426 



Discussion 



SHIN TAMIYA, HIROHARU KATO , and YOSHIAKI KODAMA 



-SETTLING SECTION 



NUCLEI GENERATIOII SECTION 



^TEST SECT ion (80x80x1000) 



FIGURE 1. General arrangement. 



The discussers appreciate the excellent re- 

 search work on cavitation inception done at NSMB*. 

 At the University of Tokyo the discussers also per- 

 formed similar experiments using both hemispherical 

 and ITTC headforms tested in our newly built cav- 

 itation tunnel. This tunnel has a filtering tank 

 containing 60 cartridge type filters, which contin- 

 uously remove air nuclei and solid particles larger 

 than ca. 1 ym from water (Figure 1) . 



Figures 2 through 7 show the effect of elec- 

 trolysis on cavitation inception. The photograph 

 in Figure 3 was taken a few seconds after that in 

 Figure 2. The flow conditions are exactly the same 

 for Figures 2 and 3; the only difference is the 

 presence of hydrogen bubble nuclei. The photographs 

 in Figures 4 and 5, as well as 6 and 7, were also 

 taken under the same conditions. 



In the discussers ' experiments the cavitation 

 caused by electrolysis nuclei generates only bubble 

 type cavitation. Even when sheet cavitation exists, 

 the cavitation bubbles caused by the electrolysis 

 nuclei seem to break up the sheet cavity. 



FIGURE 2. 

 a = 0.81. 



without hydrogen bubbles V = 6.8 m/s , 



♦Netherlands Ship Model Basin 

 #Statens Skeppsprovningsanstalt 



FIGURE 3. With hydrogen bubbles V = 6.8 tn/s, 

 a = 0.81. 



