| The application of multi-stage centrifugal pumps in industrial and agricultural production is very extensive,with the characteristics of high head and high power consumption.Therefore,in the process of hydraulic design,optimizing every detail to comprehensively improve the hydraulic efficiency of multi-stage centrifugal pumps is of great significance for energy conservation and emission reduction.In general,the primary impeller of a multi-stage centrifugal pump needs to consider both efficiency and cavitation,while the secondary impeller does not need to consider the impact of cavitation and only aims to improve efficiency.At the same time,its axial length should also be considered to consider the issue of operational stability.Therefore,this article takes the secondary impeller of a multi-stage centrifugal pump as the research object,and under the premise of using the same grid flow line,based on RNG k-εThe turbulence model is used for steady numerical calculations to explore the effects of geometric parameters such as impeller inlet diameter,blade inlet edge position,and axial shape on the hydraulic performance of multi-stage pumps.The principles and methods for determining the geometric parameters of the secondary impeller while maintaining high efficiency are clarified.Firstly,based on the hydraulic design of the original model of the secondary impeller with an inlet diameter of 290 mm,the inlet diameters of the secondary impeller were set to 260 mm,270mm,280 mm,and 300 mm,respectively.The impact of changes in the inlet diameter of the secondary impeller on the hydraulic performance of the multi-stage centrifugal pump was systematically studied.The results showed that there was a critical value for the inlet diameter of the secondary impeller to achieve the highest hydraulic efficiency of the pump,When the inlet diameter deviates from the critical value and begins to increase or decrease,the efficiency of the pump will decrease;Since the efficiency of the pump is only 0.08%lower than the highest efficiency when the impeller inlet diameter is 280 mm,it can be concluded that the optimal inlet diameter of the secondary impeller is within a specific range.If the range is defined by the Characteristic velocity at the impeller inlet,the corresponding speed value is(4.8～5.5)m/s.The practical inspection proves that the speed range is reliable and feasible.After determining the optimal value of the inlet diameter of the secondary impeller as 270 mm,in order to further study the impact of the change in the inlet edge position of the secondary impeller blades on the hydraulic performance of the multi-stage centrifugal pump,based on the optimal inlet diameter hydraulic design,the grid flow line is extended forward along the tangent direction at the inlet edge position,increasing the blade wrap angle by 5 ° and 10 ° respectively at the inlet,and two schemes for moving the inlet edge position forward are obtained;Reset the position corresponding to the 5 ° wrap angle line of the original grid to the blade inlet edge,and obtain a scheme of moving the inlet edge position back.Add the original scheme to a total of 4 groups of schemes;The research results show that when the inlet edge of the blade extends forward,the pump head decreases,the shaft power decreases,the velocity distribution in the impeller channel becomes worse,and the hydraulic loss increases,but the pressure difference on both sides of the blade decreases significantly,that is,the reduction of the shaft power is greater than the reduction of the head,so the hydraulic efficiency of the pump increases with the extension of the inlet edge of the blade,and the greater the extension of the inlet edge of the blade,the higher the hydraulic efficiency of the pump;On the contrary,when the inlet edge of the blade moves backward,although the head increases,the increase in shaft power is greater,and the efficiency actually decreases.Finally,in order to determine the impact of changes in the axial surface area of the secondary impeller on the hydraulic performance of a multi-stage centrifugal pump,based on the hydraulic optimization plan of the secondary impeller with a 10°forward extension of the blade inlet edge,two sets of schemes were designed to increase the axial surface area and one set of schemes to reduce the axial surface area by adjusting the profile of the front cover plate of the impeller axial surface.The results show that with the increase of the impeller axial area,the pump head,shaft power and efficiency increase,the uniformity of the velocity distribution in the impeller channel increases,and the pressure difference on both sides of the blade increases;But when the axial surface area increases to a certain value,the efficiency of the pump reaches a higher range,and the velocity vector field in the impeller flow channel also maintains a relatively stable structure.The optimization results of the axial plane diagram indicate that the initial axial plane diagram is the optimal structure for maintaining high efficiency of the impeller.In conclusion,during the hydraulic design of the secondary impeller of the multistage centrifugal pump,first determine the inlet diameter of the impeller according to the size of the impeller inlet Characteristic velocity,then determine the reasonable front and rear cover plate profiles according to the distribution characteristics of the critical value of the axial surface area,and keep the inlet edge of the blade as far forward as possible according to the sealing and structural requirements,which can easily and quickly determine the axial surface diagram structure of the impeller that can maintain high efficiency,Thus reducing the number of hydraulic optimizations,shortening optimization cycles,and improving optimization quality.Based on the above theory,the hydraulic design,manufacturing,and testing of a parallel split multi-stage centrifugal pump were carried out,with an efficiency of 83.7% and good results.This proves that the optimization theory and design method proposed in this article are reliable and feasible,and can provide theoretical reference and method guidance for the hydraulic design and performance optimization of the secondary impeller of multi-stage centrifugal pumps.It has practical application value. |
PDF Full Text Request