An improved mode selection criterion for Hankel-DMD and an application in the pressure pulsation signal of hydro pump turbine

The operation of counter-rotating double-suction centrifugal pumps as micro-pumped storage units has attracted increasing interest in new-energy applications. The studied micro pump-turbine comprises a semi-spiral suction chamber, back-to-back impellers and a volute. Although staggered impeller arrangements are known to mitigate pressure pulsations, the underlying mechanisms remain insufficiently explained. This work combines numerical simulation and experimental validation with an improved Hankel-DMD workflow that incorporates a modified mode-selection criterion based on discrete-time coefficient weighting. The criterion assigns greater weight to persistent time-coefficient statistics, which enhances selection of physically meaningful modes and reduces sensitivity to noise and spurious components. Using this approach, dominant modes of pressure pulsation are extracted and compared with FFT results and measurements. Findings show that pressure spectra in the suction chamber are more complex than in the volute: besides the rotational frequency (25 Hz) and its harmonics, regular low-frequency bands appear, and a mid-to-high frequency component at 180 Hz carries substantial energy. In the volute, frequency content evolves toward multi-band superposition near the outlet, driven by intensified rotor–stator interaction and boundary-layer separation. The proposed method offers a robust data-driven tool to elucidate the suppression mechanism of staggered impeller layouts and supports design and operational optimization of micro-pumped storage units.