A simple interaction law for viscous-inviscid interaction

The viscous-inviscid interaction (VII) philosophy for modelling aerodynamic boundary layers is discussed. 'Traditionally' the shear-layer equations are solved with pressure prescribed by the inviscid flow, but then the solution breaks down in a singularity related to flow separation. In the quasi-simultaneous coupling approach this singularity is overcome by making use of an interaction law. A novel mathematical analysis is presented of the essential properties of such interaction laws, which is based on classical theory for non-negative matrices. The performance of a highly simplified interaction law is demonstrated for separated airfoil flow beyond maximum lift.