Examples of data settings for source terms with scalar in a channel

Additional right-hand side source terms for scalar equations (user scalars and specific physics scalars) with the cs_user_source_terms user-defined function.

Local variables and initialization

  /* field structure */
  const cs_field_t  *f = cs_field_by_id(f_id);
 
  /* local number of mesh cells */
  const cs_lnum_t  n_cells = cs_glob_mesh->n_cells;
 
  /* mesh quantities */
  const cs_real_t  *cell_f_vol = cs_glob_mesh_quantities->cell_vol;

Only apply to thermal scalar

  /* scalar id */
  const int  key_sca = cs_field_key_id("scalar_id");
  const int  scalar_id = cs_field_get_key_int(f, key_sca);
 
  if (scalar_id < 0 || scalar_id != cs_glob_thermal_model->iscalt)
    return;

Function body

Map required fields

  /* velocity */
  const cs_real_3_t  *cvar_vel = (const cs_real_3_t *)(CS_F_(vel)->val);

Compute bulk mean velocity

  /* bulk mean velocity (x component) */
  cs_real_t  ubulk = 0;
  for (cs_lnum_t i = 0; i < n_cells; i++)
    ubulk += cvar_vel[i][0] * cell_f_vol[i];
 
  cs_parall_sum(1, CS_DOUBLE, &ubulk);  /* sum across processes if needed */
 
  ubulk /= cs_glob_mesh_quantities->tot_vol;

Compute source terms; we want to impose a total flux of 1 Watt.

  /* Flux x Total surface / (rho Cp) */
  cs_real_t tot_flux = 1.;
 
  for (cs_lnum_t i = 0; i < n_cells; i++) {
    st_imp[i] = 0.;
    st_exp[i] = cell_f_vol[i] * cvar_vel[i][0] * tot_flux / ubulk;
  }