Elements of modelling the use of particles in solid-propellant rocket motors

Important elements of the framework for numerically evaluating the usage of reactive aluminum particles in solid-propellant rocket motors are brought forward, and where possible, predicted model results are correlated to established experimental observations. A principal purpose in using inert or reactive particles is for the suppression of axial pressure wave development in the motor. In this study, a primary focus is placed on evaluating the qualitative trends associated with the time-dependent reduction in size of the reactive aluminum particles as they move downstream in the central internal flow. To narrow the scope of this preliminary study, the reactive particle size regression is stipulated to occur at a designated uniform rate for a given simulated firing. Individual transient internal ballistic simulation runs for a reference composite-propellant cylindrical-grain motor show the evolution of the axial pressure wave for a given initiating pressure disturbance, and for particle loading, initial particle size, and size diminishment rate. This study presents particle loading distributions at various locations in the motor chamber's internal flow, at different times into the given firing (pre- and post-disturbance). The limit pressure wave magnitudes at a later reference time in a given firing simulation run were collected for a series of runs at different particle size reduction rates, to assist in the evaluation of identifiable trends. The numerical results demonstrate that the ability of the particles to suppress axial combustion instability symptom development improves as the nominal particle regression rate becomes lower, for a given particle loading. There may be some advantage in using a larger starting particle size at higher particle regression rates, for improved overall symptom suppression. At higher particle regression rates, the predicted results suggest that increasing the particle loading may ultimately be the only alternative for reaching a desired symptom suppression level.