403 



PROPELLER A 



5 BLADES 



: 326B m 

 Ae/Aq ; 0.820 

 C07/D : 368 

 Vc bTl : 042 



FIGURE 3. Irregular collapse of cavitation on propeller 

 C behind the model. 



PROPELLER B 



6 BLADES 



D : 0.2183 m 

 Ae/Ao = 833 

 C07/D = 438 

 UcCT) : 040 



propeller Reynolds number was varied with a factor 

 of about three. 



-The cavitation index. Three values of the 



cavitation index were used: 



■"NT 



1=1.5, 2.0, and 2.5. 



The reference level of the cavitation index was 

 always taken at the propeller tip in the top position. 

 In this paper most cavitation observations will be 

 At higher revolutions a lower 



shown at a„ip=l-5 



cavitation index was possible: 



-'NT' 



=0.5 in the 



towing tank and aMm=1.0 in the cavitation tunnel. 



Paint Observations 



To visualize the character of the boundary layer 

 at the propeller blades a surface oil flow technique 

 was used [Maltby, ed. (1962)]. This technique was 

 adapted for use in water on propellers by Meyne 

 (1972) and Sasajima (1975). It is particularly 

 useful on rotating bodies because the difference 

 in friction coefficient between laminar and turbu- 

 lent boundary layer flow, in combination with the 

 centrifugal force acting on the paint, creates a 

 clear difference in the direction of the paint- 

 streaks in laminar and turbulent regions. 



The paint, used in our paint tests, consisted 

 of lead-oxide, diluted with linseed oil and coloured 

 with red "Dayglo" pigment. This mixture produced 

 a finely detailed pattern of streaks on the metal 

 surface of the propeller. When the propeller 

 blades were painted yellow with a thin layer of 

 zinc-chroraate primer, as is done with the cavita- 

 tion observations to improve contrast and to avoid 

 reflections, no streaks were formed. Consequently 

 the flow visualization tests were done with the 

 propellers not painted. 



The viscosity of the paint was controlled by 

 the amount of linseed oil and was chosen such that 

 the formation of the pattern took about one full 

 run in the towing tank. At least 500 revolutions 

 were always available to form the pattern. To 



PROPELLER c 



4 BLADES 



D : 300 r 

 Ae /Aq : 630 

 Cot/D : 430 

 t/clo?) : 022 



PROPELLER D 



FIGURE 4. Geometry of propellers. 



6 BLADES 



: 2120 r 

 Ae /Ao : 824 

 C07/D = 307 

 t/c(07) i 0.050 



reach the desired 

 revolutions, most 

 condition. Paint 

 cavitation tunnel, 

 were more profuse , 

 ities, because of 

 to reach a stable 



condition took about 100 

 of them very close to the final 

 tests were also done in the 

 The pictures obtained there 

 especially at high tunnel veloc- 

 the relatively long time it took 

 condition. For runs longer than 



