The distributing pipe in a Pelton turbine serves as a crucial water supply component responsible for regulating flow and inducing diversion. Its special structure, however, can lead to adverse effects such as flow separation and Dean vortices causing hydraulic losses; these losses can vary with changes in the upstream head, further affecting the incoming flow conditions. Traditionally, the pressure drop method has been primarily utilized to assess these losses, yet it fails to pinpoint the exact locations where significant hydraulic losses occur.

This study investigates the hydraulic and loss characteristics of the distributing pipe. Utilizing the SST(shear stress transport) k-ω turbulence model, we simulate the flow inside the distributing pipe and analyze entropy production distribution based on the entropy production theory. Then, according to the distribution of entropy production rate and flow pattern, the reasons for the hydraulic loss in the main channel and bifurcation 2 were analyzed detailly. Entropy production—indicative of irreversible dissipative effects during fluid flow—effectively highlights high hydraulic loss areas by converting lost mechanical energy into internal energy.

Results show a remarkable increase in total entropy production within the pipe, with values rising from 210.999 to 4 614.980. Specifically, entropy production in the main channel increases from 145.549 to 3 477.351, and in bifurcation 2 from 38.857 to 717.608. Under high-speed flow conditions, the separation between internal and external flows becomes distinct, particularly when fluid navigates bends. The hydraulic loss is dominated by fluctuation entropy production, accounting for>50%. The main flow zone and bifurcation 2 are the primary sites of hydraulic loss, accounting for approximately 90% of the total loss, whereas bifurcations 1 and 3 experience relatively small losses.

Comparative analysis of entropy generation rate contours, streamline plots, and pressure fluctuation curves highlights that high entropy generation areas experience significant pressure pulsations, accompanied by adverse flow phenomena such as Dean vortices and flow separation. At bifurcation 2, high-speed fluid is diverted and squeezed outward, creating a low-pressure vortex on the inner side, inducing significant hydraulic loss. At the bend position, the fluid tends to flow outward, resulting in high external pressure and low internal pressure distribution at the ring pipe and further in high hydraulic loss on the inside. These phenomena create large pressure gradients and significant pressure fluctuations, affecting flow stability. Furthermore, optimization strategies are proposed for the distributing pipe design, including the addition of flow-diversion baffles at bifurcation points to stabilize flow patterns, reduce vortices, and alleviate flow separation by increasing the number of nozzles and reducing curvature. This study employs numerical computation to investigate the mechanisms of hydraulic loss generation within the distributing pipe and meticulously delineates areas of high hydraulic losses, offering hydro turbine developers optimization strategies.