Study On Influence Of Clearance On Cavitation Performance Of Low Specific Speed Multistage Centrifugal Pump

Low specific speed multistage centrifugal pump is a fluid machine with wide application requirements,it plays a huge role in industrial production and life,but this pump is generally less efficient and has a lot of energy consumption.With the increase in the use requirements of the majority of users,the optimization of its performance is of great significance.The cavitation performance is also one of the main factors related to the stable operation of multistage pumps.Cavitation can cause various hazards,such as a reduction in energy characteristics,corrosion of overcurrent components,and generation of vibration and noise.Studies have shown that reflux vortices and cavitation are prone to occur at the inlet of the pump,this seriously affects the normal operation of the multistage pump,and low specific speed multistage pump has more clearance and complicated flow.So far there has not been much research on the effect of multistage pump clearance on its cavitation performance,this article examines the comparison of cavitation performance in low-speed multistage pumps with or without clearance,and studies the relationship between the size of the gap and its cavitation performance.It is of great significance to understand the effect of clearance on the cavitation performance of low specific speed multistage pump centrifugal pump.In order to explore the phenomenon and regularity of cavitation flow and the effect on cavitation performance of multistage centrifugal pump with low specific speed,design each flow-through component of a segmental multistage centrifugal pump in this case given the design parameters,and to get the performance prediction through numerical simulation and through tests to verify its reliability.Then analyze its cavitation characteristics.Combine the actual situation to increase the gap and compare the cavitation characteristics with the original model.Focus on the effect of changing the gap size under different cavitation coefficients on the cavitation performance of multistage pumps.Here are the main research contents and conclusions:1)Determine the structure of the multistage pump with the given parameters,designthe impeller,vane and suction chamber.Then modele,mesh,and begin numerical simulation.The results show that the tongue area is not in good flow,but the loss is small;the distribution of the first and second impellers on static pressure is similar.Due to differences in size specifications and blade combinations,there is a difference in the static pressure distribution between the first stage guide vanes and the secondary guide vanes.2)Set up a pump open test bench to start the experiment and through numerical simulation and experimental data comparison,the results show that the analog value is generally higher than the test value and the efficiency,head and power errors are within the allowable range.This shows that the numerical simulation is reliable.3)Analysis the cavitation characteristics of low specific speed multistage centrifugal pumps.This shows that with the reduction of the cavitation coefficient,static pressure continues to diffuse from import to export,the air bubbles in the impeller flow path are increasing,speed at the impeller outlet and the vane inlet has reduced,the function of the blade is deteriorated,the pressure value decreases and the pressure distribution is basically the same as the cavitation;with the cavitation continues to deteriorate,the area where cavitation occurs is getting bigger,and the turbulent pulsation is more severe,the loss is greater;pressure below 3474 Pa of saturation pressure first appears on the back of the blade inlet,this is consistent with the above analysis.4)Analysis from outer characteristics,cavitation performance curves,cavitation distribution and inlet pressure.It is found that the existence of the gap is unfavorable to the lift and efficiency of the multistage pump.As the cavitation coefficient decreases,the head coefficient is unchanged first,then becomes lower.No gap is worse than gap model in the early stage of cavitation and during the development of cavitation.When cavitation develops seriously,the pressure at the inlet is high and the cavitation performance is better than no gap.As the cavitation coefficient decreases,the pressure gap between the two narrows.When cavitation deteriorates severely,the appearance of the vortex caused the local pressure at the inlet to be too low and the flow rate to be too fast,import pressure becomes lower,results in worse cavitation performance;As the cavitation coefficient decreases,the pressure gap between the two narrows.When cavitation develops seriously,observing the distribution of vacuoles under different size gaps can be found that the presence of the mouth gap is beneficial to the cavitation performance of the pump's first stage impeller at the beginning of cavitation and during the development period.However,when cavitation is seriously deteriorated,it is not conducive to cavitation performance.The larger the gap of the mouth ring,the more favorable it is for cavitation performance.