Overview

In Sub-Section 7.1.4 we have noted that if the displacement properties of a boundary layer are of , it influences the pressure field, i. e. the inviscid flow field, only weakly. We call this "weak interaction" between the attached viscous flow and the inviscid flow ^[71]. If, however, the boundary layer separates, the inviscid flow is changed and we observe a "strong interaction". This phenomenon is present in all Mach number regimes, especially also in the subsonic regime.

"Shock/boundary-layer interaction", present in the transonic, supersonic, and hypersonic regimes, also leads through thickening or even separation of the boundary layer to strong interaction. "Shock/shock interaction" with the associated interaction with the boundary layer is a strong interaction phenomenon, too.

In the high supersonic and the hypersonic regime strong interaction happens also if the attached boundary layer becomes very thick, which is the case with large Mach numbers and small Reynolds numbers at the boundary-layer edge. This is the "hypersonic viscous interaction". Associated with hypersonic viscous interaction are "rarefaction effects" which appear in the continuum flow regime with slip effects, Section 2.3. They are, as we will see, directly related to large Mach numbers and small Reynolds numbers at the boundary-layer edge, too.

We consider the strong-interaction phenomena in general in their two-dimensional appearance. In should be noted that for instance shock/boundary-layer interaction usually is less severe in three-dimensional cases compared to strictly two-dimensional cases. The computation of turbulent three-dimensional interactions in general is also less problematic concerning turbulence models.