High-enthalpy unsteady pulsation flow over a double wedge

Large-scale pulsation unsteadiness is identified in the high-enthalpy shock wave-boundary-layer interaction flow over a double wedge. The objective of the study is to illustrate the transient flowfield evolution and spatiotemporal dynamics of the pulsation mode with vibrational nonequilibrium. A laminar nitrogen flow with a freestream Mach 4.11 and a total enthalpy of 3.77 MJ/kg for a 30°–55° double wedge is considered, which is a test case from the experiments in the Hypervelocity Expansion Tube. Unsteady two-dimensional Navier–Stokes equations incorporating thermochemical nonequilibrium gas model are numerically solved with a due-time stepping time marching scheme to the second-order accuracy. The simulated shock structure agrees well with the experimental Schlieren snapshots in the flow establishment course. Periodic inflation and restoration of the shock system are driven by the expansion of separation bubbles and escape of low-pressure vortices. A single main frequency is identified over the flowfield for the pressure and temperatures, indicating that the motions of the separated region, shock system, and shear layer are strongly coupled to form a synchronized pulsation mode. Finally, the variation in the non-dimensional frequency for high-enthalpy pulsation flow is illustrated based on the binary scaling law.