### 16.2.4. Variables Relevant for Compressible Flow

The following table contains a list of variables (with both long and short variable names) that can be used when working with compressible flows.

Note: Variables with names shown in bold text are not output to CFD-Post. However, some of these variables can be output to CFD-Post by selecting them from the Extra Output Variables List on the Results tab of the Solver > Output Control details view of CFX-Pre.

Long Variable Name | Short Variable Name | Units | Availability | Definition
--- | --- | --- | --- | ---
Isobaric Compressibility | compisoP | [K^-1] | 2 C, M, R |
Isothermal Compressibility | compisoT | [m s^2 kg^-1] | 2 C, M, R | Defines the rate of change of the system volume with pressure.
Mach Number | Mach | [ ] | 1 A, C, M, R, TS | For details, see List of Symbols in the CFX-Solver Theory Guide.
Shock Indicator | shock indicator | [ ] | 2 A, C, M, R, TS | The variable takes a value of 0 away from a shock and a value of 1 in the vicinity of a shock. This variable is available only if Solver Control > Advanced Options > Compressibility Control > High Speed Numerics is selected.
Isentropic Compressibility | compisoS | [m s^2 kg^-1] | 2 C, M, R | The extent to which a material reduces its volume when it is subjected to compressive stresses at a constant value of entropy.

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