Investigation On Supersonic Flow Combustion Characteristics And Flame Stabilization Mechanism Of An Axisymmetric Cavity Flameholder

It is one of the main technical challenges for the development of hypersonic vehicle to achieve effective mixing and stable combustion of the fuel in the high-speed flow of the scramjet combustor.Some disadvantages of the rectangular cavity flameholder have been gradually revealed by researchers,while more and more attention has been paid to the axisymmetric cavity flameholder.In this paper,the axisymmetric cavity flameholder is investigated by numerical method based on GPU simulation platform.The cold and combustion flow field of the axisymmetric cavity with upstream injection are studied to explore the supersonic combustion characteristics and flame stabilization mechanism.The flow and fuel mixing characteristics of the axisymmetric cavity cold flow field with upstream injection were studied by RANS simulation method,and the effects of cavity configuration and equivalence ratio on the flow field were discussed.It is found that the flow structures and fuel distribution of the axisymmetric cavity cold flow field have axisymmetric characteristics and do not change with the circumferential position.With the increase of the cavity aft wall angle,the interaction between the fuel jets and the cavity shear layer is enhanced,and the fuel penetration depth increases.The fuel mixing efficiency is improved.The variation of the cavity depth has almost no influence on the flow structures and fuel mixing characteristics of the axisymmetric cavity cold flow field.As the cavity length increases,the cavity shear layer grows thicker,which promotes fuel diffusion and mixing,while the total pressure loss of the flow field increases.The increase of equivalence ratio will lead to concentrated fuel distribution and low fuel mixing efficiency.Based on the cold flow field,the combustion flow field of axisymmetric cavity with different cavity configurations and equivalence ratios was simulated and analyzed,and the flame stabilization mechanism of axisymmetric cavity was studied.The simulation results show that the combustion flow field of the basic configuration is axisymmetric.The fuel burns uniformly in the circumferential direction.The combustion mainly occurs in the jet wake,while the cavity plays the role of the ignition source to hold the flame.The flame stabilization mode is the cavity assisted jet-wake stabilized combustion.With the increase of the cavity aft wall angle,the combustion and boundary layer separation display asymmetry characteristics.The flame stabilization mode of the cavity on the side where the combustion and separation become weak changes to the cavity shear layer stabilized combustion.The fuel combustion on this side is insufficient and the overall combustion efficiency of the flow field decreases.The depth of the axisymmetric cavity has little effect on the combustion flow field.When the cavity length increases,the cavity mass exchange rate intensifies.The fuel burns sufficiently and the combustion efficiency improves.With the increase of equivalence ratio,the mainstream velocity decreases significantly.The fuel consumption rate near the cavity is accelerated in the low-speed environment.The relationship between the asymmetric phenomenon and injection scheme in the combustion flow field of the combustor with different cross sections was numerically studied.In the rectangular combustor,the boundary layer separation tends to occur at the corner of the flow path due to the corner boundary layer effect.The separation and combustion of two corners will be significantly strengthened,while the separation and combustion of the other two corners will be suppressed.In the axisymmetric combustor,the combustion and boundary layer separation in the flow field with the single-row uniform injection scheme are basically symmetric,while the other injection schemes will induce the asymmetric phenomenon.In the flow field with multi-row non-uniform injection scheme,the direction of the asymmetric phenomenon is consistent with that of the fuel injection scheme.The direction of the asymmetric phenomenon can be controlled by changing the injection scheme,but it can also lead to slight increase of the total pressure loss of the flow field.If the fuel injectors are uniformly distributed,the direction of asymmetric phenomenon cannot be predicted.