Investigations on the influence of high-enthalpy nonequilibrium on turbulent flows: Exploring similarities through direct numerical simulation and a priori analysis

During hypersonic flight in low-altitude, vehicles encounter a complex phenomenon at their surfaces: the coupled interaction between turbulence and high-enthalpy (HE) nonequilibrium effects. This work utilizes DNS (Direct Numerical Simulation)-generated data to reveal similarities between high-enthalpy and low-enthalpy (LE) turbulence, aiming at garnering critical insights that could enhance Reynolds-Averaged Navier–Stokes (RANS) modeling. Overall, this research reveals fundamental statistical similarities between HE and LE turbulent flows, with mean velocity profiles conforming to the law of the wall, yet significant deviations in the von Kármán constant κ raise challenges for its use in RANS modeling. The Reynolds stress anisotropy tensor shows minimal sensitivity to enthalpy effects, providing potential for constructing turbulence models. Notably, Bradshaw's coefficient a1 shows a low dependence on enthalpy but reveals increased near-wall values in both HE and LE conditions compared to the incompressible scenario. Turbulent Prandtl and Schmidt numbers exhibit variations in the buffer layer (5 < y+ < 30), requiring consideration in future turbulence modeling efforts. The turbulent kinetic energy budget highlights differences in production and dissipation rates, confirming the non-negligible compressibility effects present in the viscous sublayer (0 < y+ < 5).