427 



11 * ■■ M «Mi II 



FIGURE 4. Without hydrogen bubbles V = 6.8 m/s , 

 a = 0.71. 



FIGURE 5. With hydrogen bubbles V = 6.8 m/s, 

 o = 0.71. 



FIGURE 6. Without hydrogen bubbles V = 6.8 m/s, 

 a = 0.60. 



FIGURE 7. With hydrogen bubbles V = 6.8 m/s, 

 a = 0.60. 



O. RUTGERS SON 



I would like to congratulate the author of 

 this interesting paper. As a complement to the data 

 presented I think that some results obtained at 

 SSPA# when testing high-speed propellers could be 

 of some interest. A propeller of the supercavi- 

 tating type was tested with three different gases 

 in the water. Also, two different conditions of 

 the blade surface were used, smooth polished and 

 painted with a thin spray paint giving the surface 

 some roughness. 



In Figure 1 the propeller characteristics from 

 these tests for homogenous flow at the cavitation 

 number, a = 0.6, are shown. In the partially cav- 

 itating region (J > 1.0) there is a very pronounced 

 influence due to gas content for the polished pro- 

 peller. For the painted propeller no such influ- 



ence was found. Cavitation pictures at the advance 

 ratio, J = 1.1, give the explanation for these 

 differences. Figure 2 shows the cavitation at the 

 lowest gas content (a/Og = 0.2) for the polished 

 propeller. The cavitation pattern is divided into 

 two parts. The first part is a sheet starting at 

 the leading edge. The second part is an unstable 

 sheet of bubble cavitation at the aft part of the 

 blade. Tests at higher gas contents (Figure 3, 

 a/ttg = 0.4) show that the aft part cavitation now 

 has a larger extension. The painted propeller 

 (Figure 4) shows a rather different pattern for the 

 aft part cavitation (the leading edge sheet is al- 

 most uninfluenced by gas content and roughness) . 

 The aft part cavitation now consists of a thin sheet 

 of very small bubbles. The sheet also has a rela- 



