102 



2 3 



BODY REYNOLDS NUMBER - 



UD/I/ 



FIGURE 35. Cavitation suppression by polymer injection 

 on the NSRDC body . 



0.6- 



b 



.0.4 



CL 

 LU0.3 



0.2 



2x10^ 3 4 5 6 7 8 9 Uio' 



BODY REYNOLDS NUMBER-UO/i/ 



FIGURE 37. Cavitation inception on the Schiebe body 

 in three different facilities. 



turbulence levels? From the proceeding cJiscussion 

 of the fully wetted results it appears that the 

 differences in observed critical Reynolds numbers 

 are probably due to a higher turbulence level in 

 the NSRDC facility. It follows then that the dif- 

 ferences in the type of inception for velocities 

 less than 30 feet per second can be explained in 

 teirms of the different viscous flows. However, we 



still need to account for the different freestream 

 populations of nuclei, the siibject of the next 

 section. 



Polymer Injection 



Some inception data for the hemisphere nose body 

 with polymer injections are given in Figure 38 as 

 a function of the injection rate for two concentra- 

 tions. The same data have been replotted in Figure 

 39 against the non-dimensional injection parameter 

 G. It can readily be seen that the two curves have 

 collapsed onto one. A similar happy result was 

 found when the dimensions of the laminar separation 

 bubble on the hemisphere nose body were plotted 

 versus the parameter G. These correlations of the 

 inception index and separation bubble dimensions 

 with G implies that the polymer "effectiveness" is 

 proportional only to the amount present within the 

 boundary layer, here taken to be the displacement 

 thickness. 



For the NSRDC and hemisphere nose bodies it can 

 be seen that increasing amounts of polymer in the 

 boundary layer produce an increasing suppression 



FIGURE 36. Photographs of cavitation on the (same) 

 Schiebe body in the LTWT (upper picture) at a cavita- 

 tion index of 0.52 and in the HSWT at an index of 0.41. 

 The flow speeds are 7.3 and 14 m/s, respectively. 



I 0.7 

 CL 



0.6 -, 



g 05 - 



I- 

 a. 



LxJ 

 U 



0.4 - 



2 

 O 



0.3 



< 



I- 



< 



5 10 



POLYMER INJECTION RATE -ml/sec 



FIGURE 38. Cavitation index with polymer injection on 

 the hemisphere body at a Reynolds number of 7.5 x 10^. 



