This paper presents a detailed hydraulic analysis of the effects of the casing eye rib on a pump operating as a turbine. It describes a flow-zone approach within a pump as turbine and lays out the build up for the experimental and numerical techniques applied. The pump as turbine exhibits very good characteristics with a maximum operating efficiency over 82%. The similitude between experimental and numerical results has been satisfactory. The two stages namely the ‘casing rib present’ and the ‘casing rib absent’ stage are compared at 6 different load points encompassing the entire characteristics. Both methods reveal that the performance of the PAT has enhanced without the presence of the rib. However the two methods show different causes for this behaviour. The comparison of the swirl profiles reveal that the fluid in the ‘casing rib absent’ stage has greater rotational momentum in the part-load and overload region compared to the ‘casing rib present’ stage. However the ‘casing rib absent stage’ displays more symmetric swirl profiles. At the end of the paper, an uncertainly analysis for the experimental efficiency is carried out.

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