Study On The Timing Effect Of The Guide Vanes Of Segmented Multistage Centrifugal Pumps

Multistage centrifugal pumps paly an important role in thermal power,nuclear power,fire controling,petrochemical industry,mining,desalination of seawater and other important industrial fields in economy.With the continuous improvement of energy saving and emission reduction requirements in China,higher requirements are put forward for the better running stability of multistage pumps.In recent years,clocking effect has been widely used in the optimization of multistage centrifugal pumps.However,most of these research aimed at impellers,while little attention has been paid to the clcoking position of guide vanes,which are also of great importance.In this thesis,a typical segmental multistage centrifugal pump is chosen as the research object.By combining numerical calculation with experimental test,the mechanism of the clocking effect of guide vanes is analyzed in the aspects of energy performance,pressure fluctuation,vibration characteristics and internal flow mechanism of the segmental multistage centrifugal pump,which provides a new direction and guidance for the optimization of the multistage centrifugal pump.The main contents and achievements of this thesis are as followed:1.The classification of multistage centrifugal pumps and the research progress of guide vanes are firstly summarized.Then the developping trendency of clocking effect in the field of multistage centrifugal pumps is expounded.Finally,the application status of test and numerical simulation methods in the study of internal flow of centrifugal pumps is systematically summarized.2.The Reynolds time-average method combined with the RNG k-ε turbulence model is used to simulate the inflow of the multistage pump two pump stages under different guide vane clocking schemes.The clocing effect of guide vanes is analyzed in the field of pump energy performance,pressure pulsation and radial force.The main conclusitions are as followed:(1)By changing the circumferential position of the secondary guide vanes,the head and efficiency of these two pump stages under different clocking scheme are relative,whoese difference is less than 0.5%;(2)When the clocking angle of the second guide vane is 30°,the peak fluctuation of pump head and efficiency in a cycle reaches the maximum at the same time,at 0.417 m and 2.029%,respectively;(3)With the increasing of the clocking angle of second guide vane,the main frequency amplitude of pressure fluctuation in each position of the pump stage first decreases and then increases,while the maximum reduction is 35.9%;(4)The clocking effect of guide vane has a significant influence on the radial distribution of the force on the rotor,which is most uniform when the clocking angle reaches 30°;(5)When the clocking angle of guide vanes is 30 degrees,which equal to the half of the angle between the blades,the clocking effect of the guide vanes on reducing pressure fluctuation and uniformitying radial force is the most obvious.3.A synchronous test rig is built for measuring the external characteristics,vibration and pressure fluctuation of a five-stage centrifugal pump.The test scheme of the clocking effect is determined by orthogonal design method.The performance of a five-stage centrifugal pump under different guide vane clocking schemes is tested.The test results show that:(1)Compared to the non-guide vane sequential scheme,the head and efficiency of the five-stage centrifugal pump under different clocking schemes is increased,ranging from 0.1% to 0.5%;(2)The clocking of guide vane has a great influence on the outlet pressure fluctuation of this five-stage pump.The effective value of the pump outlet pressure fluctuation under the guide vane timing scheme is 27.2% lower than that under the non-clocking scheme,and the main frequency amplitude is 35.8% lower;(3)The main frequency amplitude of inlet vibration speed can be reduced by 20% by correct clocking effect scheme,and the main frequency amplitude of outlet vibration speed can be reduced by 30% by changing the last four stage guide vanes compared to that of non-clocking scheme;(4)The staggered arrangement of the last four guide vanes of the pump has the best effect on reducing the fluctuation and vibration of the outlet pressure which can bring the best operation stability of the pump.4.The internal flow of this five-stage centrifugal pump under the no clocking scheme and the optimal clocking scheme is numerically simulated.The flow conditions of the pump in different places are analyzed one by one.The mechanism of the clocking effect of the guide vane is studied and compared.The results show that:(1)The clocking effect of guide vanes changes the shape of jet high-speed zone at the outlet of impellers of each stage,as well as the position and area of vortices on both sides,thus destroying the cumulative effect of vortices in the whole pump;(2)The clocking effect of guide vanes reduces the velocity gradient in the guide vane channel of each pump stage,making the velocity in the guide vane channel and outlet section more uniform,improving the performance of the guide vanes;(3)The clocking effect of guide vanes reduces the hydraulic loss of the guide vane channels of each pump stage.The total hydraulic loss of this pump are reduced totally to 0.4272 m,accounting for 1.11% of the total pump head;(4)The clocking effect of guide vanes can reduce the turbulent kinetic energy in the outlet channel of the pump and reduce the area of the vortex core in the channel,making the outflow more stable.