Turbine Integration with Rotating Detonation Combustors: Aerodynamic Constraints, Candidate Architectures, and Design Pathways

Rotating detonation combustors (RDCs) can improve gas-turbine and propulsion cycles only if the downstream hardware preserves the pressure-gain benefit while converting an unusually unsteady, distorted, and high-Mach-number exhaust into useful work. This paper synthesizes turbine-integration research and argues that RDC-compatible turbines form a distinct class of startability-constrained, pressure-gain-compatible work-extraction devices. The governing selection criteria are not only stage efficiency and loading, but passage startability, choking margin, shock management, reduced-frequency response, unsteady separation, thermal survivability, outlet-flow quality, and combustor backpressure coupling. Candidate architectures are compared on that basis: transonic diffusive axial vanes, fully supersonic axial turbines, smooth-wall axial bladeless turbines, wavy/helicoidal bladeless turbines, axial-inflow–radial-outflow turbines, and statorless mixed-flow turbines. The reviewed evidence spans reduced-order and mean-line methods, RANS/URANS, large-eddy simulations, multi-objective optimization, experimental demonstrations, and recent gas-turbine integration studies. The synthesis shows that near-term RDC engines will likely require architecture-specific compromise: diffusive vanes provide a robust interface for high-subsonic/transonic exhaust; supersonic axial turbines offer compact high-specific-power extraction but are constrained by leading-edge shocks and startability; bladeless machines reduce or transform the blade-passage shock problem but with limited power extraction; radial outflow turbines use increasing area to reconcile turning with started operation; and mixed-flow statorless rotors can directly ingest transonic pulsating inflow. The resulting framework provides design logic for preserving pressure-gain benefits at the engine level rather than optimizing an isolated turbine at a single averaged inlet condition. A quantitative selection rule is also provided: when flow capacity per unit annulus area must be maximized, the optimum turbine inlet condition is transonic, whereas when shaft-power extraction from a fixed annulus must be maximized, the optimal turbine inlet Mach number lies near 2.5 for constant-height annuli.