An Interactive Approach to Subsonic Flows with Separation

An accurate calculation of the lift on an airfoil requires a modeling of the interaction between the inviscid flow away from the airfoil and the viscous flow close to the surface. In many cases of interest the boundary-layer flow may separate upstream of the trailing edge, causing a strong interaction between the viscous and the inviscid flow. For such cases if a boundary-layer method is used to account for the viscous effects, the solution obtained for the prescribed pressure distribution will break down at the point of separation where the equations become singular. On the other hand, if the boundary-layer method is reformulated as an inverse procedure so that the pressure distribution is not prescribed but computed as part of the solution, the singularity at separation can be avoided [254], and flows with small separation can be computed. This paper presents an interactive method for combining such an inverse boundary-layer procedure with an incompressible potential-flow calculation.