Scramjet combustion with bumpy struts

In this study, the following strut configurations were proposed to improve the combustion performance of a scramjet combustor with a strut: (1) BS-1: strut with periodic rectangular bumps and (2) BS-2: strut with periodic trapezoidal and triangular bumps. These bumps were arranged on both sides of the rear part of the struts. By using a validated numerical simulation method, the performance and combustion flow fields of scramjet combustors with a normal strut (NS) and two BSs were compared and analyzed under an inlet Mach number of 2.0 and hydrogen jet at sonic speeds. The effects of the two BSs on the performance of the scramjet combustor and their mechanisms were investigated. The results demonstrated that in the two BS combustors, the flow disturbance and streamwise vortices induced by the bumps, additional oblique shock waves at the leading edge of the rear straight section, and upstream shift in the interaction position between the reflected oblique shock wave and shear layer resulted in a significant increase in total pressure loss. However, the flow disturbance and streamwise vortices not only significantly increased the shear layer thicknesses and interfacial area between the fuel and air, which contributed to a more stable and efficient combustion by increasing the size of the near-field high-turbulent-kinetic-energy region and expanding the combustion region, but also enhanced heat and mass convection between the core region and main stream on both sides, yielding a higher flame propagation speed. Therefore, the combustion was significantly promoted in the two BS combustors. BS-2 had a stronger disturbance effect on the flow and induced stronger streamwise vortices, resulting in a greater total pressure loss compared with that observed in BS-1. However, the triangular bumps of BS-2 increased the width of the narrow part of the recirculation zone, which made the fuel distribution downstream of BS-2 combustor more conducive to maintaining a larger combustion region, thus achieving more efficient combustion. Compared with the NS combustor, BS-1 and BS-2 combustors reduced the distances by 49.4% and 54.1%, respectively, when the combustion efficiency reached 95%, and by 47.9% and 53.1%, respectively, when the combustion efficiency reached 100%, with the total pressure loss at the outlet increasing by 2.16% and 3%, respectively. Therefore, the results suggest that the two BSs have the potential to significantly enhance the combustion of scramjet combustors, making them a promising avenue for further research and optimization.