Boussinesq approximation is a method to approximate buoyancy caused by temperature difference in incompressible fluid.

Using Boussinesq approximation, buoyancy caused by changes in density is expressed with the following equation:

ρ0 : Density for reference temperature [kg/m3]
g : Gravitational acceleration [m/s²]
β : Coefficient of thermal expansion [1/K]
T : Temperature [K]
T0 : Reference temperature [K]

When temperature change is large and momentum change accompanying density change is too big to ignore, approximation error difference becomes large.

Boussinesq approximation is named after a French physicist Joseph Valentin Boussinesq.