Numerical Simulation of Sabot Discard Projectile

• Main Author: Karlsson, Karl
• Format: Others
• Language: English
• Published: Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik 2020
• Subjects: CFD; Sabot; Simulation; Fluid Mechanics; Mechanical Engineering; Maskinteknik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-79248

When designing an armour piercing kinetic energy projectile with a discarding sabot, it is important to know how the projectile is affected by the sabot during the discard. If the projectile has no active guiding systems, small disturbances to the initial flight path of the projectile can result in a significant deviance from its intended target. To investigate whether the discard process and its effect on a projectile could be simulated a CFD model was built based on a generic design for an APFSDS projectile for the Carl Gustaf M4 system built by Saab Dynamics AB. The model had to replicate the course of a sabot discard as accurately as possible and be able to track how it affects the projectile. ANSYS Fluent was used to build a model of a quarter of the design incorporating one of the four sabot petals and the part of the projectile in between two of its four fins, utilizing symmetry at zero angle of attack. To achieve a realistic discard process, fluents 6DOF solver was used allowing the sabot to discard due to aerodynamic loads rather than by following a pre-determined path. To allow the components to move inside the domain an overset interface was implemented around the sabot to allow the mesh to update itself during the simulation, keeping its quality consistent. The models initial stage includes a small gap between the sabot and projectile which is necessary to avoid contact which causes issues with mesh creation and divergence. The projectile geometry was based on rough estimates of how a fin stabilized projectile for the M4 would look whereas the sabot design was based on earlier sabot designs and iterated to achieve a discard phase with no contact. The iterative process which produced the sabot design proved that its geometry greatly affects how it discards from the projectile. To track how the projectile is affected during the discard, the forces and moments applied to the projectile from the flow including its interaction with the sabot were tracked. To compare there forces and moments for different discard courses, the sabots centre of gravity was changed to provoke it to discard differently. The model showed a clear difference in how the projectile was affected by the flow during the different discards. This shows the importance of designing the sabot to discard cleanly and quickly so as to not alter the trajectory of the projectile in flight. Also investigated was the effect of the initial gap on the course of the discard. Adding the gap is a simplification which should affect the discard so that it no longer matches a physical test case and so will have to be tuned to find what gap provides the most realistic discard. Although this model could not be validated given the lack of a physical counterpart, it could be determined that the gap greatly affects the discard and that this model is very sensitive to the initial load put on the sabot. Before the model can be used for concept development, a few things need to be worked out. These include a contact definition, inner ballistic effects and building a model that can be test fired to generate validationdata.