The Overall Modeling And Matching Design Of Turbine-based Combined Cycle Engine Considering The Integration Of Aircraft/Engine

A general model for turbine-based combine cycle(TBCC)without fully considering the concept of aircraft/engine integration has become a key bottleneck restricting the technological progress of wide-speed hypersonic aircraft.In order to comprehensively evaluate the performance of the TBCC system under the condition of aircraft/engine integration,a systematic model was established from the levels of aircraft-engine integration design,whole propulsion system modeling and its components modeling.This model provides an evaluation method for the performance analysis of TBCC propulsion system and some optimal control strategies for a typical TBCC matching design.The specific works including 4 aspects are as follow:From the level of aircraft-engine integration design:Based on the theory of Energy-State approximation,gravitational potential energy and kinetic energy are normalized to total energy at the same Mach number of sea level,and then an Energy-State-approximation-based analysis method for aircraft-engine general proposal is proposed.In addition,the design feasible region of wide-speed range aircraft/TBCC system is obtained.It is concluded that the aircraft for cruise mission should adopt a low-thrust TBCC with an optimal acceleration of about 0.18g to reach the maximum cruising range of 7500km,while the aircraft for boost mission should adopt a large-thrust TBCC with an optimal acceleration of about 0.26g to accelerate to the cruising state as soon as possible.At this time,increasing the thrust-weight ratio of the propulsion system could achieve the same effect as increasing the specific impulse and lift-drag ratio.An increase of the cruise Mach number by 1.0 will reduce the flight time by about 15%.From the level of whole propulsion system model:Introducing the concept of optimal trajectory to evaluate aircraft performance indicators,the performance analysis problem of TBCC is transformed into the trajectory optimization problem of a specific aircraft,and then a trajectory-optimization-based evaluation method is proposed for the performance analysis of a whole propulsion system,which realizes the comprehensive evaluation of the TBCC overall scheme at the level of the aircraft/engine integration.The established aircraft-engine model shows that by introducing a rocket with 10%take-off weight thrust,the accelerating aircraft could reduce the total energy consumption from aircraft drag by 15%,and improve the vehicle efficiency ηveh effectively during the mode transition period,leading to an increasing of average vehicle efficiency ηveh by 9.9%within the entire flight envelope.Although the low specific impulse brought by rocket reduces the average engine efficiency ηengine by 6.8%,the average total efficiency ηtot still increase by 2.6%.For the cruising aircraft,due to the comprehensive effect of cruise lift-drag ratio and cruise fuel ratio,for the feasible TBCC scheme(take-off thrust-weight ratio of 1.0),the rocket with 4%take-off weight thrust can not only achieve a significant reduction in climb acceleration time,but also a 0.97%increase in cruise range.For the infeasible TBCC scheme(take-off thrust-weight ratio of 0.8),the introduction of rocket could not only assist the TBCC accelerate to cruising phase,but its voyage range could increase by up to 7.9%compared with the TBCC solution with a take-off thrust-weight ratio of 1.0.From the level of components model:Combining three parts of design works(aircraft-engine component-level modeling,multi-variable control design,and optimal-control-based matching optimization),an optimal-control-based design method for TBCC is proposed.With the consideration of the aircraft/engine integration,a matching design scheme at the TBCC component level and its optimal control regulations are obtained.Based on the spot turbine engine with a maximum operation speed of Ma2.5 given in this article,subjecting to the combined effects of the aircraft’s "climb-dive" strategy,turbine shut-off during mode transition period,small thrust per unit mass flow of the ramjet,and thrust loss of the ramjet in a subcritical state,the minimum thrust during the mode transition period is only 30%of the thrust before mode transition,exhibiting the phenomenon of "thrust pinch".When a turbine engine operates at the maximum Mach number of 2.9,the minimum thrust during the mode transition period will increase to 80%of the thrust before the mode transition,and the "thrust pinch" phenomenon tends to be flat.Demonstration of turbo/rocket/stamping three-combination power scheme:Local rocket assistance could make up for the thrust of the typical TBCC in the transonic,mode transition and high Mach speed range,which greatly reduces the demand for the maximum operating speed of the turbine engine during the mode transition period.Compared with the high-speed turbine/ramjet combined power at the maximum operating speed of Ma2.9,the existing turbine engine of Ma2.5 accompanying a rocket with 20%take-off weight thrust can reduce the size of the shared intake,nozzle and combustor chamber by 20%.It reduces the supersonic spillage loss effectively and smooths the control regulation of the intake and nozzle area.However,under low-speed conditions,it is necessary to introduce auxiliary intake valves and other drainage devices to match the operation state of the turbo engine.In summary,this article has carried out three levels works of overall modeling and matching for TBCC from the perspective of aircraft/engine integration.Considering the timing characteristics of mode transition,the "thrust pinch"mechanism of a typical turbine-based combined engine is clarified,and the advantages of turbo/rocket/ramjet three-power combined engine is first clarified from the perspective of efficiency and energy,which points out the direction for the overall performance improvement of this type of engine.