layer with only minor influence on the pressure away from the separation line. 



3 

 Previous data for this propeller indicated that the pressure at the point in 



question exhibited the same property as a function of Reynolds number. 



DTNSRDC PROPELLER 4718 



The steady pressure distribution was calculated on the surface of DTNSRDC 

 controllable-pitch Propeller 4718 at the design advance coefficient, J = 0.75. 

 The propeller has three blades with diameter of 2 feet (0.61 meters), EAR of 0.44, 

 and tip skew of 20 degrees. In Figure 14, the predicted pressure coefficients are 

 compared with experimental measurements on the blade surface with the propeller 

 operating in uniform flow at three different radii; r/R = 0.5, 0.7, and 0.9. The 

 pressure was measured by transducers mounted on both sides of the blade surface. 



The experimental values were measured at six different R values ranging from 



2.5 x 10 to 4.63 x 10 at the design J. For this range of R , the flow on the 



surface should be fully turbulent so that the pressure distribution would be nearly 



independent of R . However, the experimental measurements showed substantial 



variations for different R values. The variation is more pronounced on the 



n 



suction side than on the pressure side. In general, the pressure coefficients 



increase with increasing R values. The measured pressure coefficients shown in 

 "^ n 



Figure 14 represent the average values over the range of R . Unpublished flow 

 visualization* of the surface streamlines showed no anomolous flow over the blades. 



At r/R = 0.7, the computed values are in reasonable agreement with experi- 

 mental values. However, the agreement at the other two radii is not as good as 

 that at r/R = 0.7. At r/R = 0.5, the experimental results show some irregular 

 peaks at X = 0.12 and 0.5 on both sides. Jessup explained that some of these 

 irregularities in the measured values might be partially attributed to the effect 

 of the relatively large fairwater and hub. 



More recently, Jessup* measured blade pressure on the same Propeller 4718 

 using another technique. In this experiment, Jessup measured the pressure distri- 

 bution only on the suction side at two radii, r/R =0.5 and 0.8 at the design 

 J = 0.751. In Figure 15, the two sets of experimental values are compared with PSP 



'Private communication from S. Jessup, DTNSRDC, Code 1544, 



10 



