Research Of Solid-Liquid Two-Phase Flow On Bending Pipe Erosion Characteristics

Since the economic revolution of the eighteenth century,the shipping trade has undergone tremendous development.With the outline of the fourteenth Five-Year Plan,the country’s attention to economic development has ushered in a new opportunity for the shipping trade.With the growth of shipping capacity and efficiency,the pipeline system of ships has also developed towards intelligence and diversification.Among them,pipelines are prone to solid particle deposition when transferring liquid media.The erosion and wear behavior caused by this can cause damage to pipeline,and the hardesthit area of pipe erosion appears in the bend section of pipes.The wear of pipe walls caused by erosion can lead to shortening of pipe life in mild cases,and can cause the pipeline to malfunction in severe cases,which seriously endangers ship safety.Based on these issues,this thesis takes solid-liquid two-phase flow 90° bends,U-bends and double bends as objects and conducts analysis on their flow fields,particle trajectories and erosion characteristics by CFD method.This is of practical significance for avoiding erosion damage to pipeline systems and ship safety accidents while improving pipeline erosion resistance:(1)Based on the Euler-Lagrange method,a numerical simulation method for the prediction of erosion and wear of three kinds of bent pipes(90° bends,U-shaped pipes,and double bends)was constructed by combining the mathematical models of turbulence,discrete phases of particles and erosion and wear applicable to bends.The erosion areas and maximum erosion rates of bends from the simulation were compared with the experimental data in the literature,and it was found that the errors of similar areas were small,which verified the reliability of the numerical model.(2)The flow field,particle trajectory phenomenon and erosion wear characteristics of 90° bends under different fluid particle parameters,bend structure parameters and gravity direction were studied and analyzed.The influence of influencing factors on erosion area and maximum erosion rate is determined;The rules of particle movement and erosion and wear of U-tube and double-bend were investigated for different inlet flow velocities,particle sizes,particle mass flow velocities and gravity directions,The differences in flow field and wall shear stress distribution between the two were compared and analyzed,It was found that The maximum erosion rate of the bend is positively correlated with the particle mass flow rate,and the particle diameter decreases first and then increases;With the increase of pipe diameter or bend diameter ratio,the change of erosion area of bends shows an opposite trend,and the maximum erosion rate of bends gradually decreases.The anti-corrosion effect of bend is almost unchanged when pipe diameter exceeds 0.4m,and anti-corrosion effect of bend is weakened when bend diameter ratio exceeds 2.5;By controlling the gravity direction,the effect of different placement forms of bends on distribution of erosion area and maximum erosion rate is investigated.By controlling the direction of gravity,we studied the influence of different placement forms of bends on the distribution of erosion areas and the maximum erosion rate,and the results indicate that the "inverted L" type placement of bends is optimal for pipe longevity;The largest erosion area of the U-shaped pipe is distributed on the outer arch side of the semicircular bend section,and the largest erosion area of the double bend pipe is distributed on both sides of the first bend section,With the increase of inlet flow rate,the maximum erosion area of the double-bend pipe will also appear on the outer arch side of the second bend section;The anti-corrosion performance of the U-pipe under different fluid and particle factors and different forms of pipe placement is better than that of the double-bend pipe..(3)In view of the problem of 90° bend being abraded by particle erosion,a stomachshaped anti-corrosion bend with four times the diameter of the outer arch and twice the diameter of the inner arch is proposed based on the analysis results combined with the study of bionics.This can reduce the impact of particles on the wall by changing the trajectory of particles inside the pipe and weakening the phenomenon of secondary flow inside the pipe.This improves the anti-corrosion effect while ensuring that fluid import and export speed and pressure loss are not large.