John E. Mercer
ABSTRACT: This paper describes the theoretical basis of a computer code that numerically models firework mortars. The code analyzes both the Black Powder propelling and flight segments of a shell. Equations for the gas dynamics of Black Powder combustion, leakage flow around the shell and aerodynamics of flight are included. Representations for commonly used Black Powder grain sizes allow for simple modeling of test cases. The numerical equation solver in the code uses standard parameters for specifying any mortar test condition. This solver computes every model parameter of the gas and shell dynamics in 2 μs time steps while in the mortar and in 1 ms time steps in flight. The modeling demonstrates that the release of energy from Black Powder is a multi-step process, first from the burning of the grains, next from the latent heat release from condensation, and finally from the latent heat release from fusion. The shell flight dynamics are based on aerodynamic theory employing conventional parameters. Uses of this code include design of mortars, and parametric and safety analyses. The code even includes a crosswind drift analysis for predicting expected dud fallout location. The analytic models were verified on a multitude of test cases, taken from both firework mortars and muzzle loading firearms data. Agreement with the experimental data is within the experimental measurement variation.
Keywords: mortar, latent heat, Black Powder, thermodynamics, aerodynamics, leakage flow, shell drift, muzzle velocity, drag
Ref: JPyro, Issue 16, 2002, pp37-524
(J16_37)
© Journal of Pyrotechnics and CarnDu Ltd
