Chen Liu

Unstable internal flow structures significantly compromise the mechanical reliability of centrifugal pumps. This study elucidates the coupling mechanism between impeller geometry, vortex dynamics, and hydrodynamic forces. A hybrid optimization framework, integrating a neural-network surrogate model with both multi-objective genetic algorithm and non-dominated sorting genetic algorithm III (NSGA-III), was employed to refine the impeller. Comparative analysis reveals that the NSGA-III design offers superior stability, achieving a 31.1% reduction in peak radial force and eliminating axial-force directional reversals, while simultaneously increasing efficiency by 5.4% and reducing shaft power by 6.3%. Crucially, the stabilization mechanism is decoded using multiresolution dynamic mode decomposition (MRDMD) and entropy generation analysis. MRDMD results demonstrate that the optimized geometry attenuates low-frequency unstable modes driven by rotor–stator interaction, shifting spectral energy to stable high-frequency structures. Furthermore, thermodynamic analysis identifies a fundamental shift in dissipation pathways: the suppression of large-scale coherent vortex shedding reduces internal volumetric entropy generation by 63.6%, yielding a flow field stabilized by controlled wall shear layers. These findings provide a physics-based rationale for mitigating flow instabilities through targeted geometric refinement.

In order to reveal the coupling mechanism between hydrodynamic characteristics and entropy production rate under cavitation conditions of mixed flow pumps, this study utilized cross-wavelet transform to analyze the time-frequency domain relationship and coherence between axial force, radial force, and entropy production rate in different regions and cavitation stages. The results indicated a significant negative correlation between the axial and radial forces and the entropy production rate in the impeller region, as compared to the guide vane region. With the development of the cavitation stage, the axial and radial forces exhibited a decreasing trend (the axial force decreased by 25.7% on average and the radial force decreased by 13.1% on average), while the entropy production rate showed an upward trend (the average increase was 30.8%). In the frequency domain analysis, the axial force and radial force in the impeller area were concentrated near the blade frequency (96.67 Hz). In terms of wavelet power spectrum, the high-energy regions of axial force, radial force, and entropy production rate continued to expand in the time range and showed distribution characteristics concentrated near the blade frequency. In terms of wavelet coherence spectrum, the strong coherence regions of axial force and entropy production rate were concentrated at the blade frequency, while the time continuity, overall coherence, and phase consistency were gradually enhanced. The research reflected the strong coupling characteristics of force-energy in blade frequency and its harmonic frequency, which can provide references for improving the operating stability of the mixed-flow pump cavitation process and optimizing blade.