Modeling of Rotating Detonation Engine Refreshing Layer in Diverging Inlet Geometries

This paper presents a low-order modeling approach for the refreshing layer in rotating detonation engines (RDEs) with diverging inlet geometries, extending prior two-dimensional (2D) methods to pseudo-2D configurations. The canonical annular RDE chamber often features varying widths, yet limited data exists on the impact of diverging inlets on flow fields. To address this, quasi-2D and fully 3D computational fluid dynamics (CFD) simulations are conducted under premixed hydrogen-air conditions. These simulations guide and validate an extended method of characteristics (MOC) model that incorporates area-expansion source terms and stagnation pressure loss gradients in the refill region. Key findings reveal that diverging inlets produce partially supersonic refill flows, leading to curved characteristic lines and higher inlet velocities compared to constant-width cases. Higher expansion ratios correlate with reduced recirculation, lower static pressures, and significant stagnation pressure losses, resulting in negative pressure gains for ratios above 2.9. The MOC model accurately predicts mass flow and stagnation losses for most cases, highlighting the dominance of unsteady wave-injection vorticity. The study concludes that tapered inlets should limit expansion angles to minimize losses. This work enhances RDE design understanding by enabling efficient low-fidelity predictions of inlet physics in expanding geometries.