Modelling of the internal ballistics of mortar including polydisperse gunpowder size

Matthias Pautard (1, 2) , Christian Chauveau (2) , Fabien Halter (2) , Christophe Coulouarn (1)

1 Thales LAS France
2 ICARE - Institut de Combustion, Aérothermique, Réactivité et Environnement

The propulsion of mortar ammunition has given rise to few establishments of specific simulation models due to the reasonable costs of the experimental methods. However, the optimization of propellant architecture requires theoretical studies to better understand the phenomena involved in the propulsion phases of the projectiles into the barrel. The accessibility of simulation assets has increased in recent years, allowing fields such as interior ballistics to benefit. To deepen the theoretical knowledge of the internal ballistics of mortars by relying on advanced digital means is thus the objective of this present work. The objective of this study is to improve the understanding of the physico-chemical phenomena that take place during the propulsion phases of mortar shells. It is therefore desirable to set up theoretical, experimental and numerical studies. Thiswork is carried out as a collaborative effort between Thales and ICARE laboratory in order to enhance our understanding on the common fields of interest. These activities concern two-phase simulations as well as the combustion of solid energetic materials, all subjects currently under study. The first step was to create a 0D code based on the literature. The specificity of a mortar’s internal ballistics model is mostly the consideration of two chambers interacting with a compressible flow. Due to the inertia of the gun powder, this flow will induce erosive combustion. Another particularity of the mortar is the necessity to use a fine gunpowder, implying difficulties to produce similar sized grains in terms of dimension. Indeed, the dispersion of the grains thickness produced in series can reach 10% up to 20%, thus impacting the interior ballistics. To take this phenomenon into account, it is necessary to modify the calculation of the surface and volume according to the Population Balance Equation. In order to test the validity of our model while considering the high repeatability of the initial velocity of our mortar ammunition, a quick glance was given to the intermediate ballistic phase to estimate the velocity gain during this step. Therefore we can better link the speed of the ammunition resulting from our code to some future measurement. This presentation will describe current work and future prospects for applications to ballistics interior simulation of mortar.

Domaines: Mécanique des fluides [physics.class-ph]

Matthias Pautard, Christian Chauveau, Fabien Halter, Christophe Coulouarn. Modelling of the internal ballistics of mortar including polydisperse gunpowder size. 51st International Annual Conference of the Fraunhofer ICT, Jun 2022, Karlsruhe, Germany. ⟨hal-03714977v2⟩