programmer's documentation
Examples of data settings for radiative transfers

Activation of the module

The module can be activated in the usppmo routine in cs_user_parameters.f90. The corresponding keyword is iirayo in the cs_glob_rad_transfer_options structure.

This member can take the values:

Radiation module specific parameters.

When the module is activated, its specific input parameters should be set in the cs_user_radiative_transfer_parameters function of the cs_user_radiative_transfer.c file.

Calculation options for the radiative transfer module.

Radiative transfer parameters may be defined using the cs_user_radiative_transfer_parameters function.

/* indicate whether the radiation variables should be
initialized (=0) or read from a restart file (=1) */
/* period of the radiation module */
/* Quadrature Sn (n(n+2) directions)
1: S4 (24 directions)
2: S6 (48 directions)
3: S8 (80 directions)
Quadrature Tn (8n^2 directions)
4: T2 (32 directions)
5: T4 (128 directions)
6: Tn (8*ndirec^2 directions)
*/
/* Method used to calculate the radiative source term:
- 0: semi-analytic calculation (required with transparent media)
- 1: conservative calculation
- 2: semi-analytic calculation corrected
in order to be globally conservative
(If the medium is transparent, the choice has no effect) */
/* Verbosity level in the listing concerning the calculation of
the wall temperatures (0, 1 or 2) */
/* Verbosity mode for the Luminance (0, 1 or 2) */
/* Compute the absorption coefficient through Modak (if 1 or 2),
or do not use Modak (if 0).
Useful ONLY when gas or coal combustion is activated
- imodak = 1: ADF model with 8 wave length intervals
- imodak = 2: ADF model with 50 wave length intervals */
/* Compute the absorption coefficient via ADF model
Useful ONLY when coal combustion is activated
imoadf = 0: switch off the ADF model
imoadf = 1: switch on the ADF model (with 8 bands ADF08)
imoadf = 2: switch on the ADF model (with 50 bands ADF50) */
/* Compute the absorption coefficient through FSCK model (if 1)
Useful ONLY when coal combustion is activated
imfsck = 1: activated
imfsck = 0: not activated */

Radiative transfer boundary conditions

radiative_tr_sketch.gif
Sketch of thermal flux in boundary walls

The radiative boundary condition is based on the calculation of a new wall temperature. This temperature is computed with a thermal flux balance:

\[{ Q_{conduction} = Q_{convection} + (Q_{rayt_{absorption}} - Q_{rayt_{emission}}}) \]

Therefore :

\[ \dfrac{xlamp}{epap} (T_{fluid} - T_{wall}) = h_{fluid} (T_{fluid} - T_{wall}) + epsp (Q_{incid} - \sigma * T_{wall}) \]

Note
In Code_Saturne the flux is positive when it is oriented from inside to outside.
Corps Emissivity
polished steel 0.06
oxidized steel 0.80
steel rough 0.94
polished aluminium 0.04
oxidiezd aluminium (inside) 0.09
oxidized aluminium (wet air)0.90
brick 0.93
concrete 0.93
paper 0.8 to 0.9
water 0.96

Boundary faces identification

Boundary faces may be identified using the getfbr subroutine. The syntax of this subroutine is described in the cs_user_boundary_conditions subroutine, but a more thorough description can be found in the user guide.

Note
These usefull constant are definded
$ TKELVI = 273.16D0 $
$ SIG = 5.6703D-8 $

Initialization and finalization

The following initialization block needs to be added for the following examples:

At the end of the subroutine, it is recommended to deallocate the work array:

In theory Fortran 95 deallocates locally-allocated arrays automatically, but deallocating arrays in a symetric manner to their allocation is good pratice, and avoids using a different logic for C and Fortran.

Remaining initialisation

ivar: number of the thermal variable

Min and Max values for the wall temperatures (clipping otherwise)

$ T_{min} $ and $T_{max} $ are given in Kelvin.

Assign boundary conditions to boundary wall

Zones definition

We define zones of wall boundary, and we assign a type. This allows to apply the boundary conditions and realize balance sheets by treating them separately for each zone.

For each boundary face ifac (not just the faces of wall) the user defines his own choice by a number of zone izfrdp(ifac) from color of the boundary face or more generally, their properties (color, groups ...), or boundary conditions specified in cs_user_boundary_conditions, or even of their coordinates.

Warning
It is essential that ALL boundary faces have been assigned to a zone. The number of zones (the value of izfrdp(ifac)) is arbitrarily chosen by the user, but must be a positive integer and less than or equal to nbzrdm (value set in parameter radiat::h).

Wall caracteristics

Warning
The unit of the temperature is the Kelvin

Mandatory data

Other data (depending of the isothp)

Examples of boundary conditions

Here is a list of examples:

Gray or black wall with profil of fixed inside temperature

For wall boundary faces, selection criteria: color 1

Gray or black wall with fixed outside temperature \f$ T_{ext} \f$

For wall boundary faces, selection criteria: color 2

Reflecting wall (\f$ epsp = 0 \f$) with fixed outside temperature \f$ T_{ext} \f$

For wall boundary faces, selection criteria: color 3

Gray or black wall and fixed conduction flux through the wall

For wall boundary faces which have the color 4:

\[ \begin{array}{rcl} \frac{\texttt{xlamp}}{\texttt{epap}} \cdot (T_{wall} - T_{ext}) &=& \text{fixed conduction flux in } W.m^{-2} \\ &=& \texttt{rodcl(ifac,ivar,3)} \end{array} \]

If the conduction flux is zero then the wall is adiabatic. The array $ \texttt{rcodcl(ifac,ivar,3)}$ has the value of the flux.
Flux density (< 0 if gain for the fluid)

\[ rcodcl(ifac,ivar,3)=C_p (viscls+\frac{visct}{\sigma})\cdot \grad{T}\cdot \vect{n} \]

Reflecting wall and fixed conduction flux through the wall

For wall boundary faces which have the color 5:

\[ \frac{xlamp}{epap} \cdot (T_{wall} - T_{ext}) = \text{fixed conduction flux} \]

and $ epsp = 0 $

If the conduction flux is zero then the wall is adiabatic. Flux density (< 0 if gain for the fluid)

Warning

For all boundary faces that are not wall it is MANDATORY to impose a number of zone in the array izfrdp. For each zone, informations will be displayed in the listing.

Verification that all boundary faces have been treated

End of the loop on the boundary faces

Format

Absorption coefficient and net radiation flux

The absorption coefficient and the net radiation flux for the radiative module can be defined in cs_user_radiative_transfer.f90 through the usray3 and usray5 subroutines.

Absorption coefficient

The absorption coefficient is defined in usray3 .

Arguments of usray3

Local variables to be added

Computation of the absorption coefficient

Format

Net radiation flux

The net radiation flux is computed in usray5 .

Arguments of usray5

Local variables to be added

Initialization

At the end of the subroutine, if iok is different from zero, some faces have been forgotten and the calculation stops.

Computation of the net radiation flux

Format