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16.3.3 Modifying the Constants for the Premixed Combustion Model

In general, you will not need to modify the constants used in the equations presented in Section  16.2. The default values are suitable for a wide range of premixed flames. If, however, you want to make some changes to the model constants, you will find them under Model Constants in the Species Model panel.

You can set the Turbulence Length Scale Constant ( $C_D$ in Equation  16.2-6), the Turbulent Flame Speed Constant ( $A$ in Equation  16.2-4), the Stretch Factor Coefficient ( $\mu_{\rm str}$ in Equation  16.2-14) and the Turbulent Schmidt Number (Sc $_t$ in Equation  16.2-1).

For a non-adiabatic premixed combustion model, note that the value you specify for the Turbulent Schmidt Number will also be used as the Prandtl number for energy. (The Energy Prandtl Number will therefore not appear in the Viscous Model panel for non-adiabatic premixed combustion models.) These parameters control the level of diffusion for the progress variable and for energy. Since the progress variable is closely related to energy (because the flame progress results in heat release), it is important that the transport equations use the same level of diffusion.

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