Fluctuation And Vortex Analysis Of Internal Flow Of Double-suction Centrifugal Pump

As an important part of the water transfer project,the pump station plays an important role in the rational dispatch and management of water resources.With the improvement of living standards,the requirements for the safety and quality of water supply are higher,which requires the pumping station to have higher reliability and stability.As an important part of the pumping station system,the pump must frequently adapt to different working conditions.After deviating from the design operating point during operation,the hydraulic flow state in the pump is abnormal,which induces strong pressure pulsation,in turn causes the vibration of the pump and connecting pipes.Therefore,it is of great significance to study the unstable flow in centrifugal pump and its relationship with pressure pulsation and vibration to improve the efficiency,reduce energy consumption and ensure the safe and stable operation of pump station.This paper takes a double-suction centrifugal pump as the research object,the relationship between the complex flow phenomenon inside the pump and the pressure pulsation and vibration characteristics is studied by numerical simulation method,vibration test,simultaneous introduction and dynamic mode decomposition method（DMD）.The main contents and research results are as follows:Double suction pump pressure pulsation characteristics.Based on the unsteady calculation results of three different flow conditions,the time-domain and frequency-domain characteristics of the pressure pulsation at different flow rate conditions and monitoring points of the impeller and volute of the double-suction pump are studied.The results show that the pressure pulsation waveform of each monitoring point is stable and the periodicity is obvious from the time domain characteristics.From the frequency domain characteristics,the pressure pulsation in the runner is dominated by the rotation frequency and its multiple frequency.Under different working conditions at the same monitoring point,the amplitude of pressure pulsation in the runner is lower in the 1.0Q and 1.2Q working conditions,and the pressure pulsation in the 0.8Q working condition is significantly enhanced.The amplitude of the pressure pulsation in the volute area from the position of the tongue to the outlet of the volute shows a trend of first decreasing,then increasing and then decreasing,and the amplitude of the pressure pulsation is the strongest appear the volute tongue.And the pulsation is dominated by the blade passing frequency and its multiples.The amplitude of volute pressure pulsation under different working conditions at the same monitoring point is the highest at 0.8Q working condition.Internal flow analysis of the double suction pump.Based on the unsteady calculation results,the dynamic mode analysis of the flow field in a runner passage and the volute under three different flow conditions（0.8Q,1.0Q,1.2Q）of the double-suction pump is carried out.The results show that the stability of the coherent structure is the worst in the small flow condition among the three working conditions,and the design flow and large flow conditions are relatively stable.The position and shape of a three-dimensional coherent structure corresponding to a single frequency of the unsteady flow at different conditions are captured,as well as its temporal and spatial evolution.Furthermore,the flow field in the runner passage is reconstructed and predicted based on the DMD results,and their relative errors are evaluated.And through the comparison of velocity contour of different sections in the flow field,it is verified that the low-dimensional linear approximation mode established by the DMD method can accurately predict the flow field inside the pump.Double suction pump vibration characteristics.Double suction pump vibration characteristics.The experimental method was used to monitor the vibration of the centrifugal pump in real time during the operation,and to analyze the variation law of the vibration characteristics of the pump at each monitoring point.The results show that the vibrations of the pump casing at the monitoring points in the same direction are similar to a certain extent.11)₉)、61)₉)、21)₉)are the main excitation frequencies of the pump vibration energy,which are in good agreement with the pressure pulsation results of the numerical simulation.And the vibration of the pump casing near the monitoring point on the motor side is much more severe than the casing vibration at the monitoring point far from the motor side.