Multi-Instability Analysis of Swept-Wing Boundary Layers Part 1. A Nonparallel Model of Stability Equations

Small disturbances superimposed on the growing boundary-layer flow along a long swept wing are governed by partial differential equations with respect to the local chordwise Reynolds number and the nondimensional vertical coordinate. For a simple and widely applicable method of stability estimation, however, it is desirable to reduce the exact disturbance equations to an eigenvalue problem of the corresponding ordinary differential equations, as in the stability analysis of two-dimensional parallel flows. This paper proposes such a simple model of the ordinary differential system that includes the most important terms of boundary-layer nonparallelism and wall curvature. Numerical computations show that the eigensolutions can properly describe multi-instability characteristics of the three-dimensional boundary layers near the attachment line of a long swept wing.