449 



E 035 



(s/D)p =0.37 



o Re .094x10 = 



• Re = 1,22 xlO^ 



i Re = 1.55x10^ 



A Re-208x10^ 



A A 'U 



02 04 06 08 10 12 



Streamwise Distance to Cavitation Separation 

 over Diameter, s^/D 



FIGURE 33. Streamwise distance to cavitation separa- 

 tion over diameter, s /D, as a function of cavitation 

 number and Reynolds number for blunt nose. Also plotted 

 are some data points where no cavitation was observed 

 on one or both sides of the model. 



5 . CONCLUSIONS 



The application of in-line holography and injection 

 of a 2 percent sodium chloride solution from the 

 nose of the axisyinmetric bodies are useful methods 

 to visualize the boundary layer and to obtain 

 detailed information on boundary layer phenomena 

 and cavitation patterns . 



Laminar boundary layer separation and transition 

 to turbulence of the separated shear layer on the 

 hemispherical nose can be predicted quite accurately 

 by existing approximate calculation methods. 



Cavitation on axisyiranetric bodies may be strongly 

 influenced by boundary layer effects. For the SST 

 hemispherical nose, inception and appearance of 

 cavitation are both related to the location and 

 appearance of the separation bubble. For the 

 blunt nose, however, cavitation is apparently more 

 related to nuclei effects than to viscous effects. 

 The type of cavitation occuring in this case is 

 travelling bubble cavitation. The growth of a 

 cavity on the blunt nose is adequately described 

 by the Rayleigh-Plesset equation of motion for a 

 cavitation bubble. 



TABLE 3. Theoretical (R) and Experimental (Rgxp) 

 Values of Bubble Radius for Cavity Growth on 

 Blunt Nose (Figure 31) . 



TABLE 4. Influence of Vapor Pressure, P^, Liquid 

 Pressure, P, Surface Tension Pressure, 2 S/R, and 

 Viscosity Pressure, 4ij R/R, on Cavity Growth on 

 Blunt Nose (Figure 31) . 



Surface effects on the Teflon hemispherical nose 

 play a dominant role in both inception and appearance 

 of cavitation. 



The presence of polymers in the "inner part" of 

 the boundary layer on the SST hemispherical nose 

 leads to destabilization, whereas the presence of 

 the polymer in the "outer part" of the boundary 

 layer leads to stabilization, and the latter effect 

 is predominant. For all cases considered, laminar 

 boundary layer separation is suppressed. 



Since the influence of polymer additives is to 

 suppress laminar boundary layer separation on the 

 hemispherical nose, the strong pressure fluctuations, 

 occurring at the position of transition and reattach- 

 ment of the separated shear layer and being the 

 principal mechanism for cavitation inception, are 

 eliminated and cavitation will start at much lower 

 pressures. As a consequence, the cavitation charac- 

 teristics of the SST hemispherical nose with polymer 

 injection are approximately the same as those of 

 the blunt nose without polymer injection. 



B 



Cp 



CPmin 

 Cpg 



CPT 



D 



H 



He 

 L 



LC 



LSC 

 P 



Po 



R 

 Re 



Ref 



S 



Tu 



Sep 



NOTATION 



Constant in Equation (3) 



Pressure coefficient 



Minimum pressure coefficient 



Pressure coefficient at separation 



Pressure coefficient at transition 



Model diameter 



Height of separation bubble 



Height of cavity 



Length of separation bubble 



Length of cavity 



Length of sheet cavity 



Static pressure 



Free stream static pressure 



Minimum static pressure 



Vapor pressure 



Bubble radius 



Reynolds number, VqD/v 



Equation (4) 



Surface tension 



Turbulence level 



Velocity at edge of boundary layer 



Free stream velocity 



Injection velocity 



Amplitude of disturbance 



Amplitude of disturbance at neutral 



stability 



Friction factor 



Equation (2) 



Nose radius of cavity 



