| As a high specific speed,large flow and low lift pump,axial flow pump has mature technology and convenient operation and maintenance.At present,it is widely used in farmland irrigation engineering,water transfer engineering,flood control and drainage engineering,municipal water supply engineering,chemical industry,shipbuilding industry and other fields.The water guide cone support at the inlet of the impeller is a water guide cone that uses the baffle support to fix the water guide cone rotating with the impeller at the outlet of the water inlet channel and separate from the impeller.The imported water guide cone support has the characteristics of simple structure,convenient construction and low relative cost.It has good practicability,economy and reliability.It can significantly improve the construction efficiency and play an auxiliary role in the maintenance of the impeller during the use of the axial flow pump.The beneficial influence of impeller inlet guide cone support on construction and maintenance has been fully recognized in engineering practice.At present,the inlet guide cone of some pump stations is provided with supports in the project,and the guide cone is separated from the impeller hub body,while the inlet guide cone and the hub body of the hydraulic model of axial flow pump are integral.In this way,it becomes necessary and meaningful to explore the impact of different settings on the hydraulic performance of the pump.In order to study the influence of the setting of the inlet guide cone support of the impeller on the hydraulic performance,pressure pulsation and the stress of the impeller and guide vane of the axial flow pump,this paper explores the influence degree of the inlet guide cone support on different flow conditions of the axial flow pump,and then analyzes the advantages and disadvantages of setting the inlet guide cone support during the operation of the axial flow pump.This paper uses the methods of theoretical analysis,model test and numerical simulation The axial flow pump without inlet guide cone support is studied.The quantitative influence of the inlet guide cone support on the external characteristics of the axial flow pump is tested through the energy test.The change of the water flow in the pump after the inlet guide cone support is tracked and recorded by the high-speed camera.The disturbance of the flow field with and without the inlet guide cone support is compared and analyzed by using the non-contact LDV flow field test technology;The three-dimensional steady and unsteady flow characteristics of the axial flow pump under the condition of inlet guide cone support are studied by numerical simulation.The reliability of the numerical simulation results is verified by the external characteristics and internal flow field results of the axial flow pump model test.The flow field variation,pressure pulsation and impeller force of axial flow pump with and without inlet guide cone support are compared and analyzed.The main results obtained are as follows:1.In this paper,the model test and numerical simulation of the pump section of the axial flow pump are carried out.The results show that the energy characteristic test head results of the two schemes are in good agreement as a whole,but in small flow,the head at the lowest point of the saddle shaped characteristic curve of the pump with inlet water guide cone support increases by 1.82 m,indicating that the installation of inlet water guide cone support of the axial flow pump can effectively improve the head under small flow conditions.However,the efficiency of the high efficiency area decreased,and the maximum efficiency decreased by 2.56%.Under the design flow condition,the flow pattern at the inlet of the impeller with inlet guide cone support is uniform;When the pre rotating flow of the support is too large,it will not affect the backflow of the inlet cone and will not occur when the pre rotating flow of the support is too small.2.The hydraulic characteristics under different flow conditions are obtained by numerical simulation.The setting of inlet guide cone support affects the velocity distribution near the impeller hub;Under the small flow condition of local backflow,the setting of the support makes the negative value of the shaft surface velocity near the hub disappear and improves the backflow to a certain extent.With the advance of the water flow,the influence of the support on the velocity distribution in the impeller domain gradually decreases;Under the small flow condition in the saddle area,the velocity distribution at the inlet of the impeller area changes greatly,the circumferential velocity decreases,and the negative absolute value of the axial velocity near the hub increases.With the advance of the water flow,the influence of the support on the impeller area decreases gradually.3.Under different flow conditions,the setting of inlet guide cone support has a great impact on the surface pressure of blade position near the hub.Under the design flow condition,the change of other positions is small compared with that without support;Under the condition of small flow with local backflow,the pressure difference in the front middle increases slightly and the blade load increases;Under the condition of small flow in the saddle area,the pressure distribution on the blade surface changes greatly,and the pressure difference between the front and middle increases,which improves the work capacity of the blade to a certain extent,but the blade burden increases,and the low pressure at the blade head will lead to cavitation.4.The dynamic and static interference caused by the setting of the inlet guide cone support enhances the pulsation amplitude of the pressure pulsation of the water flow with the blade frequency as the main frequency.Under the design flow condition,the lowfrequency pulsation amplitude at the impeller inlet increases slightly;Under the condition of small flow with local backflow,a large number of low-frequency pulsations appear at the inlet and outlet of the impeller.The setting of the support increases the low-frequency pulsation amplitude at the inlet of the guide cone;Under the condition of small flow in the saddle area,the setting of the support reduces the low-frequency pulsation at the inlet of the impeller,and the pulsation changes at other positions are not obvious.5.Under the design and small flow conditions with local backflow,with or without inlet guide cone support,the axial force and radial force on the impeller change little,but under the conditions of saddle area,the axial force increases and the radial force changes little.Compared with the impeller without support,the peak and peak values of axial force and radial force under different flow conditions increase slightly.Under the design flow condition,the number of support baffles is the same as that of guide vane blades,and the force variation law of blades is the same as that without support.There are peaks and troughs the same as that of guide vane blades in one rotation cycle;Under small flow conditions,the force regularity of the impeller is poor due to the disorder of water flow and the presence or absence of inlet guide cone support. |
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