Influence of injector configuration on secondary wave formation and propagation in a rotating detonation combustor

Numerous studies of rotating detonation engines (RDEs) have noted the appearance of weaker secondary waves which travel with or counter to the primary wave system. These secondary waves can affect the speed, strength, multiplicity, and directional preference of the primary wave system, all of which have implications for engine performance and operability. As such, understanding the formation and stabilization of different wave modes is critical for developing practical RDE systems. To this end, the present work uses an adaptive mesh refinement framework to simulate two-dimensional unwrapped RDEs at high spatial resolution. Four injection configurations are considered, including a simplified continuous injection boundary, as well as three discrete injection setups with varying injector diameter and spacing. In the discrete injection cases, the effects of mass flow rate and near-wave grid resolution are also investigated. Continuous injection is found to produce a single wave, while discrete injection yields increasing numbers of co- and counter-propagating waves when the number of injectors or the reactant flow rate increases. The generation of secondary waves is linked to acoustic reflections associated with wave passage over the discrete injectors, as well as successive “micro-explosions” that occur when a reaction zone recouples to a shock wave traversing a reactant jet. These secondary waves can then coalesce in the presence of fresh reactants, providing a mechanism for new primary waves to form and the directional preference of the wave system to switch. The diameter and spacing of the injectors directly impact the sustained propagation of the primary waves, as well as the availability of reactants needed to form a strong counter-propagating wave system. The unsteadiness induced by the different injection schemes is manifested in conditional statistics for heat release and heat release rate, which show enhanced deflagrative combustion in discrete injection configurations. • Injection schemes are considered in two-dimensional rotating detonation engines. • Formation of secondary waves is linked to spacing and size of discrete injectors. • Waves propagate through successive explosive events when traversing reactant jets. • Decreasing injector number increases variability in wave speed and combustion mode. • Majority of heat release occurs through deflagration when using discrete injectors.