Significance of Armature Resistivity and Deformation in Modeling Coilgun Performance

Abstract

We have performed 2-D axisymmetric magnetohydrodynamic simulations for a single stage induction coilgun system and validated the results against in-house experiments. The simulations, besides computing the currents and electromagnetic forces, also capture the associated hydrodynamic phenomena. This paper highlights the importance of appropriate material strength for handling hydrodynamic phenomena and temperature-dependent electrical resistivity model for self-consistent electromagnetic calculations. These are very essential for accurate prediction of armature dynamics and velocity. Inappropriate resistivity model, even in case of no deformations, produced velocity deviation of up to 50% as compared with experiments. Inclusion of appropriate models shows <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&lt;}{4\%}$</tex></formula> average deviation when compared with experiments for known armature material (Al6061-T6). For higher energies, predicted armature deformations appear to be in a good agreement with experiments. If material deformation is ignored, velocities get over-estimated. Finally, subsequent to our validation at low energies, an optimized armature profile and dimensions are reported that have allowed our armatures to achieve velocity <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${&gt;}{\rm 200}~{\rm m}/{\rm s}$</tex></formula> with single stage operation and 300 m/s with two-stage operations of the coilgun. This paper shows that accurate modeling of Joule heating and armature deformation, along with self-consistent evolution of currents, is essential for coilgun modeling. Although the system is not presently optimized for efficient energy conversion <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\sim}{1.5\%})$</tex></formula> , the performance of induction accelerator at moderate velocity of armature (50–300 m/s) is not only useful for validating our code, but can act as an effective catapult for impact testing of materials.