ALE3D Simulation of Thermal Decomposition and Compressible Flow in a Fast Cookoff Experiment with PBX 9502, a TATB-Based Explosive

An Arbitrary Lagrange/Eulerian 2D and 3D (ALE3D) compressible flow cookoff model was developed for PBX 9502 (95% TATB, 5% Kel-F), and applied to a fast (1 o C/min) cookoff experiment involving a 0.79 kg PBX 9502 disk and a steel vessel with 33% free volume for product gas flow and pressurization.A two-stage autocatalytic reaction model was developed to capture thermal decomposition during the early stage of gas generation and the second stage of thermal runaway.Decomposition model parameters were determined from One-Dimensional-Time-to-Explosion (ODTX) measurements and Pressure ODTX (PODTX) measurements for TATB-Kel-F samples with varying density and cavity free volume.Density changes from pressurization and thermal expansion were modeled with polynomial equations of state for solids treated as viscous liquids, and a Gamma-Law equation for gases.For the ALE3D compressible flow framework, a reconstructed Discontinuous Galerkin (rDG) method was employed with capabilities to model convection dominated flows and phase change at a wide range of flow speeds.For the fast cookoff experiment with PBX 9502, the compressible flow cookoff model underpredicted the pressures measured by the pressure transducer.However, the model provided good predictions for the time and temperature of explosion, including the significant effects of free volume, gas flow and the reduction of pressure.