Скачать или смотреть blastFoam | Modeling Afterburn

blastFoam allows users to simulate the additional energy associated with afterburning of fuel rich (oxygen poor) high explosives).

blastFoam provides three options for including the additional afterburning energy:

1 Constant energy rate addition
2 Linear energy rate addition
3 Miller Extension

AFTERBURN

The detonation of a solid high explosive occurs in microseconds. If the explosive is not oxygen balanced, i.e. fuel rich lacking sufficient oxygen to burn all the reactants, the remaining reactants can burn and release their chemical energy at later times, on the order of milliseconds. This late burning and addition of energy is typically referred to as afterburning. The minimum requirements for this afterburning are sufficient external oxygen, i.e. from the surrounding environment, and sufficient temperature to maintain the chemical reaction.

When an explosive is detonated in a large volume of air, e.g. extremal free air detonations, any unreacted fuel is typically not converted to additional energy as the temperatures within the fireball quickly decrease and the chemical reaction is suppressed. However, when the same high explosive is detonated in an enclosed environment, i.e. within a chamber or room, the temperature, and pressure, remain well above ambient and may support the release of additional energy, if the reactants encounter sufficient additional oxygen. Some enhanced explosives are designed take advantage of late time afterburning via the inclusion of non-explosive particles, e.g. aluminum, that burn in the presence of elevated temperatures.

To include energy due to afterburning requires knowledge of the amount of energy that is released during afterburning, the time period over which the afterburning takes place and the rate of energy release over that time period.

LLNL HEAF TESTS

Kuhl et al. (1998) conducted closed cylindrical chamber tests using 0.8kg of TNT to study the effects of afterburning. The test was conducted in an air filled chamber and then repeated with the chamber filled with nitrogen, to inhibit afterburning of the TNT detonation products. The pressure histories were measured at several gauge locations.

This blastFoam simulation leverages the 'Linear' afterburn model, with a linearly increasing addition of 16.3GPa of afterburn energy starting 2.4ms and ending at 4.4ms.

The start time is defined as the time at which the first shock wave reflects from the nearest wall and interacts with the detonation products. The end time is defined as the time at which the temperature is lower than the average ignition temperature and beyond this time the afterburning is not possible.

ABOUT BLASTFOAM

blastFoam is an opensource solver for multi-component compressible flow with application to high-explosive detonation, explosive safety and airblast.

The solver is based on the OpenFOAM® framework and provides solutions to highly compressible systems including single and multi-phase compressible flow, and single- and multi-velocity systems.

blastFoam provides activation and explosive burn models to simulate the initiation and expansion of energetic materials, as well as afterburn models to simulate under-oxygenated explosives that exhibit delayed energy release.

Synthetik's opensource CFD airblast code based on the OpenFOAM framework is available on GitHub: https://github.com/synthetik-technolo...

blastFoam is developed by Synthetik Applied Technologies: https://www.synthetik-technologies.com/