Numerical Simulations of Rocket Solid Motor Engine Ignition and Duct Overpressure Waves at Reduced Scale

Abstract

In order to reduce the loads transmitted to space l auncher components and payloads during the lift-off phase, it is necessary to prope rly understand the mechanisms that are at the origin of the intense pressure waves generated during solid rocket booster ignition sequence. In the framework of the CNES-ONERA AEID research program, well mastered experiments are designed in order to help in the va lidation of prediction tools. Among these tools, the full unsteady LES simulation of the igni tion transients are considered to characterize the ignition overpressure waves genera ted at the motor exit (IOP) and the flame trench exit (DOP). Of particular concern are the po ssible effects of the recombustion of propellant combustion products with ambient air. To that purpose, the Onera CEDRE code is used to perform reactive LES computations, with several combustion models. The numerical code is applied to a subscale motor fired in vertical configuration including realistic model of the Kourou ELA 3 launch pad flame trench. The numerical results obtained with and without activating the combustion model are compared with measurements of the overpressure waves. The presented results establish the feasibility of such computations which are able to reproduce most of the pressure waves characteristics. In particular the recombustion effects are detailed and shown to modify the shape and strength of the generated overpressure waves.