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Using the Library

FLINT is designed to be embedded inside a Fortran-based reacting-flow solver. This section describes the typical workflow for:

  • Thermodynamic and transport property evaluation (ideal gas and real fluid)
  • Finite-rate chemistry
  • Chemical equilibrium

For more practical examples on how to use FLINT refers to the Examples.

Thermodynamic Properties

Both the ideal gas and real fluid models share the same module interface. The model is selected implicitly by calling the appropriate load routine; all downstream property functions operate on whichever tables are in memory.

Required Modules

use FLINT_Lib_Thermodynamic
use FLINT_Load_ThermoTransport

Ideal Gas

Loading

integer :: err
err = read_idealgas_thermo("folder")
err = read_idealgas_transport("folder") ! optional

This reads species names, molecular weights, temperature-indexed thermodynamic tables (\(c_p\), \(h\), \(s\)), and — optionally — transport tables (\(\mu\), \(k\)). Thermodynamics is also required by both finite-rate chemistry and equilibrium calculations.

Real Fluid

For single-component fluids at high pressure or near the critical point, FLINT provides a real fluid model backed by uniform 2D \((p, h)\) lookup tables.

Loading

integer :: err
err = read_realfluid_thermo("folder")
err = read_realgas_transport("folder") ! optional

read_realfluid_thermo reads the species name from phase.txt and populates a \((p, h)\) grid with density, temperature, entropy, speed of sound, \(c_p\), and two partial derivatives. read_realgas_transport populates the matching viscosity and thermal conductivity grid.

Error codes

Both routines signal errors through their integer return value:

Code read_realfluid_thermo read_realgas_transport
0 No error No error
1 phase.txt not found Transport file not found
2 Error reading phase.txt Error reading transport data
3 Thermo file not found More than one block
4 Error reading thermo file Mesh size mismatch with thermo
5 More than one block in thermo —

Property evaluation

Properties at a given state \((p, h)\) are retrieved by bilinear interpolation using ph2vars:

real(8) :: rho, T_fluid, spd

rho      = ph2vars(p, h, rho_tab)
T_fluid  = ph2vars(p, h, T_tab)
spd      = ph2vars(p, h, sound_tab)

Available tables exposed by FLINT_Lib_Thermodynamic:

Table Property Unit
rho_tab Density kg/m³
T_tab Temperature K
dT_tab \((\partial\rho/\partial T)_p\) kg/(m³·K)
hT_tab \(c_p = (\partial h/\partial T)_p\) J/(kg·K)
s_tab2D Specific entropy J/(kg·K)
rp_tab \((\partial\rho/\partial p)_h\) kg/(m³·Pa)
sound_tab Speed of sound m/s
mi_tab2D Dynamic viscosity Pa·s
k_tab2D Thermal conductivity W/(m·K)

To initialise from primitive variables \((p, T)\) rather than \((p, h)\), convert with pT2h before querying the tables:

real(8) :: h_init
h_init = pT2h(p, T)

Source Files

  • src/lib/Load_ThermoTransport.f90
  • src/lib/Lib_ThermoTransport.f90

Finite-Rate Chemistry

Finite-rate chemistry requires both thermodynamic and reaction data.

Required Modules

use FLINT_Load_Chemistry
use FLINT_Lib_Chemistry_rhs
use FLINT_Lib_Chemistry_wdot

Loading Chemistry Data

err = read_chemistry( "folder", mech_name )

This reads:

  • Mechanism name (mech_name)
  • Reaction definitions
  • Arrhenius tables
  • Falloff tables (Lindemann, Troe)
  • Third-body efficiencies

Computing Species Source Terms

To compute net production rates:

call Chemistry_Source(T, rhoi, wdot)

where:

  • T = temperature
  • rhoi = species partial densities
  • wdot = species production rates

This subroutine is built upon an abstract interface and a pointer concretization. At runtime, the pointer procedure is assigned to one of the subroutine realizations. These are divided into:

  • a general routine:

-- mechanism loaded at runtime
-- flexible
-- slightly slower

  • several explicit routines:

  • hard-coded Fortran kernels

  • maximum performance
  • recommended for production

Explicit routines are generated using the mechanism generation tool. See Chemistry Database and Chemistry Generation for more details.

RHS Evaluation for ODE Integration

For batch reactor simulations:

call Chemistry_RHS(...)

This routine computes the full time derivative vector composed of species and temperature evolution.

Source Files

  • src/lib/Lib_ChemMech/
  • src/lib/Load_Chemistry.f90
  • src/lib/Lib_Chemistry_data.f90
  • src/lib/Lib_Chemistry_wdot.f90
  • src/lib/Lib_Chemistry_rhs.f90

Chemical Equilibrium (CEA Solver)

FLINT provides a NASA-CEA-based equilibrium solver.

Required Modules

use FLINT_CEA_setup
use FLINT_CEA_solver

Thermodynamic data must be loaded before using the equilibrium solver.

Initialization

call CEA_initialize_global()

Solving Equilibrium

call CEA_solve(T_initial, rhoi, T_eq, y_eq)

Inputs:

  • T_initial — initial temperature
  • rhoi — initial partial densities

Outputs:

  • T_eq — equilibrium temperature
  • y_eq — equilibrium mass fractions

The solver performs constant-volume (UV) equilibrium.

Source Files

  • src/lib/Lib_CEA_data.f90
  • src/lib/Lib_CEA_setup.f90
  • src/lib/Lib_CEA_solver.f90

Optional Cantera Interface

FLINT can interface with Cantera for validation purposes.

Cantera is:

  • Optional
  • Not required for production runs
  • Used for verification and benchmarking

When enabled, Cantera routines can be used to compute:

  • Thermodynamic properties
  • Net production rates
  • Reactor integration results

The FLINT native implementation is the intended production backend.

See the Cantera documentation about Fortran interface for more details on this topic.