Numerical Modeling of the Internal Ballistics of a Gas Gun.

A numerical procedure is applied to three principal flow models of a gas gun, the discharge chamber, the main chamber, and the barrel chamber. In the first two models, an explicit method, the second order MacCormack scheme, is used to solve the Navier-Stokes equations for two-dimensional (axisymmetric), time dependent, compressible flow. The fluid is assumed to be a perfect gas. The flow boundaries may be arbitrary curved and time dependent. Transformations have been used to map the physical space into a computational space with uniform grid spacing. A grid generation surface has been achieved for various wall shapes. The third model investigates a detailed one-dimensional time dependent flow. In this case, the method of characteristics is used to solve the quasi-linear non-homogeneous partial differential equations of the first order. The numerical results obtained from the present solution are compared with the one-dimensional solution. The present technique shows better correlation with the experimental data.