### 1.3.2. Boussinesq Model

For buoyant flows where the density variation is driven only by small temperature variations, the Boussinesq model is used. In this model, a constant reference density is used for all terms other than the buoyancy source term. The buoyancy source term is approximated as:

| (1–129)

where is the thermal expansivity:

| (1–130)

and is the buoyancy reference temperature.

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