Numerical Study About The Influence Of Impeller Trimming To Centrifugal Pump Performance And Volute Internal Flow

Double suction centrifugal pump is widely used, whether in factories, mines, urban water supply and drainage or irrigation of farmland. Comparing with the single suction pump, which has a larger flow rate and preferably suction performance; than with the mixed-flow pump, which has a high lift. Generally, when a pump performance does not satisfy the requirements, basically which by trimming impeller diameter can meet the requirements. However, in practical applications, by flat cut impeller diameter to medium and high specific-speed double-suction centrifugal pump, tests results showed that although head dropped, but the power did not fall, which indicates that the efficiency of the pump dropped too much, for this case, researchers trimmed impeller diameter by V-mode and found pump power downed more, the efficiency was higher, so the results proved that V-trim can improve the performance of this type of pump; in addition, in practical applications, in order to weaken the vibration, noise and reduce the pressure pulsation within the pump, double suction pump impeller blades staggered at an angle on both sides is a better way.Therefore, to research the results of engineering practice, this paper will study two large double suction centrifugal pump with different speed, the whole flow passage of the original model is numerically simulated and according to the simulation results, analyzing the performance and volute flow field of the pump. then, medium and high specific-speed pump impeller diameter were trimmed three times with the pattern of flat-trim and V-trim, and the simulation results are compared; Finally, researching volute pressure pulsation under design conditions of original model and cutting models of medium specific-speed pump, meantime, exploring the influence of the double suction centrifugal pump impeller with bilateral blades staggered on pressure pulsation in volute, and obtaining the following conclusions:1. The head and efficiency in the simulation conditions of medium and high specific-speed pump original model is higher than the test results, mainly due to numerical simulation of ideal environment, without regarding to various losses; two pump volute velocity vector of each sections are extracted, and discovering that exists the spiral vortex in the volute of two pump, which will result in some energy loss.2. comparing with the original model, when trimming impeller diameter with flat pattern, head, efficiency and power of medium and high specific-speed pump are declining, but the efficiency down ratio of high specific-speed pump is higher than that of medium specific-speed pump, while power down ratio is lower. This shows that selected pump performance is poorer than that of the original model when flat trimming, but the degree of deterioration of high specific-speed pump is more serious,comparing with the original model, when trimming impeller diameter with V-pattern, head and power are declining of medium and high specific-speed pump, while efficiency of lower-high specific-speed pump is declining and efficiency of high specific-speed pump is increasing comparing with their original models, which indicates that V-trimming can improve the performance of high specific-speed pump. For any one specific-speed pump, the head and efficiency is lower when flat-trimming than V-trimming, while power is higher than V-cutting, this shows that the two kinds specific-speed pumps with V-cutting are better than flat-trimming, V-trimming is more suitable for high specific-speed pumps. This result also confirms the resulting conclusions of the practical application.3. About flow field in the volute, by comparing we can obtain that volute vortex persists of the two kinds specific-speed pump when trimming impeller diameter, through the vector velocity profile can be seen the form of spiral vortices of flat cut are more disordered than the original model,V-trimming can improve vortex form.4. There are mainly blade passing frequency and rotating frequency and their frequency multiplier pulsation in the medium specific-speed pump volute and, volute pressure pulsation amplitude in the trimming model is lower than that in the original model, which is due to the gap between the impeller and the tongue increasing; bilaterally staggering blades of double suction centrifugal pump impeller can effectively reduce the pressure pulsation in the volute, and staggering with a larger degree reduce pressure pulsation are relatively better than the small degree within the pump volute, and bilateral blades staggered can particularly weaken the blade passing frequency because of static-dynamic interference between impeller and volute; the pressure pulsation volute exiting of is less than elsewhere because of the buffering effect and the steady flow of diffusion tube; For the same model, pressure pulsation time domain features or frequency domain features in different locations are almost same.