TITLE : EXPLOSION IN AN OFFSHORE MODULE

BY : D J Freeman - CHAM UK
DATE: 1996

DETAILS:

• A natural gas explosion in a full-scale offshore module is simulated. The module has dimensions of 25m x 8m x 8m.

• The simulation is three-dimensional and the LVEL turbulence model is used in conjunction with the Multi-Fluid Turbulent Combustion model (see next page).

The Multi-Fluid Turbulent Combustion (MFTC) Model:

• The MFTC has been developed within CHAM to simulate the complex combusting flows associated with explosions and flames more accurately.

• In this example the reacting mixture consists of four fragments, of different (and fixed) composition and temperature (see next page). Mixing of the hot and cold fragments creates the intermediate fragments, with the hottest being hot enough to react (i.e. burn) to form hot products.

• The rate of combustion is therefore controlled not only by the rate of mixing (as in the Eddy-break-up model) but also by the kinetic rate of reaction.

• The MFTC may be extended to any number of fluids, depending on the requirements of the simulation.

  The Multi-Fluid Turbulent Combustion Model (cont.)

• The four fluids used in this simulation were: A, comprising of fully unburned fuel/air mixture, B, a mixture of unburned gas and products at a temperature too low for chemical combustion to proceed, C, the same mixture but at a temperature at which the chemical rate is significant, and D, fully burned gas.

• A and D mix to form B and C, while A mixes with C and B with D to form B and C respectively. C reacts to form D.

• The overall rate of combustion therefore depends on the mixing rate and the rate of reaction.

  The following pictures show the progression of the flame front (coloured green!) with time. The ignition position is at the right end of the module.

  start

  The images used in this example were produced using TecPlot, which is available as an optional post-processor for PHOENICS.

  TecPlot can be used to produce high-quality 3-dimensional images showing geometry, vectors, Gouraud-shaded surfaces and contours.

  The images have been reduced to 16 colours for use with POLIS, which can reduce the quality of the viewed image.

  wbs