Additives Injected Into the Boundary Layer of an Underwater Body 

 1.0 



0.5 



log i> 



-0.5 



-1.0 



-1.5 



-No additive 



probe 5 cm above 

 woke centre-line 



Additive 

 probe 0.5 cm above 

 woke centre-line 



Tunnel velocity - 400 cm./sec. 

 100 ppm. Polyox WSR-301 

 Flow rate — 30 ml. /sec. 



0.5 



1.0 1.5 



log k 



2.0 



Fig. 20 - Turbulent velocity power spectra 



The curves in Fig. 20 show that the injection of the polymer solution re- 

 duced the turbulence intensity over the frequency band analyzed. The highest 

 frequencies used for this analysis are about 1200 cycles per second because tl 

 frequency response of the hot-film probe falls off in this region. In Figure 21 

 the curves for the probe at the centre-line of the wake show that, for the smal 

 wave numbers, the turbulence energy is increased when the fluid is injected, t 

 as the wave number increases the curve for the additive crosses the other cur 

 and the energy at the higher wave numbers is less for the polymer in the boun 

 ary layer. For the 1.5 cm position, the additive curve is again higher, and the 

 point at which the curves appear to cross over is at a higher wave number tha 

 for the centre-line case. With the probe 3 cm above the centre-line of the wal 

 the character of the signal, as observed on an oscilloscope, contains many lar 

 spikes which indicate that the wake turbulence is intermittent in this position. 

 The curve for the additive case are still higher than for the wake without the £ 

 ditive but the slope of the curve indicates that a cross-over might occur at a 

 wave number larger than for the 1.5 cm case. 



DISCUSSION OF EXPERIMENTAL RESULTS 



This is essentially an exploratory experiment which attempts to add to th 

 knowledge of the behavior of polymer solutions in reducing the friction of a fl( 

 along a solid surface. Previous work by Fabula et al (1963) had shown that th 



221-249 O - 66 - 64 



993 



