Scheme of an over/under type TBCC inlet with variable geometry bleed cavity was presented.The general design methodology of the inlet was introduced and the design Mach number

transition Mach number and flight trajectory were provided.Discussion was conducted concerning the work mode of the inlet under different free stream conditions and the adjustment of the geometry shape of the inlet in the range of flight Mach number

based on which the major aerodynamic parameters and the selection principle of shape parameters were confirmed.Through methods of numerical simulation and high speed wind tunnel experiment

the feasibility of the scheme of the inlet was validated.The numerical simulation results indicate:when the free stream Mach number is less than 2.5

the total pressure recovery of the inlet is beyond 0.8.When the free stream Mach number is from 2.5 to 4.5

the total pressure recovery of the inlet is beyond 0.3.The aerodynamic characteristics of the inlet meet the demands of the scheme.At ramjet mode

the exit Mach number of the ramjet diffuser is below 0.4 and the exit pressure of the ramjet diffuser is beyond 0.5 standard atmosphere pressure.The ramjet diffuser can fulfil the combustion condition of the ramjet combustion chamber.The wind tunnel experiment results indicate:in mode transition

the turbojet diffuser has good matching characteristics with the engine and the turbojet/ramjet diffusers have good compatible characteristics.therefore it can be concluded that the scheme of the inlet is viable.Results of the research would provide scheme reference and technology storage for the combined cycle propulsion evolution in our country.