Amplification of Artificial Disturbances in Turbulent Boundary Layers

The behaviour of the periodic disturbances produced artificially in turbulent boundary layers is determined by means of the smoke wire method. It is found that (1) the disturbances whose wave number is between about 0.1 and 0.6 are amplified in the downstream direction (the wave number is 2 πδ * /λ, where δ * is the displacement thickness and λ the wavelength), (2) the disturbances whose wave number is about 0.3 are amplified most strongly, and (3) the disturbances whose wave number is larger than about 0.6 are damped.