Special duties rotordynamic pumps operates with non-water fluids. They have many advantages over volumetric pumps (like wider range of operative flow rates, less friction problems, etc…) so they could find a wide approval in low viscosity non-Newtonian fluid applications. High viscous and non-Newtonian fluids are extensively used in many industrial processes, in particular in Oil and Gas applications (i.e. slurries, oil, betonites, suspensions, etc). Other field of interest for high viscous and non-Newtonian fluids include the food processing industry (tomato paste, fruit juices, etc…) and pharmaceutical applications (i.e. tooth paste, cosmetics, etc…). These fluid are characterized by different properties with respect to water, and, in some cases, also to a different rheological behavior. In literature, there is still a lack of knowledge about the behavior of centrifugal pumps handling the following kind of fluids: (i) high viscosity fluid, which are characterized by a viscosity significantly higher than water, (ii) non-Newtonian fluids, which rheology follows a non-Newtonian law. In these cases the pump performance in terms of head, flow rate and efficiency can degrade consistently. Moreover, the modification of the local Reynolds number can impact on the inner flow regime. Pump design is always carried on by considering water as working fluid and then by applying empirical correction to performance according to the actual fluid processed, so every fluid need his own empirical study. The variety of non-Newtonian fluids is huge, so that a specific fluid means a specific application, so that generic empirical studies are nearly impossible. Actually, CFD techniques allow to analyze the impact of the fluid change and the effectiveness of the design correction, without building a specific test rig for a specific fluid. A CFD sensitivity analysis was performed on an industrial food processing pump originally designed for tomato paste. The simulation campaign was focused on the modelling of the tomato sauce viscosity with respect to the correct modelling of the actual flow regime within the dynamic pump. In particular there were carried out comparison between laminar and turbulence flow models for flow regime. The CFD study showed that the increase of fluid viscosity produces effects on the pump performances coherent with those reported in literature. The pump curves obtained with non-Newtonian fluid are in agreement with those obtained with the high viscous fluids. Furthermore, similarities in the 3D flow analysis were noticed comparing high viscosity and non-Newtonian fluid confirming the similarities between the pump performance curves.