62 



of the results shown in Figure 2k, it is necessary to measure the actual pres- 

 sures within the cavity for defining the cavitation number. In general, it 

 will be more satisfactory to use plane, sharp-edged obstacles for such experi- 

 ments. In using forms having surface curvature care should be taken to fair 

 out the discontinuity in cavity shape due to finite angle of separation before 

 constructing the body. 



CONCLUDING REMARKS 



Although the foregoing discussion has emphasized the progress made 

 in understanding the mechanism of cavitation, the gaps in the present knowl- 

 edge appear clearly. A great deal of research remains to be done on the pre- 

 diction of cavitation inception in "engineering" liquids, the mechanism of 

 maintenance of steady-state cavities in real liquids and the analytic descrip- 

 tion of such cavities (especially in three dimensions), and the mechanism of 

 collapse and the associated damage. 



ACKNOWLEDGMENTS 



The writer is indebted to Dr. E.H. Kennard and L. Landweber for 

 their critical reviews of this_ report and for several helpful suggestions. 



Mr. S.P. Crump assisted in the experiments leading to the results 

 of Figure 32. 



Thanks are due the following for permission to use the figures 

 listed as follows: To the Journal of Applied Physics for Figure 6; to the 

 Bureau of Reclamation for Figures 11 and 33; to Dr. R.T. Knapp, Director, 

 Hydrodynamics Laboratory, California Institute of Technology, for Figures 15 

 and 1 6; to Dr. M.S. Plesset, California Institute of Technology, for Figures 

 7 and 29; to A.M. Worthington's trustees and Longmans, Green and Co., Ltd., 

 Publishers, London, for Figure l8; and Dr. Hunter Rouse, Director, Iowa Insti- 

 tute of Hydraulic Research for Figure 3H-. 



