An Investigation On Combustion Stabilization Mechanism And Analysis Model Of Rearwall-Expansion Cavities In Supersonic Flows

The present study focused on the rearwall-expansion cavity in the conditions of supersonic combustion,and investigated the combustion mode,the combustion stabilization mechanism,and other performance of the rearwall-expansion cavity.The study is a combination work of experiments,numerical simulations,and modelling.By high speed photographing and OH* spontaneous emission photographing,the combustion modes of rearwall-expansion cavities with different configurations were observed.Through a set of experiments,it was observed that the combustion modes of rearwall-expansion cavities experienced transitions from cavity shear-layer stabilized combustion and lifted cavity shear-layer stabilized combustion to combined cavity shear-layer/recirculation stabilized combustion.It was also confirmed by the experiments that the rearwall-expansion cavity is capable of preventing the formation of thermal choke,which is of much importance to the reliability of the scramjet engines.The combustion stabilization mechanism was then studied by OH-PLIF,laser schlieren,and numerical simulations.The experiments includes cases of either jet combustion or premixed combustion conditions.In premixed combustion cases,it was observed that by the rise of the heat released from the combustion,the combustor is able to achieve lifted cavity shear-layer stabilized combustion.However,it is difficult for the rearwall-expansion cavities to achieve fierce combustion without the influence of fuel jets.The cases of near lean blowout limits were also studied,and several methods to enhance the flame stability of rearwall-expansion cavities were concluded.A quasi-one-dimensional model was developed to analyze the performance of rearwall-expansion cavities.The quasi-one-dimensional model can help to process the experimental data and analyze the flow parameters that are unable to be directly obtained from the experiments.Furthermore,the model also achieved to predict the performance of scramjet engines within a certain range of conditions.