Multiscale pressure fluctuation characteristics and vortex-enthalpy interaction in cavitating mixed-flow pump

This study investigates cavitation evolution in the M350HD-60 mixed-flow pump impeller using a multi-method approach combining Rothalpy, Liutex vortex identification, Fourier transform, and wavelet analysis. Three cavitation stages (critical, severe, and fracture) were analyzed through vapor fraction distribution, vortex evolution, Rothalpy distribution, and pressure fluctuations. Results demonstrate that cavitation development significantly increases the vapor volume fraction, peaking at 0.78% near the suction side outlet during fracture cavitation. Liutex vortex analysis reveals concentrated vortex structures predominantly along the trailing edges of both suction and pressure surfaces. Rothalpy distribution analysis indicates cavitation-induced expansion of high-enthalpy regions toward the suction surface trailing edge and tip clearance diffusion toward adjacent blades. Frequency domain analysis identifies 48.33 Hz (twice shaft frequency) as the dominant pressure fluctuation frequency across all cavitation stages, with 24.17 Hz (shaft frequency) as secondary frequency. Notably, the suction surface leading edge monitoring point (S1) exhibits pronounced high-frequency (1600–2200 Hz) pressure fluctuations with amplitude escalation during cavitation progression. Continuous wavelet transform further reveals that critical cavitation produces the most intense low-frequency (19.33–96.67 Hz) pressure fluctuations with periodic energy variations. As cavitation progresses, overall energy amplitudes decrease, but periodic high-frequency fluctuations intensify at S1, located at the front edge and tip of the blade suction surface. This study combines the Rothalpy and Liutex methods to quantify the cavitation effect in mixed-flow pumps, providing new insights into the identification and performance evaluation of cavitation stages in hydraulic machinery.