Comparison of Theory and Experiment on Ducted Propellers 



Fig. 9 - Pressure distribution on ARL duct BZ at 

 zero angle of attack (a^ = 0) 



the other hand, for this duct the prediction is generally satisfactory using the 

 method of Ref. (33) with no reduction in circulation. For duct B2, both ap- 

 proaches generally give a satisfactory prediction, Fig. 9. Both prediction meth- 

 ods are, in general, marginal to unsatisfactory near the leading edge. The 

 method of Ref. (35) shows more of a deviation on the inside of duct Bl and B2 

 and on the outside of duct B3 near the leading edge, since a nonlinear correction 

 for the velocity is not used (10). The results of the comparison for this series 

 are very interesting for two reasons: (1) the sizeable viscous effect on the cir- 

 culation distribution, and (2) the need for judicious choosing of the load distri- 

 bution to minimize these effects. 



In summary, the data reviewed show that the linearized theory gives a gen- 

 erally satisfactory prediction of the pressure distribution (both forms of the 

 Bernoulli equation) on a duct when leading-edge laminar separation does not oc- 

 cur and other viscous effects are small. The nonlinear approximation (10) im- 

 proves the prediction toward the leading edge and eliminates the theoretical 

 prediction of infinite pressures at the leading edge. The nonlinear theory of 

 Chaplin (18) gives a better prediction of the pressure distribution than the lin- 

 earized theory. It should be pointed out that the duct shapes did not deviate 

 markedly from a cylinder so that the good comparisons obtained might be 



1323 



