9.0
general documentation
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Transported scalar source terms

Source terms for transported scalars may be defined using the cs_user_source_terms user-defined function.

Field access and information

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

/* field structure */
const cs_field_t *f = cs_field_by_id(f_id);
/* mesh quantities */
const cs_lnum_t n_cells = domain->mesh->n_cells;
const cs_real_t *cell_f_vol = domain->mesh_quantities->cell_vol;

Indicator of variance scalars: To determine whether a scalar is a variance, the following info can be accessed:

int var_f_id = cs_field_get_key_int(f, cs_field_key_id("first_moment_id"));
  • If var_f_id == -1 , the scalar is not a variance
  • If var_f_id >= 0 , the field is the variance of the scalar with field id var_f_id

Density

const cs_real_t *cpro_rom = CS_F_(rho)->val;

Example 1

Example of arbitrary source term for the scalar f, named "scalar_2" in the calculation.

$ S=A \cdot f+B $

appearing in the equation under the form

$ \rho \dfrac{df}{dt}=S \: \text{(+ regular other terms in the equation)} $ In the following example:

\[A=-\frac{\rho}{\tau_f} \]

\[B=\rho \cdot prod_f \]

with:

  • tauf = 10.0 (in $ s $) (dissipation time for $f$)
  • prodf = 100.0 (in $ [f]\cdot s^{-1} $) (production of $f$ by unit of time)

which yields:

  • st_imp[i] = volume[i]*A = -volume[i]*rho/tauf
  • st_exp[i] = volume[i]*B = volume[i]*rho*prod_f

Body

Source term applied to second scalar

if (strcmp(f->name, "scalar_2") == 0) {
/* logging */
const cs_equation_param_t *eqp = cs_field_get_equation_param_const(f);
if (eqp->verbosity >= 1)
bft_printf(" User source terms for variable %s\n",
cs_field_get_label(f));
/* apply source terms to all cells */
const cs_real_t tauf = 10.0;
const cs_real_t prodf = 100.0;
for (cs_lnum_t i = 0; i < n_cells; i++) {
st_imp[i] = - cell_f_vol[i]*cpro_rom[i]/tauf;
st_exp[i] = cell_f_vol[i]*cpro_rom[i]*prodf;
}
}

Example 2

Example of arbitrary volumic heat term in the equation for enthalpy h.

In the considered example, a uniform volumic source of heating is imposed in the cells with coordinate X in [0;1.2] and Y in [3.1;4].

The global heating power if Pwatt (in $W$) and the total volume of the selected cells is volf (in $m^3$).

This yields:

  • st_imp[i] = 0
  • st_exp[i] = volume[i]* pwatt/volf

Body

Warning
It is assumed here that the thermal scalar is an enthalpy. If the scalar is a temperature. PWatt does not need to be divided by $ C_p $ because $C_p$ is put outside the diffusion term and multiplied in the temperature equation as follows:

\[ \rho C_p \norm{\vol{\celli}} \frac{dT}{dt} + ... = \norm{\vol{\celli}[i]} \frac{pwatt}{voltf} \]

with pwatt = 100.0

Apply source term

if (f == CS_F_(h)) { /* enthalpy */
/* logging */
const cs_equation_param_t *eqp = cs_field_get_equation_param_const(f);
if (eqp->verbosity >= 1)
bft_printf(" User source terms for variable %s\n",
cs_field_get_label(f));
/* apply source terms in zone cells */
const cs_zone_t *z = cs_volume_zone_by_name_try("heater");
if (z != nullptr) {
cs_real_t pwatt = 100.0;
cs_real_t voltf = z->f_measure;
for (cs_lnum_t i = 0; i < z->n_elts; i++) {
cs_lnum_t c_id = z->elt_ids[i];
st_exp[c_id] = cell_f_vol[c_id]*pwatt/voltf;
}
}
}