| Cavitation has an important impact on the hydraulic performance,service life,and mechanical vibration of the centrifugal pump.In order to improve the cavitation performance of the centrifugal pump,it is necessary to fully consider the influence of the change of the impeller geometry on the cavitation performance in the hydraulic design process.In this paper,the cavitation performance of the centrifugal pump was improved by improving the pressure distribution on the back of the blade inlet.The geometric parameters of the blade inlet were systematically discussed on the premise of keeping the impeller axis and the blade inlet position unchanged.These parameters included the influence of factors such as the blade inlet angle,thickness of the blade and the geometry of the leading edge of the blade on the cavitation performance of the centrifugal pump.And the influence of these factors on the hydraulic performance and pressure pulsation characteristics were analyzed as well.Based on the Reynolds time-averaged N-S equation with the RNG k-?turbulence model.The research was carried out through ANSYS FLUENT in this paper.And the standard wall functions were used in processing the near-wall data.The ICEM CFD was used to perform hexahedron structured grid on the computational domain,so as to effectively control the mesh size and mesh number of the near-wall surface.When the number of meshes was about 9.3 million,the mesh-independent requirements were met.The verification results of numerical calculation accuracy show that the critical NPSH has the highest accuracy when the cavitation model adopts Schnerr-Sauer,the flow state is unsteady,and the y~+value of the near-wall mesh scale is in the range of40-70.The absolute error is-0.03m and the relative error is-1.38%.The prediction of hydraulic performance is based on the method of constant calculation.The absolute error of calculation efficiency is 0.09%,and the relative error is 0.11%.Overall,the numerical calculation method used in this paper has a very high calculation accuracy,and the subsequent research on the influence of the variation of the blade inlet geometry on the pump performance has a high degree of credibility.The hydraulic design of the blade inlet geometry change is:increase the inlet angle of two groups in total again on the basis of the original model inlet angle,and increase the inlet angle from the front shroud by 2°,1°,0.5°and 3°,2°,1°,while the back shroud keeps the original inlet angle unchanged;on the basis of the second group of blade inlet angles,the blade is thickened.The original model,the second group of blade inlet angles and the blade thickening are three schemes of which the leading edges of the blades are chamfered separately,and the geometry of the leading edge of the blade is changed from a circular shape to an elliptical shape.The above numerical calculation method was used to calculate the cavitation performance and hydraulic performance of a total of seven hydraulic design schemes including the original model.The three factors of blade inlet angle,blade thickness and blade leading edge geometry,and the effect of its combination on the cavitation performance,hydraulic performance and pressure pulsation characteristics of the pump were systematically studied and analyzed.The results show that as the inlet angle of the blade is increased within a certain range,the efficiency of the pump is reduced,while the cavitation performance is improved obviously,and the pressure pulsation amplitude is also slightly decreased.When the blade thickness is increased,the pump efficiency is significantly decreased.The cavitation performance also decreased and the pressure pulsation amplitude remained basically unchanged.Chamfering the leading edge of the blade can improve the pump efficiency to a certain degree and can have a certain inhibition on the birth and development of cavitation.However,at the end of the cavitation development,a re-jet can be formed,which causes the bubble to fall off from the position closer to the inlet edge of the blade and rapidly develop into the impeller flow path,resulting in a decrease in cavitation performance.The original model chamfer hydraulic design always maintains the minimum pressure pulsation amplitude during the whole process of cavitation development,and reduced the pressure pulsation amplitude significantly even in the complete cavitation stage.The pressure pulsation amplitude of the blade thickening chamfer hydraulic design is always high in the whole process of cavitation development.Even in the complete cavitation phase,the pressure pulsation amplitude is increased by 3 times,and the main frequency is changed from the blade frequency to the axial frequency,which can generate obvious influences on mechanical vibration.There is no obvious law on the influence of the chamfering of the leading edge of the blade on the pressure pulsation.However,by comprehensively analyzing the pressure pulsation characteristics of each hydraulic design in the cavitation state,it can be found that as long as the inlet angle of the blade is appropriate and the leading edge of the blade is chamfered,the pump’s pressure pulsation characteristics are optimized.The engineering test results of performance optimization of a certain type of mixed-flow pump show that the excessive inlet angle of the blade can cause the hydraulic efficiency and cavitation performance of the pump to decrease significantly,but after grinding the chamfer of the leading edge of the blade,the hydraulic efficiency and the performance of cavitation of the pump has been greatly improved.The efficiency of the design working point has increased by 7 percentage points,and the critical NPSH has decreased from 13.05m before being chamferyed to 9.25m after being chamferyed.It can be seen that the geometry of the blade inlet can have an important influence on the hydraulic performance and cavitation performance of the pump.It is an important factor in the hydraulic design process and must be highly valued.It can also be found that chamfering the leading edge of the blade has a high application value in engineering practice.The conclusions of this paper can provide reference information on the details of the hydraulic design and optimization of the pump. |
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