Dispersion modelling

GexCon R&D develops and implements models for gaseous and liquid releases and atmospheric dispersion in the CFD code FLACS.

Release modelling

Flammable and toxic gases are usually stored and transported at elevated pressures or at low temperatures.  During an accidental release, compressed gases may undergo complex flashing processes or transition from supersonic to subsonic flow just after an orifice. It is not practical to resolve all details of these physical phenomena in CFD simulations on industrial scales, and flashing liquid releases and transition from supersonic to subsonic flows are therefore represented by models derived from theoretical and/or empirical considerations. Furthermore, releases of cryogenic liquids, or from releases of materials with boiling points above the ambient temperature may lead to the formation of liquid pools.

Research activities

  • Modelling of flashing releases
  • Modelling of pool spread and evaporation
  • Modelling of liquefied natural gas (LNG) boiling on water

Flashing releases

In spray releases, flashing releases, and releases of CO2, there is a significant mass fraction of liquid droplets or solid particles. Small droplets and particles can be modelled quite accurately by a homogeneous multiphase model. A Lagrangian particle tracking model is under development for improving the accuracy for two-phase jets containing large droplets and particles and for prediction of rain-out on walls and on the ground.   

Research activities

  • Modelling of two-phase jet releases with droplet tracking
  • Modelling of CO2 release

Atmospheric dispersion

Detailed modelling of flow phenomena in the atmospheric boundary layer by means of CFD is a powerful approach for assessing hazards related to dispersion of flammable or toxic gases in industrial and urban surroundings. Flow patterns in congested areas, around buildings, and in complex terrains, are not straightforward to describe with simplified models, and reliable calculations require CFD tools with accurate and appropriate sub-models to match the achievable resolution for a given problem.

Research activities

  • Turbulence models for complex flows
  • Modelling of stable and unstable atmospheric boundary layers
  • Terrain import from digital maps
  • Coupling with geographical information system (GIS) tools

Selected references

  • Hanna, S.R., Hansen, O.R, Ichard, M. & Strimatis, D. (2009). Computational fluid dynamics (CFD) model simulations of dispersion from railcar releases in industrial and urban areas. Atmospheric Environment, 43: 262-270.
  • Hanna, S.R., Brown, M.J., Camelli, F.E., Chan, S.T., Coirier, W.J., Hansen, O.R., Huber, A.H., Kim, S. & Reynolds, R.M. (2006). Detailed simulation of atmospheric flow and dispersion in downtown Manhattan. Bulletin of the American Meteorological Society (BAMS), December 2006: 1713-1726.
  • Hanna, S.R., Hansen, O.R. & Dharmavaram, S., (2004). FLACS CFD air quality model performance evaluation with Kit Fox, MUST, Prairie Grass, and EMU observations. Atmospheric Environment, 38: 4675-4687
  • Hansen, O.R., Melheim, J.A. & Storvik, E.E. (2007). CFD-modeling of LNG dispersion experiments. AIChE Spring National Meeting & Forty-first Annual Loss Prevention Symposium, 22-26 April 2007, Houston, USA.
  • Melheim, J.A., Ichard, M. & Pontiggia, M. (2009). Towards a computational fluid dynamics methodology for studies of large-scale LNG releases. Hazards XXI, 9-12 November 2009, Manchester, UK. IChemE Symposium Series 155
  • Melheim, J.A., Ichard, M. & Pontiggia, M. (2009). Towards a computational fluid dynamics methodology for studies of large-scale LNG releases. Hazards XXI, 9-12 November 2009, Manchester, UK. IChemE Symposium Series 155: 36-343.
  • Ichard, M., Hansen, O.R. & Melheim, J.A. (2010). Releases of pressurized liquefied gases: simulations of the Desert Tortoise test series with the CFD model FLACS, 16th Conference on Air Pollution Meteorology, Atlanta, GA, USA.
  • Savvides, C., Tam, V., Os, J.E., Hansen, O.R., van Wingerden, K. & Renoult, J. (2001). Dispersion of fuel in offshore modules: comparison of predictions using FLACS and full scale experiments. ERA conference, 27-28 November 2001.

Additional references

 

Contact persons:

Jens A. Melheim: jens(a)gexcon.com

 

Mathieu Ichard: mathieu(a)gexcon.com

Olav Roald Hansen: olav(a)gexcon.com

 

 

 

 

Lene Sælen: lene(a)gexcon.com