### 3.2.13. CFX-Solver Output File (Radiation Runs)

#### 3.2.13.1. Convergence History

When the `Thermal Radiation P1`, `Discrete Transfer`, or `Monte Carlo` model has been selected, a new variable, `I-Radiation`, is computed.

##### 3.2.13.1.1. P1 Model

    ======================================================================
    OUTER LOOP ITERATION =    1                     CPU SECONDS = 3.67E+01
    ----------------------------------------------------------------------
    |       Equation       | Rate | RMS Res | Max Res |  Linear Solution |
    +----------------------+------+---------+---------+------------------+
    ...
    +----------------------+------+---------+---------+------------------+
    | I-Radiation          | 0.00 | 3.6E-08 | 4.6E-07 |  5.2  3.5E-02  OK|
    +----------------------+------+---------+---------+------------------+

##### 3.2.13.1.2. Discrete Transfer Model

`I-Radiation` data is output every nth iteration, where n is specified by an `Iteration Interval` parameter (which can be set in Solver Control > Advanced Options > Thermal Radiation Control in CFX-Pre). The row containing this data has its own column headings, which override the table headings just for the row. The column headings are:

- `#Its` is the number of iterations required to obtain a converged radiation solution to within a specified tolerance. This number is usually 1 unless there are reflective boundaries (emissivity less than 1). The default maximum number of iterations and tolerances are 10, and 0.01 respectively. These values can be set in Solver Control > Advanced Options > Thermal Radiation Control > Ray Tracing.

- `Vol Chg` is the maximum normalized change in volumetric absorbed radiation at convergence.

- `Sur Chg` is the maximum normalized change in surface absorbed radiation at convergence.

- `%Lost` is the percentage of ray traces lost due to tracking errors, or non-overlap boundaries at domain interfaces. Values greater than 5% are an indication of a setup error.

- `%Imbal` is the percentage imbalance of radiative energy. This value should be 0 or a small value. Otherwise, the results are not reliable.

    +----------------------+------+---------+---------+------------------+
    | I-Radiation          | #Its | Vol Chg | Sur Chg | %Lost  %Imbal    |
    |   Gray               |    1 | 0.0E+00 | 0.0E+00 |  0.38    1.94    |
    +----------------------+------+---------+---------+------------------+

This variable is also included in the `Locations of Maximum Residuals` and `Peak Values of Residuals` tables that appear in the output file.

##### 3.2.13.1.3. Monte Carlo Model

`I-Radiation` data is output every nth iteration, where n is specified by an `Iteration Interval` parameter (which can be set in the Solver Control in CFX-Pre on the Advanced Options tab). The row containing this data has its own column headings, which override the table headings just for the row. The column headings are:

- `%SD Sur` is the maximum normalized standard deviation of the irradiation flux at an element face on a boundary (`Wall Irradiation Flux.Normalized Std Deviation`). The presence of values greater than 30% indicates that the value of Number of Histories is too small to resolve the radiation field. The presence of small isolated boundary regions with values of `Wall Irradiation Flux.Normalized Std Deviation` larger than 30% is an indication that the element faces in those regions were insufficiently sampled.

- `%SD Vol` is the maximum normalized standard deviation of the radiation intensity within a finite element (`Radiation Intensity.Normalized Std Deviation`). Similar to `%SD Sur`, the values of `Radiation Intensity.Normalized Std Deviation` are expected to be less than 30%.

- `%Lost` is the percentage of histories lost due to tracking errors or non-overlap boundaries at domain interfaces. Values greater than 5% are indication of a setup error.

- `%Imbal` is the percentage imbalance of radiative energy. This value should be 0 or a small value. Otherwise, the results are not reliable.

    +----------------------+------+---------+---------+------------------+
    | I-Radiation          |      | %SD Sur | %SD Vol | %Lost  %Imbal    |
    |   Full Spectrum      |      | 4.6E+01 | 1.0E+02 |  0.00    0.00    |
    +----------------------+------+---------+---------+------------------+

The `Variable Range Information` table has the output variable `Radiation Intensity` listed.

#### 3.2.13.2. Summary Fluxes

- It should be noticed that for heat flux specified boundaries (adiabatic, for example) the specified heat flux can verified by adding to the boundary flow in the H-Energy flow summary.

  | (3–3)

- An I-Radiation section is included...

       +--------------------------------------------------------------------+
       |                            I-Radiation                             |
       +--------------------------------------------------------------------+
       Boundary         : Airin                                  -1.5659E+03
       Boundary         : Combustor Default                      -3.5729E+02
       Boundary         : Downcomer Wall                         -5.1864E+02
       Boundary         : Fuelin                                 -1.0076E+03
       Boundary         : Outlet                                  1.6636E+01
       Domain           : Combustor                               5.2454E+03
       Domain Interface : Domain Interface 1                      5.3004E-01
       Domain Interface : Domain Interface 2                     -5.2638E+00
       Domain Interface : LowerGGI                               -1.9895E-01
       Domain Interface : Periodic                                1.1727E+01
       Domain Interface : UpperGGI                                1.6994E-01
                                                                 -----------
       Domain Imbalance :                                         1.8195E+03
       Domain Imbalance, in %:                                     19.2758 %

  The I-Radiation imbalances reported in the .out file represent the global heat flow imbalances due to radiation for all domains. Flows through domain interfaces are not included, therefore when radiation occurs in more than one connected domain the imbalance in any individual domain will be non-zero in general. However, the final Global Imbalance reported in the .out file should be close to zero, indicating the convergence of a solution.

  When plotting the domain-based I-Radiation imbalances for multi-domain radiation cases you should expect a non-zero value in a converged solution as noted above. The plotted domain imbalances are normalized by the magnitude of the largest flux in that domain, therefore it is not valid to sum the normalized imbalances across domains to obtain the global value.

When the Rosseland model is selected:

- No additional equation is solved. Hence, no thermal radiation flow summary will be available.

- The total heat flux is reported by the H-Energy flow summary.

  | (3–4)

- The CPU Requirements of Numerical Solution table reports the amount of CPU time spent due to the use of a thermal radiation model.

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