An explanation of how the gravitational body force term is formulated in FLUENT
Questions have arisen from time to time about how FLUENT 6 treats the gravitational body force term. A derivation and explanation of this is provided in the pdf document (below).
A complete explanation of the formulation of the gravitational body force term can be found in the following pdf document: http://www.eureka.im/downloads/gravity_body_force.pdf In brief, the document shows how the "modified" pressure (which absorbs a constant gravitational body force term) is obtained, and how the formulation differs for incompressible and compressible flows. Finally, an equation is provided for computing the absolute pressure using the computed modified pressure. This equation can be easily programmed as a custom field function in FLUENT. 

