Numerical Analysis And Optimization Design Of Two Types Super-low Specific Speed Centrifugal Pump

There have been three major problems in hydraulic performance of super-low specific speed centrifugal pump,namely:head-flow curve is easy to appear hump,shaft power is easy to appear overload under mass flow,low efficiency.The reason is defects in the design method.Based on the comprehensive summary and advantages and disadvantages of various design methods for super-low specific speed centrifugal pump,this paper has presented super-low specific speed centrifugal pump optimizing design method,namely:in the case of other key geometric parameters unchanged,multiplier D2b2(?)2tanβ2was reasonable reduced by reducing blade outlet excretion coefficient (?)2(shown as impeller passages blocked) in order to the high efficiency、overload free、 no hump.Taking conventional super-low specific speed centrifugal pump hydraulic model M12.5-23as an example,by analysis of CFD flow theory,the paper determined numerical simulation scheme for M12.5-23and carried out numeric simulation test in complete domain with cavity in all working conditions.The results were found that performance prediction curves coinsided with the experimental curves very well under complete domain.For super-low specific speed centrifugal pump, therefore,computational domain can’t ignore pump cavity.According to improved hydraulic design method,taking M12.5-23as an example, seven improvement model were set up by impeller export/import area ratio progressive decreased and carried out to numerical simulation.The results showed that seven improvement model’s head,shaft power suffered a drop though to different degrees and efficiency increased;two improvement models with the area ratio0.8/1.0and original model were respresented by all models and carried out to the analysis of inner flow field.The results showed that as the futher narrowing of impeller passage,internal axial vortex and hydraulic loss decreased;because export absolute speed increased by impeller passage narrawed,the vortex near impeller outer edge clearance strengthened and hydraulic loss increased.The partial emission pump hydraulic model QXB130-7was respresented as the special type pump.Eight improvement models for QXB130-7were designed and carried out to all woking conditions’numerical simulation.The results showed that when improvement model’s area ratio was less than1.2,the head-flow curves appeared humps and the reason is that when the partial emission pump’s straight blade was thickened impeller outlet excretion coefficient (?)2was reduced along with blade outlet setting angle increased and hump appeared necessarily.The prediction results of shaft power and efficiency were similar to the results of conventional type pump;two improvement models with the area ratio0.8/1.0and original model were respresented by all models and carried out to the analysis of inner flow field.The results showed that the axial vortex of two improvement models decreased but the intensity is always very strong;shock loss was very strong near volute tongue;with increase of flow rate,cutoff was obviously reduced on the right side of the volute chamber exit and flow field tended to be uniform under mass flow.Based on centrifugal pump area ratio principle and related theory,the paper established the mathermatic model of matching relation with super-low specific speed centrifugal pump’s impeller and volute chamber.Based on genetic algorithm and Matlab software,M12.5-23,for example,the pump was optimized and got optimized design parameters.Through the numerical simulation,the paper found that under design condition the optimized model was improved in terms of performance compared with the results of original model and the model of the area ratio0.9,especially the head increase is larger,and the static pressure distribution was more well-distributed,and axial vortex was smaller.