Morgan and Caster 



C„ 



Fig. 2 - Pressure distribution on NSRDC duct I, 

 a =6 degrees and 4> = degrees 



marginal toward the middle and trailing edge of the duct on both the inside and 

 outside. Again, the form of the Bernoulli equations has only a small effect. 



Duct II typifies a shape used to decelerate the velocity inside the duct. This 

 duct has a NACA 66 modified thickness distribution with a thickness -chord ratio 

 of 0.10, a NACA a = 0.8 mean line with a camber-chord ratio of 0.04, a chord- 

 diameter ratio of 0.8, and a 0° section angle of attack. The measured pressure 

 coefficients c along with the theoretical predicted values (33) for this duct at 

 zero angle of incidence are plotted in Fig. 4. Also shown in Fig. 4 is the theo- 

 retical pressure distribution calculated from the nonlinear theory of Chaplin (18) 

 and the nonlinear approximation of Morgan (10). All the theoretical predictions 

 are generally satisfactory, with the nonlinear theory of Chaplin (18) giving the 

 best prediction. The prediction using the linearized theory (using the linearized 

 Bernoulli equation) gives a somewhat lower pressure on the outside of the annu- 

 lar airfoil near the leading edge than measured. 



The experimental and theoretical pressure distributions on Duct n ^^ilen this 

 duct is at an 8° angle of incidence are shown in Fig. 5 for an angular position of 

 0=0 and in Fig. 6 for an angular position of </> = 180°. Figure 5 shows that at 

 the position 4, = 0°, a = 8°, the comparison between theory and experiment is 

 generally satisfactory. The linearized Bernoulli equation gives a slightly better 

 prediction on the outside of the duct and the other form gives a better prediction 

 on the inside. Figure 6 shows that at the position = 180°, a = -8°, the 



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