基于颗粒流理论的微灌砂滤层反冲洗过程砂粒速度场模拟
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摘要
砂颗粒流在石英砂滤层反冲洗流场中的速度分布,对滤层流化状态的稳定性和反冲洗效果起决定性作用。为了对滤层反冲洗过程砂颗粒的速度场进行分析,并确定最佳反冲洗速度,该文以厚度为400 mm,粒径范围为1.0～1.18 mm的石英砂滤层为研究对象,基于颗粒流运动理论,采用Eulerian-Eulerian模型对滤层反冲洗过程砂粒的速度场进行3维动态模拟。为了验证模拟结果的准确性,作者开展了室内模型试验,并将模拟结果与试验结果进行对比,结果显示,滤层膨胀高度的最大模拟误差为9.8%,能够控制在10%以内,说明数值模拟结果是可信的。在此基础上,分析了反冲洗流化倍数为1.3、1.5、1.7和1.9时,滤层高度分别为15、25和35 cm 3个横截面上,在不同的反冲洗时间,砂粒的轴向速度沿横坐标的分布规律。根据砂粒在3个横截面上运动速度的大小和方向,判断砂滤层是否达到完全流化;根据砂粒在3个横截面上运动趋势是否一致,砂粒的上升区是否保持稳定,判断滤层流化状态是否稳定。结果显示,当反冲洗流化倍数不小于1.7时,滤层才能达到稳定的流化状态,从而达到比较理想的反冲洗效果,并得出滤层最佳反冲洗流化倍数为1.7。研究结论为砂过滤器的反冲洗研究提供了理论基础和技术支撑,为反冲洗性能参数的确定提供了参考。
The velocity distribution of sand grains in the backwashing flow field is key to the backwashing performance of sand filter layer, such as the expansion height, distribution uniformity and the stability of fluidized state. To analyze the velocity distribution of sand grains in the backwashing process and find out the optimal backwashing speed, numerical simulation was used in this paper. Moreover, a geometric model of sand filter was established and the mesh division of the geometric model was carried out through Gambit software. Because the backwashing process of quartz sand filter layer is a solid-liquid multiphase flow system composed of water and quartz sand, we can conclude that the Eulerian model is suitable for the numerical simulation of the velocity field of sand grains by comparing the applicability of the current multiphase flow numerical simulation models such as Eulerian model, Mixture model and VOF(volume of fluid) model. At the same time, because the backwashing process of quartz sand filter layer is both a dynamic and a stable process, the transient simulation solver was adopted. Additionally, the granular flow theory was used to seal the momentum equation of the model, because of the formation of granular flows in the backwashing process. The simulation objects was the quartz sand filter layer whose thickness was 400 mm, and the equivalent grain diameter was 1.06 mm. In order to verify the reliability of simulation results, laboratory experiments of backwashing were conducted in Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang, China. The parameters such as the backwashing speed and the total height of the filter layer were measured during the experiments. And the simulation results were compared with the experimental results. Comparison results showed that the maximum simulation error of the sand grains velocity was 9.8%. So the numerical simulation results were proved to be reliable. On this basis, three cross-sections, with the height of 15, 25 and 35 cm, were selected in the filter layer and the axial velocity distribution of sand grains was analyzed. The fluidization ratio of backwashing for this simulation was 1.3, 1.5, 1.7 and 1.9 respectively. Based on the magnitude and direction of the velocity of sand grains in the three cross-sections, we can figure out whether the sand filter layer is completely fluidized or not. The stability of the fluidization state of the filter layer can be estimated by the consistency of the movement trend of sand grains in the three cross-sections and the stability of the rising zone of granular flows. The results showed that the bigger the fluidization ratio of backwashing is, the less time needed for completely fluidizing the filter layer. As a consequence, only if the fluidization ratio of backwashing is not less than 1.7, the filter layer might reach a stable state of fluidization. In a stable flow, the rising zone and the descending zone formed a stable circulation in the filter layer. As the grains swarm moved along a relatively fixed path, the ideal backwashing effect was achieved. It can be seen from the above that the optimal fluidization ratio of backwashing of the filter layer is 1.7. The research provide not only a theoretical basis and technical support for the study of the sand filter but also a reference for the determination of performance parameters for the backwashing.
The velocity distribution of sand grains in the backwashing flow field is key to the backwashing performance of sand filter layer, such as the expansion height, distribution uniformity and the stability of fluidized state. To analyze the velocity distribution of sand grains in the backwashing process and find out the optimal backwashing speed, numerical simulation was used in this paper. Moreover, a geometric model of sand filter was established and the mesh division of the geometric model was carried out through Gambit software. Because the backwashing process of quartz sand filter layer is a solid-liquid multiphase flow system composed of water and quartz sand, we can conclude that the Eulerian model is suitable for the numerical simulation of the velocity field of sand grains by comparing the applicability of the current multiphase flow numerical simulation models such as Eulerian model, Mixture model and VOF(volume of fluid) model. At the same time, because the backwashing process of quartz sand filter layer is both a dynamic and a stable process, the transient simulation solver was adopted. Additionally, the granular flow theory was used to seal the momentum equation of the model, because of the formation of granular flows in the backwashing process. The simulation objects was the quartz sand filter layer whose thickness was 400 mm, and the equivalent grain diameter was 1.06 mm. In order to verify the reliability of simulation results, laboratory experiments of backwashing were conducted in Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang, China. The parameters such as the backwashing speed and the total height of the filter layer were measured during the experiments. And the simulation results were compared with the experimental results. Comparison results showed that the maximum simulation error of the sand grains velocity was 9.8%. So the numerical simulation results were proved to be reliable. On this basis, three cross-sections, with the height of 15, 25 and 35 cm, were selected in the filter layer and the axial velocity distribution of sand grains was analyzed. The fluidization ratio of backwashing for this simulation was 1.3, 1.5, 1.7 and 1.9 respectively. Based on the magnitude and direction of the velocity of sand grains in the three cross-sections, we can figure out whether the sand filter layer is completely fluidized or not. The stability of the fluidization state of the filter layer can be estimated by the consistency of the movement trend of sand grains in the three cross-sections and the stability of the rising zone of granular flows. The results showed that the bigger the fluidization ratio of backwashing is, the less time needed for completely fluidizing the filter layer. As a consequence, only if the fluidization ratio of backwashing is not less than 1.7, the filter layer might reach a stable state of fluidization. In a stable flow, the rising zone and the descending zone formed a stable circulation in the filter layer. As the grains swarm moved along a relatively fixed path, the ideal backwashing effect was achieved. It can be seen from the above that the optimal fluidization ratio of backwashing of the filter layer is 1.7. The research provide not only a theoretical basis and technical support for the study of the sand filter but also a reference for the determination of performance parameters for the backwashing.
引文
[1]翟国亮,陈刚,赵武,等.微灌用石英砂滤料的过滤与反冲洗试验[J].农业工程学报,2007,23(12):46-50.Zhai Guoliang,Chen Gang,Zhao Wu,et al.Experimental study on filtrating and backwashing of quartz sand media in micro-irrigation filter[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2007,23(12):46-50.(in Chinese w ith English abstract)
[2]翟国亮,冯俊杰,邓忠,等.微灌用砂石过滤器反冲洗参数试验[J].水资源与水工程学报,2007,18(1):24-28.Zhai Guoliang,Feng Junjie,Deng Zhong,et al.Parameters experiment of backwashing on sandy filter in micro-irrigation[J].Journal of Water Resources&Water Engineering,2007,18(1):24-28.(in Chinese w ith English abstract)
[3]赵红书.微灌用石英砂滤料的过滤与反冲洗性能研究[D].北京:中国农业科学院,2010.Zhao Hongshu.Performance of Filtration and Flushing of Quartz Sand Media for Micro-Irrigation[D].Beijing:Chinese Academy of Agricultural Sciences,2010.(in Chinese with English abstract)
[4]邓忠,翟国亮,仵峰,等.微灌过滤器石英砂滤料过滤与反冲洗研究[J].水资源与水工程学报,2008,19(2):34-37.Deng Zhong,Zhai Guoliang,Wu Feng,et al.Study on the filtration and backwashing for the quartz filter in micro-irrigation[J].Journal of Water Resources&Water Engineering,2008,19(2):34-37.(in Chinese with English abstract)
[5]邓忠,翟国亮,宗洁,等.浑水质量分数对石英砂滤料过滤性能的影响[J].排灌机械工程学报,2013,31(11):1007-1012.Deng Zhong,Zhai Guoliang,Zong Jie,et al.Influence of muddy water mass fraction on performance of packed quartz sand bed[J].Journal of Drainage and Irrigation Machinery Engineering,2013,31(11):1007-1012.(in Chinese with English abstract)
[6]冯俊杰,翟国亮,邓忠,等.微灌过滤器用水压驱动反冲洗阀启闭机构的力学计算[J].农业机械学报,2007,38(12):212-214.Feng Junjie,Zhai Guoliang,Deng Zhong,et al.Mechanical calculation of opening and closing mechanism of back flushing valve driven by hydraulic pressure[J].Transactions of the Chinese Society for Agricultural Machinery,2007,38(12):212-214.(in Chinese with English abstract)
[7]蔡九茂,李莉,翟国亮,等.3种微灌砂过滤器水动三向阀性能比较试验研究[J].排灌机械工程学报,2017,35(7):596-601.Cai Jiumao,Li Li,Zhai Guoliang,et al.Comparative experiment on performance of three hydrodynamic three-way valves in microirrigation sand filter[J].Journal of Drainage and Irrigation Machinery Engineering,2017,35(7):596-601.(in Chinese with English abstract)
[8]张文正,翟国亮,邓忠,等.微灌砂滤料的表层过滤和气水反冲洗试验研究[J].灌溉排水学报,2013,30(1):86-90.Zhang Wenzheng,Zhai Guoliang,Deng Zhong,et al.Surface filtration and air-water backwashing for sandy filter media in micro-irrigation[J].Journal of Irrigation and Drainage,2013,30(1):86-90.(in Chinese with English abstract)
[9]张文正.微灌砂滤层气水反冲洗与过滤的试验研究[D].北京:中国农业科学院,2013.Zhang Wenzheng.Experiment Research of Air Water Backwashing and Filtration of Sand Layer in Micro-Irrigation[D].Beijing:Chinese Academy of Agricultural Sciences,2013.(in Chinese with English abstract)
[10]刘文娟.石英砂过滤器过滤及反冲洗特性的实验研究与数值模拟[D].北京:中国农业科学院,2014.Liu Wenjuan.Experimental Study and Numerical Simulation of Filtration and Backwashing Characteristics of Quartz Sand Filter[D].Beijing:Chinese Academy of Agricultural Sciences,2014.(in Chinese with English abstract)
[11]BovéJ,Puig-Bargues J,Arbat G,et al.Development of a new underdrain for improving the efficiency of microirrigation sand media filters[J].Agricultural Water Management,2017,179:296-305.
[12]BovéJ,Arbat G,Pujol T,et al.Reducing energy requirements for sand filtration in microirrigation:Improving the underdrain and packing[J].Biosystems Engineering,2015,140:67-78.
[13]李景海,翟国亮,黄修桥,等.微灌石英砂过滤器反冲洗数值模拟与流场分析[J].农业工程学报,2016,32(9):74-82.Li Jinghai,Zhai Guoliang,Huang Xiuqiao,et al.Numerical simulation and flow field analysis of backwashing of Quartz sand filter in micro irrigation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2016,32(9):74-82.(in Chinese with English abstract)
[14]李景海,蔡九茂,翟国亮,等.基于砂滤层内水体积分数瞬态模拟的反冲洗速度优选[J].农业工程学报,2018,34(2):83-89.Li Jinghai,Cai Jiumao,Zhai Guoliang,et al.Optimization of backwashing speed based on transient simulation of the volume fraction of water in the sand filter layer[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2018,34(2):83-89.(in Chinese with English abstract)
[15]李景海.微灌石英砂滤层清洁压降分形阻力模型与反冲洗数值模拟[D].北京:中国农业科学院,2016.Li Jinghai.Fractal Resistance Model of Clean Pressure Drop and Numerical Simulation of Backwashing Process of Quartz Sand Filter Layer in Micro-Irrigation[D].Beijing:Chinese Academy of Agricultural Sciences,2016.(in Chinese with English abstract).
[16]李景海,刘清霞,黄修桥,等.微灌石英砂滤层流态特性与分形阻力模型参数确定[J].农业工程学报,2015,31(13):113-119.Li Jinghai,Liu Qingxia,Huang Xiuqiao,et al.Flow state characteristics and fractal model parameters determination of quartz sand filter layer used in micro-irrigation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(13):113-119.(in Chinese with English abstract).
[17]李景海,刘清霞,黄修桥,等.微灌石英砂滤层清洁压降计算参数确定与分析[J].灌溉排水学报,2016,35(11):24-28.Li Jinghai,Liu Qingxia,Huang Xiuqiao,et al.Determination and analysis of the calculation parameters for the cleaning pressure drop of quartz sand filter layer used in micro-irrigation[J].Journal of Irrigation and Drainage,2016,35(11):24-28.(in Chinese with English abstract)
[18]贺靖峰.基于欧拉-欧拉模型的空气重介质流化床多相流体动力学的数值模拟[D].北京:中国矿业大学,2012.He Jingfeng.Numerical Simulation of Multiphase Fluid Dynamic in Air Dense Medium Fluidized Bed Based on Euler-Euler Model[D].Beijing:China University of Mining and Technology,2012.(in Chinese with English abstract)
[19]贺靖峰,赵跃民,何亚群,等.基于Euler-Euler模型的空气重介质流化床密度分布特性[J].煤炭学报,2013,38(7):1277-1282.He Jingfeng,Zhao Yuemin,He Yaqun,et al.Distribution characteristic of bed density in air dense medium fluidized bed based on the Euler-Euler model[J].Journal of Coal Science&Engineering,2013,38(7):1277-1282.(in Chinese with English abstract)
[20]He Jingfeng,He Yaqun,Zhao Yuemin,et al.Numerical simulation of the pulsing air separation field based on CFD[J].International Journal of Mining Science and Technology,2012,22(2):201-207.
[21]Ansys Inc.Ansys Fluent User’s Guide[M].Pittsburgh:AnsysInc,2011.
[22]Gidaspow D.Multiphase Flow and Fluidization:Continuum and Kinetic Theory Descriptions[M].California:Academic Press Inc,1994.
[23]Ogawa S,Umemura A,Oshima N.On the equation of fully fluidized granular materials[J].Journal of Applied Mathematics and Physic,1980,31(4):483-493.
[24]Ansys Inc.Ansys Fluent Theory Guide[M].Pittsburgh:AnsysInc,2011.
[25]Ding J,Gidaspow D.A bubbling fluidization model using kinetic theory of granular flow[J].Aiche Journal,1990,36(4):523-538.
[26]Gidaspow D.Hydrodynamics of fluidization and heat transfer supercomputer modeling[J].Applied Mechanics Reviews,1986,39(1):1-22.
[27]Llun C K K,Savage S B,Jeffrey D J,et al.Kinetic theory of granular flow:Inelastic particles in couette flow and slightly inelastic particles in a general flow field[J].Journal of Fluid Mechanics,1984,140(6):223-256.
[2]翟国亮,冯俊杰,邓忠,等.微灌用砂石过滤器反冲洗参数试验[J].水资源与水工程学报,2007,18(1):24-28.Zhai Guoliang,Feng Junjie,Deng Zhong,et al.Parameters experiment of backwashing on sandy filter in micro-irrigation[J].Journal of Water Resources&Water Engineering,2007,18(1):24-28.(in Chinese w ith English abstract)
[3]赵红书.微灌用石英砂滤料的过滤与反冲洗性能研究[D].北京:中国农业科学院,2010.Zhao Hongshu.Performance of Filtration and Flushing of Quartz Sand Media for Micro-Irrigation[D].Beijing:Chinese Academy of Agricultural Sciences,2010.(in Chinese with English abstract)
[4]邓忠,翟国亮,仵峰,等.微灌过滤器石英砂滤料过滤与反冲洗研究[J].水资源与水工程学报,2008,19(2):34-37.Deng Zhong,Zhai Guoliang,Wu Feng,et al.Study on the filtration and backwashing for the quartz filter in micro-irrigation[J].Journal of Water Resources&Water Engineering,2008,19(2):34-37.(in Chinese with English abstract)
[5]邓忠,翟国亮,宗洁,等.浑水质量分数对石英砂滤料过滤性能的影响[J].排灌机械工程学报,2013,31(11):1007-1012.Deng Zhong,Zhai Guoliang,Zong Jie,et al.Influence of muddy water mass fraction on performance of packed quartz sand bed[J].Journal of Drainage and Irrigation Machinery Engineering,2013,31(11):1007-1012.(in Chinese with English abstract)
[6]冯俊杰,翟国亮,邓忠,等.微灌过滤器用水压驱动反冲洗阀启闭机构的力学计算[J].农业机械学报,2007,38(12):212-214.Feng Junjie,Zhai Guoliang,Deng Zhong,et al.Mechanical calculation of opening and closing mechanism of back flushing valve driven by hydraulic pressure[J].Transactions of the Chinese Society for Agricultural Machinery,2007,38(12):212-214.(in Chinese with English abstract)
[7]蔡九茂,李莉,翟国亮,等.3种微灌砂过滤器水动三向阀性能比较试验研究[J].排灌机械工程学报,2017,35(7):596-601.Cai Jiumao,Li Li,Zhai Guoliang,et al.Comparative experiment on performance of three hydrodynamic three-way valves in microirrigation sand filter[J].Journal of Drainage and Irrigation Machinery Engineering,2017,35(7):596-601.(in Chinese with English abstract)
[8]张文正,翟国亮,邓忠,等.微灌砂滤料的表层过滤和气水反冲洗试验研究[J].灌溉排水学报,2013,30(1):86-90.Zhang Wenzheng,Zhai Guoliang,Deng Zhong,et al.Surface filtration and air-water backwashing for sandy filter media in micro-irrigation[J].Journal of Irrigation and Drainage,2013,30(1):86-90.(in Chinese with English abstract)
[9]张文正.微灌砂滤层气水反冲洗与过滤的试验研究[D].北京:中国农业科学院,2013.Zhang Wenzheng.Experiment Research of Air Water Backwashing and Filtration of Sand Layer in Micro-Irrigation[D].Beijing:Chinese Academy of Agricultural Sciences,2013.(in Chinese with English abstract)
[10]刘文娟.石英砂过滤器过滤及反冲洗特性的实验研究与数值模拟[D].北京:中国农业科学院,2014.Liu Wenjuan.Experimental Study and Numerical Simulation of Filtration and Backwashing Characteristics of Quartz Sand Filter[D].Beijing:Chinese Academy of Agricultural Sciences,2014.(in Chinese with English abstract)
[11]BovéJ,Puig-Bargues J,Arbat G,et al.Development of a new underdrain for improving the efficiency of microirrigation sand media filters[J].Agricultural Water Management,2017,179:296-305.
[12]BovéJ,Arbat G,Pujol T,et al.Reducing energy requirements for sand filtration in microirrigation:Improving the underdrain and packing[J].Biosystems Engineering,2015,140:67-78.
[13]李景海,翟国亮,黄修桥,等.微灌石英砂过滤器反冲洗数值模拟与流场分析[J].农业工程学报,2016,32(9):74-82.Li Jinghai,Zhai Guoliang,Huang Xiuqiao,et al.Numerical simulation and flow field analysis of backwashing of Quartz sand filter in micro irrigation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2016,32(9):74-82.(in Chinese with English abstract)
[14]李景海,蔡九茂,翟国亮,等.基于砂滤层内水体积分数瞬态模拟的反冲洗速度优选[J].农业工程学报,2018,34(2):83-89.Li Jinghai,Cai Jiumao,Zhai Guoliang,et al.Optimization of backwashing speed based on transient simulation of the volume fraction of water in the sand filter layer[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2018,34(2):83-89.(in Chinese with English abstract)
[15]李景海.微灌石英砂滤层清洁压降分形阻力模型与反冲洗数值模拟[D].北京:中国农业科学院,2016.Li Jinghai.Fractal Resistance Model of Clean Pressure Drop and Numerical Simulation of Backwashing Process of Quartz Sand Filter Layer in Micro-Irrigation[D].Beijing:Chinese Academy of Agricultural Sciences,2016.(in Chinese with English abstract).
[16]李景海,刘清霞,黄修桥,等.微灌石英砂滤层流态特性与分形阻力模型参数确定[J].农业工程学报,2015,31(13):113-119.Li Jinghai,Liu Qingxia,Huang Xiuqiao,et al.Flow state characteristics and fractal model parameters determination of quartz sand filter layer used in micro-irrigation[J].Transactions of the Chinese Society of Agricultural Engineering(Transactions of the CSAE),2015,31(13):113-119.(in Chinese with English abstract).
[17]李景海,刘清霞,黄修桥,等.微灌石英砂滤层清洁压降计算参数确定与分析[J].灌溉排水学报,2016,35(11):24-28.Li Jinghai,Liu Qingxia,Huang Xiuqiao,et al.Determination and analysis of the calculation parameters for the cleaning pressure drop of quartz sand filter layer used in micro-irrigation[J].Journal of Irrigation and Drainage,2016,35(11):24-28.(in Chinese with English abstract)
[18]贺靖峰.基于欧拉-欧拉模型的空气重介质流化床多相流体动力学的数值模拟[D].北京:中国矿业大学,2012.He Jingfeng.Numerical Simulation of Multiphase Fluid Dynamic in Air Dense Medium Fluidized Bed Based on Euler-Euler Model[D].Beijing:China University of Mining and Technology,2012.(in Chinese with English abstract)
[19]贺靖峰,赵跃民,何亚群,等.基于Euler-Euler模型的空气重介质流化床密度分布特性[J].煤炭学报,2013,38(7):1277-1282.He Jingfeng,Zhao Yuemin,He Yaqun,et al.Distribution characteristic of bed density in air dense medium fluidized bed based on the Euler-Euler model[J].Journal of Coal Science&Engineering,2013,38(7):1277-1282.(in Chinese with English abstract)
[20]He Jingfeng,He Yaqun,Zhao Yuemin,et al.Numerical simulation of the pulsing air separation field based on CFD[J].International Journal of Mining Science and Technology,2012,22(2):201-207.
[21]Ansys Inc.Ansys Fluent User’s Guide[M].Pittsburgh:AnsysInc,2011.
[22]Gidaspow D.Multiphase Flow and Fluidization:Continuum and Kinetic Theory Descriptions[M].California:Academic Press Inc,1994.
[23]Ogawa S,Umemura A,Oshima N.On the equation of fully fluidized granular materials[J].Journal of Applied Mathematics and Physic,1980,31(4):483-493.
[24]Ansys Inc.Ansys Fluent Theory Guide[M].Pittsburgh:AnsysInc,2011.
[25]Ding J,Gidaspow D.A bubbling fluidization model using kinetic theory of granular flow[J].Aiche Journal,1990,36(4):523-538.
[26]Gidaspow D.Hydrodynamics of fluidization and heat transfer supercomputer modeling[J].Applied Mechanics Reviews,1986,39(1):1-22.
[27]Llun C K K,Savage S B,Jeffrey D J,et al.Kinetic theory of granular flow:Inelastic particles in couette flow and slightly inelastic particles in a general flow field[J].Journal of Fluid Mechanics,1984,140(6):223-256.