90°弯管气固两相流磨损研究

STUDY ON GAS-SOLID TWO PHASE FLOW IN 90 DEGREE BEND

天然气在管道输送过程中,夹带的微小固体颗粒会对管道产生冲蚀磨损,进而引发管道失效。利用计算流体力学(CFD)软件能够模拟管内气固两相流流动预测壁面磨损量,但过往的(模拟)研究未能区分出磨损的不同阶段,仅采用单一的冲蚀磨损量预测模型。为此利用气固两相流流场结果,通过分界角β将磨损过程分为两个阶段:颗粒对壁面的冲击与颗粒对壁面的滑动或滚动。并将上述两个阶段采用不同的磨损量预测模型(Tulsa模型与疲劳磨损模型)作为用户自定义函数(UDF)加入计算软件中。计算结果表明:磨损量随着颗粒直径、颗粒密度、气体流速、弯径比的增加而增加。磨损量随不同影响因素的变化趋势,与分界角的变化趋势相似,证明了分界角是一个能综合评价弯管冲蚀磨损特征的参数。利用拉格朗日法分析了颗粒的碰撞特征,结果表明:二次碰撞位置更加靠近弯管出口,极易位于弯管焊缝的热影响区内,磨损情况将会加剧,甚至加速焊缝热影响区内的微裂纹扩展。

During the process of natural gas pipeline transportation,the tiny solid particles carried along would result in wear corrosion to pipe elbows so as to initiate further pipeline failure. The gas-solid two phase flow field and erosion in a 90 degree bend are calculated by computational fluid dynamics( CFD) software. Past researches have failed to distinguish the different stages of wear process with a single erosion prediction model. By the numerical simulation results of erosion in a 90 degree bend,the wear process can be divided into two stages by critical angle: the sand impacting the wall and sliding along the surface. Two different erosion prediction model,the Tulsa model and fatigue wear model,which can describe the above two stages accurately are added to the CFD software as the user-defined function( UDF). The calculation results show that the mass loss in the bend increases with particle diameter,particle density,gas velocity and ratio of curvature and diameter increasing. The wear trend along with the change of different impact factors is similar to the change trend of critical angle,which proves that the critical angle is a comprehensive parameter which can evaluate the wear characteristics of bend. To analyze particle collision characteristics by Lagrange method,the calculation results show that secondary collision position which located in the weld heat affected zone( HAZ) of bent pipe is closer to the export of bend than normal which will enhance the wearing and even accelerate the micro crack growth in the weld joint HAZ.