Aerodynamic effect of mode transition time on dual-flow axisymmetric inlet

To investigate the influence of mode transition time on the axisymmetric turbine-based combined-cycle (TBCC) propulsion system, the unsteady Reynolds-averaged Navier-stokes (URANS) simulations are performed using overset mesh method. Three different mode transition times from turbojet to ramjet mode are studied, namely, T=0.2s, T=0.5s and T=0.8s. The characteristics of flow unsteadiness are analyzed in detail and aerodynamic performance parameters are also obtained. Numerical simulation results reveal that the rotation of the plates can restrain flow separation to a certain extent. Within the range of T=0.2s∼0.8s, the faster the transition from turbojet to ramjet mode, the smaller the separation bubbles near the plates. The comparison of aerodynamic performance parameters further shows that, as the mode transition time decreases, the total pressure recovery coefficient increases, while the outlet distortion coefficient decreases. Conclusion can be drawn that a reduced transition time is helpful for improving the aerodynamic performance of TBCC propulsion system during mode transition.