Investigation Of Wide Mach Range Inlet And Matching Technology For Rocket Based Combined Cycle Engine(RBCC)

The Rocket-based Combined Cycle(RBCC)engine concept was proposed in the 1960s along with thirty-one other combined cycle propulsion systems.Further studies indicated that the RBCC takes advantage of the synergistic interactions between rocket engines and air-breathing engines,and therefore providing a high thrust-to-weight ratio with a high specific impulse.This highly integrated propulsion system is one of the most promising prospective approaches for reusable space access and hypersonic cruise capabilities.As an aerodynamic component of significant importance to air-breathing engines,the inlet is required to provide the proper captured atmospheric air over the entire operating range of the vehicle in a reliable and controllable manner while suffering minimum aerodynamic losses.A fixed-geometry inlet is barely able to meet these requirements over a large flight envelope..Therefore,in order to meet the demands of operating in wide envelope and trajectory,the investigations of wide Mach range inlet and matching characteristic for rocket based combined cycle engine are proposed in this dissertation.The essential function of the inlet is to provide the captured atmospheric air to the combustor at suitable Mach number,temperature,and mass flow rate.The inlet design is affected by the operating Mach number range and flight trajectory of the engine.The design method and structure features were proposed for the RBCC engine with climbing ballistic in this dissertation.The possible problems in both the high and low Mach number ranges of the RBCC inlet are illustrated based on the numerical simulations,which elicited the main research content of this dissertation,namely: the wide Mach range inlet and matching technology for rocket based combined cycle engine.Furthermore,the influences on the inlet structure and performance of the strut angle are investigated according to the structural characteristics of the central strut installed inside isolator.The optimization design of the RBCC inlet is carried out based on these research results.The total contraction ratio is one of the most important inlet structure parameters.The combined numerical-experimental results show that the increased inlet contraction ratio always results in the increasing of the compression ratio and capability of anti-counter pressure,while its impact on the mass flow coefficient is negligible.The RBCC wide Mach range inlet is proposed,which could provide the desired performance parameters in ramjet mode and scramjet mode,and meet the demand of self-starting Mach number for mode transition between the ejector mode and ramjet mode.The RBCC wide Mach range inlet with the translating cowl lip is further proposed.The results show that the translating cowl lip results in a better starting performance at low Mach number range and an increasing of the mass captured coefficient at high Mach number range.During the supersonic flight,the strength of the inlet oblique shocks is significantly affected by the angle of attack,which forces the inlet to deviate its rated operating condition.The investigation on the influence of attack angle for the RBCC inlet is carried out in this dissertation through the one dimensional theory analysis,three dimensional numerical simulation and wind tunnel experiment.The results show that at high Mach number range,the angle of attack forces the oblique shocks deviate or converge on the inlet cowl lip.The compression level of the inlet is also changed by the attack angle,and therefore affects the quality of the captured atmospheric air flowed into the combustor.While at low Mach number range,the influence of attack angle mainly focuses on the intensity and region of the bow shock.The negative attack angle helps the inlet achieving self-starting earlier,and the positive attack angle may result in the unstarting of the inlet.The airframe attitude control method which could decrease the inlet self-starting Mach number in the rated flight attack angle is proposed.Finally,the interaction influence between the inlet and the rocket engine/ramjet engine are investigated at ejector mode,ramjet mode and scramjet mode in this dissertation.The results show that the inlet would be impacted by both the freestream ram action and the strut rocket plume simultaneously in the ejector mode.The influences of the rocket plume are reflected in two aspects,namely the promotion action of the ejector effect and the suppression action of the extrusion effect.The dynamic pressure of the freestream is the key factor impacts the promotion action and the suppression action of the rocket plume.Besides,the reactive numerical simulations are performed to illustrate the impact of inlet contraction ratio on the entire engine efficiency and performance.The results shows that the coefficients of inlet drag and combustor thrust increase with the increasing of the inlet contraction ratio,while the nozzle thrust coefficient demonstrates an opposite trend in ramjet and scramjet mode.The optimization principle for the RBCC wide Mach range inlet is proposed and validated based on these research results.