The results indicate that the trend found previously of an increase in boundary-layer transition Reynolds number with increase in model cooling continued to higher Reynolds numbers. The highest transition Reynolds number obtained with cooling was 28,500,000. At this Reynolds number, the classical Tollmien-Schlichting wave type of boundary-layer number, the instability was apparently overshadowed by surface roughness effects. The results indicated that, when transition was fixed by surface irregularities or airstream flow disturbances, cooling was not effective in obtaining laminar flow behind the irregularity or disturbances.

A preliminary investigation has been made of the effects of heat transfer on boundary-layer transition on a body of revolution at a Mach number of 1.61 and over a Reynolds number range of 7,000,000 to 20,000,000, based on body length. The body had a parabolic-arc profile, blunt-base, and a fineness ratio of 12.2 (NACA RM-10). The results indicated that, by cooling the model an average of about 50 degrees F, the Reynolds number for which laminar boundary-layer flow could be maintained over the entire length of the body was increased from the value of 11,500,000 without cooling to over 20,000,000, the limit of the present tests. Heatig the model an average of about 12 degrees F on the other hand decreased the transition Reynolds number from 11,500,000 to about 8,000,000. These effects of heat transfer on transition were considerably larger than previously found in similar investigations in other wind tunnels. It appears that, if the boundary-layer transition Reynolds number for zero heat transfer is large, as in the present experiments, then the sensitivity of transition to heating or cooling is high; if the zero-heat-transfer transition Reynolds number is low, then transition is relatively insensitive to heat-transfer effects.