Cross-influence of cavitation and flow rate on pressure pulsation of a volute mixed flow pump

Mixed-flow pump is a general purpose hydraulic machinery in many fields of fluid transport for its advantages of wide efficient operation flow rate range, but its operation stability is restricted by cavitation. To obtain the cross effect of cavitation and flow rate on its pressure pulsation, a high-precision experimental system was first established to monitor the pressure signals at four key positions, obtaining their time domain; second, based on this tested results, time frequency domain analysis technique based on continuous wavelet transform was adopted to capture the temporal evolution; third, wavelet coherence value analysis was further adopted to diagnose the cavitation development speed at different spatial positions. Primary findings are as follows: (1) the secondary peaks induced by cavitation generated the discrete disturbance in low-frequency range, and the amplitudes at shaft frequency and blade passing frequency were both increased, with a worse time continuity. (2) Under 1.0 QBEP, the mixed flow pump had a best anti-cavitation performance. Under 0.8 QBEP, its internal flow pattern was easily to be disturbed by cavitation flow, while that under 1.2 QBEP had the fastest cavitation development speed. (3) Under the action of unstable potential flow, within the flow field near the rotor–static interface and the downstream, a close flow exchange was established between the cavitation bubbles and mainstream; thus, the pressure pulsation inside the volute became more sensitive to the cavitation development.