| Multistage centrifugal pump are widely used in electric power, metallurgy, fire and chemical et al. The hydraulic design method of multistage pump is the same with the method for single-stage pump. The flow interference between stages has not been considered. In recent years, more and more research and engineering practice shows that the interference of interstage flow has a significant impact on performance of multistage centrifugal pumps. As such, the research about the methods to use the interference improve various performance has become a hot topic in the field of hydraulic machinery. In these studies, the performance optimization by adjusting the circumferential clocking position of flow passage components has been developed as an important research direction.In this paper, the multistage centrifugal pump was studied by combing theoretical analysis, numerical calculation and measurements. The impact of the rotor circumferential clocking position on energy characteristics, pressure pulsation and vibration was studied intensively. The results can be used to enrich and develope the performance optimization design method of multistage centrifugal pumps. Main research work and results in this paper are as follows:1. It is summarizes the progress in clocking effect of turbomachinery. The present application situation of CFD and Finite Element Technology in internal flow simulation, strength analysis and flow-induced vibration was introduced. And the development trend of clocking effect in multistage centrifugal pump has been discussed.2. Based on the theory of CFD three dimensional viscous flow, the relevant internal turbulence model was analyzed. The boundary conditions used in centrifugal pumps were summarized. It indicated that the reasonable model to describe the internal turbulence flow in multistage pump is SST model, and the reasonable boundary condition to calculate transient flow field is total pressure for inlet boundary and static pressure for outlet boundary. On the basis of CFD calculation, the basic theory of flow-induced vibration was introduced. The computing strategy to solve flow induced vibration of multistage pumps by using the technique combined CFD with FEA was determined.3. The impact of rotor clocking effects on dynamic characteristics of a two-stage centrifugal pump was analyzed based on CFD simulations. The simulation results indicate that the head and efficiency are essentially the same when the downstream impellers circumferential clocking are adjusted. The pressure pulsation in the whole flow passage is mainly affected by the correspondence stage impeller. Howere, the phase of transient fluctuations of head and pressure deviates at the same time, and the maximum deviation is 90°. The amplitude of axial force and radial force at blade passing frequency decreases after impeller clocking. The maximum reduction rates of axial and radial forces were 84.72% and 89.8%, respectively.4. The impacts of rotor clocking effects on vibration characteristic of the two-stage pump were analyzed based on the combination of CFD and FEA methods. The simulation results indicate that the vibration level at blade passing frequency and its harmonic frequency decreased significantly after impeller clocking arrangement. And when the secondary impeller circumferential position is at the maximum clocking angle, the maximum vibration exists the largest decrease of up to 56.3%.5. The impact of the rotor clocking on energy characteristics and vibration characteristic of a five-stage centrifugal pump was analyzed based on experiments and orthogonal design. The results show that the rotor clocking adjustment has no significant influence on head and efficiency over the full flow range. However, the rotor clocking has a great impact on the amplitude of the main peak frequency(1×fn, 2×fn, 3×fn and 4×fn) under rated duty point, with the maximum amplitude reduction of up to 47.4%. The maximum vibration intensity exists at the inlet of the pump in vertical direction. With the optimal rotor arrangement, value of the vibration maximum intensity was decreased by 23.1%, and the average vibration level over the full flow range was decreased by 17.3%.6. Based on experiment studies of the five-stage pump, the optimization method of vibration characteristic by using clocking arrangement was revealed. It is preliminary proved that the continuous synchronous clocking arrangement of downstream impellers should be avoided. On this premise, upstream impeller consecutive two synchronous clocking is conducive to suppress vibration. In addition, the upstream impellers before the last stage impeller should be arranged a consecutive two synchronous clocking. Furthermore, the formula for the optimal rotor clocking arrangement is summarized with the optimal vibration characteristics. |
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