Grid Turbulence in Dilute High-Polymer Solutions 



Figure 5 shows a typical family of signal waveforms in water, when the 

 sensor is towed at x/m = 10.7, 12.6, and 20.2. Also included is the case where 

 all conditions are the same except that the sensor is being towed without the 

 grid along the tank, which is completely quiet. This noise test case will be 



labeled x/M ~ co. 



The absence or very low level of fine -scale structure in the waveforms of 

 Fig. 5 is due to the dominant action of viscosity which begins at k/k^ % 0. 1. 

 For x/M =10.7 the wavelength corresponding to k^ is roughly 0.2 cm or half of 

 one major division of the time scale. 



For all conditions the same except for tank fluid and a negligible change in 

 sensor sensitivity. Fig. 6 shows the character of the signal at x/M = 10.7, 20.2, 

 and CO in Solution F-5 (P301B; 137 ppm; prepared by the master-solution method) 

 on the third day after dispersal, and at x/M = 10.7, 11 hours later. This is a 

 typical case of significant raggedness near the grid, negligible raggedness far- 

 ther away, and (only for Polyox) a decrease of raggedness with solution age at a 

 given x/M. The lower group of sweeps in Fig. 6c is for the ordinary speed, but 

 the upper group of sweeps is for the sensor at rest. Since the noise with the 

 quartz-coated sensor at rest in quiet fluid was independent of the test fluid, the 

 upper group also applies to the case of Fig. 5d for water. Thus there was a 

 decrease in noise level when the sensor was set in motion in water but a slight 

 increase in the solution. With variation of the lateral, y and z , coordinates, 

 there were no notable changes in signal character, but some further evidence for 

 a low degree of intermittency of the raggedness. 



The decay of raggedness with solution age is illustrated for Solution F-10 

 in Figs. 7-9. At 71 hours of age, raggedness is seen at x/M - 20.2, but by 89 

 hours it is essentially gone at the same x/M but still evident at x/M = 12.6. By 

 six days of age, raggedness is still detectable at x/M = 6. The waveforms for 

 x/M = CO in Fig. 9c show distinctive blips (corresponding to depressed heat 

 transfer) which are not seen for x/M - co in Fig. 7d. This phenomenon was found 

 in several cases of the concentrated, older Polyox solutions, and visible blobs 

 could be detected when none had been found before. 



With other additives used in this work, there was more intense and age- 

 independent signal raggedness (for Separan AP-30 and JlOO), and there was a 

 higher level of solution noise which interfered more with spectral measure- 

 ments (for guar gum, Separan AP-30, and JlOO). Some tj^ical waveforms for 

 JlOO are given in Fig. 10 for Solution F-6 with a concentration of 46 ppm, pre- 

 pared by the master-solution method. The waveforms in Fig. 10 can be com- 

 pared with waveforms in water for corresponding x/M values in Fig. 5, for the 

 same sensor and only a minor change in sensitivity. The more intense ragged- 

 ness in this case seems to be related to the higher solution noise. In Fig. lOd 

 the waveforms for x/M = co are for two sensor towing speeds of about 20 and 45 

 cm/sec for the upper and lower groups respectively. A reasonable hypothesis 

 is that the cause of the higher noise level is solution inhomogeneity, and it im- 

 plies that the main result of changing speed from Uj to Uj should be a distortion 

 of the characteristic times by the factor Ui'U2. The waveforms in Fig. lOd are 

 at least superficially consistent with this requirement. 



47 



