| In recent years,the number of centrifugal pumps in China is huge,and with the development of society,the demand for centrifugal pum ps is still growing rapidly.At the same time,the performance requirements of centrifugal pump are more and more strict,in which anti-cavitation performance is a key performance parameter and a difficult research topic.When serious cavitation occurs in the centrifugal pump,the cavitation will converge in each flow channel and become larger,resulting in blockage,which greatly reduces the external performance of the pump.When the bubble collapses,it will produce high-temperature and high-pressure micro jet,which will cause erosion damage to flow passage components such as blades,that is,cavitation.When the blade is seriously eroded and damaged,it will lose its power capacity,so that the pump can not work normally.The cavitation operation of the pump will also cause vibration and noise,which greatly reduces the service quality of the pump.Therefore,it is of great practical value and significance to study the cavitation mechanism of centrifugal pump and explore the cavitation suppression strategy.According to previous research experience,the design of splitter blades in the impeller of centrifugal pump can restrain and optimize cavitation to a certain extent,but it has a great influence on the performance of centrifugal pump.In order to minimize the influence on the external characteristics of centrifugal pump and reduce the disturbance to the flow in the impeller channel,the influence of unconnected tiny blades with different radial position,offset angle,width and length parameters on the cavitation performance is studied by means of experiment and numerical simulation.The main contents and innovative achievements of this paper are as follows:This paper firstly expounds the research background and current situation of cavitation,and briefly summarizes the definition and mechanism of cavitation.Then,it summarizes the current generation mechanism of cavitation in hydrofoils,axial flow pumps and centrifugal pumps,and the suppression methods and methods to understand the current situation.The methods of cavitation control in centrifugal pumps are mainly divided into: optimizing the structural parameters of the centrifugal pump body,adding external devices,changing internal structural features,and adding some internal structures.In thi s paper,a non-connected tiny blade structure is added on the inner shroud of the impeller,and its influence on cavitation and hydraulic performance is studied.The basic governing equations,turbulence and cavitation models in numerical methods are introduced.The centrifugal pump performance and cavitation test system and test procedures are introduced in detail,and the hydraulic and cavitation performance tests are completed.The external characteristics and cavitation performance are numerically calcu lated.The external characteristics and cavitation performance curves obtained by numerical calculation are in good agreement with the experimental curves.The maximum relative error of the head is within 4.0%,and the maximum error of the efficiency is 5.9%,all meet the error requirements,which verifies the reliability and accuracy of the numerical simulation.The tiny blades arranged near the inlet in the middle of the flow channel(such as schemes A1 and A2)can inhibit cavitation better in the initial stage of cavitation,but promote cavitation in the development and severe stages of cavitation.The tiny blades arranged in the middle and rear positions(such as schemes A3 and A4)can inhibit the cavitation and improve the fracture head at all stages of cavitation,especially in the initial and severe stages of cavitation.The tiny blades can induce relatively high pressure near the impeller inlet,slow down the diffusion of the low pressure area,and sort out the structure of the flow field,which has a n inhibitory effect on cavitation.After adding tiny blades,the pump head and efficiency do not change much,and the relative errors are within ±1.0%,which has little impact on the external characteristics of the pump,and the tiny blades reduce the critical cavitation margin and increase the fracture head by 10.4%.In the initial,developing and severe stages of cavitation,the bubble volume was reduced by 73.3%,5.8% and 26.0%,respectively,and the inhibitory effect was significant.In the initial and developing stages of cavitation,the longer tiny blades can improve the confinement and diversion effect on the flow,reduce the strength of the vortex in the flow channel,and optimize the flow field structure.In the severe stage of cavitation,the tiny blades enhance the strength of the vortex.Under each cavitation allowance,the tiny blade reduces the range of low-pressure area,suppresses cavitation,has little impact on the overall pressure distribution of the flow field,reduces the amplitude of pre ssure fluctuation at the main monitoring points,reduces the vibration and noise of the pump,and makes the pump run more stable.After adding unconnected tiny blades with different offset angles,the head is slightly reduced,and the reduction range is wi thin 0.5%,and the external characteristics have little effect.Compared with the original pump,the tiny blade scheme with different offset angles has an inhibitory effect on the occurrence and development of cavitation.However,in the severe stage of ca vitation,when the tiny blades are offset to the suction surface and pressure surface of the main blade,the inhibition effect on cavitation is weakened,and the fracture head is reduced.When the tiny blade is in the middle position of the flow channel θ=0°,the head is the highest,the bubble volume is the smallest,and the cavitation suppression effect is the best.There is an optimal tiny blade width parameter to optimize the cavitation suppression effect.When the tiny blade width of the model pump is equal to 3/4 of the main blade width,the cavitation performance of the centrifugal pump is the best;The widened tiny blades have little effect on the hydraulic performance of centrifugal pump.Compared with the prototype pump,the head is slightly reduced,the efficiency is slightly increased,and the relative change rate is within 1.0%.In the initial and developing stages of cavitation,the widened tiny blades have little effect on the flow field structu re,and slightly increase the turbulent kinetic energy near the impeller inlet.However,in the severe stage of cavitation,the widened tiny blades intensified the vortex strength at the rear end and further weakened the turbulent kinetic energy near the outlet.After adding tiny blades with different length parameters,the influence on the head and efficiency of the centrifugal pump is also small under each working condition.In each stage of cavitation,the longer and shorter tiny blades have inhibitory effects on cavitation,and the cavitation inhibition effects are equal and better.In the initial and developing stages of cavitation,the longer tiny blades can optimize the flow field structure,while the shorter tiny blades have less influence on the flo w field structure,but both strengthen the vortex strength in the flow channel in the severe cavitation stage.The shorter tiny blades also slightly increase the turbulent kinetic energy near the blade inlet,induce relatively high pressure near the inlet,and reduce the turbulent kinetic energy in the high turbulent kinetic energy region near the impeller outlet.At the same time,it also reduces the overall pressure pulsation in the pump,thereby reducing noise and vibration,making its ca vitation operation more stable.The method of arranging unconnected tiny blades on the shroud of impeller is of great significance to inhibit the occurrence and development of cavitation in centrifugal pump. |
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