Thermodynamics Performance Analysis Of The Full-range Fan-augmented Ramjet Based Combined Cycle Engine

Airbreathing combined cycle engine is one of the most potential propulsion systems for hypersonic vehicles,and suits for the future hypersonic aircrafts and other reusable vehicles.This dissertation has proposed a novel full-range fan-augmented ramjet based combined cycle engine and conducted studies on the overall parameters matching of the novel engine and the performance optimization.The main research work is as follows:From the perspective of reducing working Mach number of the ramjet,mechanical compression by fan is used to further reduce the minimum working Mach number of the ramjet channel.By integration of the fan bypass channel and the ramjet channel,the full-range fan-augmented ramjet based combined cycle engine has been conducted.At Ma₀=0～3,the two flow channels work together,and the two cycles of the core and bypass channel are connected by the fan.Thermodynamics cycle analysis shows that the full-range fan-augmented ramjet based combined cycle engine has advantages on specific impulse when the bypass ratio is 2.Through the optimization of the engine cycle,there exits optimal fan pressure ratio that leads to the highest specific impulse in the acceleration mission,and the variation of optimal fan pressure ratio with the bypass ratio and the flight Mach number has been determined.It can help engineers select the optimal parameters in the overall design stage of the combined cycle engine to ensure its performance.The design constraints of the full-range fan-augmented ramjet based combined cycle engine are analyzed from the perspectives of thrust requirements,thermal protection constraints,cross-section area matching,flow channel matching,etc.Parameters like the overall size of the combined cycle engine and the length of every component can be determined by the design requirement,and then the matching relationship of components can be determined by the constraints of flow channel length.Research found that the combined cycle engine with existed turbine engine is oversized,which will increase the length of ramjet channel and reduce the performance of ramjet channel.From the perspective of meeting the constraints of ramjet channel,the length to diameter ratio of the turbine of axisymmetric turboramjet is small,which can provide a guide to the overall design of turbine-ramjet combined cycle engine.The optimization analysis for the heating process is conducted for the high-speed adjustable ramjet channel,and the working boundary of the constant-area combustor and the adjusting regulation of the combustor geometry and the fuel to air ratio are obtained.The results show that the variable geometry combustor can better meet the operation requirements of ultra-wide conditions,and the flow path suitable for the high-speed channel in the full-speed range is obtained.This dissertation also analyzed the influence of parameters of isolator entrance on the ramjet performance.The optimum compression ratio of the inlet increases with the increase of flight Mach number.The increase of the compression ratio of the inlet leads to the increase of the contraction ratio demand of the inlet.Considering the operation demand of wide speed range and equivalence ratio range,and reducing the adjustment requirement of the inlet,the total contraction ratio of the inlet is about 7.The analysis shows that the expansion ratio of the combustor is less sensitive to the performance of the ramjet.Only when the expansion ratio changes in a large range,the ramjet performance will change significantly.The specific impulse is most sensitive to the combustion efficiency,and improving the combustion efficiency can effectively improve the ramjet performance.The geometrically adjustable ramjet channel and the bypass channel of the supersonic fan turbine engine are integrated to form an axisymmetric full-range fan-augmented ramjet based combined cycle engine scheme,which reduces the minimum working Mach number of the ramjet channel.The supersonic though flow fan makes the two channels work together under the freestream Mach number range of 0～3,and significantly reduces the thrust requirement for the inner channel and the size of the turbine engine.The supersonic through-flow fan can largely reduce the requirement of diffuser section and reduce the length of the inlet,so the flow channels match easier.In the acceleration mission,the afterburner and the bypass channel are working at the equivalence ratio of 1 to improve the output thrust of the combined cycle engine,and the thrust provided by the bypass channel is relatively large.Specific impulse can be improved by reducing the afterburner equivalence ratio.The thermodynamic analysis shows that the specific impulse of the full-range fan-enhanced ramjet combined engine is relatively good in the flight Mach range of 0～6.