= Strong Boussinesq approximation
In the constant-property convection convention, the strong <Boussinesq approximation> supplements small relative <mass density> changes with constant <dynamic viscosity>, <thermal diffusivity>, <specific heat capacity> and <thermal expansion coefficient> throughout the modeled temperature interval. A uniform reference density replaces density in inertia and <mass conservation>, while a linear density anomaly is retained in gravitational <buoyancy>. The temperature obeys an <advection-diffusion equation> with constant coefficients. The term “strong” is not uniform across all fluid-mechanics literature: some stratified-flow treatments instead emphasize the use of a globally constant reference density. The constant-property convection usage is explained in https://courses.physics.ucsd.edu/2021/Spring/physics218c/Spiegel%20Convection.pdf .
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