Explosion

Explosion — ANSYS Fluent CFD Simulation

Description

This project presents a CFD simulation of a TNT explosion, a problem central to engineering safety, defense applications, structural protection, and blast planning. An explosion is an extremely fast exothermic reaction that suddenly generates large volumes of hot gaseous products, producing a sharp spike in pressure and temperature and launching compression waves that propagate outward through the surrounding air. This project models the rapid decomposition of TNT, in which 2 moles of TNT generate 22 moles of gaseous products, and tracks the resulting spherical pressure wave as it propagates and dissipates across the domain. As the capstone of the Species Transport: Beginner CFD Training Package, it is the most complex reacting-flow case in the set — a rapid reaction producing a propagating blast wave.

Methodology

The module covers the underlying physics of an explosion, including the fast exothermic reaction, the sudden pressure rise, and the resulting sequence of compression and expansion waves. The computational domain is a half-sphere of 5 m radius containing a central TNT charge modeled as a 5 cm radius half-sphere, built in SpaceClaim using symmetry to reduce computational cost, and meshed with a large structured grid of approximately 2.67 million elements capable of resolving a traveling pressure wave. The problem demands a transient solver to correctly capture the moving wave front. The Species Transport model is configured with a defined species mixture and volume reaction to represent the TNT decomposition, using finite-rate turbulence-chemistry interaction with the direct source chemistry solver, the Realizable k-epsilon turbulence model, and the energy equation activated. A critical modeling decision is defining the mixture density using the ideal-gas law, which is what allows the simulation to capture the wave propagation correctly.

Analysis

Post-processing generates temperature and pressure contours over time, along with an animation of the propagating compression wave, and quantifies the resulting wave speed, found to be approximately 420 m/s. From these results you can follow how the rapid exothermic reaction spikes the pressure and temperature at the charge and launches the spherical blast wave that travels outward and dissipates. Blast modeling plays a critical role in protecting buildings, vehicles, and people from explosive events, and the reacting-flow, ideal-gas, and transient workflow developed here transfers directly to detonations, deflagrations, gas explosions, and pressure-vessel safety analysis across the defense, oil and gas, and process industries. By the end of this project, you'll be able to set up a transient reacting Species Transport simulation of an explosion, configure a volume reaction with finite-rate chemistry, apply the ideal-gas density needed to capture wave propagation, and interpret the pressure and temperature fields of a blast wave.