One-Dimensional Prediction and Three-Dimensional CFD Simulation of the Fluid Dynamics of Regenerative Pumps

Regenerative pumps, also referred to as “peripheral” or “side channel” pumps, are characterized by a specific speed that contextualize them between rotary positive displacement and purely radial centrifugal pumps. Although regenerative pumps are not widely distributed, they are interesting for many industrial applications. In fact, for a given flow rate they operate at lower rotational speed with respect to purely radial pumps. Furthermore, they are less affected by mechanical problems with respect to positive displacement pumps. The energy transfer mechanism is the same of centrifugal pumps, but the presence of the side channel imposes to the fluid to pass several times through the impeller, thus obtaining higher pressure rise (as for multi-stage machines) with respect to classical purely radial pumps. Unfortunately, the complexity of the flow field, the large amount of wetted surface and a disadvantageous inflow/outflow configuration contribute to limit the maximum value of hydraulic efficiency, which is also very sensitive to the design choices. Moreover, the intrinsic complexity of the helical flow path makes the theoretical performance estimation a challenging task. It is worth underlining that an accurate performance prediction using one-dimensional models would allow to accelerate greatly the design process, with a non-negligible reduction of demanding three-dimensional Computational Fluid Dynamics (CFD) campaigns. The aim of the present work is to deeply investigate the fluid dynamics of regenerative pumps and to understand how accurately the fundamental physical phenomena can be reproduced by one-dimensional theory. To comply with these aims, a systematic post-processing of the results of several steady and unsteady three-dimensional CFD simulations is exploited for the validation of the in-house one-dimensional tool DART (Design and Analysis tool for Regenerative Turbomachinery), developed at the University of Florence. The theory underlying DART is detailed, and the assumptions of the model are verified by means of comparison with the numerical results underlining the key aspects to be considered for a reliable prediction of the pump performance.