Investigation On Shock Train And Its Interaction With Combustion In A Supersonic Combustor

In this dissertation,the flow combustion process of a dual-mode scramjet engine is studied.Aiming at the combustion organization scheme of ethylene injection upstream of the upper cavity,the shock wave train structure,combustion process and its interaction in the supersonic combustion chamber are systematically analyzed by means of experimental observation and numerical simulation.The dynamic process of shock train establishment,shock train characteristics and pressure distribution characteristics in unreactive flow are analyzed by two-dimensional unsteady numerical calculation.The result shows that: in the straight channel,the first shock wave will go through a series of processes such as symmetrical λ structure,asymmetric λ structure and asymmetric x structure,the flow channel separation area will be transformed from symmetrical separation to asymmetric separation,and the shock train will be transformed from symmetrical structure to asymmetric structure.Under the same backpressure,the first shock wave changes from an symmetricλ structure to an asymmetric x structure and the shock train changes from a symmetric structure to an asymmetric structure in both unilateral and bilateral diverging channels.The flow separation is strengthened by the wall spreading effect,the separation zone is expanded,the starting point of the separation zone moves upstream,the shock train advances upstream,and the length of the shock wave series and the number of shock wave nodes increase.The increase of the expansion angle and the increase of the backpressure will further strengthen this effect.In the flow channel with flame stable cavity,the first shock wave will move upstream and pass over the cavity,so that the separation starting point will finally stabilize at a certain position in the upstream of the cavity.The shock wave series will stretch across the entire cavity and form a stable structure above the cavity.Besides,the separation area and the pressure starting point are closer to the inlet of the flow channel than the flow channel without the cavity.The effects of jet distance from the orifice to the leading edge of the cavity and the flow pressure ratio of jet/incoming flow on the interaction between the wall jet and shock train are analyzed by three-dimensional numerical simulation.The result shows that the first shock wave has an asymmetric structure at different injection distances,and the shock train are similar in structure.When the injection distance is small,the jet is in the separation zone,and the jet penetrability is high.The injection distance increases,and the jet gradually approaches to the starting point of the separation zone.When the injection distance is large,the jet is upstream of the separation zone and the jet penetration is low.Under different efflux/incoming flow pressure ratios,the first shock wave structure of the shock train changes,the efflux/incoming flow pressure ratio increases,the efflux penetration increases,and the vorticity in the separation region increases.The effects of equivalent ratio,injection distance and total temperature on the shock train and combustion characteristics were analyzed by means of three-dimensional numerical simulation and experiment.Under the conditions studied in this dissertation,the flame is periodically switched between the cavity stabilized mode and jet-wake stabilized mode,and the shock train then reciprocates periodically before and after the occurrence of flow direction.As equivalent ratio and injection distance increases,shock train length increase,the separation of the starting point in advance,the separation zone area is expanding,the jet penetration depth increases,the shear layer separation zone,jet-coming flow vorticity shear layer increases,the fuel and air mixing enhancement,combustion intensity increases,the peak combustion pressure,the greater the shock train and combustion coupling is increased;With the increase of the total inlet temperature,the length of the shock wave string decreases,the separation starting point falls back,the area of the separation zone decreases,the jet penetration depth decreases,the vorticity of the shear layer of the separation zone and the jett-incoming shear layer decreases,the mixing of fuel and air decreases,the intensity of combustion decreases,and the peak pressure of the combustion chamber decreases,the coupling between the shock wave string and combustion weakens.