Analysis of hydraulic mechanism of dynamics flow visualization in an axial pump with impeller blades based on novel transient characteristics conditions and vibration techniques

Pumps operated in turbine mode have attracted considerable attention for hydropower generation and water conveyance applications due to their economic advantage over conventional hydroturbines. Despite this benefit, their deployment remains constrained by limited flow controllability and pronounced instability when operating away from the design point. To address these challenges, the present work combines experimental measurements with numerical simulations to examine the unsteady flow behavior of an axial-flow pump under five distinct operating regimes, spanning deep part-load conditions at 5 L/min through the design point and into overload operation at 12.5 L/min. Pump stability was evaluated through detailed analyses of velocity distributions and pressure fluctuations in both the time and frequency domains. The results reveal a strong dependence of unsteady behavior on operating condition. At part-load operation, pressure pulsations intensify markedly, with peak-to-peak amplitudes increasing by as much as 15% relative to the design flow rate. Spectral analysis shows that rotor-stator interaction phenomena dominate the unsteady response, with the blade passing frequency and its harmonics contributing over 12% of the total spectral energy across most monitoring locations. As the flow rate approaches overload, the magnitude of pressure oscillations is reduced by approximately 14%, indicating a progressive improvement in hydraulic stability. The effect of impeller blade stagger was further investigated for three configurations, namely - 3°, 0°, and + 3°. Deviations from the baseline geometry (0°) significantly amplify flow unsteadiness, particularly in the rotor-stator interaction region. In these cases, pressure pulsation amplitudes increase by up to 16%, highlighting the sensitivity of unsteady flow structures to blade-angle modification. Overall, the findings demonstrate that both operating regime and impeller blade angle exert a decisive influence on the stability and dynamic performance of axial-flow pumps, offering valuable insights for their optimal design and operation under variable flow conditions.