Localized coherent structures in a boundary layer (Q2714047)

A Blasius laminar boundary layer and a steady turbulent boundary layer on a flat plate in an incompressible fluid are considered. The spectral characteristics of the Tollmien--Schlichting (TS) and Squire waves are numerically determined in a wide range of Reynolds numbers. Basing on the spectral characteristics, the author studies relations determining the three-wave resonance of TS waves. It is shown that the three-wave resonance is responsible for the appearance of a continuous low-frequency spectrum in the laminar region of the boundary layer. The spectral characteristics make it possible to obtain quantities that enter the equations of dynamics of localized perturbations. By analogy with the laminar boundary layer, the three-wave resonance of TS waves in a turbulent boundary layer is considered.