Effects of a Bionic Fish-Tail Bulb Body on Wake Flow, Energy Loss, and Pressure Pulsation in a Bulb Tubular Pump for Agricultural Irrigation and Drainage

Low-head, high-discharge agricultural irrigation and drainage pumping stations require efficient and stable operation under variable-flow conditions, while flow separation and wake vortices downstream of the bulb body can intensify energy dissipation and pressure pulsations. To mitigate these effects, three bulb body configurations—the original configuration, salmon-tail configuration, and grouper-tail configuration—were investigated numerically using the SST-CC model, with vortex structures, entropy production, and pressure pulsations analyzed. The results show that the bionic tails have little influence on head but improve efficiency over 0.93–1.13 Qdes, with the grouper-tail configuration providing more consistent enhancement. At 0.80 Qdes, the vortex-structure volume fraction decreases from 2.69% to 1.65–1.71%. Entropy production analysis shows that the impeller remains the main loss region, whereas the outlet channel loss contribution increases with flow rate, indicating stronger effects of wake transport and residual swirl under high-flow conditions. At 1.13 Qdes, the bionic tails reduce the overall pressure-pulsation amplitude by about 62.5%, the low-order energy proportion from 6.39% to about 1.40%, and the dynamic pressure stability index by 44.49–49.39%. In contrast, at the design condition Qdes, the DPSI increases from 0.186 for the original configuration to 0.266 and 0.323 for the salmon-tail and grouper-tail configurations, respectively, indicating deteriorated dynamic pressure stability. These findings demonstrate the strongly condition-dependent effects of bionic fish-tail geometries on energy performance and dynamic pressure stability, revealing a trade-off between hydraulic performance improvement and pressure stability rather than a uniform benefit across the entire operating range.