Erosion affects the geometry of the Centrifugal pump. I don't think there is an option to add its effects in ANSYS Fluent directly.
I believe you should first analyze how the erosion alters the geometry of the pump over time, and then simulate these different geometries one by one to compare their results.
As one researcher/expert has suggested, the erosion effect can be incorporated in geometry for simulation. The baseline simulation can be done with no-erosion and geometry matching to the drawing minus manufacturing deviations. With known erosion level or expected erosion for a specific period in service (at mid life as well as at end of life) the geometry can be suitably redrawn and simulation program can be run. The history, trend and service feedback of erosion help in redrawing the controlling geometry.