244 



O 8URSNALL a LOFTIN (19511 



D FACE a FALKNER II93I) 



O ROSMKO 119531 

 8 - 



5x10" 10' 5x10= 



REYNOLDS NUMBER (Reo) BASED ON SHAFT DIAMETER 



FIGURE 34. Base pressure coefficients of cylin- 

 drical shafts as a function of Reynolds number 

 based on shaft diameter. 



be a difference in trim between model- and full- 

 scale. Because the model was ballasted to the 

 draft of the ship, further work will be required 

 to identify the source of these differences. 



The longitudinal velocity component ratios for 

 the full-scale trial show a much greater scatter 

 than the tangential and radial components . For 

 this reason it is unclear that any difference is 

 shown by these data, when compared to model-scale 

 data. The innermost radius (r/R = 0.456) does show 

 that the high longitudinal velocity component 

 normally measured at these inner radii is not found 

 full scale. This may not be the result of scale 

 effects on the shafting and strut bossing, but the 

 fact that the full-scale bossing is longer than the 

 model-scale bossing. This is a result which will 

 have to be investigated by further model experi- 

 ments . 



The results from model experiments in both the 

 wind tunnel and in the towing tank, and from the 

 full-scale trial indicate that for a circumferential 

 position near the hull, there was little difference 

 in longitudinal velocity component ratio for speeds 

 corresponding to Reynolds numbers greater than 10 . 

 Therefore, when measuring only the longitudinal 

 velocity component ratios experimentally, the model 

 should be run at the trim corresponding to that of 

 the Froude-scaled speed and at a speed high enough 

 to yield a Reynolds number of greater than 10^. 



The attempt at predicting the wake for this high- 

 speed displacement ship showed that the most im- 

 portant contribution to the variation in tangential 

 and radial velocity component ratios was the shaft 

 angle to the flow. The calculation of the potential 

 flow around the hull and the resulting velocity 

 components showed that the effect of the perturba- 

 tion due to the hull was small. The effects of the 

 boundary layer of the hull on the wake were also 

 shown to be small. 



In summary it may be stated that the full-scale 

 and model wakes differ by approximately ten percent 

 of the ship speed. These differences cannot be 

 adequately explained at this time. Further work 

 on wake of appendages is recommended as one step in 

 improving the understanding of these differences. 



ACKNOWLEDGEMENTS 



This work was performed under the controllable- 

 pitch propeller research program sponsored by C. L. 

 Miller of the Naval Sea Systems Command (NAVSEA 

 0331G) administered by the David W. Taylor Naval 

 Ship Research and Development Center (DTNSRDC) . 



The authors wish to express their appreciation 

 to personnel of the Ship Performance Department of 

 DTNSRDC, the University of Michigan, and the crew 

 of R/V ATHENA from MAR Inc. for their assistance 

 in conducting the full-scale trial and model experi- 

 ments which provided the data for this paper. CHI 

 Associates, Inc. and Rosenblatt Inc. are also 

 acknowledged for their assistance in the prepara- 

 tion of this paper. 



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