a consequence 

 of the lack of knowledge about the pressure field) 

 further complicates interpretation of experiments 

 and theory. Therefore it is also strongly recom- 

 mended that the problem of the response of cavita- 

 tion nuclei to turbulence receive particular attention. 

 Such experiments have been proposed by Arndt (1978) . 



ACKNOWLEDGMENTS 



R. E. A. Arndt gratefully acknowledges the support 

 of the Air Force Office of Scientific Research and 

 the Seed Research Fimd of the St. Anthony Falls 

 Hydraulic Laboratory. W. K. George gratefully 

 acknowledges the support of the National Science 

 Foundation under grants from the Engineering (Fluid 

 Dynamics) and Atmospheric Sciences (Heterology) 

 Programs and the Air Force Office of Scientific 

 Research. Both authors are grateful to Mrs. Sandra 

 Peterson who typed the manuscript. 



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