Pressure characteristics of a ram-RDE diffuser

Abstract

This work focuses on dynamic simulations of a representative ram RDE subsonic diffuser to study ram RDE compatibility with a supersonic inlet. Of particular interest is the propagation of pressure perturbations due to the detonation waves in the RDE combustion chamber. Three-dimensional CFD simulations were completed using a notional diffuser for a ram RDE device operating at 42,000 ft and Mach 2.5. A previous RDE code was used to provide an exhaust forcing function assuming a slot injector plate. A total of 8 different exhaust forcing functions were used, representing RDE air inlet area ratios between 0.3 and 0.6 in single and dual wave operation. Simulations were then completed for the diffuser with the Propel code for each of these exhaust forcing functions. Analysis indicates that the amount of pressure variation seen near the diffuser inlet is very sensitive to the shape of the forcing function at the diffuser exit. The broad pressure rise of the lower area ratios tend to remain intact through the diffuser to the intake with minimal dissipation, while the sharper pressure peak of the higher area ratios tend to be substantially dissipated. For single-wave operation, the broad pressure rise yields pressure variations at the intake that vary from 20.5% (area ratio of 0.3) to 39.1% (a=0.6). For the dual-wave operation, the sharper peak of the pressure rise exhibited even more dissipation. Thus, for dual-wave operation, the amount of pressure variation at the intake varies from 21.0% (a=0.3) to 21.9% (a=0.6) for the different area ratios.