Numerical simulation and validation of influence of end clearance in half vane diffuser on hydraulic performance for centrifugal pump

Centrifugal pumps are widely used in general machines and the demand of the efficiency and the stable operation can be higher. All kinds of clearances appear easily in the centrifugal pump, such as the tip clearance and wear-ring clearance. Meantime, the gap flow of tip clearance and wear-ring clearance results in the complicated turbulent flow and clearance vortex easily which has a great effect on the hydraulic performance and operation stability of a centrifugal pump. Thus, the study on mechanism of the gap clearance flow in the centrifugal pump is important. The half-height diffuser can be widely used in compressors and fans and can improve the performance of the compressors and fans. However, the application of the half-height diffuser in the centrifugal pump is seldom and the influence law of the clearance of the half-height guide vane on the hydraulic performance of the centrifugal pump is not clear. For the first time, the half-height diffuser is introduced into the centrifugal pump in this paper. Based on the numerical simulation and experimental methods, using SST k-ω model, research on effect of the half-height guide vane end clearance on the hydraulic performance and the internal flow field of centrifugal pump was conducted. The results show that the appropriate half-height guide vane end clearance can effectively improve the centrifugal pump's hydraulic performance, and broaden its high efficient area. When the guide vane height is 1.0, the maximum efficiency occurs at the position with the flow of 37.5 m3/h, however, it can be at 42.5 m3/h when the guide vane height is 0-0.8. The effect of the interaction between rotor and stator can be the main reason for the internal flow field of the general guide vane centrifugal pump, and the high pressure zone of the impeller outlet channel occurs when the impeller blade is near the leading edge of the guide vane. The asymmetric geometry of the volute is the main factor, which influences the internal flow field of the centrifugal pump with the end face gap. The impeller blade load in the conventional guide vane centrifugal pump is affected by the wake flow-jet flow and is higher than that of the centrifugal pump with the half-height guide vane. With guide vane end gap of 0.4-0.6 guide vane height, the efficiency and the head of the centrifugal pump are the optimal, and the maximum efficiency is 57.5%. In low flow condition, the hydraulic performance of impeller and diffuser is the key influence factor to hydraulic performance of centrifugal pump. The total pressure loss of the impeller in the centrifugal pump with the half-height guide vane end gap is higher than that of the ordinary diffuser centrifugal pump at the flow condition of 0.6, 0.8 and 1.0 time, however, the total pressure loss of the impeller in the centrifugal pump with the half-height guide vane end gap is lower than that of the ordinary guide vane centrifugal pump at 1.2 and 1.4 times flow condition. The performance of the impeller when guide vane height is 1.0 can be 7 m lower than that when guide vane height is 0-0.8 at the 0.6 flow condition. Meantime, the total pressure loss of diffuser while guide vane height is 0 can be 6.66 and 4.47 m higher than those with 1.0 guide vane height at the 0.6 and 0.8 flow condition, respectively. The total pressure loss of the volute in the centrifugal pump with the end clearance of the guide vane is less than that of the ordinary guide vane centrifugal pump. With the flow rate increasing, the influence of the interaction between impeller and diffuser on the centrifugal pump with the half-height guide vane decreases gradually, and the effect of the interaction between impeller and volute tongue on the centrifugal pump with the half-height guide vane increases gradually. The results provide theoretical basis and new ideas for the design and reconstruction of the guide vanes in centrifugal pumps. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.