Pressure Characteristics of a Diffuser in a Ram RDE Propulsive Device

Abstract

Abstract : This report focuses on dynamic simulations of a representative ram RDE subsonic diffuser to study ram RDE compatibility with a supersonicinlet. Of particular interest is the propagation of pressure perturbations due to the detonation waves in the RDE combustion chamber. Simulationswere 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 providean exhaust forcing function assuming a slot injector plate. A total of 8 different exhaust forcing functions were used, representing RDE air-valvearea ratios between 0.3 and 0.6 in single and dual shock operation. Simulations were then completed for the diffuser with the Propel code foreach of these exhaust forcing functions. Analysis indicates that the amount of pressure variation seen near the inlet is very sensitive to the shapeof the forcing function. The broad pressure rise of the lower area ratios tend to remain intact through the diffuser to the intake with minimaldissipation, while the sharper pressure peak of the higher area ratios tend to be dissipated to a larger degree. For single-shock operation, theamount of pressure variation at the intake varies from 20.5 (area ratio of 0.3) to 39.1 (a=0.6). Dual-shock operation further sharpens the peakof the forcing function. For dual-shock 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.