Pressure fluctuation suppression of a mixed flow pump with T shape tip by circumferential uniformity and vortex stability

Pressure fluctuations induced by the tip leakage vortex (TLV) in mixed flow pumps are the primary source of structural vibration and noise, which affects operation stability. The T shape blade tip is introduced to suppress pressure fluctuation of a mixed flow pump in this work. A closed-loop test rig of mixed flow pump is established to measure the pressure fluctuation on pump shroud wall with high-frequency pressure sensors. The numerical simulation is conducted to capture the detailed flow pattern and pressure fluctuation in pump with high-fidelity stress-blended eddy simulations. Results show that the T shape blade tip significantly reduces the spatially averaged pressure fluctuation intensity in the whole operating region, and the pressure fluctuation intensity reductions are 4.55% at part-load condition, 7.88% at design point condition, and 2.10% at over-load condition. Two mechanisms of pressure fluctuation suppression in the mixed flow pump are revealed. The first suppression mechanism is the improvement of circumferential uniformity in the time-averaged pressure field. The T shape tip effectively weakens the TLV strength and mitigates the low-pressure region on the shroud induced by the vortex, which suppresses the periodic pulses at the blade passing frequency. The second suppression mechanism is the improvement of vortex stability. The T shape tip controls the TLV trajectory to a position closer to the blade suction surface, which disrupts the feedback loop and prevents the periodic breakdown of vortex structure. Consequently, the broadband fluctuations caused by flow instability are suppressed.