Simulation of the Influence of Propellant Grain Geometry on Bulk Density

The bulk density is a key factor in the development process of new propellant grain geometries, that directly determines the energy content and thereby the performance of the propellant in the corresponding gun system. Additive manufacturing, such as 3D printing, offers new and great opportunities in shape and structure design for propellant grains. Unfortunately, the bulk density must be determined experimentally, which is quite expensive, time consuming and not resource-saving. In order to assess the bulk density of new geometries, a discrete element method is used predicting this characteristic property. The measurement process, consisting of pouring the grains into a reference vessel and dividing the weight of the grains by the volume of the vessel, is imitated in the simulation. To show the influence of the propellant grain geometry on bulk density, 6 different configurations of a seven perforated cylinder grain are defined, varying the cutting angle and the shape of the end faces. The main results of our simulation studies are, that the bulk density for a seven perforated cylindrical grain can be increased by 1.5 % and 4.4 %, respectively, by using a cutting angle of 60° and a spherical cap radius equal to the grain radius.