Investigation On The Variable Cycle Engine Characteristics And Integration Design With Aircraft

Variable cycle engine(VCE),which could achieve excellent working cycle and low installed drag because of its ability to regulate the flow rate,has become one of the best options for civilian or military aircraft propulsion equipment.Its two main structural forms,core driven fan stage(CDFS)and fan on blade(FLADE),can form three kinds of variable cycle engines,which are double bypass VCE with CDFS,double bypass VCE with FLADE,and three bypass adaptive cycle engine(ACE)with both of CDFS and FLADE.A study on the further research of those VCEs and their working mechanism was conducted to reveal the essential differences between VCE and turbofan by researching VCE numerical simulation methods,steady performance,flow path,weight,transient performance during mode transition,performance optimization and integration design with airframe.First is the numerical simulation method of VCE.Based on single-angle characteristic variable geometry revising and multi-angle characteristic three-dimensional interpolating,the computational model of variable-geometry fan,high-pressure compressor(HPC),CDFS and low-pressure turbine(LPT)was established respectively,and the mismatch between VCE design point and CDFS design point was solved.The FLADE calculation method was developed by calculating bypass flow and core flow independently.By changing static pressure balance of fixed mixer to mass flow rate balance of variable geometry mixer,and considering local pressure loss caused by area sudden expansion or contraction,the computational methods of VCE mode select valve(MSV),forward variable area bypass injector(FVABI)and rear variable area bypass injector(RVABI)were improved.An engine parameter restricted processing algorithm was proposed,which can adapt the engine to the required performance when solving nonlinear equations.The VCE flow path and weight estimation model was built and examined by the YF120 VCE's dimension and weight data.The transition-state calculation method considering rotating shaft inertia effect and vessel volume effect was modeled and tested by the experimental data of NASA's VCE mode conversion.Based on the intake and exhaust system characteristic database,the internal and external flow losses of intake and exhaust computing model was established and validated by GE21J11B4 VCE's performance data.All the established models lay the foundation for the calculation and analysis of VCE performance.Second is the design parameters matching and steady regulation characteristic analysis of VCE.The matching laws of FLADE VCE and CDFS VCE main design parameters were studied.Under the restricted conditions of section temperature and the stage of components,the bypass ratio distribution,the pressure ratio distribution,and the FVABI and RVABI exit Mach number were obtained.The regulating characteristics of CDFS VCE's and FLADE VCE's variable geometry parameters were analyzed.The results showed that adjusting CDFS inlet guide vane(IGV)or HPC IGV has an opposite effect on the CDFS VCE's overall bypass ratio,overall pressure ratio and LP shaft rotating speed.Adjusting nozzle throat area has different effects on HP shaft rotating speed depending on MSV's different locations.During subsonic cruise,the CDFS IGV should be closed,the FVABI inner bypass area should be reduced,the nozzle throat area should be increased,and the FLADE IGV should be opened while the FLADE nozzle area should be increased.During supersonic cruise,the CDFS IGV should be opened,the FVABI inner bypass area and the nozzle throat area should both be increased,Adjusting LPT nozzle area appropriately could mitigate the conflict of the limited rotating speed and the lack of sufficient surge margins.Third is the transient characteristic analysis on VCE during its mode transition.An analysis was conducted on the VCE's operation characteristic during MSV or FLADE opening/closing.The results showed that opening or closing MSV alone could not convert VCE's mode smoothly.When closing MSV,the CDFS IGV should be opened,the FVABI inner area should be increased,and vice versa.When opening/closing FLADE,the FLADE IGV should be opened/closed,and the FLADE nozzle area should be increased/decreased simultaneously.The sudden change of FLADE mass flow rate would not cause other parameters to fluctuate wildly.The operation characteristics of opening/closing MSV of ACE are similar to those of the CDFS VCE,while the operation characteristics of opening/closing FLADE of ACE are similar to those of the FLADE VCE.For ACE,the coupling degree between the FLADE opening/closing and the MSV opening/closing is low.Forth is the research on the VCE performance optimization method.An improved differential evolution algorithm was developed and it performed well in the benchmark functions test.A multipoint integration optimization approach was proposed for VCE.By comparing optimized design schemes with maximum sea level static thrust among CDFS VCE,FLADE VCE,ACE and turbofan,it was found that FLADE VCE has the maximum thrust and lowest specific fuel consumption,while turbofan has the minimum weight,shortest length and highest thrust-weight ratio.The performance of VCE could be significantly improved by optimizing variable geometry parameters and control law.The overall performance of VCE can be further enhanced by optimizing combined design point with one off-design point.If VCE design point and multi off-design points are optimized together,different design demands,which are required by different flight conditions,can be effectively satisfied,even though the engine performance cannot be further improved obviously.Fifth is the research on the airframe/VCE integration design method.The computing models of airframe aerodynamic characteristic calculation,constraint analysis and mission analysis were established respectively,and were coupled with engine steady performance,internal and external flow losses of intake and exhaust calculation model,to constitute airframe/engine integration design model.For supersonic cruise without afterburner flight mission of fighter,the flight performances of CDFS VCE,FLADE VCE,ACE and turbofan were compared.The results showed that during subsonic cruise segment,the CDFS VCE has 11.2% more inlet mass flow,37.7% less inlet external drag,4.77% less boat tail drag and 2.39% lower installed special fuel consumption than the turbofan,and that the FLADE VCE and ACE have around 20% more inlet mass flow,over 60% less inlet external drag,around 10% more boat tail drag and 3% lower installed special fuel consumption than the turbofan.During supersonic cruise and transonic acceleration segments,the benefits of VCE decrease owing to the fact that all of CDFS VCE,FLADE VCE and ACE are in single bypass operating mode.The aircraft take-off weight can decrease 3%~4% after installing VCE.FLADE VCE performs best,and the next are ACE and CDFS VCE,respectively.