Initial Values (Radiation in Participating Media and Radiation in Absorbing–Scattering Media Interfaces)
This node adds an initial value for the radiative intensity I (when Discrete ordinates method is selected as the Radiation discretization method) or the incident radiation G (when P1 approximation is selected as the Radiation discretization method) that can serve as an initial condition for a transient simulation or as an initial guess for a nonlinear solver.
Initial Values
Discrete Ordinates Method
When Discrete ordinates method is selected as the Radiation discretization method for the physics interface, you should define the initial radiative intensity using one of the following options, depending on the Wavelength dependence of radiative properties set in the Participating Media Settings section of the interface.
If the Wavelength dependence of radiative properties is Constant, choose between the following options:
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Use the Blackbody assumption and set a value for the Initial temperature T, to define I = Ib(T). This option is only available in the Radiation in Participating Media interface.
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Set a User defined value for the Initial radiative intensity I. The default is 0 in the Radiation in Absorbing–Scattering Media interface, and rpm.Ibinit in the Radiation in Participating Media interface.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands, choose among the following options:
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When Initial value is set to Blackbody, enter a value for the Initial temperature T, to define I = Ib(T). The blackbody radiation is distributed between all bands with respect to the fractional emissive power FEP. This option is only available in the Radiation in Participating Media interface.
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When Initial value is set to User defined for each band, enter a value for the Initial radiative intensity for each spectral band in the table displayed underneath. Within a spectral band, each value is assumed to be independent of wavelength.
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When Initial value is set to User defined distribution, enter a value or expression for the Initial radiative intensity distribution Iλ. The wavelength can be accessed through the rpm.lambda or rasm.lambda variable. This distribution is integrated over each spectral band to obtain the radiative intensity Ii,k for each spectral band.
If Wavelength dependence of radiative properties is Weighted Sum of Gray Gases Model, choose among the following options:
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When Initial value is set to Blackbody, enter a value for the Initial temperature T, to define I = Ib(T). The blackbody radiation is distributed between all gray gases with respect to the weight factors a. The weight factors are evaluated at the temperature given in Initial temperature.
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When Initial value is set to User defined, enter a value for the Initial radiative intensity that is distributed between all gray gases with respect to the weight factors a. The weight factors are evaluated at the temperature given in Initial temperature.
P1 Approximation
When P1 approximation is selected as the Radiation discretization method for the physics interface, you should define the initial incident radiation using one of the following options, depending on the Wavelength dependence of radiative properties set in the Participating Media Settings section of the interface.
If the Wavelength dependence of radiative properties is Constant, choose between the following options:
•
Use the Blackbody assumption and set a value for the Initial temperature T, to define G = 4πIb(T). This option is only available in the Radiation in Participating Media interface.
•
Set a User defined value for the Initial incident radiation G. The default is 0 in the Radiation in Absorbing–Scattering Media interface, and (4*pi)*rpm.Ibinit in the Radiation in Participating Media interface.
If Wavelength dependence of radiative properties is Solar and ambient or Multiple spectral bands, choose among the following options:
•
When Initial value is set to Blackbody, enter a value for the Initial temperature T, to define G = 4πIb(T). The blackbody radiation is distributed between all bands with respect to the fractional emissive power FEP. This option is only available in the Radiation in Participating Media interface.
•
When Initial value is set to User defined for each band, enter a value for the Initial incident radiation for each spectral band in the table displayed underneath. Within a spectral band, each value is assumed to be independent of wavelength.
•
When Initial value is set to User defined distribution, enter a value or expression for the Initial incident radiation distribution Gλ. The wavelength can be accessed through the rpm.lambda or rasm.lambda variable. This distribution is integrated over each spectral band to obtain the incident radiation Gk for each spectral band.
If Wavelength dependence of radiative properties is Weighted Sum of Gray Gases Model, choose among the following options:
•
When Initial value is set to Blackbody, enter a value for the Initial temperature T, to define G = 4πIb(T). The blackbody radiation is distributed between all gray gases with respect to the weight factors a. The weight factors are evaluated at the temperature given in Initial temperature.
•
When Initial value is set to User defined, enter a value for the Initial incident radiation that is distributed between all gray gases with respect to the weight factors a. The weight factors are evaluated at the temperature given in Initial temperature.
Theory for Radiation in Participating Media
Location in User Interface
Context Menus
 Radiation in Participating Media > Initial Values
 Radiation in Absorbing–Scattering Media > Initial Values
Ribbon
Physics tab with Radiation in Participating Media or Radiation in Absorbing–Scattering Media selected:
Domains > Initial Values