SECONDARY INSTABILITY MECHANISMS IN COMPRESSIBLE AXISYMMETRICAL BOUNDARY-LAYERS

Secondary instability mechanisms in compressible, axisymmetric boundar y layers are analyzed using spectrally accurate mean-flow and stabilit y codes. Results show that subharmonic disturbances are the most dange rous secondary disturbances in an environment with a low to moderate i ntensity of the primary disturbance. The relation between spatial and temporal analyses of the secondary disturbance is explored at Mach 1.6 along a flat plate and Mach 6.8 along a cone. Spatial direct numerica l simulations are utilized to confirm the quantitative predictions fro m spatial secondary instability theory.