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工程科学与技术:2017,49(2):254-261
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高压干气密封流场数值模拟
(四川大学 化学工程学院, 四川 成都 610065)
Numerical Simulation of Flow Field for High Pressure Dry Gas Seals
(College of Chemical Eng., Sichuan Univ., Chengdu 610065, China)
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投稿时间:2016-09-19    修订日期:2017-02-05
中文摘要: 干气密封在高温、高压以及各种腐蚀性介质的应用越来越广泛,对高压高温给干气密封带来的影响,研究者们的认识还不足,特别是理论计算中存在许多问题。在高压工况下,干气密封端面气膜流场的压力和温度变化较大,而介质密度、黏度应是随压力和温度的变化而变化的,特别是气体的密度受压力的影响较大。以往的传统干气密封数值模拟中,密封介质的密度大多按照假设温度和压力值选定,并未曾考虑到密封介质物性参数变化对密封性能的影响,因此研究结果难免有些误差。作者提出了高压干气密封流场计算的变密度方法,考虑了流场和温度场变化对密度的影响。首先使用ANSYS Workbench软件对密封环进行热分析,得到了密封环的温度场分布,并推导出端面气膜的温度分布;采用用户自定义函数(UDF)将密封介质N2的密度定义为压力和温度的区间函数,用加载了UDF的Fluent软件对端面气膜流场进行数值模拟计算,通过不断地迭代计算得到端面流场的压力分布和开启力。分别采用变密度(自定义密度为压力和温度的函数)和定密度(直接将密度设定为定值)两种方法,通过Fluent软件对干气密封流场进行了模拟仿真,并进行了网格尺寸在模拟仿真时的无关性验证。对比模拟结果可以看出变密度方法所得到的计算结果更接近工况实际情况,该算法解决了模拟计算中介质物性参数设置的问题,值得借鉴。研究发现:使用Fluent的UDF功能来描述干气密封端面间隙气体密度的变化是可行的,为更精确地模拟端面间隙流场提供了一种新方法。在高压工况下,压力变化对气体密度影响较大,变密度方法能够更加真实地反映其流场。此外还应考虑温度变化对气体密度的影响。
中文关键词: 干气密封  密度  流场  螺旋槽  数值模拟
Abstract:The dry gas seals have wide applications in the conditions of high temperature,high pressure and a variety of corrosive media,but it has been not enough to understand the effects of high pressure and high temperature on dry gas seals,especially the problems in the numerical simulation.Both pressure and temperature of end-face gas film field in dry gas seals change greatly,especially at the working condition of high pressure.The density and viscosity of sealing medium or nitrogen change with varying pressure and temperature.Especially,the effect of pressure on the former is greater.In usual numerical simulation for dry gas seals,the density of sealing medium is determined according to the given temperature and pressure,which does not take into account the influences of physical parameters of sealing medium on seal performance so that the results might have errors.A new way used for the simulation of flow field of high pressure dry gas seals was proposed with the consideration of the effects of the changes of flow field and temperature field on the density of sealing medium in order to decrease the errors.Firstly,ANSYS Workbench software was used to make a thermal analysis for sealing rings to obtain the temperature field.The temperature distribution in the gas film field was then estimated by CFD.Then,user defined functions(UDFs) were created to relate the density of nitrogen (sealing medium) to pressure and temperature.Fluent software was used to complete the simulation with UDF loaded.Pressure distribution of end-face gas field and the opening force of the seal were obtained after continuous iteration.The flow fields of high pressure dry gas seals were reflected more truly.The flow fields of a dry gas seal were simulated using Fluent soft ware by the methods of variable-density (to define the density as a function of pressure and temperature) and the given density (to take density as the given directly),respectively.The grid size independent verification was carried out.The comparison of simulation results showed that the variable-density method could make the results closer to the conditions of the actual situation.It is feasible to use UDFs of Fluent to describe the variable-density of gas film between the sealing faces of a dry gas seal,which provides a new method to more accurately simulate gap flow field between sealing faces.The effect of pressure on the density of sealing gas is great under high pressure.The flow fields of high pressure dry gas seals are reflected more truly by the methods of variable-density.Moreover,the influence of temperature change on the density of sealing gas should be taken into account.
文章编号:201601049     中图分类号:    文献标志码:
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陈志,高昀皞,赵鹏,吉华.高压干气密封流场数值模拟[J].工程科学与技术,2017,49(2):254-261.
CHEN Zhi,GAO Yunhao,ZHAO Peng,JI Hua.Numerical Simulation of Flow Field for High Pressure Dry Gas Seals[J].Advanced Engineering Sciences,2017,49(2):254-261.