Static pressure (absolute)

material.operating.p_abs Unit: Pa Step 04 · Material

The absolute static pressure of the gas, the operating pressure. The panel beside it lists the gas properties at this pressure and the gas temperature: density, speed of sound, characteristic impedance, viscosities and the ratio of specific heats.

Last updated 2026-11-04

Theory

The density and the characteristic impedance scale with the pressure; the speed of sound and the dynamic viscosity do not, so the kinematic viscosity falls as the pressure rises. A pressurised gas therefore has thinner viscous boundary layers in small holes: the perforate constant $k$ of a micro-perforated plate rises with the pressure. The panel states the factor by which $k$ of the same hole at the same frequency differs from dry air at 1 atm and 20 °C.

Equations

\rho = \frac{p_{op}\,M}{\mathcal{R}\,T}, \qquad c = \sqrt{\gamma(T)\,\frac{\mathcal{R}}{M}\,T}, \qquad \nu = \frac{\mu(T)}{\rho}

(1)

where	meaning	unit
$\rho$	Density	kg/m³
$p_{op}$	Operating static pressure	Pa
$M$	Molar mass of the gas	kg/kmol
$\mathcal{R}$	Universal gas constant, 8314.47	J/(kmol K)
$T$	Gas temperature	K
$c$	Speed of sound	m/s
$\gamma$	Ratio of specific heats at $T$	-
$\nu$	Kinematic viscosity	m²/s
$\mu$	Dynamic viscosity (Sutherland)	Pa s

\frac{k}{k_{ref}} = \sqrt{\frac{\nu_{ref}}{\nu}}

(2)

where	meaning	unit
$k/k_{ref}$	Ratio of the perforate constant to its value in dry air at 1 atm, 20 °C	-
$\nu_{ref}$	Kinematic viscosity of dry air at 1 atm, 20 °C	m²/s

Default and rule

Default: ambient pressure + gauge pressure
Rule: Computed from the ambient pressure and the gauge pressure.
Source: The ideal-gas relations of the program's gas model.

Valid range at least 20 kPa

Typed or read-only

It can be typed only when the flow is not solved; then the gauge value is stored.

Theory

Equations

Default and rule

Valid range at least 20 kPa

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