Field models

KFX® is developed for 3D and transient fire and gas dispersion simulations. The governing equations that have to be solved are partially differential equations (PDE) describing the transient behavior of the different field variable in space. The PDE describing fluid flow are commonly referred to as transport equations because they have the same type of terms

Terms:

  • Transient term
  • Convective term
  • Diffusion term
  • Source term.

 

The transport equations are discretized into difference equation of the finite volume form which focus on conservation of the different variables solve.

The following field models are solved in KFX®:

  • Conservation of momentum
    Equations for U, V and W velocities
  • Conservation of mass
    Pressure correction equation
  • Conservation of energy
    Equations for total enthalpy and species mass fractions
  • The k-ε turbulence model
    Equations for turbulent kinetic energy and dissipation of turbulent kinetic energy
  • The Eddy Dissipation Soot model
    Equations for soot nucleus and soot mass fractions

 

The different sub models used in KFX® provides information used in the source terms for the equations of the different field variables.

  • Pool model.
    Model of pool spreading including “stair case“ model and evaporation model due to flashing, convection and boiling.
    Source term for the pressure correction equation and the energy and species equations.
  • Spray model.
    LaGrangian model following parcel of droplets with uniform properties.
    Source term for the momentum equations, pressure correction equation and the energy and species equations.
  • Radiation model.
    The discrete transfer model of Shah and Lockwood. Source term in the energy equation
  • Absorption model.
    Mean absorption coefficient based on Leckners model of CO2 and H2O absorption and Felske and Tien’s model of soot absorption. Used by the radiation model
  • Wall model for turbulent flow.
    Dissipation of turbulent kinetic energy adjacent to the wall are found by assuming flat plate theory of turbulent shear flow. In addition momentum transfer coefficient and heat transfer coefficient is calculated. Used in source terms for momentum, enthalpy and k-ε
  • Wall temperature model.
    Surface temperature of solid surfaces. Used in the radiation model and source term for enthalpy.
  • The EDC turbulence combustion model by Magnussen.
    Describes the mean reaction rates as a function of mass fraction of reacting structures and the residence times of these structures. Source term in the equations of species mass fractions.
  • The EDC Soot model by Magnussen.
    Describes the formation and destruction of soot and soot nucleus according to EDC and the Tesner soot formation model. Used by the absorption model.
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