Correlation Analysis of the Hydrodynamic Characteristics and Stability of a Self-balancing Multistage Pump

The BB5 series multistage centrifugal pump is commonly utilized for its capacity to deliver a large head. However, due to the long rotor system in the BB5 series multistage pump, the unsteady flow field structure of each impeller at every stage inevitably results in more complex mechanical characteristics of the pump, thereby affecting its operational stability. This paper conducts a numerical study on the stability of a 12-stage self-balancing multistage pump. The results indicated that significant pressure load fluctuations on the working surface occurred at the inlet of the impeller blades at all levels in the low-pressure section. At low flow conditions, the coincidence of the pressure loads on different blade working surfaces and back surfaces of the same impeller was poor; this resulted in an inadequate uniformity of the force distribution on each blade. A negative correlation was observed between the intensity of the pressure pulsation and the flow rate. In the inlet section the intensity of pressure fluctuation was stronger than that in the outlet section. The spectrum characteristic diagram of radial force shows that the frequencies with higher amplitudes occurring at each stage impeller are approximately 298 Hz and 48 Hz. The cause is the interference between the impeller blades and the guide vanes. At low flow rates, the amplitude of the radial force of the impeller was significantly higher than that at other flow rates. The magnitude of the residual axial force fluctuated to a certain degree, but its direction remained unchanged. The stability of the flow field and mechanical performance were inferior at low flow rates. At the same flow rate, the stability of the inlet section was worse. These research results could provide references for the stability design and optimization of self-balancing multistage pumps.