19 



The effects of air content on cavitation inception in flowing water 

 has been the subject of many investigations. It will be sufficient here to 

 discuss the experiments carried out by Crump 37 and Numachi and Kurokawa. 38 ' 39 

 Using a smooth nozzle with a very gradual diffusor, Crump was able to obtain 

 tensions as high as 60 feet of water for an air content of 5 cm 3 per liter of 

 water, and showed a general increase of tension with decreasing air content, 

 Figure 14. On the other hand, Numachi and Kurokawa showed somewhat different 

 results although a careful analysis of their results Indicated that they also 

 obtained tensions. 37 ' 39 Whereas Crump's experiments showed a decrease in 

 critical pressure with increased absolute velocity, Numachi 's results showed 

 an opposite trend. An explanation of Numachi's results is rather easily formu- 

 lated, but the reasons for Crump's results are quite obscure. It was at first 

 thought that the trend observed In Crump's experiments was related to the time 



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Velocity in Constriction in feet per second 



Figure 14- - Cavitation Inception in Fresh Water of Varying 

 Air Content — From Reference 37 



