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 = cs_glob_mesh->n_cells;
  const cs_real_t  *cell_f_vol = cs_glob_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 ) (dissipation time for )
prodf = 100.0 (in $[f]\cdot s^{-1}$ ) (production of 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_var_cal_opt_t  *var_cal_opt
      = cs_field_get_key_struct_const_ptr(f,
                                          cs_field_key_id("var_cal_opt"));
    if (var_cal_opt->iwarni >= 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 because 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_var_cal_opt_t  *var_cal_opt
      = cs_field_get_key_struct_const_ptr(f,
                                          cs_field_key_id("var_cal_opt"));
    if (var_cal_opt->iwarni >= 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 != NULL) {
 
      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;
      }
 
    }
 
  }