Multi-objective optimization design of an axial-flow pump intake for energy saving and flow stabilization

In the global energy transition, improving the energy efficiency of inter - basin water transfer pump stations is crucial. Swirling flow in the intake sump causes substantial hydraulic losses and operational instability. The hydraulic structure of the inlet sump (suspended height Cs, backwall clearance Ts, sump width Bs, roof height Hs) is taken as the research object, and the optimization framework based on RBF surrogate model and NSGA-II algorithm is established to study the multi-objective optimization and the vortex dynamics mechanism. The results indicate that the optimized scheme selected from the Pareto front achieves the most balanced improvement in hydraulic efficiency, flow uniformity, and vortex suppression by increasing Cs, Ts, and Bs while maintaining a low Hs. Under design conditions, it achieves approximately a 0.2% increase in unit efficiency, a more than 2.5% improvement in inlet velocity uniformity, and suppresses pressure fluctuation intensity. Local hydraulic loss rate (LHLR) analysis based on the differential balance equation of kinetic energy reveals that the scope and intensity of the high-loss region beneath the bellmouth are effectively inhibited after optimization, with both dissipation and transport terms of loss maintained at low levels. By applying rigid vorticity decomposition theory, we discover a strong correlation between LHLR beneath the bellmouth and enstrophy of rigid vorticity, while the correlation with the enstrophy of shear vorticity is weak. The rigid vorticity stretching term is the primary source of vortex core deformation and energy transport, directly leads to high hydraulic dissipation and transport losses through its pronounced three-dimensional stretching effects, especially the spanwise and vertical components.