In multi-unit rural irrigation and drainage pump stations, unstable intake flow in side pump sumps often leads to vortex formation, jeopardizing safe operation. Therefore, this study investigates the influence of frictional hysteresis effects on flow patterns in the side pump sump of multi-unit rural irrigation and drainage pump stations through physical model experiments and theoretical analysis. Here, frictional hysteresis refers to the delayed and asymmetric development of wall-induced friction gradients along the sidewall and separating pier, resulting from different boundary-layer growth histories under asymmetric geometric constraints, which leads to persistent lateral momentum imbalance and biased inflow in the sump. The research reveals that due to structural asymmetry (the coexistence of a single-sidewall and a separating pier), frictional gradient deviation in side pump sump exhibits significantly non-uniform distribution along the flow direction. Specifically, the frictional gradient offset near the separating pier is greater than that near the sidewall and decreases along the flow direction while remaining relatively stable. By introducing the concept of the relative offset of inflow frictional gradient, the proportion of gradient offset to pump sump width was quantified. Experimental results show that when the width-to-length ratio is optimized to the range of 0.22–0.28. This significantly promotes a more laterally symmetric velocity distribution and effectively suppresses the formation of wall-attached vortices in side pump sumps. The findings provide a theoretical basis for optimizing rural irrigation and drainage pump station's intake structures, and it is recommended to control width-to-length ratio to reduce frictional hysteresis effects, thereby enhancing operational efficiency and stability.
Xi et al. (Wed,) studied this question.