The tufts were used to define the gross flow structure over the model and to 

 provide some guidance for the paint flow application. The tufts were cemented on 

 the hydrofoil in relation to a grid which was penciled onto the foil surface. The 

 tuft flow patterns, which agreed with the paint flow patterns discussed next, indi- 

 cated the major regions of flow separation. 



The paint flow studies provided much more detail of the flow characteristics in 

 the foil boundary layer on the model surface. Several interesting aspects of the 

 flow over the foil are revealed by the paint flow patterns: 



(a) . A representative flow pattern for the foil pressure side is shown in Fig- 

 ure 13 for design angle of attack a = 0.5 deg and R ~ 5 x 10 . With the flow from 

 left to right, note the leading edge of the model. The dark area, where the high 

 local velocities have removed the paint, represents the laminar flow region. Just 

 aft of this region, the ridge of accumulated paint represents laminar separation 

 which is followed by laminar reattachment. Aft of this region the flow is turbulent 

 over the remainder of the foil chord. The approximate transition to chord ratio is 



X /C ~ 0.06, indicating that the flow over the foil is almost totally turbulent. 



17 

 Transition data for a 2-D NACA 0018 section at similar conditions gives x /C ~ 



0.15. This is presented only for comparative purposes; obviously, an accurate com- 

 parison would require identical geometries and depend upon the rate of amplification 

 of the unstable disturbances and on the intensity of the turbulence in the free 

 stream. 



Focusing attention spanwise along the trailing edge in Figure 13, the flow is 

 basically chordwise. However, in the region close to the tip, approximatley 1 in. 

 (0.0254 m) inboard, the flow starts to exhibit an outboard spanwise component which 

 becomes stronger near the foil tip. This spanwise flow is directed into the tip 

 vortex core. Although not shown, the corresponding paint flow for the suction side 

 showed an inboard spanwise component near the tip region, indicating that the suction 

 side tip flow does not enter the tip vortex core. 



(b). A paint flow pattern for the foil suction side is shown in Figure 



i/i 



a = 10 deg and R ~ 5 x lo . Again, with the flow from left to right, ...at 

 although the leading edge laminar-to-turbulent region is similar to tha^ of the 

 a = 0.5 deg case, the transition point has moved forward, as expected for the 

 larger angle of attack. 



21 



