Numerical simulation of fundamental breakdown of a laminar boundary-layer at mach 4.5

The transition process of a flat plate boundary layer at a free-stream Mach number of M_∞ = 4.5 initiated by a pair of linearly most unstable oblique first mode waves is investigated by direct numerical simulation up to laminar breakdown. An explicit spectral/finite-difference scheme employing the temporal model is used. In contrast to the subhannonic transition, the primary instability immediately leads to weakly nonlinear interactions. A staggered A-vortex pattern evolves. Finite-amplitude A-vortices initiate the buildup of detached high-shear layers, which appear in a characteristic Y-shape. The shear-layer evolution has been observed up to the first level of shear-layer break-up. A strong decrease of the shape factor and an increase of the skin friction coefficient indicate the final breakdown stage. The evolution of mean-flow profiles shows similarities with that of the subharmonic transition process.