A priori tests of turbulence models for the compressible Reynolds-Averaged Navier--Stokes (RANS) are performed by using Direct Numerical Simulations (DNS) data of zero-pressure-gradient flat-plate turbulent boundary layers. The DNS database covers a wide range of operating conditions, ranging from supersonic ($M_\infty = 2.25$) up to the high-enthalpy hypersonic regime ($M_\infty= 12.48$). Several RANS closures and compressibility corrections in the literature are assessed against the exact terms from the DNS. Particular attention is paid to closure models for the turbulent heat fluxes and the dilatational dissipation, as well as to the analysis of turbulence/chemistry and turbulence/vibrational relaxation interactions for the high-enthalpy simulations.
