Reduced-order variational Mode decomposition of transient flow fields in mixed-flow pumps during startup

Transient flow phenomena during mixed-flow pump startup significantly affect energy system efficiency and stability, yet their multi-scale dynamics remain poorly understood. This study employs reduced-order variational mode decomposition (RVMD) to systematically reveal flow evolution patterns during transient startup. Compared to conventional methods (POD/DMD), RVMD effectively isolates low-frequency transient modes (shift mode) and high-frequency periodic modes (blade-passing harmonics) via adaptive frequency-band segmentation and narrow-band mode extraction. Parameter optimization shows that α = 500 and K = 20 balance frequency resolution with physical interpretability. The first two modes (Mode 1: 56 %; Mode 2: 34 %) capture >90 % of the energy, accurately characterizing the static-to-steady flow transition. This work provides a theoretical basis for suppressing transient energy losses and optimizing mixed-flow pump design.