Influence of stator–rotor clearance on hydraulic performance and flow dynamics in full tubular pumps

The full tubular pump is a novel integrated motor–pump system in which the stator–rotor clearance flow strongly influences hydraulic performance and internal flow characteristics. In this study, numerical simulations combined with model tests are employed to investigate the mechanisms by which local flow in the clearance region affects the overall flow field. A key innovation of this work lies in revealing how variations in stator–rotor clearance simultaneously affect head, efficiency, and entropy-based energy losses within different pump components. Results show that an increase in clearance size leads to a reduction in head and efficiency: the head decreases by 0.83 m and efficiency by 2.87% between the smallest and largest clearances. Larger clearances cause earlier stall onset, narrower high-efficiency operating ranges, and reduced operational stability, while slightly improving cavitation resistance. Rotor frictional losses account for 9%–12% of the total torque and increase as clearance decreases. Entropy production analysis reveals that larger clearances increase energy losses in the impeller and guide vane by approximately 39% and 50.7%, respectively, while reducing losses in the clearance region by 23.74%. The clearance flow significantly affects local flow losses near the impeller periphery and guide vane passages. Although smaller clearances slightly increase rotor friction losses, they improve impeller and guide vane flow structures, thereby enhancing the overall hydraulic performance.