Aerodynamic Design and Analysis of High Performance Nozzles for Mach 4 Accelerator Vehicles

Abstract

The aerodynamic design and performance analysis of two exhaust nozzles considered for use on a vehicle following an accelerating flight profile to a maximum flight speed corresponding to Mach 4.2 is presented. The vehicle operational requirements were set by the Air Vehicle Baseline Study commissioned by the Office of Naval Research. An afterburning engine cycle was assumed in the design and analysis process. The two nozzles investigated here were an axisymmetric convergent-divergent (C-D) nozzle with variable throat and exit area and an isentropic plug nozzle with variable throat area enabled by a translating outer cowl. Computational fluid dynamics was used to assist in the design process and to investigate the installed performance of the two nozzles at flight points from Mach 1.2 to Mach 4.2. For both nozzle configurations, the nozzles could not achieve perfectly expanded exit areas at the highest Mach numbers in order for the nozzle exit area to not exceed the vehicle cross sectional area. At the lower Mach numbers, the installed performance of the C-D nozzle was higher than that of the plug nozzle while at the highest Mach numbers, the performance of the two nozzles was similar.