Resumo:
This work presents a geometric optimization study of the gas system of the IMBEL IA2 rifles
using Computational Fluid Dynamics (CFD) combined with Design of Experiments (DOE)
methods. The IA2 operating system, responsible for diverting part of the propellant gases from
the barrel and converting them into mechanical energy for weapon cycling, was originally dimensioned
through empirical procedures. Considering the absence of gas regulation in the current
design and the requirement for high reliability under different operational conditions, a
detailed understanding of the transient flow phenomena inside the system becomes essential.
Experimental tests were conducted by instrumenting the rifle with pressure transducers, enabling
the acquisition of real pressure curves inside the barrel and gas cylinder. High-speed
camera recordings were also performed to determine the displacement–time curve of the bolt
carrier. These experimental data were used to validate a two-dimensional transient numerical
model with dynamic mesh and moving wall motion equation implemented in ANSYS Fluent.
After validation of the baseline configuration, a factorial design was applied to evaluate the influence
of relevant geometric parameters, in this case gas port diameter and initial gas cylinder
length, on objective functions related to peak pressure, peak time, and total impulse delivered
to the system. An analysis of variance (ANOVA) was performed, and response surfaces were
generated for each objective function, enabling the identification of the most influential parameters.
Finally, alternative geometries were proposed and assessed, including the addition of a relief
orifice and a pressure accumulation chamber. The results indicate that it is possible to delay
and smooth the pressure curve inside the gas cylinder, reducing peak pressure without compromising
the total impulse required for proper cycling. The study provides technical support for
the optimization of the IA2 gas operating system and for the development of future IMBEL
firearms, contributing to improved reliability and reduced experimental effort during the design
process.
