Analysis of Flow and Structural Characteristics of Y-Shaped Bifurcated Pipe with Crescent Rib Under Hydraulic Short-Circuit Mode

Hydraulic short-circuit (HSC) has gained widespread attention as a novel approach to enhancing the flexibility of pumped-storage power plants (PSPPs). This paper investigates the flow and structural characteristics of bifurcated pipes in PSPPs, conducting numerical simulations under multiple operating conditions under pumping, generating, and HSC modes. Computational fluid dynamics (CFD) simulations indicate that the flow pattern deteriorates significantly under the HSC mode, with energy loss increasing notably as the flow split ratio (FSR) rises, though peaking at only 1.2% of total energy. Driven by secondary flow, a pair of counter-rotating Dean vortices develops from the upstream main pipe to the generating branch as the FSR increases. The entropy production rate reveals the energy dissipation mechanisms in the main flow region, namely, the shear interaction between high-velocity outflow and low-velocity vortex flow, along with the viscous dissipation within the Dean vortices. Furthermore, fluid–structure interaction (FSI) simulation results confirm that the structural reliability of the bifurcated pipe is ensured under the HSC mode, as the dominant load stems from the high static pressure of the upstream reservoir, with fluid impact loads playing a relatively insignificant role. This study provides a theoretical foundation for the practical operation of hydraulic short-circuit with respect to the performance and safety of a bifurcated pipe.