Final Report Summary - SAFELNG (Numerical characterization and simulation of the complex physics underpinning the Safe handling of Liquefied Natural Gas) The main hazard of Liquefied Natural Gas (LNG) is the flammable vapour which can extend to kilometres as a greenhouse gas; or be ignited resulting in fire and explosions. SafeLNG focuses on six specific areas which are most relevant to facility risk management but for which both theoretical insight and predictive tools are lacking.SafeLNG is hosted by Kingston University London as only legal participant and supported by six Associated partners including the University of Warwick (UK), the Health and Safety Laboratory (UK), GexCon AS (Norway), The European Centre for Research and Advanced Training in Scientific Computation (France) and the Universitat Politècnica de Catalunya (Spain).All six research topics are primarily based on numerical study using computational fluid dynamics (CFD) techniques. The open source CFD code OpenFOAM is used by all six fellows as the basic numerical frame for model development. Excellent progress has been achieved towards the scientific objectives. A summary is provided for the state of play for each of the six topics below: 1. LNG/fuel cascades and flammable cloud formation (ESR: Marco Macchi) - CascadeFOAM, a new solver for modelling fuel cascades has been developed within the frame of the OpenFOAM toolbox. Both the buoyancy terms in the momentum equations, the film and splashing models have been modified. The multiphase nature of the flow, the splashing process and the turbulence formed by the flammable cloud moving close to the ground are the main challenges which have been addressed successfully. The model has also been applied to hypothetical scenarios involving LNG cascade. Since no liquid LNG was available in the OpenFOAM library, this had to be developed using the thermophysical properties at its boiling point (-162°C). The study revealed a main difference between a gasoline and an LNG spill, i.e. the cascading LNG fully evaporates much more quickly; and in the example considered for a cascade from a 50 m high tank, the LNG fully evaporated before reaching the ground. This has laid the foundation for simulating LNG fires without relying on the crude assumption of mass burning rates used in previous numerical studies. 2. Development of a robust model for accurate prediction of rollover (ESR: Dr. Antoine Hubert) - RolloverFOAM, a dedicated solver has been developed within the frame of OpenFOAM for reliable predictions of rollover occurrence as well as the generated boil-off rate while giving 3D visualisation of the phenomenon. The code has been validated with small-scale experiment with Freon but also with an experiment conducted in Nantes between 1989-1990. Further developments have also been carried out to consider sloshing in stratified liquid to facilitate the study of rollover in more complex geometries while giving more information on the mechanisms of rollover. 3. LNG vapour cloud explosion (ESR: Reza Khodadadi) - DDTFOAM, a density based solver has been assembled within the frame of OpenFOAM for flame acceleration (FA) and deflagration to detonation transition (DDT) in flammable mixtures with and without concentration gradients. As experimental data is lacking for the explosions of LNG vapour could, the initial numerical tests and validations have been conducted with a horizontal obstructed channel filled with inhomogeneous hydrogen/air mixture and achieved reasonably good agreement with the experimental data. Predictios have also been conducted for large scale LNG explosions using the LNG vapour could generated by ESR Marco Macchi following LNG cascading. 4. LNG jet release (ESR: Konstantinos Lyras) – OpenFOAM has been modified to treat the two phase jets with the homogeneous relaxation method. The model is able to to capture the heat transfer under these conditions accounting for the non-equilibrium vapour generation. In addition to this, an algorithm which links the pressure-velocity coupling algorithm to the thermodynamic model is employed. Validation studies have shown that the predicted critical mass flow rates (shown in Figure 6 as an example) and vapour mass fraction inside the nozzle are in reasonably good agreement with the measurements. Predictions have also been conducted for LNG jets but there lacks data for validation. 5. LNG pool fires (ESR: Maqsood Alam) - A combined CFD fire model with full coupling between gaseous and liquid phases to predict burning rates of liquid fuel pool fires has been developed within the frame of FireFOAM, the large eddy simulation (LES) based fire simulation solver within OpenFOAM. This work is dedicated to simulating the entire process of liquid fuel pool fire; buoyancy driven flow with combustion, soot formation and oxidation, radiative heat transfer, evaporation of liquid fuel and prediction of fuel burning rate. For validation, comparison has been made with published experimental data for burning rate histories versus time and achieved reasonably good agreement. The model has also been successfully applied to simulate LNG pool fires without the need to use empirically based mass burning rates.6. LNG pool spread, evaporation and dispersion: SpreadFOAM, a dedicated solver, has been developed within the frame of OpenFOAM. The model simulates the entire pool spread, evaporation and dispersion scenarios for different spill scenarios (land or sea) and subject to different thermophysical conditions in relation to the ambient heat sources such as air, substrate and radiation. Particular consideration has been given to computational efficiency. The entire process is solved through three different physical regimes, in which the flow is solved with three independent solvers. However, all three domains and solvers are numerically coupled and implement predictions of the others. TRAINING: A dedicated training course has been organised through Open CFD Limited, the vendor of OpenFOAM to address a list of topics compiled by the fellows concerning OpenFOAM as well as essential C++ required for programming. A number of other training courses have also been organised by inviting external experts from both industry and academia have delivered lectures on a range of topics covering LNG production, transport and utilization, LNG safety, CFD modelling for the oil and gas industry and Radiation modelling in OpenFOAM. The fellows have also been provided access to additional online training on the research topics. The Fellows have also been encouraged to share knowledge among themselves, e.g. one Fellows who already gained ample experience in mesh generation with OpenFOAM delivered a training course on this to other fellows. The fellows have also received complimentary skills training on a wide range of topics. Website: http://www.safelng.org.uk.
