Cavity impact on the base flow unsteadiness for a high-speed exhaust system

Abstract

Future propulsion systems could enable high-speed flight and routine space access. Such concepts employ base-embedded nozzles and cavities to allow space for nozzle gimballing, thus altering the flow dynamics at the base in comparison to contemporary launch vehicles. This article presents a numerical investigation on the impact of a cavity on the base flow unsteadiness for a sub-scale, high-speed exhaust at over-expansion. The delayed detached eddy simulation approach is used to investigate the base flow. The configuration featuring the cavity is compared to a baseline apparatus, where the cavity is removed, thus allowing for its impact to be identified. The computational approach is validated against experimental data. Results show that the cavity region can reduce the base pressure fluctuations by up to 20% and acts in a damping-like manner for the base flow unsteadiness. The total energy of the base pressure fluctuations spectrum can be reduced by up to 38% compared to the baseline configuration. Finally, the cavity has a notable effect on the nozzle side loads, which are reduced by an order of magnitude compared to the baseline case. This indicates that the cavity could reduce undesirable off-axis loads.