Influence of vibrational excitation of the gas on the position of the laminar–turbulent transition region on a flat plate

The influence of thermal nonequilibrium on the laminar–turbulent transition is studied with the use of the $e^N$-method for two widespread flow regimes in a supersonic boundary layer at the Mach number $\mathrm{M}=4.5$. The set of the actual frequencies of spatial disturbances is determined on the basis of the neutral curves for temporal disturbances. Families of the curves of $N$-factors are calculated for selected frequencies. Then, based on the envelopes of these curves, the transition Reynolds number $\mathrm{Re}_{\delta T}$ for a given transition factor $N_T$ is determined. The calculations show that the transition region in the case with $N_T=8$ and vibrational excitation level below the dissociation limit is located $12$–$14\%$ downstream as compared to the transition region in a perfect gas.