Spatiotemporal Dynamics of the Oscillation Mode in Spiked Blunt-Body Flow

The physical mechanism of oscillatory instability in spiked-body flow at a freestream Mach number of 6 and a Reynolds number of 0.13 million, based on the cylinder diameter, is investigated using high-fidelity delayed detached-eddy simulation (DDES). The simulation successfully captures the unsteady shock structures and global flow features, enabling a detailed analysis of the underlying dynamics. A dominant low-frequency mode governing the large-scale oscillation is identified and shown to be intrinsically linked to the evolution of the complex coupled interaction among shock waves, shear layers, and separation regions. The oscillation cycle is characterized by the periodic advance and retreat of the separation zone, accompanied by the flapping motion of the separation shock and the shear layer. The bidirectional propagation of inner compression waves and their convection velocities are identified, revealing their key role in sustaining the feedback loop among the separation shock, shear layer, and recirculation region. These findings provide a new physical understanding of the origin and sustaining mechanism of large-scale oscillations in hypersonic spiked-body flows.