Research On Variable Cycle Engine Control Schedule Design

In the 1960 s,the requirement for supersonic cruise aircraft propulsion system had turned to the concept of variable cycle engines(VCE).Since then,the VCE has been a focus for aircraft propulsion engineers.One of the key technologies for VCEs is ‘Variation’.One can fully develop VCEs’ potential only by knowing how the ‘variation’ happens.How to vary a VCE is in fact a matter of control schedule design.Thus,VCEs’ control schedule,including the steady and transient state control schedule,is of great significance for the development of a new VCE.Focusing on the VCE control schedule design,the work of this thesis includes: 1)VCE performance modelling.The mechanisms of key components in VCEs are analized and their models are established or modified.Based on these components models,the performance model of the variable cycle engine with core driven fan system(CDFS VCE)and the adaptive cycle engine with Flade fan(Flade ACE)are established.The performance models of the CDFS VCE and the Flade ACE are in fact 7 and 8 dimensional nonlinear equation groups respectively.Models for VCE transient performance simulation and size and weight estimation are also introduced,which lays the foundation for control schedule design.2)The integrated installed performance of aircrafts and gas turbine engines.The aircraft and engine integral mission assessment model is introduced at first.Then the matching mechanism between the supersonic inlet and the gas turbine engine is reviewed.The focus is put on the estimation of the installed drag for supersonic inlets,based on which the installed performance model is established in terms of inlet and engine matching.The nozzle installed drag estimation method is also introduced.Results show that the installed performance simulation model is valid for different flight conditions and inlet-engine matching states.Comparison with authoritative data shows that the deviations of the inlet performance data are within 1.5% while the inlet drags within 9%.3)VCE steady state control schedule design.The steady state reverse method(SSRM)is developed to overcome disadvantages of traditional engine simulation model.Then the reverse method is coupled with the Isight software to establish optimization models for VCE steady state control schedule design.The FVABI operating mechanism is reviewed to establish its independent closed loop control schedule.Results show that the reverse method can improve the convergency and efficiency of VCE performance model while maintaining high accuracy.The VCE throttle control schedule designed can decrease the installed specific fuel consumption(TSFC)of subsonic conditions by 16%,and is valid under different conditions.The closed loop FVABI control schedule can avoid dangerous flow phenomenon such as critical flow in the first bypass or reverse flow in the second bypass.4)VCE transient control schedule design.The transient state reverse method(TSRM)of a turbojet engine is established by combining the virtual power extraction method(VPEM)and the SSRM.Then the influences of variable geometries on the VCE transient performance are revealed,based on which the TSRM for VCEs are established.Then the TSRM are again coupled with the Isight software to establish the optimization model for VCE acceleration and deceleration control schedule design.The mechanism of VCE mode transition is reviewed to establish its control schedule design method.Results show that the acceleration and deceleration control schedule designed can decrease the dynamic response time by 50%.The mode transition control schedule design method is valid under different working conditions.Over temperature,over speed and surge are avoided during acceleration,deceleration and mode transition.5)Comparison between traditional turbofan,CDFS VCE and Flade ACE in terms of integerated installed performance.The traditional turbofan,the CDFS VCE and the Flade ACE are designed according to the requirement of the versatile supersonic cruise fighter.Their flow passes and weights are assessed respectively.The steady state and transient control schedule for CDFS VCE are designed.The integral mission assessment of a supersonic aircraft is performed employing these three engines.Results show that in comparison with the traditional turbofan available in 2000 s,the CDFS VCE and the Flade ACE can decrease the subsonic TSFC by 16.4% and 19.5% respectively,and the supersonic TSFC is decreased by 7.3%.Thus,for the same payload,the operational radius is improved by 17%(CDFS VCE)and 20%(Flade ACE)respectively.It can be concluded that the VCE steady and transient state control schedule design methods developed in this thesis can improve VCEs’ performance in both steady state and transient state and has good adaptability,which offer technical support for the development of VCEs.