Simple decompression test case


This test case aims to prove correlation for a simple three volumes rapid decompression.

Equations, and even physics, are not the same at all between 1D thermodynamical study and 3D CFD csimulation ; it would therefore be naive to expect an exact correlation between them. However on a simple case, it is very interesting and informative to correlate one against the other.


The model consists of three chained volumes of 3m³, connected via 0.5m² orifices.

The cabin parameters are defined as follows:

  • \(P = 1 bar\)
  • \(T = 296 K (22.85 degC)\)

The atmosphere is defined as follows:

  • \(P = 0.2 bar (alt=11.806 km)\)
  • \(T = 216.66 K (-56.49 degC)\)

model definition

CFD study

The CFD study is performed with openFoam ( The solver used is the transient sonic compressible solver called “sonicFoam”.

Mesh for the CFD study

numeric internal decompression software

numeric‘s decompression program was run using the isentropic engine, based on the parameters described above.

As per common references, the discharge coefficient should be taken between 0.61 and 0.8. Two analysis were performed simulating two different discharge coefficients for internal vents.

Compared Results

To extract values from the CFD results, two cells per volume (close to volume center) were selected and averaged.

Correlations in pressure

correlation in pressures

Pressures from the CFD are clearly included inside the tiny pressures envelop given by the two analysis A0 and A1. CFD fits perfectly into it.


The DeltaP are the most use full values for a decompression analysis:

correlation in Delta pressures

Correlations in temperature

Temperature are expected to correlate more badly, compared to pressure, since the unique parameter taken into account is the gas detent (thus pressure and mass), whereas the CFD will also take into account the calories transfer dur to massflows.

correlation in temperature


The correlations are really good with pressures using the regular Discharge Coefficients.


Tags cloud

Links and friends