Effects of the Cavity Flameholder with Varied Forewall Angles on Supersonic Combustion

Ramjet and scramjet engines are air-breathing power systems that work more efficiently than gas turbine engines at hypersonic speeds. However, their high-speed operation demands specific design strategies to ensure flame stabilization and adequate residence time. In the present study, the effect of the forewall inclination angle of the cavity-based flame holder on combustion characteristics was investigated numerically in 2D geometry using Ansys Fluent. For this purpose, the combustion reactions of a total of 9 different forewall approaches, in which the angle of the forewall with the vertical axis was changed between -40 and 40 degrees at 10-degree intervals, were modeled with a 2.5 Mach inlet speed and 1 Mach hydrogen fuel injected from the cavity bottom. Results show that positive forewall angles are more efficient than neutral or negative inclined forewalls. Nevertheless, they lead to drag penalty compared to lower inclined wall angles. Qualitative evaluations show that a positive cavity with forewall angle enhances vortex in the upstream of fuel injection, hence improves combustion efficiency while sacrificing static parameters such as temperature and drag. Although the global combustion efficiency gain remains slight at 0.69%, positive forewall angles significantly optimize local recirculation and thermal distributions, offering better conditions for reactive flow stability inside the cavity. As a result, a positive inclined forewall is promising to improve combustion; however, temperature and drag rise should also be considered during the design process.