3D turbulent Navier Stokes simulations of ignition transients in solid rocket motors

Abstract

A numerical model has been used to compute the ignition transients in solid rocket motors. The model consists of a multi-dimensionnal unsteady turbulent Navier Stokes code coupled with a ID unsteady heat conduction model in the propellant. The unsteady behavior of the propellant combustion during the ignition transient is taken into account. The numerical model has been validated on subscale test motors. Parametric studies were made to select the procedures fitting at best the experimental results. These procedures have then been retained for evaluation of the numerical model in full scale simulations. Two full scale motors ignitions related to actual complex 3D motor configurations were simulated. Calculated pressure transients are in good agreement with test results. The ignition process shown in the computed flow field is very complex; the 3D simulation proves to be a powerful mean of understanding this process. Useful information concerning the design of igniters can be deduced. Further work is needed on other motor configurations and physical models in order to achieve a complete validation. Introduction Solid rocket motor ignition is a complex process involving competing or successive physical mechanisms within the tridimensional flow field and the propellant grain surface. Design of igniters and analysis of test firings require numerical tools modelling these mechanisms. 3D turbulent Navier Stokes simulation of ignition is considered as the best way of predicting and understanding this process. The numerical code to be used in the 3D simulations must include advanced physical models to represent the energy transfers from the igniter jet to the motor propellant and the unsteady combustion processes involved at the surface of the propellant. Copyright © 1998 by SEP, Division de Snecma. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. This paper describes the 3D model used to examine the ignition transient of solid rocket motors and some of its applications. Validation computations on subscale motors are detailed. Two examples of computations of full scale motors ignition transients are given.