The annular centrifugal contactor has been developed for solvent extraction processes used in the reprocessing of spent nuclear fuel. The compact size and high efficiency of these contactors have made them the choice for advanced reprocessing schemes and the central equipment for a future advanced fuel cycle facility. While a sufficient base of experience exists to facilitate successful operation of current contactor technology, a more complete understanding of the fluid flow within the contactor would enable further advancements in design and operation of future units and greater confidence for use of such contactors in a variety of other solvent extraction applications. This research effort has coupled computational fluid dynamics modeling with experimental measurements and observations to provide a valid detailed analysis of the flow within the centrifugal contactor. CFD modeling of the free surface flow in the annular mixing zone using the Volume of Fluid (VOF) volume tracking method combined with Large Eddy Simulation (LES) of turbulence was found to have very good agreement with the experimental measurements and observations. From this, detailed study of the flow and mixing for different housing vane geometries was performed. Flow within the separation zone was also modeled providing a useful description of the flow in this region and identifying critical design features which are the cause of specific experimentally observed effects. It is anticipated that this work will form a foundation for additional efforts at improving the design and operation of centrifugal contactors and provide a framework for progress towards simulation of solvent extraction processes.