Afterburning effects on confined blast loads with a Runge–Kutta discontinuous Galerkin solver

Confined trinitrotoluene (TNT) explosions exhibit a short shock-dominated stage followed by a millisecond-scale quasi-static pressure rise driven by secondary combustion of detonation products. In such flows, repeated shock reflections, wave superposition, and the continued interfacial interaction between hot fuel-rich products and surrounding air govern the transition from an initially non-uniform compressible wave field to a late chamber-scale pressure buildup. In this work, these processes are modeled within a three-dimensional Euler framework solved by a Runge–Kutta discontinuous Galerkin method. Afterburning is represented by a single progress variable with a first-order rate law, interpreted as an effective chamber-scale closure for unresolved mixing-controlled energy release. The model is validated against nitrogen-filled chamber tests, in which afterburning is suppressed, and against air-filled chamber tests, in which afterburning raises the quasi-static plateau and accumulated impulse. For the present chamber, inversion of Unified Facilities Criteria quasi-static correlations gives afterburning energies about 80% higher for 90 g TNT and about 70% higher for 160 g TNT than a correlation derived from confined-explosion measurements; the latter is therefore adopted for subsequent analysis. With the calibrated rate constant, the predicted cumulative impulse in nitrogen is within about 3%–15% of the measurements, and the quasi-static plateaus and impulses in air are reproduced within about 5% over the tested charge masses. Parametric results show that afterburning has only a minor influence on the earliest shock peaks but substantially elevates the quasi-static pressure level while preserving the qualitative dependence of the loads on chamber volume, charge position, and charge mass.