Effect of external pulse on solid propellant rocket internal ballistics

An introductory evaluation of the effects of an externally induced pulse on the internal ballistics of solid propellant rocket motors (SRMs) is performed in this study. The main reason for the study was to demonstrate numerically that the axial wave motion generated inside the rocket combustion chamber resulting from an external pulse has enough strength to cause a motor to go into nonlinear combustion instability. In doing so, this study modelled two practical scenarios that would induce a pulse inside the SRM. The first scenario modelled was one in which a missile in its mission flight encounters a blast wave resulting from a nuclear explosion at a distance. The pulse generated within the SRM as a result of missile/blast wave interaction is evaluated. Another scenario modelled was a case in which the SRM is being tested on the static thrust test-stand when suddenly the load-cell fails causing a sudden acceleration of the motor, resulting in the motor impacting an end-wall from which it may bounce back and forth until it reaches a new equilibrium position. The effect of a pulse induced through this scenario is evaluated. Further, a pulsing unit is designed for pulsing an SRM artificially to test the effect of externally induced pulses on the internal ballistics of SRMs.; The results of the project demonstrate that the first scenario creates weak pressure waves inside the SRM, however, they are strong enough in some situations to be above the minimum criterion required to cause combustion instability. The result of the second scenario also produces weak pressure waves inside the SRM, however they are stronger in comparison to the first scenario. It indicates that the externally induced pulse resulting from this scenario will more likely cause nonlinear combustion instability in inherently susceptible SRM designs.