Performance of Expansion-Deflection Nozzles for Rotating Detonation Rocket Engines

Pressure-gain in Rotating detonation combustion (RDC) engines due to the detonation mode of combustion enables greater extractable energy potential, generating thrust more efficiently than conventional combustion engines. This increased efficiency is critical for both hypersonic air-breathing applications to enable high-speed, long-range flight, and for in-space propulsion which benefits from the increased delta-v and compact geometry of rotating detonation rocket engines (RDRE). Exhaust nozzle design determines the overall performance at the design point, contributes significantly to the total engine weight, and can affect the stability of the detonation, yet it remains an under-researched aspect of RDREs. In the Phase I effort, expansion-deflection (ED) nozzles were explored as a solution to maximize the thrust potential of RDREs operating in vacuum conditions. High fidelity CFD simulations of candidate RDRE experimental configurations were conducted to identify performance trends and transient forces and thermal loads on candidate ED nozzle designs with and without a central plug and compared to a conventional bell nozzle. A reduced-order modeling (ROM) approach was adapted to provide more rapid evaluation of candidate nozzle contours, and a novel shock-tracking numerical approach was implemented to enable more efficient CFD simulations. The proposed Phase II effort builds off of these findings by developing a framework for RDRE nozzle design, evaluation, and optimization supported by physically-accurate combustor ROMs. The ROMs will be verified against detailed CFD simulations aided by cutting-edge acceleration techniques. Performance trends and detonation stability of parametric nozzle designs will be evaluated with respect to geometric parameters and operating conditions. An experimental RDRE test campaign featuring simulated altitude conditions will be conducted at UAH to validate the performance trends for multiple candidate nozzles.

The performance gains afforded by RDRE-ED technology would benefit missions to the Moon, Mars, and beyond. Ongoing research and design of RDREs at NASA, such as the 3D-printed engine developed in collaboration with IN Space LLC, would immediately benefit, and there is potential for insertion into programs including Artemis and Commercial Lunar Payload Services. Rapid evaluations enabled by the ROM approach will support early-phase vehicle evaluations conducted by the Advanced Concepts Office. Applications include hypersonic engines, e.g., GE Aerospace’s dual-mode ramjet with rotating detonation combustion, and conventional RDREs such as the one recently developed by Venus Aerospace and DARPA. Rotating Detonation Augmentors are another area of commercial interest due to their potential for integration into existing aircraft engines for increased thrust and specific impulse.

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