Analysis about effect of unequal spacing blade on performance and pressure pulsation of centrifugal pump

Abstract: In order to analyze the effect of unequal spacing blade on the performance of a centrifugal pump, a centrifugal pump with specific speed of 132.7 was chosen as the research object. Three kinds of unequal spacing blade models were established based on automatic rotor balance theory, and the whole flow field in the model pump under 0.8, 1.0 and 1.2 times of designed flow was simulated by the computational fluid dynamics (CFD) method. Based on the simulation results, the performance, the internal flow distribution and the pressure fluctuation in the model pump were obtained. The performance experiments of the model pump were conducted in an open loop, which consisted of a reservoir open to air, a suction valve, a test pump, a discharge pipe, and a discharge valve. The test performance results were used to check the CFD results and they showed good agreement. Then the simulation results of unequal spacing blade models and the original equal spacing blade model were compared and analyzed in detail. The results showed that unequal blade spacing arrangement would reduce the pump head and increase pump efficiency, and the smaller the minimum angular separation, the more obviously the head declined and the efficiency increased. When the minimum angular spacing was 45°, 50° and 55°, the variation ranges of the head and efficiency under the 3 flow rates were all less than 5%, which could meet the design requirements. At the design point, the internal flow in each impeller model was more regular, and the flow from impeller inlet to outlet was very smooth. The velocity at impeller inlet was relatively low, and the velocity at exit was relatively high. Compared with the original model, there was a certain range of low-speed area near the pressure side of unequal spacing impeller, especially in the wider flow channel, which could result in a large pressure gradient and pressure pulsation. The smaller the minimum angular spacing, the larger the range of low-speed area. Compared with equal spacing model, in addition to BPF (blade passing frequency), pressure pulsation within the volute of 3 models with the minimum angular spacing of 45°, 50° and 55° at 145 Hz (0.5×BPF) had new peaks. For the model with the minimum angular spacing of 45° and 50°, the pulsation amplitude at 145 Hz was larger than that at the BPF, while the pulsation amplitude for the minimum angular spacing of 55° at 145 Hz was less than that at the BPF. maybe because the form of blade distribution of the minimum angular spacing of 55° was very close to the equal blade spacing, the pulsation amplitude at the BPF was the most obvious. And this made pressure pulsation spectrum of unequal blade spacing model denser than that of the original one; the pressure pulsation spectrum of equal blade spacing model changed dramatically, while 3 new models had new peaks at the BPF and other new frequency, which could improve the smoothness of pressure pulsation spectrum to some extent. The study can provide a reference for the centrifugal pump design and optimization.