Tollmien–Schlichting waves in a transonic boundary layer : Excitation from the outer flow and from the surface

Perturbations in a boundary layer when there is unsteady free viscous-inviscid interaction at transonic velocities are investigated using a modified “triple-deck” model. Two problems are considered: the effect of acoustic perturbations arriving from outside and of perturbations excited from a streamline surface with a vibrator situated on it. The modification of the model consists of taking into account singular terms of the transonic expansion, which enables the Lin–Reissner–Tsien equation to be improved and enables non-stationary and non-linear phenomena in the flow to be described more correctly. It is shown that the modified model enables additional perturbations, overlooked when using the classical triple-deck model, to be taken into account.