A comprehensive numerical analysis of scramjet combustor has been carried out for reacting flows in constant-area channel type and divergent nozzle type combustors with and without a cavity. Hydrogen fuel is transversely injected into the supersonic combustor with a broad range of injection pressure. The corresponding equivalence ratio of the overall fuel/air mixture ranges from 0.167 to 0.50. To this end, a DES (Detached Eddy Simulation) turbulence model was applied to a scramjet combustor using compressible Navier-Stokes equations with a detailed chemistry mechanism for hydrogen combustion. Solutions were post-processed by time averaging techniques. Present work exhibits the detailed resolution of flow and flame dynamics of supersonic combustor, which were not typically available in most of the previous studies. In particular, the oscillatory and time averaged flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Results indicate that much of flow unsteadiness is related not only to the cavity, but also to the intrinsic unsteadiness in the flowfield. The interactions between the unsteady flow and flame evolution may cause a large excursion of flow oscillation. The unsteady simulation shows the time-evolving process of combustor choking of the constant area combustor. The averaged field for the nozzle type combustor shows the overall characteristics of the stabilized oscillating combustion. The roles of the cavity, combustor divergence, injection pressure, and heat release in determining the flow dynamics could be examined systematically from the averaged field.