Variables and properties can be accessed using the cs_field API.

First, let us specify a few conventions used in code_saturne:

The dynamic variables designation includes velocity, pressure, and variables related to the turbulence model (k, ε, R_ij, ω, ϕ, $\overline{f}$ , α, ν_t).
The designation “scalar” refers to (usually scalar) variables which are solution of an advection equation, apart from the dynamic variables listed above; for instance the temperature, scalars which may be passive or not, user-defined or model-defined.

The mean value of the square of the fluctuations of a “scalar” is a “scalar”, too.

Scalars may be divided into two groups: user-defined scalars and model-defined (sometimes referred to as “specific physics”) scalars.
Depending on the thermal model used; the solved thermal scalar variable may be the temperature, the enthalpy, or in the case of the compressible module, the total energy. When the temperature is not the solved thermal variable, it is usually available as a property.
When a user scalar represents the mean of the square of the fluctuations of another scalar (i.e. the average $\overline{\varphi^\prime\varphi^\prime}$ for a fluctuating scalar ϕ). This can be made either via the interface or by declaring that scalar using cs_parameters_add_variable_variance in cs_user_parameters.c.

Accessing variables and properties in C:

The most general way of accessing a field is to use its name:

cs_real_t *cvar_pr = cs_field_by_name("pressure")->val;
then:
cvar_pr[cell_id]
The main variables and properties can be accessed using the CS_F_ macro:
- For one-dimensional arrays:
  pressure = CS_F_(p)->val[cell_id],
  cp = CS_F_(cp)->val[cell_id]
  temp = CS_F_(t)->val[cell_id]
- For multidimensional arrays:
  uz = CS_F_(vel)->val[3*cell_id + 2]
  
  These arrays can also be cast as follows (for a 3-D array):
  cs_real_3_t *cvar_vel = (cs_real_3_t *)CS_F_(vel)->val
  
  The cell value can then be accessed as
  ux = cvar_vel[cell_id][0]
  
  vel, p, or cp are defined in cs_field_pointer.h.
Indexed variables (such as user scalars) and indexed properties are accessed as:
CS_FI_(name,ii-1)->val[cell_id].
The thermal scalar can be accessed using the cs_thermal_model_field function:
field_t *tf = cs_thermal_model_field();
then:
tf->val[cell_id].
if there is no thermal scalar, cs_thermal_model_field returns NULL.
In any case, all variables can be accessed using the function cs_field_by_name :
cs_real_t *cvar_pr = cs_field_by_name("pressure")->val
A field's scalar_id key-word should be ≥ 0 if it is a scalar.
When a field is user-defined (rather than model-defined), its type flag should also match the CS_FIELD_USER mask:
if (f->type & CS_FIELD_USER) ...

Remarks: Note that indexes in C begin at 0.

Cross-reference tables are available for the variables and properties of the standard solver and the specific physics features:

Variables

The C variables names are defined in cs_field_pointer.h.
Note that dt is accessible by its name (using the cs_field_by_name family of functions), but not through a permanent index..

C code	Description
`CS_F_(p)->val`	`Pressure`
`CS_F_(vel)->val`	`Velocity`
`CS_F_(void_f)->val`	`Void fraction for Volume of Fluid model`
`CS_F_(k)->val`	`Turbulent kinetic energy`
`CS_F_(eps)->val`	`Turbulent dissipation`
`CS_F_(rij)->val`	`Reynolds stress tensor (symmetric components, in the following order for each cell: xx, yy, zz, xy, yz, xz)`
`CS_F_(phi)->val`	`for model`
`CS_F_(f_bar)->val`	`for model`
`CS_F_(alp_bl)->val`	`for or EBRSM model`
`CS_F_(omg)->val`	`for SST model`
`CS_F_(nusa)->val`	`for Spalart-Allmaras`
`CS_F_(mesh_u)->val`	`Mesh velocity`
`CS_F_(h)->val`	`Enthalpy`
`CS_F_(t)->val`	`Temperature`

Properties

These properties are defined in cs_field_pointer.h.

C code	Description
`CS_F_(dt)->val`	`Local time step`
`CS_F_(mu)->val`	`Molecular viscosity`
`CS_F_(mu_t)->val`	`Turbulent dynamic viscosity`
`CS_F_(cp)->val`	`Specific heat`
`CS_F_(rho)->val`	`Density (at cells)`
`CS_F_(rho_b)->val[face_id]`	`Density (at boundary faces)`
`cs_real_t *cpro_smago = cs_field_by_name("smagorinsky_constant^2")->val`	`Field id of the anisotropic turbulent viscosity`
`cs_real_t *cpro_cour = cs_field_by_name("courant_number")->val`	`Courant number`
`cs_real_t *cpro_four = cs_field_by_name("fourier_number")->val`	`Fourier number`
`cs_real_t *cpro_prtot = cs_field_by_name("total_pressure")->val`	`Total pressure at cell centers`
`cs_real_t *cpro_visma_s = cs_field_by_name("mesh_viscosity")->val`	`Mesh velocity viscosity (scalar) for the ALE module`
`cs_real_t *cpro_visma_v = cs_field_by_name("mesh_viscosity")->val`	`Mesh velocity viscosity (vector) for the ALE module`
`cs_real_t *cpro_tsrho = cs_field_by_name("dila_st")->val`	`Global dilatation source terms`
`cs_real_t *cpro_beta = cs_field_by_name("thermal_expansion")->val`	`Thermal expansion coefficient`
`CS_F_(poro)->val`	`Porosity`
`CS_F_(t_poro)->val`	`Tensorial porosity`
`cs_real_t *bpro_forbr = cs_field_by_name("boundary_forces")->val`	`Field id of the stresses at boundary`
`cs_real_t *bpro_yplus = cs_field_by_name("yplus")->val`	`Field id of at boundary`
`cs_real_t *dttens = cs_field_by_name("dttens")->val`	`Field id for the dttens tensor`
`CS_F_(t_b)->val`	`Boundary temperature`

Some physical properties such as specific heat or dynamic diffusivity are often constant (depending on the model or user parameters). In that case, these properties are stored as a simple real numbers rather than in a field over all mesh cells.

This is the case for the specific heat C_p.
- If C_p is constant, it is based on the reference value cs_glob_fluid_properties->cp0.
  When this is the case, cs_glob_fluid_properties->icp should remain set to 0.
  When icp is initialized to 1 (by the GUI, or in cs_user_parameters.c, it is automatically reset to the id of the cell-based property field referenced in the above table.
This is the same for the dynamic diffusivity K of each scalar.
- When K is constant, its value is based on the field's reference dynamic diffusivity, accessible through the scalar field's diffusivity_ref keyword.
  
  When it is variable, the matching field can be specified and accessed using the base scalar field's diffusivity_id key (accessible using cs_field_key_id("diffusivity_id")).
  For example, for a scalar field f:
  int k_f_id = cs_field_get_key_int(f, cs_field_key_id("diffusivity_id")); cs_field_t *kf = cs_field_by_id(k_f_id);

Reference physical values

Reference physical values represent either the fluid properties if they are constant, either simple mean values for the initialization if properties are variable and defined in cs_user_physical_properties. Reference values can be set in the GUI or in cs_user_parameters.c.

C code	Description
`cs_glob_fluid_properties->p0`	Reference total pressure
`cs_glob_fluid_properties->ro0`	Reference density
`cs_glob_fluid_properties->viscl0`	Reference molecular dynamic viscosity
`cs_glob_fluid_properties->cp0`	Reference specific heat

Specific physical models

Atmospheric

Defined in cs_field_pointer.h. Note, esp_id = iesp -1.

C code	Description
`CS_F_(pot_t)->val`	Potential temperature
`CS_F_(ym_w)->val`	Total water content
`CS_F_(ntdrp)->val`	Total number of droplets
`CS_FI_(chemistry,esp_id)->val`	Chemistry species (indexed)

Coal combustion

Defined in cs_field_pointer.h. Note, esp_id = iesp -1.

C code	Description
`CS_FI_(np,esp_id)->val`	Particles per kg for coal class
`CS_FI_(xch,esp_id)->val`	Reactive coal mass fraction for coal class
`CS_FI_(xck,esp_id)->val`	Coke mass fraction for coal class
`CS_FI_(xwt,esp_id)->val`	Water mass fraction for coal class
`CS_FI_(h2,esp_id)->val`	Mass enthalpy for coal class (permeatic case)
`CS_FI_(f1m,esp_id)->val`	Mean value light volatiles for coal class
`CS_FI_(f2m,esp_id)->val`	Mean value heavy volatiles for coal class
`CS_F_(f4m)->val`	Oxydant 2 mass fraction
`CS_F_(f5m)->val`	Oxydant 3 mass fraction
`CS_F_(f6m)->val`	Water from coal drying mass fraction
`CS_F_(f7m)->val`	Carbon from coal oxidyzed by O2 mass fraction
`CS_F_(f8m)->val`	Carbon from coal gasified by CO2 mass fraction
`CS_F_(f9m)->val`	Carbon from coal gasified by H2O mass fraction
`CS_F_(fvp2m)->val`	f1f2 variance
`CS_F_(yco2)->val`	CO2 fraction
`CS_F_(yhcn)->val`	HCN fraction
`CS_F_(yno)->val`	NO fraction
`CS_F_(ynh3)->val`	NH3 enthalpy
`CS_F_(hox)->val`	Ox enthalpy

Compressible

Defined in cs_field_pointer.h.

C code	Description
`CS_F_(e_tot)->val`	`Total energy`
`CS_F_(t_kelvin)->val`	`Temperature, in Kelvin`

Electric arcs

Defined in cs_field_pointer.h. Note, esp_id = iesp -1.

C code	Description
`CS_F_(potr)->val`	`Electric potential, real part`
`CS_F_(poti)->val`	`Electric potential, imaginary part`
`CS_F_(potva)->val`	`Vector potential`
`CS_FI_(ycoel,esp_id)->val`	`Constituent mass fraction`

Gas combustion

Defined in cs_field_pointer.h.

C code	Description
`CS_F_(fm)->val`	`Mixture fraction`
`CS_F_(fp2m)->val`	`Mixture fraction variance`
`CS_F_(fsm)->val`	`Soot mass fraction`
`CS_F_(npm)->val`	`Soot precursor number`
`CS_F_(ygfm)->val`	`Fresh gas fraction`
`CS_F_(yfm)->val`	`Mass fraction`
`CS_F_(yfp2m)->val`	`Mass fraction variance`
`CS_F_(coyfp)->val`	`Mass fraction covariance`

Radiative transfer

Defined in cs_field_pointer.h. Note, esp_id = iesp -1.

C code	Description
`CS_F_(rad_energy)->val`	Radiative luminance
`CS_F_(rad_q)->val`	Radiative flux
`CS_FI_(rad_ets,esp_id)->val`	Radiative flux explicit source term
`CS_FI_(rad_its,esp_id)->val`	Radiative flux implicit source term
`CS_FI_(rad_abs,esp_id)->val`	Radiative absorption
`CS_FI_(rad_emi,esp_id)->val`	Radiative emission
`CS_FI_(rad_cak,esp_id)->val`	Radiative absorption coefficient
`CS_F_(qinci)->val`	Radiative incident radiative flux density
`CS_F_(xlam)->val`	Wall thermal conductivity
`CS_F_(epa)->val`	Wall thickness
`CS_F_(emissivity)->val`	Wall emissivity
`CS_F_(fnet)->val`	Boundary radiative flux
`CS_F_(fconv)->val`	Boundary radiative convective flux
`CS_F_(hconv)->val`	Radiative exchange coefficient

Eulerian-Eulerian multiphase flows

Defined in cs_field_pointer.h.

C code	Description
`CS_FI_(yf_ncond,inc)->val`	Non-condensable gas mass fractions
`CS_FI_(qp,ip)->val`	Particles turbulent kinetic energy Q2
`CS_FI_(qfp,ip)->val`	Covariance of the turbulent Q12
`CS_FI_(qfpxx,ip)->val`	XX component of qfp
`CS_FI_(qfpxy,ip)->val`	XY component of qfp
`CS_FI_(qfpxz,ip)->val`	XZ component of qfp
`CS_FI_(qfpyx,ip)->val`	YX component of qfp
`CS_FI_(qfpyy,ip)->val`	YY component of qfp
`CS_FI_(qfpyz,ip)->val`	YZ component of qfp
`CS_FI_(qfpzx,ip)->val`	ZX component of qfp
`CS_FI_(qfpzy,ip)->val`	ZY component of qfp
`CS_FI_(qfpzz,ip)->val`	ZZ component of qfp
`CS_FI_(gamma,ip)->val`	Interfacial mass transfer
`CS_FI_(ia,ip)->val`	Interfacial area
`CS_FI_(x2,ip)->val`	Droplets x2
`CS_FI_(d32,ip)->val`	Droplets Sauter mean diameter
`CS_FI_(drag,ipcpl)->val`	Drag between phases
`CS_FI_(ad_mass,ip)->val`	Added mass
`CS_FI_(th_diff,ip)->val`	Thermal dynamic diffusivity ( $kg.m^{-1}.s^{-1}$ )
`CS_FI_(th_diff_t,ip)->val`	Turbulent thermal dynamic diffusivity ( $kg.m^{-1}.s^{-1}$ )
`CS_FI_(drho_dp,ip)->val`	dRho over dP
`CS_FI_(drho_dh,ip)->val`	dRho over dH
`CS_FI_(tau12_t,ip)->val`	Turbulent tau12 for particles
`CS_FI_(lift,ip)->val`	Particles lift
`CS_FI_(disp_t,ip)->val`	Particles turbulent dispersion
`CS_FI_(drift_vel,ip)->val`	Particles drift velocity

Liste of reserved advanded field names.

A list can be found in liste of predefined fields.