| As an important device for transporting ore,cinder,mud and hydraulic dredging engineering,solid-liquid two-phase flow centrifugal pump is mainly used in metallurgy,coal,energy,mining,water conservancy and other industries,Because the conveying medium contains a large amount of hard particles,the material of the pump’s flow-through parts is severely worn during the operation,resulting in the decline of pump performance and short service life.Therefore,it is a key scientific problem to study the movement law of solid particles in the solid-liquid two-phase flow pump and improve the anti-erosion performance of the flow passage parts in the pump.The predicted internal erosion of the pump provides engineering reference for the designing pump with strong erosion resistance,and helps to have a deeper understanding of the complex solid-liquid two-phase flow in the pump.Traditional pump erosion is mainly based on experimental research,but the detailed flow field information of solid-liquid two-phase flow in the pump can not be obtained by experimental research.At the same time,the erosion of pump inner wall involves a variety of micro mechanisms,and the experimental study can not study the effects of these mechanisms on pump erosion separately.In this paper,a solid-liquid two-phase flow centrifugal pump is studied,Computational Fluid Dynamics(CFD)for continuous phase flow field,and Discrete Element Method(DEM)was used to solve the force and velocity of solid particles in discrete phase.Through the coupling interface program,the source term of momentum exchange between flow particles and fluid is obtained,the Discrete Random Walk model(DRW)and particle turbulence modulation model are customized to the CFD-DEM model.Considering the influence of turbulence fluctuation on particle motion and particle modulation on turbulence.The CFD-DEM numerical simulation method mostly focuses on simple geometric structures in solving complex two-phase flow,and ignores the interaction between particles and turbulence.In fact,unlike pipe flow and elbow flow,the distribution and intensity of turbulence in the pump are more complicated because of the existence of jet and eddy in the pump,so it is necessary to consider the interaction of particles and turbulence when simulating two-phase flow in the pump containing particles.Compared with the existing experimental data,the model’s accuracy is verified,the effects of particle volume concentration,dimensions,and topological structure on the head,efficiency and distribution of solid particles in the centrifugal pump were studied.The E/CRC erosion prediction formula is implanted through the secondary development function of the DEM simulation program,and the erosion caused by the particle characteristics to the hydraulic parts of the pump is calculated.The research work and achievements are summarized as follows:(1)A fully coupled CFD-DEM numerical model is established to study the effect of particle concentration on pump performance.The study found that the hydraulic performance(head and efficiency)of the pump is improved when low solid volume fraction particles enter the pump.The simulation results are consistent with the experimental results of Shi et al,there is a lack of quantitative analysis to explain this phenomenon.This paper restores a composite vane centrifugal pump model tested in the experiment,using the established CFD-DEM fully coupled numerical model.It is found that turbulent kinetic energy in the pump is weakened by the addition of small concentration particles,the flow in the pump is more stable,and the head and efficiency are improved.Under the condition of high concentration,the agglomeration of particles in the pump is serious,and the turbulent kinetic energy in the pump is increased,resulting in reduced head and efficiency,The numerical model established in this paper can simulate solid-liquid two-phase flow in the pump more accurately.(2)Then,taking a solid-liquid two-phase flow centrifugal pump model as the research object,the effects of different particle concentration,particle size and shape on pump head and efficiency,particle velocity and distribution,and turbulent kinetic energy are studied.It is found that the addition of particles with low solid volume concentration can reduce the flow separation loss and improve the pump head and efficiency.The shape of particles has a great influence on the particle distribution of the spiral case tongue and the outlet pipe section.The particle shape has a significant effect on the particle distribution of volute tongue and outlet pipe.As the particle size increases,the particle velocity in the pump decreases The particle concentration and particle shape have little effect on the particle velocity in the pump.(3)Analyzed the motion trajectory of particle in solid-liquid two-phase flow in centrifugal pump,preliminarily predicted the main locations of erosion,and systematically studied the particle concentration,particle size,particle shape and different flow conditions.It was found that the erosion of impeller blade mainly occurred at blade head and blade working face,The higher the particle concentration is,the more serious the blade erosion is.As the particle size increases,the erosion of impeller blade first reduces and then increases,and the main erosion position is basically unchanged.The erosion of the blade with different particle shape mainly occurs from the head of the blade to the length of the pressure surface of the blade,as well as the part of the tail of the blade.Particles gathered at volute tongue,and the erosion is the most serious at the volute tongue,when the sphericity is 0.84,the erosion of the volute is the most serious.(4)The maximum annual erosion rate of the main flow components in the pump under the conditions of different particle concentration and particle diameter is calculated.The results show that the impeller blade is the most seriously worn part in the whole pump.With the increase of flow rate,the maximum erosion rate of blade,impeller front cover and volute increases gradually.Compared with the rated flow rate,the maximum erosion rate of impeller front cover increases at low flow rate. |
