Numerical research on impeller diameter influencing the performance of hydraulic turbine with forward-curved blades

In the practical application of hydraulic turbine, when the pressure head or the flow rates deviating from the high efficiency area, trimming the impeller or replacing the impeller with a smaller size impeller is a convenient way. It is necessary to research the impeller diameter of the curved impeller on the performance of the hydraulic turbine. Experiment is carried out on a single-stage centrifugal PAT. The results of experiment and the results of computational fluid dynamics(CFD) simulation are very close, verifying the accuracy of CFD simulation. The performance curves of three different impeller diameters of hydraulic turbine are obtained by using CFD simulation. It can be seen from the figure that, with the impeller diameter increase, the best efficiency points(BEPs) has a tendency to move to the large flow area; Head drops significantly, shaft power and efficiency improves with the impeller diameter increase in the large flow area; Head rises, shaft power slightly decreases and efficiency decreases significantly in the small flow area with the impeller increase. The velocity field of the three impeller diameters shows that the circular flow rate between the impeller and the base circle of the volute is reduced and the flow condition is improved with the increase of the impeller diameter. Theoretical formulas are used to predict the performance of the hydraulic turbines as the impeller diameter changed. Possible reasons for the deviations between the performances predicted by theoretical formulas and the results of CFD simulation are explored. Theoretical analysis about the shaft power and head of the hydraulic turbines has been studied. It is found that theoretical head, efficiency and shaft power increases, the head decreases with the impeller diameter increase. © 2016 Journal of Mechanical Engineering.