| The solid and liquid two-phase mixed transportation system is very important in deep sea and deep resource exploitation.The elbow is an indispensable component to control the conveying direction,and the pump is the power core of the system.Because the transport medium contains a large amount of hard solid particles,which will impact the inner wall surface of the elbow and the flow-through component of the pump during operation,causing the material of the component to wear,thereby jeopardizing the operation safety of the entire mixed transportation system.Due to the complex installation and operation of deep-sea and deep-ground equipment,and the high cost of maintenance and replacement,it is important to research the erosion mechanism of the elbows and pump caused by particles in the solid-liquid two-phase flow mixed transportation system,which has great scientific and application value.In recent years,there are many relevant scholars have used different methods to study the mechanism of elbow erosion formation,and many scholars have studied the erosion characteristics of over-flow components in solid and liquid two-phase flow pumps and explored the formation mechanism.As an important research method,numerical simulation plays a key role in the study of the mechanism of erosion formation,which can obtain data that is difficult to measure in experiments,such as the impact speed and angle of particles,the various forces of fluids on particles,etc.,and analyzes the contribution of various factors to erosion rate from a microscopic perspective.However,the solid and liquid two-phase may interact in mass,momentum,turbulence and energy,due to the strong interaction between particles and fluid in the two phases flow,which rise many challenges for constructing accurate numerical models.In this paper,from this perspective,an accurate and reliable solid-liquid two-phase flow numerical model has been attempted to establish,and explore the erosion characteristics and formation mechanism caused by particles in the elbow and pump.This paper is based on the Computational Fluid Dynamic(CFD)method to solve the fluid,and the Discrete Element Method(DEM)to solve the particle.The fluid and particle are coupled under the Euler-Lagrange framework,the force and momentum transfer between the two phases is established.Random sampling of turbulent velocity is used to consider the effect of velocity fluctuations on particle motion,and source terms to the turbulent kinetic energy and turbulent dissipation equation are used to consider the effect of particles on turbulent intensity based on the RANS calculation method.the erosion model modified according the wall roughness correction is embedded through the application programming interface(API)of the software,and the appropriate erosion model is selected by compared with the experimental data of the elbow erosion.Finally,the effect of particle size,shape,concentration and flow rate on the erosion of the inner wall of the 90 ° elbow and the flow-through components of a mixed flow pump has been studied.The main research work and innovations of this paper are as follows:(1)A solid and liquid two-phase flow model considering the interaction between particles and turbulence was established based on the CFD-DEM method.The CFD-DEM model was used to calculate the particles fluid velocity distribution considering the effect of particle motion on turbulence intensity,and the accuracy of model is verified by comparing the calculation data with experiments of Shigeo Hosokawa et al.and Alajbegovic et al..In addition,the elbow geometry model is established according to the erosion experiment of Zeng et al.,and the modified E/CRC erosion model and Oka model model are embedded in the software to couple for calculation,the E/CRC model was selected to calculate the erosion in liquid and solid two-phase flow after comparing the calculation data with the experimental results of Zeng et al..(2)The fluid and particle motion characteristics in the 90 ° elbow were studied.Analysis of particle shape,size,concentration and the influence of particle velocity on particle motion shows that particle agglomeration in the elbow mainly occurs in the range of 75 °-90 °.It continues to the downstream straight pipe section under the action of the particle,and the relationship between the particle force and the particle-fluid relative velocity is closed.(3)The erosion characteristics and formation mechanism of the 90 ° elbow were studied.The results show that the maximum erosion rate occurs at the position around 87 ° of the elbow.The particles are greatly dragged by the fluid and contact the wall surface after exceeding the curvature angle of 50 °.Scratch cutting is the main reason to damage of the elbow.The more severe the erosion of the outer wall of the elbow due to the great particle concentration and the higher the speed,but the growth rate of the erosion rate decreases with the greater concentration,and increases with the higher speed.The follow ability of the particle to the fluid is worse when the particle size is larger,and the particles are easier to collide with the wall surface,causing the more severe the wall.(4)The erosion characteristics and formation mechanism of a mixed flow pump are studied.The effect of particle concentration,shape and different flow conditions on blade erosion was studied based on a self-developed two-stage mixed-flow pump.The results show that the erosion of the first-stage impeller and guide vane is more serious than the secondary-impeller and guide vane.Impeller erosion mainly occurs at the junction of the blade pressure side and the back cover plate,guide vane erosion mainly occurs at the junction of the concave surface of the blade and the front cover plate.There are greater the number of particles retained in the flow channel,the greater impact frequency and the less impact angle when the particle sphericity is 1.0. |
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