Study On Performance Influence Regulation Of Ramjet Variable Geometry Combustor With Wide Range Velocity

The ability to fly for wide-range velocity and long periods are the inexorable trend for the future development of scramjet.With the flight Mach number range from 2 to 7,the ramjet would not only face the issues of combustion release heat,flow field characteristics,and combustion mode variations,but the thrust performance is insufficient for the ramjet.For a fixed geometry combustor,the ramjet often operates in the off-design performance characterization conditions in a long time.There is a small thrust to operate in an acceleration progress for the ramjet.However,a variable geometry supersonic combustor is suitable for the wide range velocity flight for the performance.Numerical simulation and experimental studies are carried out in a variable ge ometry supersonic combustor with a wide range velocity,equivalence ratio,and divergence ratio in the paper.The effect of deflection angle on the flow field characteristics and combustion performance is analyzed in a variable geometry combustor.In cold state flow field,the effect of the deflection angle on the total pressure recovery coefficient and drag coefficient is investigated and there is better total pressure recovery coefficient at deflection angle range of 11°~13°.In a hot state flow field,th e flow field characteristics are investigated in the variable geometry combustor.Results indicate that the total pressure recovery coefficient and combustion efficiency increase with the increasing of the deflection angle,then decrease,and there is a better value to be obtained at the deflection angle range of 11°~13°.On the one hand,the total pressure loss and entropy loss are generated by c ombustion heat release and backpressure variation caused by deflection angle variation On the other hand,the result is analyzed due to the interaction between the dominant shock wave and the additional shock wave caused by the deflection angle.The better deflection angle range of 11°~13° is obtained by thrust increment variation regulation for the variable geometry combustor flow design.The effect of geometry throat on ramjet combustor performance are conducted.Results indicate that the thermal blockage position moves forward the entrance of the combustor by decreasing the divergence ratio or increasing fuel equivalence ratio with geometry throat or no geometry throat.The comparison between geometry throat and no geometry throat on combustor performance is explicated.Results indicate that the combustion efficiency and total pressure recovery coefficient are improved by geometry throat.Meanwhile,irreversible entropy increase decreases.However,there is a potential balance between increasing in combustion efficiency and total pressure recovery coefficient and the reduction in thrust increment by the geometry t hroat.The thrust increment can be improved by geometry throat in the optimal Mach number flight,which is obtained in a range from 5.5 to 6.The scope of geometric throat in the wide range Mach number provides a theoretical basis for the regulation of the variable geometry combustor.The hysteresis is analyzed caused by divergence ratio variation with the variable geometry combustor.Results indicate that the hysteresis characteristic is not only associated with path variation of divergence ratio,but ass ociated with divergence ratio itself size.The hysteresis is disappeared with the increasing of divergence ratio.The variation of hysteresis width is also obtained.The hysteresis in combustor parameter is also studied.The Mach number hysteresis and thru st increment hysteresis is obtained.It is found that the hysteresis phenomenon is produced due to the oblique shock train motion in the isolator and the boundary layer separation and attachment caused by variation of divergence ratio,which also leads the variation of total temperature and back pressure in the isolator exit.The combustion system is transformed from one state to another.The optimal performance regulation is analyzed with the variable geometry combustor.Results show that the combustor thrust increment can be improved by decreasing divergence ratio for a given fuel equivalence ratio within stability margin.The mechanisms between the divergence ratio and combustion heat release is elaborated.On the one hand,Irreversible entropy increas e analysis is extended specifically,the entropy loss is different with different sections in combustor.The irreversible entropy loss increases with the increasing of the divergence ratio.On the other hand,from the thermodynamic cycle analysis,the comb ustor performance loss is influenced by the total temperature increment and Mach number in combustor.The optimal thrust increment regulation is obtained based on the ramjet stability margins for variable geometry combustor with a wide range Mach number flight.