叶轮外径对前弯型液力透平性能的影响*

为研究前弯型叶轮外径对液力透平水力性能的影响，进行试验，获得了液力透平外特性数据，与计算流体动力学(Computational fluid dynamics， CFD)的结果进行对比分析，发现两者结果十分接近，验证了CFD模拟的准确性。利用CFD技术获得了215 mm、235 mm和255 mm叶轮外径液力透平的外特性曲线，发现随叶轮外径的增加，高效点向大流量区域偏移，在大流量区域，扬程大幅下降，轴功率小幅提升，效率有较明显提升，在小流量区域，扬程上升，轴功率略微下降，效率下降明显。对215 mm、235 mm和255 mm外径叶轮的速度场分析，发现随叶轮外径的增加，叶轮与蜗壳基圆之间的循环流量逐渐减小，流动状态得到明显改善，叶轮内水力损失也有较为明显的减小。利用理论公式推测改变了叶轮外径后的液力透平的高效点参数，发现普遍高于CFD模拟结果，分析产生差值的可能原因。对液力透平的轴功率、扬程进行理论分析，探讨其随叶轮外径增加的变化趋势。

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.