408 



FIGURE 10. Calculated pressure distribution on the 

 suction side at 60% slip. 



These pictures were taken with UV-illuiiiination. 

 At the leading edge the paint is removed, due to 

 high local velocities. The streaks are formed 

 gradually, either in a nearly tangential direction 

 (the turbulent region) or pointed outwards (the 

 laminar region) . The transition from laminar to 

 turbulent boundary layer flow is shown by a change 

 in direction of the streaks. 



Laminar boundary layer flow occurs in all cases 

 near the leading edge. Transition in chordwise 

 direction to turbulent boundary layer flow occurs 

 gradually, but a transition region can be distin- 

 guished and at the trailing edge the boundary layer 

 is turbulent. When the paint streaks are nearly 

 in the radial direction the flow is separated. At 

 inner radii the boundary layer if often close to 

 separation. Laminar separation was clearly present 



on propeller D, as is shown in Figure 12. At 60^ 

 slip the radius where laminar separation is replaced 

 by natural transition can be seen by the sharp 

 corner in the paint streaks. 



At the suction side near the tip a turbulent 

 region exists immediately from the leading edge 

 (Figure 11) . An increase in propeller loading 

 showed a radial increase of the turbulent region at 

 outer radii, as illustrated in Figure 12. The 

 change in radial direction of the laminar region 

 near the leading edge to the turbulent region at 

 outer radii on the suction side is abrupt and 

 nearly discontinuous, as sketched in detail in 

 Figure 13. The laminar region is cut off and the 

 region of natural transition at inner radii does 

 not reach the leading edge. We will designate the 

 radius where this discontinuity occurs, the critical 



