Research On Transient Characteristics Of Centrifugal Pump During Variable Speed Regulation

Centrifugal pumps are widely used in many industrial production fields because of their simple structure and low maintenance cost.In the actual operation of the centrifugal pump,the impeller speed needs to be adjusted in real time according to the production tasks and system requirements.Different from the research on steady-state conditions of the centrifugal pump,the external characteristic parameters such as flow rate change rapidly during the rise and fall of the centrifugal pump speed,and the shape size and energy loss distribution of the vortex group in the pump also change correspondingly.This series of unstable flows affect the healthy and stable operation of the pumping station.Therefore,this paper establishes a single-stage single-suction clean water centrifugal pump model and uses UDF to control the speed change rule of the centrifugal pump.The variable speed regulation process of the centrifugal pump is studied from three aspects:pressure pulsation response,vortex structure recognition and energy loss.The contents of this paper can be summarized as follows:(1)The three-dimensional numerical model of centrifugal pump was established through the three-dimensional modeling software UG and mesh partitioning software ICEM.The average value of y~+on the blade wall was 4.46,which met the requirements of turbulence model.The grid number was determined to be 5093506 by using GCI criterion for grid independence test.On this basis,several flow points are selected for numerical simulation,and the calculation results show that the errors of the simulation results and the test results are within the allowable range,which can be used for the following research on the variable speed regulation process.(2)By inserting UDF in multiple speed conditions for iterative calculation to obtain the corresponding flow rate of the speed,it is found that in the process of variable speed and variable pressure regulation,the regulating range of the flow rate of the centrifugal pump becomes larger,indicating that there is an error between the flow result obtained according to the proportional law and the actual situation.Based on the calculation results,the pressure,velocity and turbulent kinetic energy changes at the five working conditions of 0.6n_r,0.7n_r,0.8n_r,0.9n_r and 1.0n_r were studied to explore the pressure pulsation response,vortex structure evolution and energy loss rule in the pump under each working condition.The results show that:(1)Under the condition of low speed,the pressure pulsation changes near the septal tongue and the monitoring point at the bottom of the volute failed to show periodicity due to the intense vortex movement in the pump.(2)Liutex-Omega vortex criterion has the best recognition effect.In low speed conditions,a large number of vortices in the impeller are distributed in the middle of the flow passage,and the vortices in the diffusion section of the volute near the tongue move violently.(3)Under the condition of low rotational speed,the entropy production area in the middle of the impeller passage increases,while the inlet of the centrifugal pump is affected by the vortex motion and the reflux occurs,resulting in the increase of turbulent dissipation entropy production.(3)Based on the research results in Chapter 3,the speed variation rules of centrifugal pump speed rise and decrease process are set,the changes of pressure,speed and turbulent kinetic energy in the process of variable speed regulation are studied,and the vortex structure identification method and entropy generation theory are used to analyze the transient regulation process.The results show that:(1)In the process of centrifugal pump speed rise,the phenomenon of unstable flow is gradually reduced,and a large number of vortex groups are distributed in the tail of the suction surface of the blade.When passing through the tongue,the wake vortex undergoes the process of falling off,breaking and merging.(2)In the process of reducing the speed of the centrifugal pump,the leakage vortex increases,the overflow and reflux phenomenon of the leading edge of the blade becomes more and more serious,and a large number of vortex groups are blocked in the center of the flow channel,which leads to the aggravation of the vibration and noise of the centrifugal pump.(3)The entropy generation region is mostly distributed in the tail of the blade suction surface when the speed is high,and the entropy generation region gradually shifts to the inlet of the blade and the center of the flow channel when the speed decreases,which indicates that the severe vortex movement increases the energy loss in the pump and leads to the increase of entropy generation in the corresponding region.