Additives Injected Into the Boundary Layer of an Underwater Body 



POLYMER SOLUTION 



Three types of poly(ethylene oxide) were used; these are manufactured by 

 the Union Carbide Chemicals Company and are designated: POLYOX WSR-35, 

 which has a weight-average molecular weight of several hundred thousand, 

 POLYOX WSR-205, which has a weight-average molecular weight of about 

 500,000 and POLYOX WSR-301, which has a molecular weight of about 4 million. 

 POLYOX resins are made up of very long linear molecules which are com- 

 pletely soluble in water at room temperatures. At concentrations of 1% or more, 

 aqueous solutions of poly(ethylene oxide) with a molecular weight of a million or 

 more exhibit a stringy consistency and are classed rheologically as "shear 

 thinning" (Powell and Bailey, 1960). For very dilute solutions, however, the rhe- 

 ological properties are indistinguishable from water (Fabula et al, 1963). 



Because previous work (Hoyt and Fabula, 1964) indicated that the reduction 

 in friction was very sensitive to polymer molecular weight and to mechanical 

 degradation, a standard mixing technique was employed to minimize and to 

 standardize the degradation. The solutions were mixed in 4000 ml amounts, 

 using a standard laboratory stirrer rotating at about 5 revs/sec. A large pro- 

 peller with cylindrical blades was used to reduce the chopping of the molecules, 

 which could occur with a sharp edge propeller. The poly(ethylene oxide) was 

 used as received from the manufacturer and was slowly added to the water to 

 prevent lumps forming. The length of the mixing was between 30 seconds and 

 one minute, depending on the concentration being mixed. In order to ensure that 

 the polymer was fully hydrated, the solution was left at least four hours before 

 it was used. Usually the solution was left standing overnight. Before being put 

 into the pump the solution was gently stirred to make certain that none of the 

 polymer had settled out. 



APPEARANCE OF THE SOLUTION 



Concentrations of up to 250 ppm of POLYOX WSR-35 and WSR-205 were 

 used for these tests. They were easily mixed, and at the 250 ppm concentration 

 had a slippery feel but did not exhibit any stringiness. POLYOX WSR-301 was 

 easily mixed up to concentrations of 500 ppm but at higher concentrations the 

 material had a tendency to form lumps which, at the highest concentration used, 

 (2,500 ppm) sometimes did not disperse even after the solution had been left 

 standing for several days. In these cases the solution was re-mixed with the 

 stirrer, with no apparent adverse effect. At about 400 ppm the WSR-301 solu- 

 tion began to exhibit stringiness; this stringiness increased markedly as the con- 

 centration was increased. Concentrations up to 2,500 ppm of the WSR-301 were 

 used in these tests and it was found that, once mixed, these solutions were 

 readily diluted, which indicated that even the highest concentration would mix 

 with the boundary layer fluid when it was injected. 



DRAG REDUCTION 



A series of runs was carried out to examine the state of the boundary layer 

 at different tunnel velocities. In order to ensure that the boundary layer would 

 be turbulent over the body even at the lowest tunnel speeds used, it was decided 



979 



