98 



' |x|0= 2x10' 3x10* 4x10* 



BODY REYNOLDS NUMBER -UD/i/ 



FIGURE 26. The length of the laminar separation as a 

 fxinction of polyox injection on the NSRDC body. 



Comparison of Present Results with those of van 

 der Meulen 



van der Meulen (1976) has studied the influence of 

 dilute polymer solutions {Polyox, WSR 301) upon the 

 fully-wetted flow and cavitation inception for a 

 hemisphere nose body and was the first, to our 

 knowledge, to observe the Schiebe body (Cpj^^j = 

 -0.75) . He also was the first to inject the polymer 

 solution at the stagnation point. To observe the 

 flow on the test models , van der Meulen used pulsed 

 ruby laser holography. However, to make the flow 

 visible a salt was added to the polymer solution. 

 In his case the injectant was a 2 percent salt — 

 SOOwppm Polyox solution. 



On the hemisphere nose body he observed that the 

 injection of the salt-polymer solution eliminated 

 the laminar separation and he further speculated 

 that the polymer caused an early transition to a 

 turbulent non-separating bovmdary layer. On the 

 Schiebe body, which has no laminar separation, the 

 laminar to turbulent transition point was found to 

 move upstream of the no-injection position. The 

 present results for this body are seen to agree 

 qualitatively with those of van der Meulen (Figure 

 28) , although the deduced injection rates of the 



>■ 

 o 

 o 



2 004 

 O 



< 

 tr. 

 < 

 a. 



3x10= 5xl0' 7x10' 



BODY REYNOLDS NUMBER - UD/v 



9x10' 



Q 



J;5 



8 1.2 



< 



CC 1.0 



'0.8 



< 

 HO.6 



O0.4 



Z 

 LlI 



_l 



o 



CC 



< 





— I 1 1 1 



>G = 0, PRESENT RESULTS 



D -2x10"^ PRESENT RESULTS 



i -7x10"^ 



> -13X10"^ 



I -15x10"* von der MEULEN (1976) 



I -20x10"' 



1 xlO^ 2x10^ 3x10^ 



BODY REYNOLDS NUMBER-UD/i/ 



4x10^ 



FIGURE 27. The length of the laminar separation as a 

 function of polyox injection on the hemispehre nose 

 body. 



FIGURE 28. The position of transition on the Schiebe 

 body as a function of polymer injection. 



latter are rather larger. Even though freestream 

 conditions of these two tests may not quite be the 

 same, it is evident because of the nearly one order 

 of magnitude change in Reynolds number that the 

 polymer fluid is the chief agent of boundary layer 

 instability. 



5. EFFECT OF FLOW VISUALIZATION ON TRANSITION 



It is now well documented that heating a laminar 

 water boundary layer, tends to stabilize it [see 

 for example Wazzan et al. (1968a, 1970)]. This 

 point was further discussed with reference to the 

 hemisphere and ITTC test bodies by Arakeri and 

 Acosta (1973) who concluded that for the separating 

 flows of these bodies, the effect of heating was 

 on the order of only a few percent. Since the heat- 

 ing rate and velocity ranges are similar in the 

 present experiments, it is expected that the in- 

 fluence of heating on the hemisphere and NSRDC 

 bodies is not significant. However, there is some 

 question as to the influence of heating on the non- 

 separating flow on the Schiebe body. Shown in Fig- 

 ure 22 are averaged observed values of the position 

 of transition calculated by Wazzan with and without 

 wall heating. First, it can be seen that there is 

 good agreement between Wazzan 's calculation for an 

 unheated boundary layer with e" amplification and 

 the observed position of transition. However, the 

 point to be noted is that (with a wall temperature 

 10 °F above the ambient water temperature) these 

 same calculations predict a 40 percent delay in 

 transition at Rep = 2.5 x 10^. This would suggest 

 that wall heating is important although not perhaps 

 sufficient to alter major trends in the present ex- 

 periments. There is however the qualification that 

 the calculation assumes a constant wall temperature 

 while this is not the actual case. 



An attempt to measure the actual wall tempera- 

 ture was made by installing six thermocouples near 

 the surface of the model at positions of S/D = 0.4, 

 0.6, 0.8, 1.0, 1.2, 1.4. The position of neutral 

 stability on this body is S/D = 0.37 and the average 

 position of transition varied from S/D = 1.0 to 

 S/D = 0.8. Since it is the heating in the boundary 

 layer prior to transition that is of importance, 



