Purpose

Choose the compressibility treatment appropriate to the flow speed and physics.

Steps

1. Estimate the expected flow speed relative to the speed of sound.

   

2. Choose the incompressible, subsonic compressible, or high-speed compressible option in Flow type as appropriate.
3. Review material, pressure, temperature, boundary, and time settings after changing the flow type.

Inputs and units

Input or value	Meaning	Units
Mach number M	Velocity divided by local speed of sound; low-speed flow below about 0.3 is commonly treated as incompressible.	Dimensionless
Flow type	The selected compressibility / solver family.	No physical units

Limitations

• Use high-speed compressible mode for high-speed flows, including flows at and above Mach 1. Gas mixture cases require subsonic compressible flow. Supported model combinations and inlet checks may restrict a selection.

Related topics

• Materials
• Boundaries
• Iterations
• Mixture