Vibrational excitation effects on thermodynamic fluctuations in shock–vortical turbulence interaction

The effect of vibrational excitation on thermodynamic fluctuations in shock-vortical turbulence interaction (SVTI) is investigated using direct numerical simulations and extended linear interaction analysis (LIA). Comparing thermally perfect gas and calorically perfect gas models at shock Mach numbers (Ms) of 4.0 and 6.0 reveals that vibrational excitation enhances pressure variance but attenuates entropy and temperature variances. Specifically, at Ms=6.0, the far-field pressure variance increases by approximately 14%, whereas entropy and temperature variances decrease by 12% and 14%, respectively. Kovásznay mode decomposition indicates that, for density variance, vibrational excitation suppresses the entropy mode while amplifying the acoustic mode at higher Ms. The reduction in temperature variance is attributed to a consistent decrease across all constitutive modes. Extended LIA shows that vibrational excitation modifies the critical incidence angle, intensifying the mean velocity gradient production and dilatation terms in the density and temperature variance jumps across the shock. While the dominant transport mechanisms for thermodynamic fluctuations remain unchanged, their streamwise evolution is altered. In particular, the increased specific heat capacity suppresses the conversion of acoustic work into temperature fluctuations, slowing the near-field decay of temperature variance. This necessitates a compensatory accelerated decay of the density-dilatation term to satisfy the linearized equation of state, causing the density fluctuation peak to shift upstream. These findings underscore the necessity of including vibrational excitation in hypersonic SVTI analyses.