Numerical and Optimization Study on the Hydraulic Performance of a Closed Pump Intake Sump with Variable Bellmouth Clearance

In coastal pumping stations, the intake sump geometry strongly affects flow uniformity, hydraulic loss, and vortex formation. This study establishes an Isight-based automated simulation and optimization framework for an axial-flow pump with a closed-type intake to clarify the influence of bellmouth diameter and clearance height on sump hydraulics. A Radial Basis Function surrogate model combined with the NonLinear Programming by Quadratic Lagrangian (NLPQL) was employed to minimize hydraulic loss and improve flow uniformity. The results show that hydraulic loss first decreases and then increases with bellmouth diameter, whereas velocity uniformity and the mean inflow angle exhibit nonlinear variations with clearance height. The optimal configuration increases efficiency by 3.82% and the velocity uniformity by 1.62% compared with the baseline. Helicity density and the Ω-criterion were used to identify vortex structures, revealing that small clearances intensify bottom and wall-attached vortices, whereas larger clearances promote symmetric inflow. An improved tangential-velocity method based on iso-vorticity contours effectively captured near-wall vortex dynamics. These findings provide theoretical support for achieving low head loss, stable inflow, and controlled vortex behavior in axial-flow pump intake systems.