Effect of Tip Clearance on Hydraulic Performance and Energy Dissipation Mechanisms in a Semi-Open Centrifugal Pump

Semi-open centrifugal pumps are widely used in various fluid transport applications because of their good passage capability and ease of maintenance. However, a certain clearance must be maintained between the blade tips and the pump casing, and the resulting tip leakage can significantly affect the internal flow and energy conversion performance of the impeller. Existing studies have mainly focused on the effects of tip clearance on head, efficiency, and local flow structures, while the locations where tip-leakage-induced energy losses primarily occur, the mechanisms by which different flow structures contribute to irreversible energy dissipation, and how such dissipation further leads to pump performance degradation remain insufficiently understood. In this study, steady full-passage numerical simulations were conducted for nine dimensionless tip-clearance (Cδ) schemes, and the numerical method was validated against experimental data. Entropy production theory was further introduced on the basis of analyses of head, efficiency, axial force, shaft power, total pressure, velocity, and turbulent kinetic energy distributions. The results show that, as the dimensionless tip-clearance ratio Cδ increases from 0.05 to 0.25, the pump head decreases from approximately 1.07 m to 0.71 m, corresponding to a reduction of approximately 33.6%, while the efficiency decreases from approximately 58% to 45%, corresponding to a decrease of approximately 13.1%. The axial force decreases from approximately 1218 N to 1197 N, while the shaft power exhibits an overall decreasing trend. Meanwhile, the clearance-induced flow disturbance becomes more pronounced, accompanied by increased local velocity gradients and turbulent mixing. The high-turbulent-entropy-production regions progressively extend from the blade-tip vicinity toward the adjacent blade passages, revealing the spatial connection between clearance-induced mean-flow restructuring, turbulent irreversible dissipation, and hydraulic-performance degradation.