The computation of a compressible flow will affect pressure, density and temperature, which are usually related to each other through the ideal gas law. With that in mind, modeling compressible flows in CFD-ACE+ requires a few specific settings that are described below.

In compressible flows, one important quantity is the speed of sound, a, which in CFD-ACE+ is calculated as

G and R are calculated as follows:

The molar mass (referred to as "Molecular Weight" in CFD-ACE-GUI), M, is specified by the user under the 'VC/Phys' tab when the VC Setting Mode is set to "Properties". The specification M is automatically available when the Flow Module is activated.

The specific heat at constant pressure, C_p, is specified by the user under the 'VC/Therm' tab when the VC Setting Mode is set to "Properties". The specification of Cp requires the Heat Module to be activated.

Alternatively, if Chemistry/Mixing is used and the Material (i.e. Gas) is imported from the Database Manager, M and Cp will be taken from the Database.

Figure 1.  Database Manager: Species Molar Mass.

M is also necessary for the computation of the ideal gas law:

Finally, and probably most importantly, for the simulation to be correct, the energy transfer arising from Work done on the gas needs to be taken into account in the compuation, and this requires the Heat Module to be activated.

Note: tested with V2010.0