Name: SpectraSim
Availability: InStock

Theory

The value enters:

the energy equation of the compressible solver (hConst thermodynamics, $h = c_p (T - T_\mathrm{std})$ (OpenFOAM user guide, 2026));
the heat balance of heat-transfer runs;
the ratio of heat capacities, equation (1), which sets the speed of sound in the acoustics.

It must exceed the specific gas constant; otherwise $c_v = c_p - R$ would not be positive, equation (2).

Equations

\gamma = \frac{c_p}{c_p - R}

(1)

c_v = c_p - R > 0, \qquad R = \frac{\mathcal{R}}{M}

(2)

where	meaning	unit
$c_p$	Specific heat capacity at constant pressure	J/(kg K)
$c_v$	Specific heat capacity at constant volume	J/(kg K)
$\gamma$	Ratio of heat capacities	-
$R$	Specific gas constant	J/(kg K)
$\mathcal{R}$	Universal gas constant, 8314.47	J/(kmol K)
$M$	Molar mass	kg/kmol

Default: 1006 (air) in a new material
Rule: A new material starts at 1006 J/(kg K) (air at room temperature).
Source: Ideal-gas relations; the hConst thermodynamics of OpenFOAM (OpenFOAM user guide, 2026).

Lower bound

Above $R$ : a monatomic gas has $c_p = 2.5 R$ , a diatomic gas about $3.5 R$ .