19 



percent of the model length has been shown for models of U-shaped bow sec- 

 tions. The reference cited reports similar boundary surveys made by visual 

 methods at the National Physical Laboratory in England. The conclusions de- 

 duced from British tests, 7,8 are largely substantiated by the present hot-wire 

 survey. Furthermore, exploratory experiments made by W. Hinterthan at the 

 Taylor Model Basin— using a chemical technique to determine the character of 

 the boundary layer flow on models and flat plates — have also confirmed the gen- 

 eral shape of the laminar region as found by the hot-wire method. 



An additional result from the TMB survey is that the flow on the 

 bottom, 3 ft from the bow and 4 inches off the centerline (£) , was turbulent 

 at speeds as low as 0.8 knot, or R = ~5 Ak x 10 . At this value the mean po- 

 sition of transition on the side was found to be much farther aft at x = 6.9 

 ft. Evidently the flow immediately enters an unstable region just after rapid 



passage around the turn of the bilge forward of Station 2. This effect is 



7 

 also noted in the British paper. 



A curious result was obtained from the first series of tests in 

 which the model was towed without turbulence stimulation. Analysis of the 

 hot-wire responses produced sketches of the regions of the laminar and turbu- 

 lent boundary layers at each speed similar to that shown in Figure lUa. It 

 was suggested that these anomalous results were caused by minute paint parti- 

 cles. Upon close examination of the surface small regions of roughness were 

 found where the model had been repaired with shellac. The rough spots of 



TURBULENT 



ROUGH PAINT REGION 

 TRANSITIONAL (ABOUT O.OI INCH IN HEIGHT) 



Figure 14a - Turbulent Pattern Caused by Paint Roughness 



Towing Speed = l.UO knots 



STA4 



■30 



<A Model Reynolds Number = 6.02 x 10 6 



STA2 



/l.W.L. 



Figure lUb - Laminar Pattern Found After Bough Paint Region was Smoothed 



Figure 14 - Boundary-Layer Flow Patterns Showing the Effect of 

 Small Surface Roughness 



