MODELING THE EFFECTS OF OBSTACLES ON THE DISPERSION OF DENSER-THAN-AIR GASES

The three-dimensional, finite volume code ADREA-HF is used to perform a computational simulation of the Thorney Island Dense Gas Trial No. 21. In order to avoid excessively fine discretisation to model the thin circular fence and still take into account the real shape and dimensions of the fence, a special technique is adopted: the computational cells which are in contact with the fence are characterised as ''blocked'' or ''partially blocked''. In the blocked cells, the flow is completely obstructed, while in the partially blocked cells, a flow resistance coefficient is evaluated. The above technique, in conjunction with a one-equation turbulence closure model gives rather satisfactory results in comparison with the experimental data in the form of concentration-time histories. The model has a tendency to underestimate the maximum gas concentration and the dose (integral of the concentration with time). The differences between model predictions and experimental data can be reduced by taking into account concentration fluctuations and possible improvements of the turbulence modelling.