Add a Domain Sources node to define the mass source, volume force source, and heat source, the right-hand-side of Equation 4-2. These can, for example, model varying thermal sources in a combustion chamber or a pulsating laser. Notice that the mass source term enters both the continuity and the momentum equation, this results from a consistent derivation of the governing equations. A mass source term will, when convected also result in a momentum source.