Modelling internal gas flows in a single stage gas gun using Eulerian/Lagrangian coupling in LS-DYNA

Most research on gas guns for impact testing investigates the velocity reached by the projectile or sabot when it hits the target. In this research attention is paid to the effect of initial loading conditions on the velocity reached by the projectile upon exit from the barrel. The work is focussed on the single stage nitrogen gas gun at the Department of Applied Mechanics in the School of Engineering at Cranfield University of this research. This gas gun was used to generate test data for a range of initial pressures in the pressure vessel. An LS-DYNA model of the gas gun which uses the Eulerian/Lagrangian coupling feature is described. The LS-DYNA model results, as well as results from an analytical model, are compared to the test results. The results indicate that, while the analytical model over predicts the projectile velocity, the LS-DYNA model is capable of accurately predicting the projectile velocity as a function of the initial pressure in the pressure vessel. The results also indicate that the opening time of the valve affects the projectile velocity at higher initial pressures.