Research On Fuel Injection,Mixing And Combustion Characteristics Downstream Of The Cavity In The Supersonic Flow

In this paper,we use high-speed photography,high-speed grain shadowing and spontaneous radiation as the object of study,combined with the OpenFOAM open-source platform-based custom solver rho Centrol Foam to carry out numerical simulation and analysis of the mixing flow field and combustion characteristics of simultaneous injection upstream and downstream of a cavity combustor in a supersonic flow.The mixing process and combustion characteristics of downstream injection in the cavity in the supersonic flow are studied in depth,and the laws and internal mechanisms are summarized;the effects of different combustior cavity configuration parameters and downstream injection strategies are compared,and key analyses on pressure distribution,penetration depth and combustion efficiency are given to optimize the combustion chamber configuration and injection method of the sramjet engine.Firstly,the background of this paper and its significance at home and abroad are introduced in an overview.Firstly,the background of the proposed simultaneous upstream and downstream injection method of the supersonic incoming flow cavity is briefly analysed.Then,the interaction between the transverse jet and the cavity and the flame stabilisation of the cavity in the supersonic flow are reviewed respectively.The experimental equipment,optical observation means,simulation and calculation platform and modern numerical calculation research methods used in this paper are introduced,and the controlling equations for the chemical reaction of multi-component gas mixture,the sublattice closure model for LES large vortex simulation and the chemical reaction model and chemical reaction acceleration method used in the simulation of this paper are given.The reliability of the computational methods used in this paper.The flow mixing process of the upstream and downstream simultaneous injection method of the supersonic cavity is then investigated for the cold flow field.Combining experiments and numerical simulations,a series of analyses are carried out on the flow field characteristics of simultaneous upstream and downstream injection in the cavity,the different downstream injection positions and the flow mixing process under different combustion chamber configurations.It is found that,compared with the traditional upstream injection of a single cavity,the simultaneous upstream and downstream injection of a cavity results in a more stable shape with a significant coiling effect and the presence of an internal reflux zone with the leading and trailing edges of the cavity.It is also possible to introduce a large number of low velocity vortex structures on the leeward side of the downstream injection.By introducing downstream injection into the cavity,the flow field structure inside the cavity and downstream of the cavity is altered,and when comparing the effective penetration area of the two,it is found that the effective penetration area increases significantly in the cavity and downstream area,and the fuel/air mixing capacity increases.When the downstream injection position is far from the rear edge of the cavity,the surge converges at the rear of the cavity and forms a large high temperature and low velocity area during the refraction process downstream of the cavity,which is conducive to the mixing of the fuel.And for the upstream and downstream simultaneous injection scheme,because it disperses the fuel injection,the resulting surge intensity is lower,the total pressure loss is smaller,and the total pressure recovery is increased by 10% compared to a single upstream injection.When the downstream double injection with simultaneous upstream and downstream injection of the concave cavity is adopted,the flow pattern in the cavity changes to a closed cavity pattern when the downstream injection position is close to the trailing edge of the concave cavity,and the shear layer is close to the bottom of the cavity,while the downstream CVP structure is no longer symmetrical,the perturbation of the flow field increases and the vortex distribution is highest,but it also brings more total pressure loss.Finally,through experimental optical observation and data analysis,the simultaneous injection combustion and flame stabilisation processes upstream and downstream of the cavity combustion chamber are investigated.The experimental results show that the simultaneous upstream and downstream injection in the cavity chamber significantly improves the combustion performance compared to a single upstream injection in both cases where hydrogen and ethylene are used as fuel.The two extreme conditions,where the downstream injection position is close to and far from the rear edge of the cavity,result in higher combustion intensities compared to the conditions where the injection position is in between.The fuel mixing and combustion efficiency is further enhanced when simultaneous upstream and downstream injection of the concave cavity is carried out in a downstream double injection mode.The reaction zone is increased and flame propagation is more stable,while the position of the downstream injection has little effect on the ignition and flame stabilisation time.When the fuel injection is ethylene,the characteristics of the flow field under the simultaneous injection mode of upstream and downstream of the cavity are basically similar to that of hydrogen injection,but the downstream injection position has a greater influence on the ignition delay time of ethylene.