A systematic assessment method for the thermochemical characteristics of the inviscid shock layer in hypersonic reentry flows is proposed based on the Damköhler number. A one-dimensional post-shock analysis with a two-temperature, five-species air model including N, O, NO, O \(_2\) , and N \(_2\) is used to evaluate the chemical and thermal reaction timescales across a wide range of freestream conditions. Flow timescales were estimated via equilibrium shock relations and a potential-flow stagnation line velocity profile. Four types of Damköhler numbers were defined, chemical and thermal, each in equilibrium and frozen forms, to characterize key transitions in thermochemical regions. A high-resolution database was constructed over a velocity range of 1000–8000 m/s and an altitude range of 10–80 km. Thermochemical characteristic maps were generated based on these Damköhler numbers, revealing clear trends and boundaries associated with the dissociation of O \(_2\) , N \(_2\) , and NO. The boundaries predicted by the maps agreed with high-fidelity numerical simulations within discrepancies of 1.3–2.4 km in altitude and 50–210 m/s in velocity. These discrepancies mainly arise from the equilibrium-based estimation of the flow characteristic time. The resulting maps provide a practical framework for the preliminary assessment of the inviscid shock-layer state, guiding the selection of appropriate thermochemical models for subsequent high-fidelity simulations.
