Characterization of Combustion Instabilities in 2D Premixed Rotating Detonation Combustors

This paper explores combustion instabilities in rotating detonation engines (RDEs) using simplified numerical methods. Instabilities in RDEs are prevalent across numerical and experimental studies and understanding them is crucial in research as RDEs are pushed to higher performing conditions. The RDE upstream reactant plenum, injector plate, and combustion chamber are modeled in a URANS 1-step premixed hydrogen-air scheme. Multiple geometric and inlet conditions are varied in this study, including the injector area ratio, nozzle area ratio, inlet plenum length, and inlet reactant temperature. Injector area ratios are varied from very stiff (0.15) to very open (0.5). Nozzle area ratios are increased by increasing the back pressure of the combustor up to 4 bar. The inlet reactant temperature is varied to rise and lower the stiffness. Across the completed studies, stability is tracked in various ways. Furthermore, the relationship between injector stiffness, pressure gain, and case stability is tracked. Different modes of unstable operation are identified, including bobbing, transverse, and bursting modes. These modes are tracked and visualized using Spectral Proper Orthogonal Decomposition (SPOD) and x-t diagrams. The impact of these instabilities is quantified by the frequency they occur and their impact on performance parameters such as pressure gain and thrust.