Effects of combustor length on solid fuel scramjet combustor performance

Based on foreign researchers' experimental data about solid fuel scramjet's, the numerical simulations concerning about the characteristics of the flow field in the solid fuel scramjet and the combustor performance were described by changing the length of the cylindrical section and the length of the diverging section respectively. A second-order-upwind difference scheme and the pressure-based solver were used for simulating the dynamic flow associated with an axis symmetric physical model. The combustion model in the numerical simulations was finite-rate/eddy-dissipation and the turbulence model was the shear stress transport (SST) k-ω model. The boundary of polymethyl methacrylate (PMMA) solid fuel was defined by the user-defined function. Results indicate that as the length of the cylindrical section increases, the combustion efficiency at combustor outlet decreases from 72.74% to 66.81%, while the total pressure loss decreases, the thrust in the combustor increases from 85.83 N to 108.55 N. The variation of the length of diverging section makes rarely difference on the flowfield characteristics of the combustor, as the length of the diverging section increases, both the combustion efficiency at combustor outlet and the thrust in the combustor slightly decrease. In the design range of combustor length, if the length of the combustor needs to be increased, it's better to increase the length of the cylindrical section rather than the length of the diverging section.