河谷型城市风场及污染物扩散的CFD数值仿真
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摘要
为研究河谷型城市地形及其引起的风场和污染物扩散的复杂问题,利用CFD(计算流体力学)方法和复杂地形网格生成技术,建立河谷型城市风场及大气污染分布的数值仿真模型,实现CFD方法在复杂地形空气运动和污染物扩散方面的应用.分别使用LES(large eddy simulation)模型和mixture模型研究兰州市地面风场特征和污染物扩散形态,计算得到的污染物分布结果与实测结果分布一致.结果表明:复杂地形对空气运动的影响很大,如风速因山体屏障作用会呈现带状分布特征,山体后侧易出现弱风区域;同时,风场会密切影响污染物扩散,决定了污染物扩散形态,如幅散能够影响污染物扩散范围及污染水平.而给定西北风条件下,如地面以上10 m、风速为5 m/s、不受地形阻挡情况下,工业区污染物浓度被稀释10倍,约扩散2.2 km;山体阻挡会抑制污染物纵向扩散,表现在山体阻挡情况下污染物稀释100倍时的扩散长度约为相对平坦区域的1/3.此外,不同的入口风向会引起空气运动与山体相互作用发生变化,进而会使得地面风速、局部风场存在差异,造成污染物扩散及分布形态差异.研究显示,CFD方法可行,模型可靠,可以用来研究地形对风场和污染物扩散的影响.
To study the complex terrain of valley cities and its wind fields and pollutants diffusion,computational fluid dynamics( CFD)and complex terrain grid generation technique are used to establish the numerical simulation model,realizing application of CFD in complex terrain air movement and pollutants diffusion. To set up the boundary in CFD,the digital terrain of the study area was obtained by extracting altitudes using Google Earth elevation extraction software and then imported into Gambit software. In Gambit,the computational meshes over complex terrain were established using journal files written in program. In the CFD model,the turbulence was modelled by using the large eddy simulation( LES),and the pollutant dispersion patterns were described by the mixture multiphase model. The validity of the proposed approach was verified by the good agreement between the simulated distributions of air pollutant in Lanzhou City and monitoring results. The result showed that the complex terrain has a great impact on the wind field. For example,wind speed showed strip distribution characteristics due to the role of the blocking effect of mountains. The wind is weak at the back of the mountain. Meanwhile,the wind fields will determine the pollutants diffusion,as the divergence of the wind fields can affect the pollutant diffusion scope and pollution level. Under the given northwest wind conditions that air speed is 5 m/s above 10 m from the ground,the concentration of industrial air pollution on flat terrain is diluted about 10 times at the distance of 2. 2 km from the pollution center. With mountainblocking,the pollution diffusion distance at which pollution concentration diluted 100 times is about one third of that distance in the relatively flat area,indicating that mountain blocking can inhibit the longitudinal diffusion of pollutants. In addition,the different inlet wind directions would change the interaction between the wind and the mountain,which will change the ground wind speed and local wind fields,resulting in the variations of the pollutant diffusion and distributions. Studies have shown that CFD method is feasible to study the influence of terrain on wind fields and pollutants diffusion.
To study the complex terrain of valley cities and its wind fields and pollutants diffusion,computational fluid dynamics( CFD)and complex terrain grid generation technique are used to establish the numerical simulation model,realizing application of CFD in complex terrain air movement and pollutants diffusion. To set up the boundary in CFD,the digital terrain of the study area was obtained by extracting altitudes using Google Earth elevation extraction software and then imported into Gambit software. In Gambit,the computational meshes over complex terrain were established using journal files written in program. In the CFD model,the turbulence was modelled by using the large eddy simulation( LES),and the pollutant dispersion patterns were described by the mixture multiphase model. The validity of the proposed approach was verified by the good agreement between the simulated distributions of air pollutant in Lanzhou City and monitoring results. The result showed that the complex terrain has a great impact on the wind field. For example,wind speed showed strip distribution characteristics due to the role of the blocking effect of mountains. The wind is weak at the back of the mountain. Meanwhile,the wind fields will determine the pollutants diffusion,as the divergence of the wind fields can affect the pollutant diffusion scope and pollution level. Under the given northwest wind conditions that air speed is 5 m/s above 10 m from the ground,the concentration of industrial air pollution on flat terrain is diluted about 10 times at the distance of 2. 2 km from the pollution center. With mountainblocking,the pollution diffusion distance at which pollution concentration diluted 100 times is about one third of that distance in the relatively flat area,indicating that mountain blocking can inhibit the longitudinal diffusion of pollutants. In addition,the different inlet wind directions would change the interaction between the wind and the mountain,which will change the ground wind speed and local wind fields,resulting in the variations of the pollutant diffusion and distributions. Studies have shown that CFD method is feasible to study the influence of terrain on wind fields and pollutants diffusion.
引文
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[21]LU Bona,WANG Wei,LI Jinghai.Searching for a meshindependent sub-grid model for CFD simulation of gas-solid riser flows[J].Chemical Engineering Science,2009,64(15):3437-3447.
[22]崔桂香,张兆顺,许春晓,等.城市大气环境的大涡模拟研究进展[J].力学进展,2013,43(3):295-328.CUI Guixiang,ZHANG Zhaoshun,XU Chunxiao,et al.Research advances in large eddy simulation of urban atmospheric environment[J].Advances in Mechanics,2013,43(3):295-328.
[23]彭杰纲,傅新,陈鹰.旋进旋涡流量计旋涡进动效应的数值模拟研究[J].中国机械工程,2005,16(5):402-406.PENG Jiegang,FU Xin,CHEN Ying.Numerical simulation study on vortex precession in swirlmeter[J].China Mechanical Engineering,2005,16(5):402-406.
[24]YOSHIZAWA A,TSUBOKURA M,KOBAYASHI T,et al.Modeling of the dynamic subgrid-scale viscosity in large eddy simulation[J].Physics of Fluids,1996,8(8):2254-2256.
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[26]HUGHES T J R,MAZZEI L,OBERAI A A,et al.The multiscale formulation of large eddy simulation:decay of homogeneous isotropic turbulence[J].Physics of Fluids,2001,13(2):505-512.
[27]ABDI D S,BITSUAMLAK G T.Wind flow simulations on idealized and real complex terrain using various turbulence models[J].Advances in Engineering Software,2014,75:30-41.
[28]ZHAO Suping,YU Ye,YIN Daiying,et al.Meteorological dependence of particle number concentrations in an urban area of complex terrain,northwestern China[J].Atmospheric Research,2015,164:304-317.
[29]ZHAO Shuyu,TIE Xuexi,CAO Junji,et al.Impacts of mountains on black carbon aerosol under different synoptic meteorology conditions in the Guanzhong region,China[J].Atmospheric Research,2015,164:286-296.
[30]刘敏,孙杰,杨宏青,等.湖北省不同地形条件下风随高度变化研究[J].气象,2010,36(4):63-67.LIU Min,SUN Jie,YANG Hongqing,et al.The study on wind speed change with height under different terrain conditions in Hubei Province[J].Meteorological Monthly,2010,36(4):63-67.
[31]李江林,陈玉春,吕世华,等.利用RAMS模式对山谷城市冬季局地风场的数值模拟[J].高原气象,2009,28(6):1250-1259.LI Jianglin,CHEN Yuchun,LV Shihua,et al.Numerical simulation of local circulation in valley city in winter using RAMS model[J].Plateau Meteorology,2009,28(6):1250-1259.
[32]NYLEN T H,FOUNTAIN A G,DORAN P T.Climatology of katabatic winds in the Mc Murdo dry valleys,southern Victoria Land,Antarctica[J].Journal of Geophysical Research:Atmospheres,2004,109(D3):323-350.
[33]LETZEL M O,HELMKE C,NG E,et al.LES case study on pedestrian level ventilation in two neighbourhoods in Hong Kong[J].Meteorologische Zeitschrift,2012,21(6):575-589.
[34]ZHANG Jie,LONG Zhengwei,LIU Wei,et al.Strategy for studying ventilation performance in factories[J].Aerosol and Air Quality Research,2016,16(2):442-452.
[2]BRULFERT G,CHEMEL C,CHAXEL E,et al.Assessment of 2010air quality in two Alpine valleys from modelling:weather type and emission scenarios[J].Atmospheric Environment,2006,40(40):7893-7907.
[3]GREEN M C,CHOW J C,WATSON J G,et al.Effects of snow cover and atmospheric stability on winter PM2.5concentrations in western US valleys[J].Journal of Applied Meteorology and Climatology,2015,54(6):1191-1201.
[4]CARVALHO A C,CARVALHO A,GELPI I,et al.Influence of topography and land use on pollutants dispersion in the Atlantic coast of Iberian Peninsula[J].Atmospheric Environment,2006,40(21):3969-3982.
[5]RITTER M,MULLER M D,TSAI M Y,et al.Air pollution modeling over very complex terrain:an evaluation of WRF-Chem over Switzerland for two 1-year periods[J].Atmospheric Research,2013,132:209-222.
[6]LEE S M,PRINCEVAC M,MITSUTOMI S,et al.MM5 simulations for air quality modeling:an application to a coastal area with complex terrain[J].Atmospheric Environment,2009,43(2):447-457.
[7]DE MEIJ A,VINUESA J F.Impact of SRTM and Corine Land Cover data on meteorological parameters using WRF[J].Atmospheric Research,2014,143:351-370.
[8]GSELLA A,DE MEIJ A,KERSCHBAUMER A,et al.Evaluation of MM5,WRF and TRAMPER meteorology over the complex terrain of the Po Valley,Italy[J].Atmospheric Environment,2014,89:797-806.
[9]MEIJ A,GZELLA A,CUVELIER C,et al.The impact of MM5 and WRF meteorology over complex terrain on CHIMERE model calculations[J].Atmospheric Chemistry and Physics,2009,9(17):6611-6632.
[10]THAKER P,GOKHALE S.The impact of traffic-flow patterns on air quality in urban street canyons[J].Environmental Pollution,2016,208:161-169.
[11]张传福,曾建荣,文谋,等.高架桥对街道峡谷内大气颗粒物输运的影响[J].环境科学研究,2012,25(2):159-164.ZHANG Chuanfu,ZENG Jianrong,WEN Mou,et al.Influence of viaducts on dispersion of air particles in street canyons[J].Research of Environmental Sciences,2012,25(2):159-164.
[12]SILVA J,DA SILVA F M,COUTO A,et al.A method to correct the flow distortion of offshore wind data using CFD simulation and experimental wind tunnel tests[J].Journal of Wind Engineering and Industrial Aerodynamics,2015,140:87-94.
[13]SIMEES T,ESTANQUEIRO A.A new methodology for urban wind resource assessment[J].Renewable Energy,2016,89:598-605.
[14]李沁怡,蔡旭晖,康凌.建筑扰动条件下大气流动与扩散的CFD模拟[J].环境科学研究,2013,26(8):829-837.LI Qinyi,CAI Xuhui,KANG Ling.CFD simulations of flow and dispersion under construction disturbance conditions[J].Research of Environmental Sciences,2013,26(8):829-837.
[15]HACENE F B,ABBES M T,MERZOUK N K,et al.Development of a simulation model for a three-dimensional wind velocity field using Ténès Algeria as a case study[J].Renewable and Sustainable Energy Reviews,2012,16(1):29-36.
[16]LIU Benli,QU Jianjun,NIU Qinghe,et al.Computational fluid dynamics evaluation of the effect of different city designs on the wind environment of a downwind natural heritage site[J].Journal of Arid Land,2014,6(1):69-79.
[17]李磊,张立杰,张宁,等.FLUENT在复杂地形风场精细模拟中的应用研究[J].高原气象,2010,29(3):621-628.LI Lei,ZHANG Lijie,ZHANG Ning,et al.Application of FLUENT on the fine-scale simulation of the wind field over complex terrain[J].Plateau Meteorology,2010,29(3):621-628.
[18]程雪玲,胡非,曾庆存.复杂地形风场的精细数值模拟[J].气候与环境研究,2015,20(1):1-10.CHENG Xueling,HU Fei,ZENG Qingcun.Refined numerical simulation of complex terrain flow field[J].Climatic and Environmental Research,2015,20(1):1-10.
[19]马敏劲,郭世奇,王式功.近11年兰州空气污染特征及其边界层结构影响的分析[J].兰州大学学报(自然科学版),2012,48(6):69-73.MA Minjin,GUO Shiqi,WANG Shigong.Analysis of the characteristics of air pollution and its boundary layer structural effect in recent 11 years over Lanzhou[J].Journal of Lanzhou University(Natural Sciences),2012,48(6):69-73.
[20]DJAFFAR A A Y,GUIDO B,WAGDI G H,et al.Anisotropic mesh adaptation:towards user-independent,mesh-independent and solver-independent CFD.Part II:structured grids[J].International Journal for Numerical Methods in Fluids,2002,39(8):725-744.
[21]LU Bona,WANG Wei,LI Jinghai.Searching for a meshindependent sub-grid model for CFD simulation of gas-solid riser flows[J].Chemical Engineering Science,2009,64(15):3437-3447.
[22]崔桂香,张兆顺,许春晓,等.城市大气环境的大涡模拟研究进展[J].力学进展,2013,43(3):295-328.CUI Guixiang,ZHANG Zhaoshun,XU Chunxiao,et al.Research advances in large eddy simulation of urban atmospheric environment[J].Advances in Mechanics,2013,43(3):295-328.
[23]彭杰纲,傅新,陈鹰.旋进旋涡流量计旋涡进动效应的数值模拟研究[J].中国机械工程,2005,16(5):402-406.PENG Jiegang,FU Xin,CHEN Ying.Numerical simulation study on vortex precession in swirlmeter[J].China Mechanical Engineering,2005,16(5):402-406.
[24]YOSHIZAWA A,TSUBOKURA M,KOBAYASHI T,et al.Modeling of the dynamic subgrid-scale viscosity in large eddy simulation[J].Physics of Fluids,1996,8(8):2254-2256.
[25]HOLMEN J,HUGHES T J R,OBERAI A A,et al.Sensitivity of the scale partition for variational multiscale large-eddy simulation of channel flow[J].Physics of Fluids,2004,16(3):824-827.
[26]HUGHES T J R,MAZZEI L,OBERAI A A,et al.The multiscale formulation of large eddy simulation:decay of homogeneous isotropic turbulence[J].Physics of Fluids,2001,13(2):505-512.
[27]ABDI D S,BITSUAMLAK G T.Wind flow simulations on idealized and real complex terrain using various turbulence models[J].Advances in Engineering Software,2014,75:30-41.
[28]ZHAO Suping,YU Ye,YIN Daiying,et al.Meteorological dependence of particle number concentrations in an urban area of complex terrain,northwestern China[J].Atmospheric Research,2015,164:304-317.
[29]ZHAO Shuyu,TIE Xuexi,CAO Junji,et al.Impacts of mountains on black carbon aerosol under different synoptic meteorology conditions in the Guanzhong region,China[J].Atmospheric Research,2015,164:286-296.
[30]刘敏,孙杰,杨宏青,等.湖北省不同地形条件下风随高度变化研究[J].气象,2010,36(4):63-67.LIU Min,SUN Jie,YANG Hongqing,et al.The study on wind speed change with height under different terrain conditions in Hubei Province[J].Meteorological Monthly,2010,36(4):63-67.
[31]李江林,陈玉春,吕世华,等.利用RAMS模式对山谷城市冬季局地风场的数值模拟[J].高原气象,2009,28(6):1250-1259.LI Jianglin,CHEN Yuchun,LV Shihua,et al.Numerical simulation of local circulation in valley city in winter using RAMS model[J].Plateau Meteorology,2009,28(6):1250-1259.
[32]NYLEN T H,FOUNTAIN A G,DORAN P T.Climatology of katabatic winds in the Mc Murdo dry valleys,southern Victoria Land,Antarctica[J].Journal of Geophysical Research:Atmospheres,2004,109(D3):323-350.
[33]LETZEL M O,HELMKE C,NG E,et al.LES case study on pedestrian level ventilation in two neighbourhoods in Hong Kong[J].Meteorologische Zeitschrift,2012,21(6):575-589.
[34]ZHANG Jie,LONG Zhengwei,LIU Wei,et al.Strategy for studying ventilation performance in factories[J].Aerosol and Air Quality Research,2016,16(2):442-452.