Examples of volume exchange coefficient computation for SYRTHES coupling (cs_user_syrthes_coupling_volume_h)

The Examples function is required to compute a volume exchange coefficient for SYRTHES coupling.

Examples

The following code blocks show two examples of computation of a volume exchange coefficient.

Example 1

The first example corresponds to a constant volume exchange coefficient:

  cs_real_t hvol_cst = 1.0e6;
 
  for (cs_lnum_t i = 0; i < n_elts; i++) {
    h_vol[i] = hvol_cst;
  }

Example 2

The second example corresponds to a variable volume exchange coefficient defined as follows :

with S is the surface area where exchanges take place by unit of volume and

First, the values of the different fields that will be needed for the computation of the volume exchange coefficient are retrieved.

  const cs_real_3_t  *cvar_vel = (const cs_real_3_t *)CS_F_(vel)->val;
  const cs_real_t  *cpro_rom = (const cs_real_t *)CS_F_(rho)->val;
  const cs_real_t  *cpro_mu = (const cs_real_t *)CS_F_(mu)->val;
 
  const cs_real_t  cp0 = cs_glob_fluid_properties->cp0;
  cs_real_t  visls_0 = -1;
 
  const cs_real_t  *cpro_cp = nullptr, *cpro_viscls = nullptr;
  cs_lnum_t  cp_step = 0, viscls_step = 0;
 
  if (CS_F_(cp) != nullptr) {
    cpro_cp = (const cs_real_t *)CS_F_(cp)->val;
    cp_step = 1;
  }
  else {
    cpro_cp = &cp0;
  }
 
  /* Get thermal field and associated diffusivity
     (temperature only handled here) */
 
  const cs_field_t *fth = cs_thermal_model_field();
 
  const int viscl_id = fth->get_key_int("diffusivity_id");
 
  if (viscl_id > -1) {
    cpro_viscls = (const cs_real_t *)cs_field(viscl_id)->val;
    viscls_step = 1;
  }
  else {
    visls_0 = fth->get_key_double("diffusivity_ref");
    cpro_viscls = &visls_0;
  }
 
  const int is_temperature = fth->get_key_int("is_temperature");

Then the coefficient can be computed and assigned to all cells.

  cs_real_t sexcvo = 36.18;  /* Surface area where exchanges take
                                place by unit of volume */
  cs_real_t l0 = 0.03;       /* Characteristic length */
 
  for (cs_lnum_t i = 0; i < n_elts; i++) {
 
    cs_lnum_t c_id = elt_ids[i];
 
    cs_real_t rho = cpro_rom[c_id];
    cs_real_t mu = cpro_mu[c_id];
    cs_real_t cp = cpro_cp[c_id*cp_step];
 
    cs_real_t lambda, lambda_over_cp;
 
    if (is_temperature) {
      lambda = cpro_viscls[c_id*viscls_step];
      lambda_over_cp = lambda / cp;
    }
    else {
      lambda_over_cp = cpro_viscls[c_id*viscls_step];
      lambda =  lambda_over_cp * cp;
    }
 
    /* Compute a local molecular Prandtl **(1/3) */
 
    cs_real_t  pr = mu / lambda_over_cp;
 
    /* Compute a local Reynolds number */
 
    cs_real_t uloc = cs_math_3_norm(cvar_vel[c_id]);
    cs_real_t re = fmax(uloc*rho*l0/mu, 1.);  /* To avoid division by zero */
 
    /* Compute Nusselt number using Colburn correlation */
 
    cs_real_t nu = 0.023 * pow(re, 0.8) * cbrt(pr);
    cs_real_t h_corr = nu * lambda / l0;
 
    /* Compute hvol */
    h_vol[i] = h_corr * sexcvo;
  }

Not that in this example, no test is done on the coupling id or Syrthes instance name. The corresponding arguments can be used to apply specific computations in cas of multiple couplings.

Also, although a test is done to check if the scalar behaves as a temperature regarding multiplication by Cp for more generality, the Syrthes volume coupling currently only handles the temperature variable.