The proper design of the manifold, distributing the flow to the individual nozzles, is crucial for the Pelton turbine performance. The generation of both energy losses and secondary flows must be reduced to a minimum to provide optimal water jet quality and, hence, efficiency. However, the inflow state due to the penstock is commonly disregarded at the design stage. By numerical flow simulation, we show how such penstock perturbations affect the water jet cross-section and axis deviation by considering different pipe bends upstream of the manifold. The two-phase flows resulting in a typical Pelton turbine manifold are predicted using the Volume-Of-Fluid (VOF) approach in conjunction with the SST turbulence closure model. Pipe bends are attached five manifold inlet diameters upstream of the manifold itself. The consequences on the secondary flows in the nozzles and the free water jet quality are reported quantitatively. The analysis shows that even small inflow perturbations into the manifold due to penstock piping significantly affect the water jet quality. A yet unreported mechanism is revealed, where the secondary flows mitigate the impact of the flow rate imbalance across the nozzle on the water jet deviation.

中文翻译：

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冲击式水轮机分配管中的流入扰动对水射流质量的影响

歧管的正确设计，将流量分配到各个喷嘴，对于冲击式水轮机的性能至关重要。能量损失和二次流的产生必须减少到最低限度，以提供最佳的水射流质量，从而提高效率。然而，设计阶段通常忽略压力钢管的流入状态。通过数值流量模拟，我们通过考虑歧管上游的不同弯管，展示了压力钢管扰动如何影响水射流横截面和轴线偏差。使用流体体积 (VOF) 方法结合 SST 湍流闭合模型来预测典型冲击式水轮机歧管中产生的两相流。弯管连接在歧管本身上游五个歧管入口直径处。定量报告了对喷嘴中二次流和自由水射流质量的影响。分析表明，即使由于压力钢管管道而进入歧管的微小流入扰动也会显着影响水射流质量。揭示了一种尚未报道的机制，其中二次流减轻了喷嘴上的流速不平衡对水射流偏差的影响。