Defining the Firebox Physics

Reacting physics models simulate combustion in the firebox. Co-simulation models exchange data between the firebox and the plug flow reactor code for reacting channels.

You specify the physics models that are used to model hot flow within the Firebox. You also activate the co-simulation model.
  1. For the physics continuum, Continua > Physics 1, select the following models, in order:
    Group Box Model
    Space Three Dimensional (selected automatically)
    Time Steady
    Material Multi-Component Gas
    Reaction Regime Reacting
    Reacting Flow Models Flamelet
    Flamelet Models Flamelet Generated Manifold (FGM)

    FGM Reaction (selected automatically)

    Flow

    Segregated Flow (selected automatically)

    Gradients (selected automatically)

    Ideal Gas (selected automatically)

    Turbulent (selected automatically)

    Segregated Fluid Enthalpy (selected automatically)

    Reynolds-Averaged Navier-Stokes (selected automatically)

    Progress Variable Source Turbulent Flame Speed Closure (TFC)
    Reynolds-Averaged Turbulence

    K-Epsilon Turbulence

    Realizable K-Epsilon Two-Layer (selected automatically)

    Wall Distance (selected automatically)

    Two-Layer All y+ Wall Treatment (selected automatically)

    Optional Models Radiation

    Surface Materials (selected automatically)
    Radiation Participating Media Radiation (DOM)
    Radiation Spectrum (Participating) Gray Thermal Radiation
    Optional Models Co-Simulation
    Co-Simulation Models

    Reacting Channel

    Reacting Channel Steady Coupling (selected automatically)

    Optional Models Cell Quality Remediation
  2. Click Close.
Specify the chemistry within the Firebox:
  1. Right-click the Physics 1 > FGM Table Generator > Table Chemistry Definition node and select Import Chemistry Definition (Chemkin format).
  2. In the Import Chemkin Files dialog:
    1. Make sure that Import Transport Properties File is activated.
    2. Import the files that are specified in the table below:
      Chemical Mechanism File grimech30.dat
      Thermodynamic Properties File thermo30.dat
      Transport Properties File transport.dat
    3. Click OK.
Before building the FGM table, make sure that the table contains all of the species that are required for analysis at the post-processing stage. For example, it is useful to monitor emissions of CO from the firebox. Also, visualising the intermediate species OH can give a rough indication of where the flame front is.
  1. Add species for post-processing:
    1. Select the FGM Table Generator > Parameters > Species for Tabulation node, then click (Custom Editor).
    2. In the Species for Tabulation - Species window, select CO2, CO, and OH.
    3. Click OK.
  2. Create the FGM table:
    1. Select the FGM Table Generator > Fluid Streams > Fuel node, then next to Fluid Stream Components, click (Custom Editor) and set the following:
      CH4 0.052244
      H2 0.003158
      N2 0.724412
      O2 0.220186
      By default, the oxidiser composition is set to that of air.
    2. Click OK.
    3. Right-click the Physics 1 > FGM Table Generator > FGM Table node and select Generate FGM Library and Construct Table.
    The progress of the FGM table generation is displayed in the Output window.
To reflect the behavior of the gas components accurately, several material properties are specified. Since participating media radiation is used in this simulation, the optical path length must be specified to compute the absorption coefficient. The optical path length (OPL) was calculated previously using the result of two sum reports—Volume and Total Surface Area—in the relationship:
图 1. EQUATION_DISPLAY
OPL⁢=3.6VolumeTotal⁢   Surface⁢  Area
(5262)
  1. Expand the Multi-Component Gas > Material Properties node and set the following properties:
    Node Property Setting
    Absorption Coefficient Method Weighted Sum of Gray Gases
    Weighted Sum of Gray Gases Optical Path Length 0.75 m
    Turbulent Prandtl Number
    Constant Value 0.7
    Turbulent Schmidt Number
    Constant Value 0.7
  2. Define the surface materials and specify radiation properties:
    1. Select the Physics 1 > Surface Materials > Surface Materials > Default node and rename it to Furnace Walls.
    2. Select the Furnace Walls > Material Properties > Emissivity > Constant node and set Value to 0.85.
    3. Right-click the Surface Materials > Surface Materials node and select Select Surface Materials.
    4. In the Select Surface Materials dialog, Cast Iron (Cast Iron), then click Apply and Close.
    5. Select the Cast Iron node and rename it to Furnace Pipes.
    6. Select the Furnace Pipes > Material Properties > Emissivity > Constant node and set Value to 0.6.
  3. Set up the ignitor:
    1. Right-click the Physics 1 > Ignitors node and select New.
    2. Expand the Physics 1 > Ignitors > Progress Variable Ignitor 1 node and set the following properties:
      Property Setting
      Progress Variable Ignitor 1 Parts ignitor1 and ignitor2
      Pulse Ignitor Ending Iteration/Time 50.0
  4. Save the simulation.