| Centrifugal pump is a kind of mechanical equipment which uses liquid as working medium for energy conversion,it has the advantages of simple structure,convenient start-up and reliable performance,and so on.as the core component of centrifugal pump,impeller shape is mainly determined by blade profile,blade thickness and blade number.Therefore,these parameters have an important impact on centrifugal pump performance.At present,there are many research results about the influence of blade profile and blade thickness on centrifugal pump performance with different specific speed at home and abroad,while the research about the influence of blade number on centrifugal pump performance is relatively less.Therefore,this paper emphatically analyses the influence of blade number on centrifugal pump performance with different specific speed.The main research contents and results are as follows:1.In this paper,three kinds of single-stage single-suction centrifugal pumps with different specific speed(n_s=32?96?232)are studied,five schemes of blade number Z=4?5?6?7 and 8 are selected respectively,the numerical simulation of these schemes is carried out based on the SST k-?turbulence model,and the accuracy of the numerical calculation is verified by comparing the test results of centrifugal pump.The results show that the error between numerical results and experimental results of centrifugal pump efficiency and head is not more than 5%.2.By simulating five blade number schemes of three specific speed centrifugal pumps,the changes of head and hydraulic efficiency under different flow conditions are studied.The results show that the head of centrifugal pump with different specific speed increases with the increase of blade number in the whole flow range,and the rise rate of head under small flow condition is less than that under large flow condition,which shows that the influence of blade number on the head of centrifugal pumps with different specific speed is basically the same.The regulation that the hydraulic efficiency of centrifugal pump with different specific speed varies with blade number is different.The hydraulic efficiency at design operating point of low specific speed centrifugal pump increases with the blade number increasing firstly,and then decreases,the highest efficiency is achieved When the blade number is 6,and the highest efficiency of pump shifts to the condition of large flow rate.The hydraulic efficiency of medium and high specific speed centrifugal pumps varies with the blade number are basically same,the hydraulic efficiency at design operating point increases with the blade number,and reaches the maximum when the blade number is 8.3.Based on the analysis of external characteristics,the internal flow field characteristics of centrifugal pumps with different specific speed under five blade number schemes are studied.The results show that the pressure distribution in the impeller intermediate section of centrifugal pumps with different specific speeds is more uniform with the increase of blade number,and the range of inlet low pressure zone is smaller.With the increase of the blade number,the load distribution along the streamline direction of the centrifugal pump with medium and low specific speed is more reasonable,while the load of the centrifugal pump with high specific speed fluctuates.By analyzing the distribution of relative velocity and circumferential velocity in the middle section of impeller,it can be seen that the velocity distribution in impeller is more uniform with the increase of the blade number,the phenomena of outlet wake jet and secondary flow are weakened,and the hydraulic efficiency of impeller is improved.The reason is that more blades can better restrict the flow,make the fluid flow closer to the blade profile and flow in the pump,so the condition has been improved;however,centrifugal pump with high specific speed dues to the shorter flow passage and lower diffusivity of the blade,the restriction ability of the blade on the flow is poor,so the velocity of the impeller intermediate section is almost same with the increase of the blade number.4.Finally,based on the external characteristics,the ZGB cavitation model is used to study the cavitation performance of low specific speed centrifugal pump with different blade number.The results show that the blade number has an important influence on the cavitation performance of low specific speed centrifugal pump.At the design operating point,with the increase of the blade number,the anti-cavitation performance of the pump increases firstly,and then decreases.When the number of blade is 5,the anti-cavitation performance is the best,With the further increase of the blade number,the anti-cavitation decreases rapidly.The reason is that the increase of the blade number leads to squeezing at the blade inlet seriously,and the increase of the inlet flow speed leads to a faster drop of the inlet pressure,which makes cavitation occur easily. |
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