Comparison of Lam-Rott and Brown-Stewartson eigensolutions of the boundary-layer equations

In studies of the boundary layer on a flat plate, two very different sets of asymptotic eigenfunctions of the linearized unsteady boundary-layer equation have been analysed. One set, usually known as Lam-Rott eigenfunctions, decay exponentially with a shortening wavelength, while the other set, known as Brown-Stewartson modes, decay more slowly. Lam-Rott eigenfunctions have been extensively studied, and the presence of these eigenfunctions in the boundary-layer solution is important when studying the receptivity of the boundary layer to free-stream disturbances. In contrast, the Brown-Stewartson modes have been largely ignored. In this paper the two sets of eigensolutions are compared, and the presence of both Lam-Rott and Brown-Stewartson modes in numerical solutions of the boundary-layer equation is demonstrated.