The method for determining blade inlet angle of special impeller using in turbine mode of centrifugal pump as turbine

Due to that the conventional backward-curved blades centrifugal impellers do not effectively match the turbine's running, the performance of the pump-as-turbine (PAT) was usually not ideal. Therefore, to improve significantly the performance of PAT, one kind of special impeller with forward-curved blades was designed for the turbine's working condition, and the method for determining blade inlet angle that played important role in the energy conversion was also studied deeply in this paper. Moreover, four forward-curved blades impellers with different blade inlet angles were numerically investigated by using a verified computational fluid dynamics (CFD) technique, and relevant external characteristic experiments were also conducted to benchmark the numerical calculation. Based on the results, the flow rate of numerical best efficiency point (BEP) is very close to that of theoretical BEP, and the flow rate of BEP increases with extending the blade inlet angles. Additionally, the energy loss within the impeller reaches the minimum if suitable blade inlet angle is selected, so the value of blade inlet angle is recommended in a reasonable range in special impeller used in turbine mode of PAT. Furthermore, compared with the original backward-curved blades impeller, the maximum efficiency of the forward-curved blades impeller increases from 59.98% to 67.91%, and the flow-efficiency curve is more flat, which reflects that the forward-curved blades impeller in the PAT has obvious superiority. This paper is very instructive to the design of the special impeller using in the PAT.