Asymptotics of the Lower Branch of the Neutral Stability Curve for the Transonic Interacting Boundary Layer on a Flat Plate

Essential advancements in analytical investigations of the stability of transonic boundary layers have been obtained for a three-deck model constructed using asymptotic joined expansions of flow parameters over inverse degrees of the Reynolds number with the latter tending to infinity. The linear profile was selected when investigating the stability of the boundary layer for the unperturbed velocity. The investigation of the equation for small perturbations in a viscous medium manifests the existence of a special critical layer in the flow, which is formally determined by the multiplier at inertial terms entering the equation. The comparison of thicknesses of the critical and boundary layers shows that the critical layer turns out the more considerable manifestation region of the viscous interaction of viscous nonviscous flows. Thus, the selection of a three-deck model for investigating the flow remains the upper branch of the neutral curve out of the analysis limits.