Suppression of the ignition overpressure generated by launch vehicles

The main objective of this study is to gain an understanding of the mechanisms responsible for the suppression of the ignition overpressure observed when water is added to a rocket engine exhaust. A simplified launch-vehicle/launch-pad configuration of relevant importance is selected for this study. This configuration is then numerically simulated with a representative engine start-up sequence and a series of water addition configurations. A total of eleven water addition configurations was studied. The study demonstrated that ignition overpressure is strongly affected by the cooling of the plume and the amount of obstruction restricting the expansion of the plume. Also, the study suggests the existence of an optimal water addition rate with a weak dependence on the water nozzle pressure drop.