236 



0.781 RAD 



1 .: 

 1 .1 



1 .0 

 0.9 



> 



■^ 0.8 



X 



> 



0.7 



0.6 



0.5 



O.i 



0.3 



0.2 



0.) 

 > 



■^ 

 > 

 -0.1 



-0.2 



0.2 



0.1 



i ° 



>■ 

 -0.1 



FIGURE 17. Velocity component 

 ratios for R/V ATHENA and DTNSRDC 

 model 5365 at 0.781 radius. 



-20 20 40 60 80 100 120 UO 160 130 200 220 240 260 280 300 320 340 360 380 



ANGLE IN de;oree:s 



full-scale wake survey radii, slowing a direct 

 one-to-one comparison of the data. The data from 

 this wake survey are plotted on Figures 15 through 

 18. 



It is customary to perform wake survey experi- 

 ments in the towing tank by towing the model at a 

 speed corresponding to the Froude-scaled speed of 

 the ship. In order to investigate the effects of 

 Reynolds number on the model-scale wake, a second 

 wake survey was run at an increased speed. This 

 second speed was the highest speed for which steady 

 data would be obtained, 13.5 knots (6.9 m/s) . For 

 this second wake survey, the sinkage and trim of 

 the model were kept the same as at the 5.2 knot 

 condition. This was done in an attempt to separate 

 the effects of sinkage and trim, which is dependent 

 on Froude number, from other speed effects. 



The data from the model-scale wake surveys at 

 5.2 knots (Fn = 0.36, R^ = 1.56 x lo'^) and 13.5 

 knots (Fn = 0.93, Rn = 4.04 x lo'') are presented 

 in Figure 26. The longitudinal and radial velocity 

 component ratios at these two speeds show no dif- 

 ference. However, the tangential velocity compo- 

 nent ratios obtained at 13.5 knots have peaks which 

 are 4 to 6 percent lower than those obtained at 

 5.2 knots. This is contrary to what might be 

 exepcted, in that the increased Reynolds number 

 should produce a thinner boundary layer and there- 

 fore, a flow which more closely approaches the 



potential flow around the hull. This anomalous 

 result is probably due to the increased Froude num- 

 ber and the corresponding change in the wave pattern 

 around the model. 



The model-scale boundary layer profile measure- 

 ments were made in a wind tunnel using hot wire 

 anemometers. The double model was manufactured so 

 as to take into account the dynamic trim of the 

 ship. Although this cannot take into account the 

 effects of the free surface, it does account for 

 the angle of the shafting to the free stream, which 

 contributes significantly to the radial and tangen- 

 tial velocity components. 



The model scale boundary layer profile was 

 obtained at a Reynolds number of 1.68 x 10'', which 

 was intended to equal the Reynolds number of the 

 model in the towing tank at a Froude number of 0.36. 

 The Reynolds number in the wind tunnel in fact 

 turned out to be about 8 percent higher than the 

 Reynolds number in the towing tank. However, this 

 was not considered to be critical to the correlation 

 of the model and ship data. 



The boundary layer profiles obtained in the wind 

 tunnel, without the propeller operating, at Loca- 

 tions 1, 2, and 3 are given in Figures 20, 21, and 

 22; where they are plotted against the full scale 

 data at the corresponding locations. The data 

 obtained at the same locations with and without 

 the propeller operating are plotted against the 



