Scheme of variable geometry bleed cavity which was used in over/under type of turbine-based combined cycle(TBCC) inlet in full Mach number range and its design method were presented.The characteristic of inlet flow field and the inlet aerodynamic performance affected by bleed cavity and the configuration of cavity geometry parameters were investigated

based on which the law of inlet aerodynamic performance affected by cavity geometry parameters was abtained.Three-dimensional numerical simulation of over/under type TBCC inlet with bleed cavity was performed. The paper presents the influence of free stream Mach number on variable geometry design parameters

and aerodynamic characteristics of the inlet in full Mach range. Once the bleed cavity is opened

the width of the cavity entrance and the height of the throat keep decreasing. The decreasing rate is very high at the beginning

but becomes relatively low later. When the free stream Mach number is lower than 2.0

or higher than 2.5

the leading angle at the entrance of the bleed cavity is decreasing as the increase of Mach number. 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 all below 0.4 and the exit pressure of the ramjet diffuser is all beyond 0.5 standard atmosphere pressure(50.6625kPa). The ramjet diffuser can fulfill the combustion condition of the ramjet combustion chamber.The feasibility of the variable geometry bleed cavity scheme was confirmed by the numerical and wind tunnel test results.