The flat plate boundary layer. Part 3. Comparison of theory with experiment

A study of Tollmien–Schlichting waves in the Blasius boundary layer has been carried out under good flow conditions. The maximum r.m.s. amplitude of u , the downstream component of perturbation velocity, was limited to about 0·06% of U 0 , the free-stream velocity. Measurements of the wave-number and of the distribution of u / U 0 normal to the plate agree closely with the theoretical results obtained in parts 1 and 2 of this paper. The experimental critical Reynolds number, R c , is 400; the theoretical R c derived from the imaginary part of the eigenvalue is 500 (part 2), but additional amplification carried by the eigenvector removes most of this discrepancy.