Analysis of Explosion Consequences Using CFD Tools

Tools used for the analysis of explosions can be divided into two groups according to the manner in which the pressure is calculated. The simpler approaches predict the pressure at a point in space over time based on empirical and semi-empirical models. However, the more rigorous models use currently Computational Fluid Dynamics (CFD) codes. CFD models solve Navier–Stokes equations of fluid flow (conservation of mass, energy, momentum and scalar quantities) in a two (2D) or three-dimensional (3D) space. The problem is reduced to the solution of a system of partial differential equations that needs to specify appropriate boundary conditions for their numerical solution.

In this paper the overpressure due to the shock wave from an explosion is simulated using CFD tools. In particular, the software FLUENT® (ANSYS) is used to perform all the 2D simulations presented. In the first place, we analyze the influence of boundary conditions in the problem solution. Secondly, since FLUENT allows the user to enter C code as User-Defined Function (UDF), we discuss alternatives to include boundary conditions programmed by the user. Using these capabilities, the initial pressure profile of the blast is introduced as time-varying boundary conditions.

To show the behavior of blast waves, two cases are developed. In the first example, the shock wave produced by a primary vessel explosion hits a second vessel that resists the impact. In this case it is possible to observe effects such as the overlapping pressure waves between the primary and the second vessel (due to the wave rebound in the second vessel). The “shadow effect” behind the second vessel can be also seen. The second case presents the same shock wave hitting and breaking a pipe in the second vessel. This equipment failure leads to domino escalation involving the dispersion of a toxic substance.

REFERENCES

FLUENT, User’s Guide 14.0, Fluent Inc., USA. (2012).

Larcher, Martin “Pressure-Time Functions for the Description of Air Blast Waves”, PUBSY JRC 46829 (2008).

Ramezan Ali Izadifard1 et. al., “Blastwave parameters assessment at different altitude using numerical simulation”, (2009).

Tonelli, Stella, Agustín A. D'alessandro and Carlos E. Gigola. “Domino Accidents in the Process Industry – A Review of Current Analysis Methods and Upcoming Trends”. 5th CCPS Latin America Conference – 12 al 15 de Agosto, Cartagena, Colombia (2013).