Analysis Of Internal Flow Characteristics And Pressure Pulsation Of Vertical Long-shaft Fire Pump Based On Optimization Of Impeller And Space Guide Vane

Multi-stage long-shaft pumps with space guide vane are often used in important fields such as electric power,mines,offshore platforms,and large terminals due to their compact structure,convenient maintenance and simple pipelines.The space guide vane acts as a pressurized water chamber,which makes the fluid change from radial outflow to axial outflow,and there is a complicated flow phenomenon in the flow channel.Similarly,the space guide vane long shaft pump also has the problem of low performance.In order to improve the performance of the pump and the internal flow field,most researchers have performed a single optimization on the impeller and the guide vane,without considering the compatibility of the two.Therefore,this subject takes the XB4.3/240-300LC offshore platform large-flow high-lift vertical long-shaft fire pump as the research object,and optimizes the space guide vanes on the basis of completing the optimization of the long-shaft pump impeller,and analyzes and explores the characteristics of pressure pulsation,aiming to provide basis and support for improving the hydraulic performance and stable operation of the space guide vane long-shaft pump.The main research contents and conclusions of this paper are as follows:（1）Through analysis and research on the performance of the original model and the internal flow field,it provides direction for the optimization of the impeller.Under the condition that the basic design parameters of the impeller,the width of the impeller outlet,the axial distance from the middle position of the impeller outlet to the impeller inlet and the flow area of the outlet remain unchanged,the impeller outlet edge is tilted.Design six schemes of impeller outlet inclination angleθ=0°,5°,10°,15°,20°and 25°,and use the digital software CFturbo to draw the water body of impeller,matching with the original guide vane for constant constant value simulation.The results show that the inclined outlet edge of the impeller has a significant influence on the external characteristics of the long-shaft pump.Changing the angle of inclination will result in a smaller increase in the lift and efficiency under small flow conditions;in the range of large flow conditions,the increase will be relatively large.There is an optimal inclination angle of the impeller outlet,so that the head and efficiency of the long-shaft pump can reach the best.Through the analysis of the absolute velocity components,it is found that the tangential component C_u2and the radial component C_r2of the absolute velocity at the outlet of the impeller have good consistency in the distribution of large flow conditions,but the distribution law is worse under the small flow conditions.（2）In order to improve the flow efficiency of the space guide vane of the vertical long-shaft pump,a reasonable optimization method is selected to optimize it and analyzed the influence of the geometric parameters of the space guide vane of the vertical long-shaft pump on the head H and efficiencyηindex,and find out the primary and secondary factors of the test factors and put forward the best space guide vane design scheme based on the optimized impeller matching the space guide vane of the long-shaft pump to improve the flow efficiency and take into account its head.In this study,the geometric parameter of the space guide vane is introduced as the blade edge inlet inclination angleγ,blade outlet angleα₄,guide vane blade wrap angleΦ,and the distance between the intersection of the guide vane blade outlet edge and the outer side of the guide vane and the guide vane body outletδas the four factors of the orthogonal experiment.The four-factor four-level L₁₆（4⁴）orthogonal table is selected,and 16 kinds of schemes are designed and numerical simulations are carried out respectively,and the range analysis is carried out on the results of the design operating points to obtain the best combination scheme.The results show that the wrap angleΦhas the greatest effect on the lift and efficiency of the long-shaft pump.The primary and secondary order affecting the head index isΦ,δ,α₄,γand the primary and secondary order affecting the efficiency index isΦ,δ,γ,α₄.Under the design conditions,the head of the optimized pump model is increased by 1.83m,and the efficiency is increased by 1.11%compared with that of the pre-optimized pump model.The internal flow characteristics of the optimal scheme were analyzed,and it was found that the internal flow field of the guide vane of the model pump space was significantly improved after optimization.The meridional velocity at the middle of the guide vane,the blade outlet and the guide vane outlet is improved to a certain extent,the axial velocity is lower than that of the original guide vane,and the number of vortices in the flow channel is reduced.（3）Through the unsteady-state numerical simulation of A pump model（inclined outlet angleθ=0°impeller and original space guide vane）,B pump model（inclined outlet angleθ=15°impeller and original space guide vane）and C pump model（inclined outlet angleθ=15°impeller）and optimized space guide vane),the unsteady information of different monitoring points is obtained,and compare the time-frequency domain information and analyze and study the radial force distribution law under different working conditions,and explore the characteristics and law of pressure pulsation in the long-shaft pump.The results show that there are three forms of pressure pulsation:white noise,leaf frequency and shaft frequency.The inclined outlet of the impeller can better improve the pressure pulsation in the pump,especially under large flow conditions.As the flow rate increases,the radial force of the long-axis pump basically gradually decreases.