SRM Igniter Jet Simulation

Abstract

The design and development of solid rocket motor (SRM) need to predict the internal gas-dynamic phenomena that happen during the SRM operative life. The operative life of a SRM can be divided in a sequence of different phases: the first phase is the ignition transient during which the solid propellant is ignited; the second phase is the quasi-steady phase during which the SRM reaches the design operative conditions; finally there is the combustion-tail during which the combustion of solid propellant extinguishes. The phenomena happening during ignition transient are often more critical than those occurring in the subsequent phases; within a fraction of a second hot igniter gases flow in the combustion chamber reaching supersonic conditions; pressure jumps of tenths of atmospheres and temperature peaks of thousands of Kelvin degrees can occur. The ignition transient unsteady behaviour can cause net thrust and pressure transients, over-pressure peaks, hang-fires or misfires, propellant grain stresses, dynamic loads on the launch vehicle (and on its payload) and on the ground segment etc... All the above phenomena can compromise the performances of the SRM and often the successful of the launch. The study of the SRM ignition transient is the research background of this Ph.D. dissertation. It is common and well confirmed practice in industry to analyze ignition transient using zero-dimensional, volume-filling or one-dimensional physical models, and only recently two-dimensional approaches can be found. Presently the increasing of the computational capabilities allows to a fully three-dimensional study. The reasons to develop a three-dimensional model are numerous: first of all the combustion chamber of a common SRM has often a three-dimensional geometry; second the igniter nozzles has a three-dimensional configuration with both axial and radial nozzles. Therefore the gas-dynamic phenomena generated by the igniter jets have strong three-dimensional behaviour that is impossible to study by means of a non fully three-dimensional model. The aim of this research is to present and provide suitable three-dimensional model and numerical tools able to describe the SRM ignition transient with particular interest to study the gasdynamical aspects of SRM ignition transient