for the two cases. Inspection of runs at other speeds also produced no effect of 

 the tripped boundary layer. It was concluded that the boundary layer was essentially 

 fully turbulent without the sand, even for the run at the lowest Reynolds number of 



2.5 x 10 for Propeller 4718, and 3.08 x 10 for Propeller 4679. This result agrees 



31 

 with data from Meyne who predicts a fully turbulent boundary-layer to occur for 



Reynolds number values greater than about 10 . 



Attempts to correlate the speed effects at certain gage locations with possible 

 separation could be advisible without a better understanding of three-dimensional 

 separation and other boundary-layer flow phenomena, as could be determined with flow 

 visualization on the two propellers. Unfortunately, little insight can be drawn 

 from experiments correlating the effects of two-dimensional separation phenomena with 

 static surface pressures. 



Three-dimensional separation could be influenced by many effects. At the root 

 of the blade, local separation forms and is dependent upon the thickness and mean- 

 line of the inner radius sections and on the fairness of the blade fillets. Also, a 

 secondary-flow horseshoe vortex is formed around the root of the blade, and is shed 

 downstream, inducing flow on the blade. The rotation of the blades produces a 

 boundary- layer flow component radially outward, directing the surface shear stress 



also radially outward. The effect is more pronounced for laminar than turbulent 



31 

 flow. The large thickness ratios at the inner radii, especially on Propeller 4718, 



could also contribute to possible three-dimensional separation related to strong 



adverse pressure gradients in the radial and chordwise directions. At the tip, the 



formation of the tip vortex could cause extreme local pressure gradients contributing 



to separation. Influences from these effects could lead to separation in various 



regions of the blade. 



More detailed predictions of boundary-layer flow and separation could be made 



only through boundary- layer flow visualization techniques. By applying a paint 



31 

 (or oil) to the leading edge of the blades, the paint-film flow patterns produced 



after running can indicate the details of the boundary-layer flow. This would pro- 

 vide a base to compare variations in pressure coefficients with Reynolds number. 



24 



