CFD BASED EVALUATION OF THERMODYNAMIC PARAMETERS AND FLOW FIELD FOR HYDROGEN AIR DEFLAGRATIONS
In nuclear reactor, during severe accidents, hydrogen may be released in the containment. The risk associated with ignition and subsequent combustion of hydrogen represents an important safety concern. In the present study, an open-source numerical CFD library has been leveraged for modeling of premixed combustion of hydrogen and air in enclosures. The model is based on the progress variable representation of turbulent premixed combustion with the Zimont turbulent flame speed closure. This model has been used to study deflagration induced pressure and temperature rise, deflagration index and flame propagation characteristics in enclosures. The CFD predicted pressure and temperature compares well with the thermodynamically obtained Adiabatic Isochoric Complete Combustion (AICC) limit at hydrogen mol fractions higher than 10%. For leaner mixtures, the difference between AICC and CFD has been attributed to incomplete combustion. A systematic parametric study has been carried out to evaluate the impact of initial conditions such as hydrogen mole fraction, initial temperature and volume of the domain on both steady state and transient characteristics. In addition to thermodynamic parameters, detailed flow field characterization has been carried out. Marked differences have been observed in flame propagation at concentrations leaner than 10%. This has been attributed to buoyancy dominated hydro-dynamic phenomenon and the associated entrainment based mixing. The isolated effect of buoyancy has been studied in a hypothetical situation without gravity.