Flow investigations of reverse running volute pumps with backward vanes in comparison to forward type turbine vanes

The use of centrifugal pumps as turbines in the recent years has come as a boon to small and micro power application given its simplicity and robustness. However, attempts are continuously being made to improve the performance by modifying the geometry, and yet to retain its simpleness. This paper proposes a new design to the impeller of an existing pump with forward-shaped vanes in an unchanged volute that is in complete contrast to the conventional backward vanes. Three methodologies are involved in the analysis starting with classical theory, experiment and simulations. The theory entails the focus on optimizing the nozzle shape of the impeller to reduce viscous and eddies. The forward vane having shorter nozzle length has proved to be more efficient compared to the longer backward vane impeller, with an efficiency increase of nearly 5%. The experimental and CFD analysis to study the internal flow saw similitude in the streamline change in Euler moment. It also showed that there were not only increased viscous effects but also enhanced flow separation in the backward vanes at overload flows. The study also found radial clearance losses to be unacceptable for both the shapes. The overall conclusion was to move ahead with the forward design and convince the industry to adopt them for there have been greater strides in cost-effective manufacturing processes. The paper also recommends more study of intermediate blade angles since there was still persistence of small degree of vorticities in the forward blade nozzle. The optimization of volute-impeller interface along with the influence of non-flow zone would be other areas for future investigation. Synergy of academia and industry is also welcome to lend improved understanding in pumps as turbines and better translation to praxis.