Experimental Study on the Stability of Mixed-Flow Pump During Segmented Start-Up Process

To improve the safety and stability of pumps in the start-up process, a novel start-up strategy named segmented start-up mode is proposed. This paper carries out an experimental study on the stability of mixed-flow pumps in the segmented start-up process. Shaft vibration and pressure pulsation in the pump are important indicators to characterize the stability of mixed-flow pump. And they are collected during segmented and linear start-up modes. Then, based on the complementary ensemble empirical mode decomposition (CEEMD) algorithm and wavelet transform, time–frequency and correlation analyses of the two types of signals are performed. The results indicate the rubbing between the rotor and bearing leading to high-order harmonic components of the shaft vibration spectrum within the frequency range of 2.5f_n–5f_n, which may cause mechanical resonance. For the segmented start-up mode of fast followed by slow, the amplitude of the pressure pulsation at the impeller outlet is smaller than the other two start-up modes. Furthermore, the high-order harmonics of the blade passing frequency in the spectrum are induced due to the phase resonance phenomenon. In the early stage of segmented start-up, the strong interaction between the shafting and water results in the alternating leading of the shaft vibration and the pressure pulsation at the impeller outlet. But then the impeller outlet pressure pulsation occupies the leader position due to the full development of turbulence flow in the impeller. The segmented start-up mode of fast followed by slow can reduce the probability of mixed-flow pump instability during start-up.