Altitude-dependent performance analysis of bell, aerospike and Expansion-Deflection nozzles for Rotating Detonation Engines

A Rotating Detonation Engine (RDE) is a promising alternative to traditional combustion engines found on rockets and aircraft. Conventional combustion engines rely on deflagration, or subsonic combustion, whereas RDEs utilize detonation, where the combustion front propagates at supersonic velocities. RDEs offer increased theoretical efficiency compared to conventional combustion engines, which are plateauing in terms of performance improvements. Because of this, RDE technology could significantly impact the aeronautical, astronautical, and defense industries once fully mature. Despite the growing interest in RDEs, research and analysis on the influence of nozzle geometries on RDE performance across varying pressures is still limited. This study addressed this gap by evaluating three nozzle designs–a conventional bell nozzle, aerospike nozzle, and expansion-deflection (ED) nozzle–at pressures ranging from sea level (101 kPa) to near-vacuum conditions. The ED nozzle was hypothesized to perform best relative to the ideal across the entire pressure range. Nozzle performance metrics were obtained from 2D Computational Fluid Dynamics (CFD) simulations using averaged detonation conditions. Results showed that design pressure exerted a much greater impact on performance than geometry. At low altitudes, the aerospike and bell optimized for 50 kPa significantly outperformed the ED nozzle. At high altitudes, the ED nozzle outperformed both while maintaining operability at sea level without destructive flow separation. These findings suggest that experimental designs such as the aerospike and expansion-deflection could boost RDE performance for certain operating pressure regimes and that further optimization of RDE nozzles could enhance the viability of RDE-powered launch systems.