Viscous/Inviscid Interaction Procedures

In the previous chapters, small disturbance potential flow theories for 2-D and 3-D, incompressible and compressible, steady and unsteady flows over aerodynamic configurations are studied. The main results are the surface pressure distributions and the associated lift and “inviscid” drag coefficients. Also, boundary layer theory for the corresponding flows is discussed and the main result is the prediction of the skin friction drag, assuming the surface pressure distributions are known from the inviscid calculations (Fig.9.1).

The feedback effects of boundary layers on the inviscid flows can be represented through the displacement thickness. This concept, for both laminar and turbulent flows, allows uncoupled calculations at least for the cases with no separation. The mutual strong interaction between the thin viscous layer over the body and in the wake, for high Reynolds numbers, and the main inviscid flow is the subject of this chapter. Beside the displacement thickness methods, other approaches based on domain decomposition techniques will be discussed as well. A challenging prob­lem pertinent to this chapter concerns the shock wave/boundary layer interaction, an example of which is shown in Fig. 9.2 for an 18% thick biconvex circular arc airfoil, from [1].

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