3-DIMENSIONAL INSTABILITY OF FLAT-PLATE BOUNDARY-LAYERS - THEORY AND EXPERIMENT

The 3D instability of the flat-plate boundary layer has been investiga ted. Experimental results obtained in the Blasius flow excited by a po int source were analyzed by means of a spatial Fourier decomposition. The data are compared with theoretical solutions of the Orr-Sommerfeld equation based on a parallel-flow approximation of the Blasius flow. Very good agreement was found for the dispersion characteristics of th e wavenumbers and phase velocities as function of the wave angle, of t he frequency parameter and of the Reynolds number. The growth rates sh owed mainly a qualitative agreement.