表面活性剂与水环输送流动特性的大涡模拟研究

【作者】 黄海涛；

【导师】 江帆；

【作者基本信息】 广州大学 ， 机械电子工程， 2022， 硕士

【摘要】 当今世界对石油资源的依赖依然强劲,储量丰富的稠油必将成为未来重要的替代资源,作为一项高效节能的输油技术,稠油的水环输送越来越受重视。在稠油的输送过程中,不可避免地要流经某些局部管件,流动边界发生改变,造成局部损失,水环流动结构容易失稳进而大幅降低其输送效率;而往水中加入一定表面活性剂,能抑制涡旋的产生和发展,降低局部损失,提高水环流动的稳定性。因此,本课题着重研究局部管件内环状流流体的流动特性,探讨表面活性剂对其流动特性的影响和对水环稳定性的作用机理。论文的主要研究内容包括:搭建油水环状流实验系统进行实验研究并进行仿真结果验证,模拟结果与实验结果大致吻合,证明本文选用的数值计算方法应用到本课题研究的可行性。大涡模拟能更好地捕捉涡旋的形态,通过大涡模拟对各种局部管件内的油水环状流进行研究,结果表明:环状流的油水流动分布主要受涡旋、二次流和浮力影响,油水界面波动主要由两相速度梯度和涡旋等相互作用产生。当曲率比减小或入口流速增大时,弯管内涡旋和双螺旋流的强度增大,曲率比为2时环状流稳定性和节能效果较佳,给不同曲率比的弯管选择合适的入口流速能提高环状流的稳定性和输送能力。突缩管的突缩比越大,涡旋对环状流的影响越明显,界面波动越大,输油效率急剧降低;同等输油量下,减少油水入口速度比能减少环状流的偏心,流速比为1.33时可获得较高的输油效率。同等流量下,突扩管的管径比越小,回流区范围越大,输油效率越低。入口流速变化对突扩突缩管内环状流的影响显著,入口流速为1.5～2m/s,环状流的稳定性较好且输油效率较高,大于等于2.5m/s,油水界面的波动幅度较大且出现油触粘连,小于1m/s,环状流完全偏心失稳,输油效率急剧降低。进一步研究表面活性剂溶液对水环稳定性的作用机理和对局部管件内环状流流动特性的影响,结果表明:表面活性剂能减少局部损失,减少油水界面波动和影响二次流运动,在油流偏心程度较高的流动中,能防止水环失稳,除粘弹性流体产生的第二法向应力外,表面活性剂可能通过增大水相粘度和降低油水界面张力来阻止环状流的偏心失稳。在水环结构没失稳的流动中,表面活性剂会增大溶液的粘度,增加沿程损失,只有在湍流充分发展的流动中才能减少流动损失,提高输送效率。在弯管流动中,加入表面活性剂后,弯管内压差增大,压差引起的双螺旋二次流运动增强,弯管内环状流偏心程度更高。在突缩管流动中,油水入口流速比为2时,表面活性剂能防止水环的失稳,提高输油效率;油水入口流速比为0.667～1时,表面活性剂对输油效率影响不大。在突扩管流动中,加入表面活性剂后,经过突扩截面时环状流维持稳定的距离变长,但输油效率有所下降,管径比越大,输油效率下降的幅度越小,CTAC浓度为200ppm时输送效率更高。在突扩突缩管流动中,表面活性剂能大幅降低界面波动,防止水环失稳,减少稠油粘壁程度,同时能减少变径段和出口段压降。入口流速大于等于2.5m/s时,CTAC浓度为600ppm时环状流有更高的稳定性和输油效率。更多还原

【Abstract】 Nowadays the reliance on oil resources remains strong,heavy oil with abundant reserves will become an important alternative resource in the future.As an efficient and energy-saving transfer technology,water ring transport of heavy oil has attracted more and more attention.It is inevitable to flow through complex local pipes in transportation process,the flow boundary changes,causing local losses,water ring flow structure is prone to destabilization,the stability of water ring loss will greatly reduce the transfer efficiency.Adding some surfactant into water can improve stability of water circulation,inhibit the generation and development of vortexes and reduce local losses.This subject focuses on the flow characteristics of annular flow in local pipe fittings,and studies the influence of surfactants on the flow characteristics and the mechanism of water ring stability.The main contents of this paper include:Oil-water ring flow experimental system is built to carry out experimental research and verify the simulation results.The simulation results agree roughly with the experimental results,which proves that the numerical calculation method selected in this paper is applicable to the research of this subject.LES model can better capture the vortex shape,oil-water annular flow in various local pipe fittings is studied through LES,the results show that oil-water flow distribution of annular flow is mainly affected by vortex,secondary flow and buoyancy,oil-water interface fluctuation is mainly caused by the interaction of two-phase velocity gradient and vortex.When the curvature ratio decreases or the inlet speed increases,the intensity of the vortex and double helical flow in the elbow increases.When the curvature ratio is 2,the stability and energysaving effect of the annular flow are better.Choosing the appropriate inlet speed for elbows with different curvature ratios can improve the stability and transmission capacity of the annular flow.The larger the collapse ratio of the sudden contraction pipe is,the more obvious the influence of the vortex on the annular flow is,the greater the interfacial fluctuation is and the dramatically lower the oil transfer efficiency is.At the same oil delivery rate,reducing the oil/water inlet speed ratio can reduce the eccentricity of the annular flow,and a higher oil delivery efficiency can be achieved when the inlet speed ratio is 1.33.At same speed,the smaller the diameter ratio of the sudden expansion pipe,the wider the return area and the lower the transfer efficiency.The change of inlet speed has a significant influence on the annular flow in the sudden expansion and contraction pipe.when inlet speed is 1.5～2m/s,annular flow has a good stability and high oil transfer efficiency,which is greater than or equal to 2.5m/s.Oilwater interface fluctuates greatly and oil contact adhesion occurs,when inlet is less than 1m/s.The annular flow is completely eccentric and unstable,and the oil transfer efficiency decreases sharply.The mechanism of surfactant solution on stability of water ring and its influence on flow characteristics of annular flow in local pipe fittings were further studied.The results show that surfactant can reduce local loss and oil-water interface fluctuation,affect the movement of secondary flow.In flow with high eccentricity of oil flow,it can prevent instability of water ring except for the second normal stress caused by viscoelastic fluid.Surfactants may prevent eccentric instability of annular flow by increasing the water phase viscosity and decreasing the oil-water interfacial tension.In the unstable flow of water ring structure,surfactant can increase the viscosity of solution and increase the loss along the flow path.Only in the fully developed turbulent flow can the flow loss be reduced and the transportation efficiency be improved.In elbow flow,the pressure difference in the elbow increases with the addition of surfactant,the double helical secondary flow motion caused by the pressure difference increases,and the circumferential flow in the elbow becomes more eccentric.Surfactants can prevent the instability of water ring and improve the oil transfer efficiency when the speed ratio of oil to water inlet is 2 in the abrupt tube flow.Surfactants have little effect on oil transfer efficiency when the speed ratio of oil to water inlet is 0.667～1.In the sudden expansion pipe flow,the distance from which the annular flow maintains stability becomes longer after adding surfactant,but the oil transfer efficiency decreases somewhat.The larger the pipe diameter ratio,the smaller the decrease in oil transfer efficiency.The higher the CTAC concentration is at 200 ppm,the higher the oil transfer efficiency is.Surfactants can greatly reduce the interfacial fluctuation,prevent the water ring from destabilizing and reduce the sticky wall of heavy oil,as well as the pressure drop in variable diameter section and outlet section during the sudden expansion and contraction pipe flow.When the inlet speed is greater than or equal to 2.5m/s,the annular flow has a higher stability and oil transfer efficiency when the CTAC concentration is 600 ppm.更多还原