EXAMPLE 3: BODY OF REVOLUTION WITH STERN APPENDAGES 



This example provides a further comparison of computed and measured 

 thrust deduction and exhibits the separate contribution of stern appendages. 

 The analysis is applied to an appended body of revolution, represented by 

 DTNSRDC Model 5224-1. This model, with appendages removed, is a geosym of 

 the wind-tunnel model, DTNSRDC 5225-1, described previously in Example 2. 

 The afterbody profile and appendages are illustrated in Figure 14, together 

 with the quadrilateral representation used in the calculations. Note that 

 each control surface is represented properly (in contrast to Example 1), but 

 the forebody is again approximated by the afterbody image. 



The propeller, DTNSBUDC Model 4567A, (a geosym of the wind-tunnel model 

 4577), was designed specifically for the appended body. All calculations 

 are therefore based on the design loading characteristics. The circulation 

 and hydrodynamic pitch distributions are shown in Figure 15. 



Calculated propeller induced velocities on the body are given in Figure 

 16 showing both the lifting-line sink disk and lifting-surface contributions. 

 The results derived from a simple point sink located at the shaft centerline 

 are also presented. At distances beyond one propeller diameter the veloci- 

 ties derived from the point sink, lifting-line, and lifting-surface propeller 

 representation agree to within 10 percent. Closer to the propeller, the 

 lifting-line velocities are about 25 percent too large, while the point-sink 

 velocities are as much as 50 percent too large. 



Calculated and measured values of the thrust deduction are presented in 

 Table 5. The higher lifting-line velocities result in a prediction of t 

 which is 21 percent larger than that derived from the lifting surface calcu- 

 lation. The predicted value of (1-t) , while lower than the measured value, 

 is within experimental accuracy. The contribution of the stern appendages, 

 as shown in Table 5, is 24 percent of the total thrust deduction. (Although 

 not discussed in Example 1, a comparable value of 25 percent is found in that 

 case). Finally, the distribution of interaction force on the afterbody is 

 displayed in Figure 17, shown as the integrated force as a function of 

 distance from the stern. The significant contribution is over the last 30 

 percent of the body length with 50 percent of the force concentrated in the 

 last 5 percent (i.e., within a distance of one propeller diameter). 



44 



