Gas Nuclei Trajectories and Cavitation Inception 



The results presented are, of course, limited because of the simplifying 

 assumptions which were made. The bubble trajectories will be modified by the 

 influence of the boundary layer. Furthermore, the trajectories will be influ- 

 enced by the distortions from a spherical shape caused by the forces acting on 

 the bubbles. Also, for very small bodies and high speeds, the dynamic effects 

 which were neglected in the analysis presented may become important. Never- 

 theless, the screening mechanism of the body pressure gradients will persist 

 and this phenomenon must eventually contribute to a final imderstanding of cavi- 

 tation inception. 



REFERENCES 



1. Johnson, V.E., Jr., "Report to the Fourteenth American Towing Tank Con- 

 ference on Cavitation," Hydronautics, Inc., Sept. 1965 



2. Ripken, J.F., and Killen, J.M., "Gas Bubbles: Their Occurrence, Meas- 

 urement, and Influence in Cavitation Testing," Proc. lAHR Symposium on 

 "Cavitation in Hydraulic Machinery," ed. Numachi, N.F., Sendai, Japan, 

 pp. 37-57, Sept. 1962 



3. Langmuir, I., and Blodgett, K.B., "A Mathematical Investigation of Water 

 Droplet Trajectories," Army Air Forces Technical Report 5418, Feb. 

 1946 



4. Haberman, W.L., and Morton, R.K., "An Experimental Investigation of the 

 Drag and Shape of Air Bubbles Rising in Various Liquids," DTMB Report 

 802, Sept. 1953 



5. Taylor, G.I., "The Force Acting on a Body Placed in a Curved and Con- 

 verging Stream of Fluid," Reports and Memoranda 1166 (Ae 330), Apr. 1928 



DISCUSSION 



C.-A. Johnsson 



Swedish State Shipbuilding Experimental Tank 



Goteborg, Sweden 



We have seen outlined here a very elegant mechanism for explaining the 

 scale effect at cavitation tests. In this mechanism the minimum diameter of the 

 bubbles present in the tunnel is an important parameter. I would like to men- 

 tion that another measure of this diameter can be obtained by calculating the 

 resorption capacity of the tunnel circuit. This will give you the largest diame- 

 ter for complete resorption and thereby the diameter of the smallest bubble 

 present. Equations for such calculations have been given by, for instance, 

 Silverleaf. 



179 



