B. P. Xu

Dispersion of carbon dioxide from vertical vent and horizontal releases—A numerical study:

Numerical simulations of far-field carbon dioxide dispersion were conducted for a vertical vent release and a horizontal release from a shock tube. These scenarios had also been studied experimentally at field scale commissioned by National Grid. This work and the experiments both form part of the National Grid dense phase CO2 pipeLine TRANSportation (COOLTRANS) research programme. All tests involved releases of dense phase CO2 into an atmospheric flow. The dispersing plumes were subjected to transient wind conditions where both the direction and magnitude of the wind fluctuated with time. As part of the COOLTRANS research programme, the far-field dispersion simulations started from source terms derived from the near-field simulations conducted by the University of Leeds and outflow simulations conducted by University College London. The numerical model used for the far-field simulations is based on OPENFOAM, which is an object-oriented open source computational fluid dynamics toolbox. A dedicated solver CO2FOAM has been developed within the framework of OPENFOAM for simulating dispersion from dense phase CO2 releases. This has included the implementation of the homogeneous equilibrium method for fully compressible two-phase flow, treatment of the transient atmospheric boundary conditions and the time-varying inlet boundary conditions. The experimental measurements were supplied to the authors after the predictions were completed and submitted to National Grid. Hence, the validation reported here is indeed “blind.” While further fine tuning of the model and validation is still underway, the relatively good agreement between the predictions and measurements in the present study has demonstrated the potential of CO2FOAM as an effective predictive tool for far-field CO2 dispersion in the context of pipeline transportation for carbon capture and storage.

Large eddy simulation of fire dynamics with the improved eddy dissipation concept

The eddy dissipation concept (EDC) for turbulent combustion modeling was originally proposed by Magnussen in the Reynolds averaged Navier-Stokes (RANS) context. This study has extended it to the large eddy simulation (LES) framework. Since the fine structures in EDC are still not resolved in LES, they are modeled with SGS turbulent kinetic energy and its dissipation rate instead of the mean quantities in RANS. A new expression is proposed for the reacting fraction of the fine structures to alleviate the limitations of the original formula. Three fire cases including a 7.1 cm methane fire, a 30 cm heptane fire and a 30.5 cm methanol fire are simulated to verify the improved EDC (M-EDC), which has been implemented in the FireFOAM solver. The predictions from the M-EDC are found to be in reasonably good agreement with the measurements, while the original EDC tends to under-predict temperature and velocity.