This software predicts flow through the initiator of a Primer Chamber Assembly Valve. These valves exhibited a potential failure mode for specific operating conditions where dual simultaneous firings of the initiator occurred. The software tool was able to identify a fluid dynamic source for this potential failure mode. Furthermore, the software was also used to provide new conceptual designs that may alleviate or eliminate these failure modes.
The objective is to develop a comprehensive, three-dimensional analysis tool that will model the complex interaction among transient shock propagation, pressure-dependent combustion, and the effects of device geometry in pyrovalves. A thermal model will be integrated with the gas-dynamic analysis to model temperature rise in the solid material for these transient problems.
The numerical framework developed for this study has proven its capability for predicting the flow through a pyrotechnic actuator. This framework includes the fully coupled solution of the gasphase equation with a non-equilibrium dispersed phase for solid particles. In addition, the capability to model conjugate gradient heat transfer has been clearly demonstrated. Finally, through a hierarchy of increasingly complex simulations, a hypothesis for the failure mode of the dual nearly simultaneous NASA Standard Initiator (NSI) firings has been proven.
The simulations performed indicate that the failure mode for simultaneous dual NSI firings may be caused by flow interactions between the flame channels. The shock waves from each initiator interact in the booster cap region, resulting in high pressure that prevents the gas and particle velocity from rising in the booster cavity, and preventing the bulk of the particulate phase from impacting the booster cap. This reduces the heat transfer to the booster cap both because the particles do not reach the booster cap, and because the heat transfer coefficient is reduced due to lack of convective effects. Moreover, a conceptual design modification has been proposed and numerically shown to mitigate the effects of the failure mode.