摘要
为计算管路系统中的气液两相瞬变流动,该文基于改进的双流体气液两相计算模型,对管道中由于水锤造成液柱分离现象的进行了分析,计算中考虑了管壁面随压力变化对波速的影响,并在数值求解中对方程中的不守恒项及不守恒方程进行了单独处理,以确保模型计算的稳定性。通过对2种弛豫计算方法对计算影响的研究,并与试验比对可以看出:对于采用有限弛豫参数计算时,需要考虑由于空化引起的相变,同时需要选择合理的泡粒数量以保证计算精确度;对于采用无限弛豫参数计算时,可忽略空化模型,直接对水锤造成的液柱分离现象进行分析模拟;通过采用改进的双流体气液两相流计算模型,并构建合理的数值计算方法,可以对带有明显液柱分离现象的管路气液两相瞬变现象进行预测。该种方法计算精度高,对于工业管道中的水锤防护计算具有较好的应用价值。
In this paper,we improved an existed two-fluid model for simulating the transient flow with liquid-column separation in the pipeline system.An improved NND numerical algorithm was proposed to ensure the accuracy and stability of the model.The finite relaxation and the infinite relaxation methods were compared.It was concluded that when using the finite relaxation calculation method,the relaxation coefficient was too large,resulting in the reverse correction for vapor-liquid phase pressure difference in the equation,which would cause the interruption of calculation.When the calculation method of the infinite relaxation coefficient was used,a stable calculation could be performed without setting the initial concentration of the foam particles,whilst the transient phenomenon could be described more accurately with increasing intensity.In the meantime,due to the forced correction of the void fraction and internal energy distribution after each time step,the method would often produce a larger void fraction and void fraction residue.The water hammer transient tests in two different laboratories were compared to verify the accuracy and applicability of the improved gas-liquid two-phase two-fluid model.We found that for the calculation using the finite relaxation parameters,the phase changes due to cavitation needed to be considered,and also needed to select reasonable bubble concentration to ensure the accuracy of calculation.For the calculation using infinite relaxation parameters,the cavitation model can be neglected,but the model could be used to directly analyze the phenomenon of liquid column separation caused by water hammer phenomenon.As the infinite pressure relaxation calculation method was a kind of mandatory correction calculation method,after each time step,it was considered that the gas phase and the liquid phase pressure reached the equilibrium state,and in fact,the relaxation time of the pressure was usually 1 ms.If the calculation time step was less than 1 ms,due to the forced correction of the calculation method,the two-phase flow in the unbalanced state was forced to be in equilibrium,which led to the correction of the void volume became too large,making reduction of the cavitation model in the low pressure area.The use of improved two-fluid gas-liquid two-phase flow calculation model with a reasonable numerical calculation method and infinite relaxation parameters can be used to predict the transient phenomenon of gas-liquid two-phase pipelines with obvious liquid column separation.The method had high calculation accuracy and it was suitable for water hammer protection in industrial pipelines calculation with a better value of application.
作者
富友
蒋劲
李燕辉
应锐
Fu You;Jiang Jin;Li Yanhui;Yin Rui(School of Energy and Power Engineering,Lanzhou University of Technology,Lanzhou 730050,China;Key Lab of Hydraulic Machinery Transients,MOE,Wuhan University,Wuhan 430072,China)
出处
《农业工程学报》
EI
CAS
CSCD
北大核心
2018年第15期58-65,共8页
Transactions of the Chinese Society of Agricultural Engineering
基金
国家自然科学基金资助项目(51279145)
关键词
压力
模型
液柱分离
瞬变流
气液两相流
水锤
pressure
models
liquid-column separation
transient flow
the gas-liquid two-phase flow
water hammer