Research On Changing The Operating Conditions Of Centrifugal Pump By Axial Translation Of The Shroud Of Impeller

Because the impeller of the large-flow centrifugal pump used in the Yellow River irrigation project has the characteristics of welding and assembly,this paper proposes a method of axially cutting the blade before welding and translating the shroud of the impeller to change the hydraulic performance of the centrifugal pump,which has engineering application value.This started the research.As the most important hydraulic component of a centrifugal pump,the method of cutting its outer diameter changes the hydraulic performance of the pump,increase product versatility,and reduce the operating cost of pumping station.In this paper,the research purpose of the axial translation impeller shroud corresponds to it.This article uses five centrifugal pumps MS124,M129,S700-500,M93,HS800-700-700 as the research objects,and the influence of the axial translation impeller shroud on the performance of the centrifugal pump is studied by the method of numerical simulation,and combined with the theoretical analysis,the prediction formula of the performance change of the centrifugal pump is derived.The main research results of this paper are as follows:(1)The study found that the H-Q curve of the centrifugal pump tends to be steeper while moving downward along with the translation of the shroud,and the curve shape of the centrifugal pump with the higher specific speed changed more drastically.The shroud of the translational impeller reduces the hydraulic loss caused by flow separation in the impeller and volute.However,under large flow conditions,the secondary flow and backflow are aggravated.The flow conditions between the impeller and the volute further deteriorate,resulting in an increase in hydraulic loss.Therefore,after the shroud is translated,the efficiency of small flow conditions increases significantly,while the efficiency of large flow decreases.The highest efficiency point shifts to the small flow,and the value of the high efficiency point does not decrease significantly.The?-Q curve of the centrifugal pump shows a trend of shifting to the left as a whole.(2)Compared with the method of cutting the outer diameter of the impeller,it is found that the centrifugal pump after axially translating the shroud of the impeller obtains relatively high head and efficiency under small flow conditions,which effectively broadens the type spectrum of the pump,and has engineering value and theoretical significance.Based on the theory,the conversion formula of the H-Q curve of the centrifugal pump changing with the translation of the shroud of the impeller is deduced.Based on the numerical simulation data,the conversion formula is corrected by the method of multiple linear regression analysis.After verification,it is found that when the translational amplitude of the shroud of the impeller is small,the corrected formula converts the H-Q curve of the centrifugal pump with a medium specific speed(120-140),and the accuracy is relatively high under the working conditions of 0.6Q_dto 1.2Q_d.(3)The study found that the axial translation of the shroud of the impeller reduces the dynamic and static interference between the impeller and the diaphragm under small flow conditions,and reduces the amplitude of the low-frequency pressure pulsation caused by the vortex in the impeller channel.However,the intensity of the low-frequency pulsation caused by the secondary flow increases under the large flow condition.Translating the shroud of the impeller reduces the amplitude of the low-frequency pressure pulsation caused by the blade shedding vortex impacting the volute diaphragm,while the dynamic and static interference of the semi-helical suction chamber is strengthened.The steady-state radial force acting on the impeller under small flow and design flow conditions decreases with the axial translation of the shroud,and the pulsation amplitude of the unsteady-state signal of the radial force also decreases.(4)With the translation of the shroud of the impeller,the deterioration of the periodic cavitation performance of the impeller flow channel caused by the diaphragm structure of the suction chamber under small flow conditions is alleviated.The anti-cavitation performance of the centrifugal pump increases with the translation of the shroud.However,there is a turning point.After the turning point is exceeded,continuing to translate the shroud will cause the flow in the impeller and volute to deteriorate and the anti-cavitation performance to decrease.This turning point appears in advance as the working flow increases.