Grid Turbulence in Dilute High-Polymer Solutions 



+3.6 db to the solution curve (due to sensor replacement by one of much lower 

 sensitivity) is made, the spectral level shift data in Fig. 21 are obtained. 



The amount of the spectral shift can be compared with the predicted shift 

 due to simple viscosity increase according to Kolmogoroff similarity with con- 

 stant dissipation. Using the relative viscosity measurements on Solution F-5 

 discussed earlier, the viscosity ratio v' '"ly for 66 hours can be estimated as 1.27. 

 Thus the dashed curve in Fig. 21 results from the viscosity spectral shift rela- 

 tion of Eq. (5). The agreement is as good as in the case of the cold-water tests. 

 Thus there is no evidence of any non-Newtonian effects. 



Spectral shift curves for solution F-5 for various solution ages and x/M = 

 10.7 are given in Fig. 22. The theoretical dashed curve is for 73 hours, but ap- 

 plies for all three solution ages, since the decrease of viscosity ratio from 1.27 

 to 1.23 for 66.5 to 85 hours produces only a 4% decrease in log (v' /v) . 



The changes in signal waveforms in Fig. 6 for x/M = 10.7 between 72 and 83 

 hours can be compared with the changes in spectral shift for the same x/M in 

 Fig. 22 for roughly the same period. It is clear that as the solution ages the 

 decrease of raggedness reveals more and more of the spectral shift due to the 



Fig. 22 - Spectral level shift in Solution 

 F-5 compared with water for x/M = 10.7 

 and various solution ages 



65 



