Effects Of Impeller Vane Staggered Angle On Pressure Fluctuations For A Double-suction Centrifugal Pump

Double-suction centrifugal pumps are widely used in water diversion,agriculture,energy and chemical fields.The pressure fluctuation of double-suction centrifugal pump has close relationship with vibration,noise,and cavitation.It is one of typical unsteady features of the pumps.In this paper,by designing and manufacturing one double-suction centrifugal pump with five differient blade stagger angle impellers and carrying on systematic experimental investigation and CFD computing with it,The effects of blade stagger angle for double-suction centrifugal pump on pressure fluctuations and hydraulic properties are revealed systematically.One experimental unit of typical double-suction centrifugal pump is built and the test investigation is performed on pressure fluctuation characteristics including five impellers with different blade stagger angles(0°,12°,24°,36°,48°)and different flow rates.It is obtained that the relationships between impellers stagger angles and pressure fluctuation characteristics.The results show:(1)There is no obvious effect of stagger angles on head and efficiency for double-suction centrifugal pump.(2)The distributions of pressure fluctuation are relatively uniform along the suction chamber,and the maximum value of the pressure fluctuation amplitude is found near the suction inlet tongue region.The pressure fluctuation is affected largely by the impeller rotation,whose dominant frequencies include impeller rotation frequency and its harmonic frequencies,and half blade passage frequency.Stagger angle has a small effect on pressure fluctuation in suction chamber.(3)Stagger angle has more effect on the pressure fluctuations in volute casing,especially remarkable on the amplitude of blade passage frequency.Among the tested cases,when the blade stagger angle is close to middle stagger positon(360°/2*N),the distributions of pressure fluctuation in the volute become more uniform,and the pressure fluctuation amplitude is lowest.The pressure fluctuation amplitude decreases over 50%than non-staggered impeller.(4)It is obtained that the relationships between flow rates and pressure fluctuation characteristics.The pressure fluctuation is lower at normal operation scope(0.6Qn?1.2Qn),but increased at the lower flow rates.In suction chamber,pressure fluctuation amplitudes of half blade passage frequency at 0.2Qn and 1.2Qn flow rates are 3.86 times and 1.11 times of rated flow.In the volute,the pressure fluctuation dominant frequency is blade passage frequency,and the amplitudes at 0.2Qn and 1.2Qn flow rate are 0.98 times and 2.01 times of rated flow.The numerically study on relationships between blade stagger angles and pressure fluctuations of double-suction centrifugal pump are performed.The simulationed hydraulic properties and pressure fluctuation results nearly correspond with the test results.According to analysis of the pump fluid time-frequency distributions,pressure field distributions and vorticity magnitude evolutions for the different stagger angle impellers,it is found that the magnitude of moving vorticities decreases with blade stagger angle closing to middle stagger position from parallel postion,and the secondary flow formed by jet-wake flow at the exit of impeller is also weakened continuously.This is the main reason caused the change of pressure fluctuations with blade stagger angle difference in double-suction centrifugal pump.The numerically study is carried out on relationships between of double-suction centrifugal pump flow rates and pressure fluctuations.By analysis of pump fluid pressure fluctuation's time-frequency distribution,static pressure distribution and volecity distribution for the different flow rates,it is discoved that the fluid volecity direction distribution is extremely nonuniform at lower flow rates of 0.2Qn and 0.AQn.There are apparent inherent lateral flows,even inverse flows can be found.This indicates that there are plenty of vorticity fields and secondary flows at lower flow rate cases.The fluid volecity distribution is more stable and pressure fluctuation decreases when flow rate increases.As a result,this study reveals the reason,to some extent,why the pressure fluctuations of double-suction centrifugal pump decrease with flow rate rise.The investigation achievements of this paper give a valuable guidance to improve the hydraulic design and operating stability for double suction centrifugal pumps.