## 1.3. Buoyancy

For buoyancy calculations, a source term is added to the momentum equations as follows:

| (1–127)

The density difference is evaluated using either the Full Buoyancy model or the Boussinesq model, depending on the physics.

When buoyancy is activated, the pressure in the momentum equation excludes the hydrostatic gradient due to . This pressure is related to the absolute pressure as follows:

| (1–128)

where is a reference location. The buoyancy reference location option is set under the `Ref. Location` option in CFX-Pre and can be set to a particular location. For details, see Buoyancy and Pressure.

Absolute pressure is used to evaluate fluid properties that are functions of pressure; it can be visualized in CFD-Post.

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