Hypervelocity flows of nitrogen and air over a 30-55 degrees double-wedge configuration are numerically investigated under the condition corresponding to recent experiments conducted with total enthalpy of 8.0 MJ/kg. Time-accurate two-dimensional and three-dimensional simulations are performed to resolve the unsteady shock interaction process. For the nitrogen flow, it is found that the three-dimensional simulation predicts a much smaller separation bubble and reduced surface heat flux and pressure peaks. Good agreement can be observed with the experiments in terms of the shock location, the flow structure, and the time-averaged surface heat flux when the three-dimensional effects are considered. For the air flow, the shock interaction mechanisms are similar to those in nitrogen. The real-gas effects tend to decrease the separation bubble and reduce the standoff distance of the detached shock induced by the second wedge, leading to a lower surface heat flux peak compared with the nitrogen result. However, the trend of the experimental heat flux data shows the opposite. To explain the discrepancies, effects of thermochemical nonequilibrium models are investigated. The results indicate that the air flow under the current condition is insensitive to air chemistry and vibration-dissociation coupling models. Suggestions for further study are presented. (C) 2019 Elsevier Ltd. All rights reserved.