Performance Analysis And Optimization Of Double Impeller Tandem Axial Flow Pump

With the development of China’s water conservancy industry and the continuous advancement of the South-to-North Water Diversion Project,more and more large-flow,high-lift water transfer occasions have emerged.The existing axial flow pump has a large flow rate but a low lift,rarely exceeding 10.0 m,and the cavitation performance deteriorates after deviating from the design operating point.In order to improve the performance of the axial flow pump and appropriately improve the lift of the single-stage pumping station,a new pump type,namely a double-impeller tandem axial flow pump,is studied.The double impeller tandem axial flow pump is a combination of two stages of impellers and vanes,which reduces the guide vanes in the middle stage compared to the two-stage axial flow pump.In this paper,the numerical analysis is used to numerically analyze the hydraulic performance and internal flow of a double impeller tandem axial flow pump.Based on the Isight platform,the experimental design method is applied to optimize the structural parameters of the same impeller serial axial pump;At the same time,different impeller tandem axial flow pumps are designed,and the design parameters are optimized by the gradient optimization algorithm.The main contents and conclusions of the study are as follows:1.Analysis of hydraulic performance of the same impeller tandem axial now pump by numerical calculation.The research shows that the difference between the external characteristics and the ideal result is large.When the flow rate is small,the lift is improved,but the gap is gradually reduced with the increase of the flow rate.The efficiency is obviously lower than that of the single-stage pump,and the efficiency difference is about 6%.At the same time,the front impeller plays a major role in the work of the pump.The rear impeller has almost no work or even negative work,and its internal flow is relatively poor.2.Through the experimental design method,the front and rear impeller angles,axial distance and circumferential declination are changed to improve the performance of the same impeller tandem axial flow pump.In this process,a parametric modeling method for each structural parameter is proposed,and use the Matiab editing program to adjust the blade placement angle.After two optimizations,the hydraulic performance of the same impeller serial axial pump has been improved,the lift is increased by about 0.54m,and the efficiency is increased by 3%,but it still has a large gap with the ideal effect3.Regression analysis was carried out on the experimental design results of the same impeller serial axial pump to study the influence of its structural parameters on its performance.The research shows that the impeller series axial flow pump with the same structural parameters has great influence on the performance of the impeller,and the rear impeller angle has the greatest influence,followed by the front impeller angle,followed by the circumferential declination.The least affected is the axial distance4.The design method of different impeller tandem axial flow pumps was studied.The geometric parameters such as the inlet and outlet triangles of the front and rear impellers,the front and rear impeller load distribution,the hub ratio,the cascade density,the number of front and rear impeller blades,the airfoil thickness and the circumferential impeller angle of the front impeller are studied5.Three sets of impellers are proposed for the front and rear impeller load ratio distribution The automatic design and parametric modeling of the front and rear impeller blades are realized by Matlab editing program.At the same time,Isight is used to optimize the front and rear impeller cascade density and the front impeller circumferential deflection angle of the three groups of impellers6.After optimizing the design of different impeller tandem axial flow pumps,the hydraulic performance is obviously better compared with the scheme of the front impeller load.This indicates that the front impeller should be assigned more load when designing the double impeller tandem axial flow pump.This scheme was selected for further numerical analysis,and its hydraulic performance and internal flow field were studied in depth,and the following conclusions were obtained:The head and efficiency of different impeller series axial flow pumps have a certain gap from the ideal effect,but it is greatly improved compared with the same impeller series axial flow pump.The optimized double-impeller tandem axial pump has a lift head of about 1.6 times that of the designed single-stage pump,and the high-efficiency area is about twice that of the ordinary axial-stage pump.The shaft power curve becomes flatter and has good regulation performance.The energy characteristics of the front and rear impellers also change significantly.