| Scramjet engines operate for a long time under the coupling conditions of extreme aerodynamic frictional resistance and thermal load caused by ultra-high velocity inlet flow and high intensity combustion.In high Mach number flight,the ratio of internal flow frictional resistance of scramjet to the net thrust of aircraft can be up to more than half,and the inner flow wall faces a great aerodynamic thermal load,so scramjet is faced with a huge risk of high Mach number flight power shortage and easy to burn down.Therefore,whether drag reduction and heat prevention can be carried out effectively on the inner flow channel of scramjet engine determines whether the engine can run safely while giving full play to its maximum performance,and efficient drag reduction and heat prevention technology is one of its key bottleneck technologies.Aiming at the high Mach number hydrocarbon fuel scramjet flight requirements,the feasibility of hydrocarbon fuel gas film/high temperature resistant non-metallic material active and passive thermal protection scheme was studied.Membrane/high temperature resistant material was set up and the main passive composite quasi one-dimensional model of the cooling system,and further to the reference enthalpy method and the coupled convective heat transfer formula to solve passive thermal protection form wall temperature is obtained,the quasi one-dimensional model can evaluate hydrocarbon fuel gas film/high temperature resistant non-metal material master passive cooling performance of thermal protection scheme.By quasi one-dimensional model assessment Ma6-8 combustor thermal protection scheme and shows that under the condition of high Mach number flight with hydrocarbon fuel gas film/high temperature resistant non-metal materials C/Si C main passive thermal protection scheme can meet the demand of the combustion chamber wall temperature cooling,at the same time to consider hydrocarbon fuel film combustion efficiency and drag reduction performance of engine performance improvement.Under the condition of high Mach number,the gas film cooling characteristics and combustion drag reduction characteristics of hydrocarbon fuel will change.Numerical study on the cooling characteristics and combustion drag reduction characteristics of hydrocarbon fuel gas film under high enthalpy supersonic flow condition shows that the influence mechanism of the flow heat transfer mechanism and combustion drag reduction mechanism of macromolecular hydrocarbon fuel gas film change greatly under MA6-8 flight condition.With the increase of flight Mach number,the mixing efficiency of mainstream air and macromolecular hydrocarbon fuel film decreases,and the increment of combustion thermal load is small,while the aerodynamic thermal load increases sharply.The favorable cooling space of macromolecular hydrocarbon fuel film is longer and the decrease of wall temperature is larger.Combustion mechanism of drag reduction characteristics influence changes,along with the flight Mach number increases,the combustion chamber wall wall shear stress increase due to the speed gradient,a sharp rise in the pneumatic friction resistance,and the mixing efficiency drop caused combustion heat makes the air density is decreased,and the boundary layer in lower Reynolds stress decreases,the impact near wall viscous stress change is small,As a result,the drag reduction effect of combustion is relatively weak.And through specific parametric analysis,studied the combustion chamber center flow parameters and membrane change of the macromolecular hydrocarbon fuel gas combustion in film cooling characteristics and boundary layer the i nfluencing laws of gas drag reduction characteristics,affected by the mainstream and jet mixing efficiency,in turn,affects the hydrocarbon fuel pyrolysis gas film oxidation combustion reaction to its cooling properties and combustion characteristics of drag reduction has had a huge impact.Finally,according to the optimal flow parameters and structural parameters of the high Mach number ramjet macromolecule hydrocarbon fuel gas film,the combustion efficiency and drag reduction performance parameters of the hydrocarbon fuel gas film were obtained through numerical research results,so as to correct the one-dimensional model.The cooling performance and specific impulse performance of the full-size combustion chamber of the engine using hydrocarbon gas film/high temperature resistant non-metallic material thermal protection scheme were analyzed and evaluated. |
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