Comparison of Theory and Experiment on Ducted Propellers 



C„ 



Fig. 1 - Pressure distribution on NSRDC duct 1 

 at zero angle of attack (a^ = 0) 



the flow is distorted so that the theoretical pressures are not valid. The differ- 

 ence in results from the two forms of Bernoulli equation is small, with the com- 

 plete form giving slightly better results. 



The separation occurring near the leading edge of this duct is undoubtedly 

 laminar separation and Fig. 1 indicates that the flow reattaches itself probably 

 near the transition region. This type of separation is, in general, predictable 

 (34) and was predicted for this duct from the theoretical pressure distribution. 

 Thus, for predicting separation this pressure distribution was satisfactory. 



The experimental and theoretical pressure distributions on Duct I when this 

 duct is at a 6° angle of incidence are shown in Fig. 2 for an angular position 

 = and in Fig. 3 for an angular position of ^ = 180°. The angular position 

 0=0 refers to the duct section at the uppermost point of the duct and at a duct 

 incidence angle of 6°, the local section angle to the flow is 12°. The angular 

 position / = 180° refers to the duct section at the lowermost point of the duct 

 and at a duct incidence angle of 6° the local section angle to the flow is 0°. As 

 before, two forms of the Bernoulli equation were used for the theoretical calcu- 

 lations. Figure 2 shows that a^ = 6°, a = 12°, the theoretical predictions are 

 unsatisfactory on both the inside and outside of the duct. Flow separation cov- 

 ers more of the duct for this position and incidence than for zero incidence and 

 apparently is severe enough to affect the pressure distribution on the inside of 

 the duct. On the other hand. Fig. 3 shows that at = 180°, a = 0°, the theo- 

 retical predictions are generally satisfactory near the leading edge but only 



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