CFD analysis of sump flow characteristics at El-Buts pumping station: a comparative study of original and modified geometries

This paper presents a detailed computational fluid dynamics (CFD) study to model and improve the hydraulic and water management problems at the sump intake of El-Buts pump station, Fayoum governorate, Egypt. The station has four large horizontal split-case axial pumping units consisting of three pumps working and one standby all running at 670 RPM. The pumps are sized for a duty point discharge of 1.5 m3/s (5400 m3/h) against a total static head of 49 m. It has been proven that the velocity distribution disturbance leads to hydraulic instability of pumping units that is a source of failures, damages, and many operational and maintenance problems. For the identification and alleviation of the hydraulic problems at the suction side, a three-dimensional CFD model was developed to simulate flow conditions for eight distinct pump operating combinations under the critical design minimum water level. The analysis of the original geometry showed a large non-uniformity of the flow. The maximum swirl angles measured near the impeller eye were 9.56°, which is above the limit of 5° recommended by the Hydraulic Institute Standards. The present study investigated several different situations to evaluate both the actual operating conditions and the effect of geometric modifications to the suction sump. By applying certain modifications including curtain walls, bottom-central wall splitters, step walls, and four-vane flow straighteners, a uniform flow with low swirl was achieved into the pump chambers. The maximum swirl angle was effectively reduced from $${9.56}^{\circ }$$ in the original layout to $$-{2.84}^{\circ }$$ in the modified configuration, representing a $$70.3\text{\%}$$ reduction in maximum swirl angle magnitude and satisfying the ANSI/HI 9.8 allowable threshold. The modified geometry was numerically validated across seven pump operating combinations (test cases 2–8) under the critical design minimum water level, demonstrating consistent pre-swirl reduction and improved velocity uniformity. While these findings confirm the hydrodynamic effectiveness of the proposed flow conditioners under worst-case submergence conditions, physical testing across the full operating water level envelope remains essential for complete standard qualification.