Figure 1 . 



theory. The study is being conducted on a flat-plate boundary layer with zero pres- 

 sure gradient and wind speed of 50 feet per second. 



Figure 1 represents the intensity of the longitudinal fluctuation and shows its 

 distribution in the z-direction, which is the direction parallel to the plate and normal 

 to the flow. The measurements were made one foot downstream from the vibrating 

 ribbon, at which point transition began, and at a distance from the surface equal to 

 half the boundary layer thickness. The intensity is plotted in terms of the root-mean- 

 square value and is referred to the intensity u ', which is the value at a fixed point 

 1.2 inches above the center line of the plate, and was on the order of 1 percent. 

 Although the vibrating ribbon excites a wave which is 2-dimensional and uniform 

 along its crest for a distance of about one foot there has developed a strong 3-dimen- 

 sionality as shown by the large variation of intensity. This variation had its beginning 

 well upstream from transition where the wave is still quite pure. The breaking pattern 

 associated with transition is also shown. At the peak the breaking pattern is different 

 from that in the hollow. The breaking pattern at the peak consists of bursts of high 

 frequency fluctuations occuring each cycle on the low-velocity side of the primary 



367 



