Study On Operation Characteristics Of Scramjet With Expansion Cycle

As an economical and effective propulsion system for hypersonic cruise and space access,design and integration technology of scramjet engine system is of great significance for the promotion of scramjet engineering process.Reliable long-time working scramjet with kerosene-based regenerative cooling system is distinguished with narrow working range,strict parameter matching requirements and coordinate work involving multiple components,such as combustion chamber,fuel supply system and long duration thermal protection device.In this thesis,turbine driven by supercritical/cracking kerosene and ethylene assistant system for ignition and start-up were designed,and operation performance study for scramjet expansion cycle scheme was carried out by theoretical and numerical methods.The expansion cycle scheme of kerosene-based scramjet system with regenerative cooling was developed.Based on the functional requirements analysis,the expansion cycle scheme with pump-fed system was presented,the design methods of kerosene turbo-pump with small flow rate were integrated,a mathematical model of combustion chamber was established.Flow and heat transfer characteristics of kerosene in cooling channels and under supercritical pressure were investigated numerically with accurate calculations of thermophysical properties.A numerical method was established based on a two-layer turbulent model and a kerosene surrogate model of PPD mechanism.Three-dimensional conjugate and convective heat transfer was analyzed,and Stiegemeier correlation in heat transfer of kerosene was validated.Under supercritical pressure,it looks like a single-phase forced convective heat transfer,and turbulence is the main reason for the variation of heat transfer coefficient;the heat transfer coefficient decreases slightly as bulk temperature approaches pseudo-critical temperature,and channel pressure is positively related to heat transfer coefficient;the stronger the heat flux is,the lower the heat transfer coefficient is,because there exists chemical reactions near the wall.Turbo-pump operation performance study was carried out based on i SIGHT platform to realize an automation process for configuration design,3D digital modeling,grid generation and flow field simulation.Detailed structure parameters and geometric model were obtained.The multi-block grid was applied to varied parts according to the flow-field characteristics.Numerical methods suitable for stable/transient calculation were established and validated.Operation characteristics of scramjet with expansion cycle were studied on the basis of the former two parts.For centrifugal pump,back pressure almost has no influence on pump head;both the efficiency and the shaft power required would be greater if the mass flow rate is smaller while adopting throttling adjustment,but the efficiency almost remains the same while adopting variable-speed adjustment;comprehensive regulation method is suitable for variable-pressure regulation,and shunt regulation is propitious to constant voltage regulation.For blowdown turbine,efficiency is overall low according to the relation curve about efficiency and speed ratio,which means that turbine design scheme needs to be improved;the turbine can provide enough shaft power for pump under 25000 rpm,if the flow rate is greater greater than 1kg/s;while adopting throttling adjustment,variable-pressure-ratio regulation,pressure ratio and adiabatic power is positively related to output shaft power,but speed ratio and efficiency is negatively related to output shaft power.During engine start-up processor with ethylene assistant subsystem,the internal flow field and operation characteristics of pump vary rapidly over time;the turbine driven by ethylene has a problem of supersonic usage,and the internal flow field almost do not change with time;the turbine can satisfy the need of pump shaft power during start-up processor.Numerical study on operation characteristics of scramjet with expansion cycle lays a solid foundation for later research of such system.