along with the quadrilateral representation used in the calculations. The 

 other two bodies, DTNSRDC Models 5225-2 and 5225-3, differ from the parent 

 in afterbody shape only and are also illustrated in Figure 12. 



One 7-bladed propeller model, DTNSRDC Model 4577, was used for the 

 three body experiments. The principal characteristics and geometry of the 

 propeller are summarized in Table 4. Pressure measurements were obtained 

 at two advance ratios, J = 1.25 and J = 1.07. Since the propeller was not 



operating in its design wake, it was necessary to predict the load distribu- 



21 

 tion using an inverse performance calculation. This was an iterative 



process, starting with the measured nominal wake, computing a load distribu- 

 tion, recomputing the wake, and so on. Convergence was achieved after two 

 iterations. 



The computed and measured differences in afterbody pressure distribu- 

 tion are shown in Figures 13a, 13b, and 13c. The agreement is excellent 

 for body 5225-1 and very good for body 5225-2. There is a marked dis- 

 crepancy for 5225-3. This body was intentionally designed to have boundary 

 layer separation in the absence of the propeller with the hope that the 

 propeller influence would reattach the flow. However, flow separation 

 occurred at x/L = 0.92 which is too far upstream. The thrust deduction 



fraction, t , was derived by integrating the measured pressure difference 

 exp 



and dividing by the calculated propeller thrust (no self-propulsion experi- 

 ments were conducted). The results are compared in Figure 13 with the 

 theoretically computed values, t . The agreement for body 5225-3 is 

 considered fortuitous in view of the difference in pressure distribution. 

 The thrust deduction for body 5225-2 is larger than for 5225-1 which is 

 expected on physical grounds since the fuller afterbody places the frontal 

 area closer to the propeller. Body 5225-3, which has the fullest after- 

 body, is actually finer in the immediate vicinity of the propeller; hence, 

 the calculated thrust deduction is also lower than for body 5225-2. 



39 



