Theoretical work addition is derived in a form analogous to that of classical Rayleigh heat addition. From this derivation it is evident that work terms can be added to the Navier- Stokes momentum and energy equations representing work interaction. A second-law-based effectiveness parameter controlling the ratio of realizable work interaction to the ideal work interaction is required for nonideal analysis. Thus, the theoretical limits on work interaction are parameterized, and a method is developed for easily modeling isentropic and non-isentropic work interaction in computational fluid dynamics. This fundamental theoretical approach is independent of the method employed for the work interaction, that is, turbomachinery, magnetohydrodynamics, etc....