Transport Properties and Material Closures

User purpose. This page explains the fluid-property methods selectable in the Materials GUI and how viscosity, conductivity and diffusion laws affect the coupled solution. Use it together with the thermochemistry chapter to distinguish caloric properties from transport properties.

Heat capacity and sensible thermodynamics

Fluid heat capacity is evaluated as either a constant or a piecewise temperature polynomial. In polynomial range ,

The evaluator uses Horner form,

and clamps temperature to the nearest endpoint outside the complete range. The polynomial enthalpy is integrated analytically,

For constant heat capacity, . The EOS determines the corresponding :

The complete EOS relations are documented in Equations of State and Caloric Models.

Dynamic viscosity

The active fluid-material state accepts constant, piecewise-polynomial, Gupta-type and Sutherland viscosity closures. A polynomial range uses

The Sutherland form is

The Gupta-type viscosity correlation is

Polynomial viscosity is clamped to the nearest valid endpoint when lies outside the total property range.

Thermal conductivity

Thermal conductivity may be constant, piecewise polynomial, kinetic-theory based, or Gupta-type. The polynomial form is

The kinetic-theory option used by the fluid material class is

The Gupta-type conductivity law is

For GE turbulence, turbulent conductivity is added as

Species diffusion

The laminar material/mixture diffusion coefficient is augmented by turbulent species diffusion when GE turbulence is active. The turbulent diffusivity is

At an internal face, the laminar and turbulent diffusivities are independently harmonically interpolated. For a generic coefficient and ,

The independent-species face flux is the sum of the orthogonal and non-orthogonal contributions,

The density multiplying the diffusive coefficient is selected from the carrier upwind side. Species enthalpy diffusion contributes to the thermal/energy row through

For the constant-density system, the dependent-species enthalpy is subtracted in this energy coupling so that the eliminated composition constraint is respected.

Species-mixture and VOF mixture rules

For a reacting ideal-gas species mixture with mass fractions ,

The mixture molecular weight follows

For an ideal-gas mixture,

The homogeneous VOF material state is different: each constituent is evaluated at common pressure and temperature and volumetric quantities are volume-fraction weighted,

Mass-specific mixture enthalpy is obtained from the volumetric sum,

Property admissibility

Before solving, the material state validates the property method and the resulting state. The basic admissibility set includes

together with finite EOS derivatives. Stiffened-gas materials additionally require , and . The property evaluator does not silently convert an unsupported generic property method into an active fluid closure.