Study On Internal Flow Characteristics And Rotor Dynamics Of Multistage Pump As Turbine

In today ’s increasingly global energy shortage,China is actively carrying out energy conservation and emission reduction work to provide a strong guarantee for the realization of ’ carbon peak ’ and ’ carbon neutral ’ ecological civilization construction.Generally,there is a large amount of liquid residual pressure energy in the industrial process.As an energy recovery device,the hydraulic turbine can convert the pressure energy of the liquid into the mechanical energy of the impeller,so as to realize the recycling of energy.Because the multistage pump as turbine can arbitrarily increase or decrease the number of impeller stages,the multistage pump as turbine can achieve a wide range of pressure recovery.Therefore,it is of great significance to study the multi-stage pump reversal as a hydraulic turbine.In this thesis,a multistage pump as turbine is taken as the research object.The main research contents are as follows:1.Study on steady flow characteristics of multistage pump as turbine.In order to study the internal steady flow characteristics of the multistage pump as turbine,this thesis first analyzes the external characteristics and internal flow field of the multistage pump as turbine,and then studies the influence of the number of last stage impeller blades on the turbine performance.The results show that the efficiency of the primary overcurrent component is the highest,the efficiency of the secondary overcurrent component is the second,and the efficiency of the final overcurrent component is the lowest.In the process of energy recovery,the hydraulic loss of the outlet chamber of the multistage pump as turbine decreases first,then increases and then decreases with the increase of the flow rate,and the hydraulic loss of other flow components increases with the increase of the flow rate.When the last stage impeller is six blades,the hydraulic loss is the smallest under the optimal working condition,and the hydraulic loss of the corresponding annular outlet chamber is also the smallest.2.Study on unsteady pressure fluctuation characteristics of multistage pump as turbine.In order to study the unsteady pressure pulsation inside the multistage pump as turbine,different pressure monitoring points are set up in each flow passage component of the multistage pump as turbine,and the time domain and frequency domain characteristics of each flow passage component are studied.The results show that the pressure fluctuation in the impellers of the multistage pump as turbine changes significantly periodically,and the number of fluctuation peaks of the pressure coefficient of the impellers is equal to the number of blades of the positive guide vane.Along the direction of liquid flow,the closer the monitoring points in the positive guide vanes are to the impeller,the greater the pressure pulsation is,while the frequency domain diagram of the reverse guide vanes has no obvious law.The variation law of pressure pulsation at the monitoring points in the inlet chamber and the outlet chamber is similar,and the variation law of pressure pulsation is mainly related to the setting position of the monitoring points.3.Modal analysis of multistage pump as turbine rotor components.In order to study the natural frequency and critical speed of multistage pump as turbine rotor components,the dry mode and wet mode of multistage pump as turbine with or without prestress are numerically simulated.The results show that the change rule of the dry modal mode shape diagram is similar with or without prestress,and the natural frequency of the dry modal becomes larger obviously with prestress.The natural frequency of the wet mode is smaller than that of the dry mode at the same order.The critical speed of the multistage pump as turbine rotor component when the forward whirl occurs is much larger than the normal operation speed,so multistage pump as turbine will not resonate during normal operation.