某不稳定边界层单体建筑后方点源污染扩散的大涡模拟
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摘要
首先产生大涡模拟所需要的入流湍流条件,然后应用标准Smagorinsky模型对位于某不稳定边界层的单体建筑后方点源污染扩散问题进行了数值模拟。结果表明,在不稳定条件下,使用大涡模拟能够较好地预测单体建筑的绕流特性和污染物分布。单体建筑绕流的湍流场十分复杂,空气流经建筑后发生了分离,在建筑后方形成了再循环区域,使高浓度气体被输送到建筑背面附近。受周期性涡脱落现象的影响,污染气体被释放后逐渐向建筑两侧及下游扩散,形成了较宽的扩散区域。气体的高浓度和低浓度瞬时等值面表现出了不同的特征。
The flow around an isolated obstacle is complex because of the existence of vortex shedding phenomena. Additionally,the influence of buoyancy is crucial in a non-isothermal field.As a result the gas dispersion around the obstacle is affected.This study provides a CFD simulation view of turbulent flow field and its impact on gas dispersion behavior around an isolated building in an unstable boundary layer. Because of the importance of inflow turbulence for large eddy simulation( LES),firstly we introduced a precursor method to generate turbulent inflow data for LES in unstable condition,an entire wind tunnel experiment and all the roughness elements were reproduced using a buoyant solver in the pre-simulation domain. Then this method was validated by comparison with the wind tunnel experiment.Subsequently,the flow and gas dispersion around an isolated building in an unstable boundary layer were simulated using a standard Smagorinsky model. One of the purpose of this study is to validate the accuracy of LES in a non-isothermal field. The calculated turbulent flow data and gas distribution showed favorable agreement with the experimental data in unstable condition. The simulation revealed a complex turbulent flow field. A recirculation region was formed behind the building after the separation of the flow,and higher concentration of gas accumulated near the leeward surface of the building due to the reverse flow. Because of the influence of vortex shedding phenomena,a large portion of discharged gas was transported to the lateral direction and a large diffusion area was formed in horizontal direction. The instantaneous isosurfaces of high concentration and low concentration of gas showed different dispersion behavior. The vortex shedding phenomena can be clearly observed from the distributions of instantaneous isosurfaces of concentration. This study indicated that LES model is indeed a powerful tool for the prediction of complex unsteady flow and gas dispersion phenomena.
The flow around an isolated obstacle is complex because of the existence of vortex shedding phenomena. Additionally,the influence of buoyancy is crucial in a non-isothermal field.As a result the gas dispersion around the obstacle is affected.This study provides a CFD simulation view of turbulent flow field and its impact on gas dispersion behavior around an isolated building in an unstable boundary layer. Because of the importance of inflow turbulence for large eddy simulation( LES),firstly we introduced a precursor method to generate turbulent inflow data for LES in unstable condition,an entire wind tunnel experiment and all the roughness elements were reproduced using a buoyant solver in the pre-simulation domain. Then this method was validated by comparison with the wind tunnel experiment.Subsequently,the flow and gas dispersion around an isolated building in an unstable boundary layer were simulated using a standard Smagorinsky model. One of the purpose of this study is to validate the accuracy of LES in a non-isothermal field. The calculated turbulent flow data and gas distribution showed favorable agreement with the experimental data in unstable condition. The simulation revealed a complex turbulent flow field. A recirculation region was formed behind the building after the separation of the flow,and higher concentration of gas accumulated near the leeward surface of the building due to the reverse flow. Because of the influence of vortex shedding phenomena,a large portion of discharged gas was transported to the lateral direction and a large diffusion area was formed in horizontal direction. The instantaneous isosurfaces of high concentration and low concentration of gas showed different dispersion behavior. The vortex shedding phenomena can be clearly observed from the distributions of instantaneous isosurfaces of concentration. This study indicated that LES model is indeed a powerful tool for the prediction of complex unsteady flow and gas dispersion phenomena.
引文
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[3]TOMINAGA Y,STATHOPOULOS T.Numerical simulation of dispersion around an isolated cubic building:model evaluation of RANS and LES[J].Building and Environment,2010,45(10):2231-2239.
[4]CUI Guixiang(崔桂香),SHI Ruifeng(史瑞丰),WANG Zhishi(王志石),et al.Large eddy simulation of urban micro-atmospheric environment[J].Science China G:Physics,Mechanics&Astronomy(中国科学G辑:物理学、力学、天文学),2008,38(6):1-12.
[5]HUANG Xuechi(黄雪驰),MA Guiyang(马贵阳),YANG Qirui(杨奇睿),et al.Numerical simulation of unsteady leakage and diffusion of the gas pipeline[J].Journal of Safety and Environment(安全与环境学报),2017,17(1):183-188.
[6]ABE S,TAMURA T,NAKAYAMA H.LES on turbulence structures and gaseous dispersion behavior in convective boundary layer with the capping inversion[J].Journal of Wind Engineering,2008,33(4):131-148.
[7]YOSHIE R,TANAKA H,SHIRASAWA T.Technique for simultaneously measuring fluctuating velocity,temperature and concentration in non-isothermal flow[J].Journal of Environmental Engineering,2007,73:799-806.
[8]TOMINAGA Y,MOCHIDA A,MURAKAMI S,et al.Comparison of various revisedκ-εmodels and LES applied to flow around a highrise building model with 1:1:2 shape placed within the surface boundary layer[J].Journal of Wind Engineering and Industrial Aerodynamics,2008,96(4):389-411.
[9]SMAGORINSKY J.General circulation experiments with the primitive equations[J].Monthly Weather Review,1963,91(3):99-165.
[10]VAN DRIEST E R.On turbulent flow near a wall[J].Journal of the Aeronautical Science,1956,23(11):1007-1011.
[11]TOMINAGA Y,STATHOPOULOS T.Turbulent Schmidt numbers for CFD analysis with various types of flow field[J].Atmospheric Environment,2007,41(37):8091-8099.
[12]SHAH K B,FERZIGER J H.A fluid mechanicians view of wind engineering:large eddy simulation of flow past a cubic obstacle[J].Journal of Wind Engineering and Industrial Aerodynamics,1997,67/68:211-224.
[2]TAMURA T,NAKAYAMA H.LES analysis on turbulence and dispersion fields around a normal plate[J].Journal of Wind Engineering,2005,30(2):21-36.
[3]TOMINAGA Y,STATHOPOULOS T.Numerical simulation of dispersion around an isolated cubic building:model evaluation of RANS and LES[J].Building and Environment,2010,45(10):2231-2239.
[4]CUI Guixiang(崔桂香),SHI Ruifeng(史瑞丰),WANG Zhishi(王志石),et al.Large eddy simulation of urban micro-atmospheric environment[J].Science China G:Physics,Mechanics&Astronomy(中国科学G辑:物理学、力学、天文学),2008,38(6):1-12.
[5]HUANG Xuechi(黄雪驰),MA Guiyang(马贵阳),YANG Qirui(杨奇睿),et al.Numerical simulation of unsteady leakage and diffusion of the gas pipeline[J].Journal of Safety and Environment(安全与环境学报),2017,17(1):183-188.
[6]ABE S,TAMURA T,NAKAYAMA H.LES on turbulence structures and gaseous dispersion behavior in convective boundary layer with the capping inversion[J].Journal of Wind Engineering,2008,33(4):131-148.
[7]YOSHIE R,TANAKA H,SHIRASAWA T.Technique for simultaneously measuring fluctuating velocity,temperature and concentration in non-isothermal flow[J].Journal of Environmental Engineering,2007,73:799-806.
[8]TOMINAGA Y,MOCHIDA A,MURAKAMI S,et al.Comparison of various revisedκ-εmodels and LES applied to flow around a highrise building model with 1:1:2 shape placed within the surface boundary layer[J].Journal of Wind Engineering and Industrial Aerodynamics,2008,96(4):389-411.
[9]SMAGORINSKY J.General circulation experiments with the primitive equations[J].Monthly Weather Review,1963,91(3):99-165.
[10]VAN DRIEST E R.On turbulent flow near a wall[J].Journal of the Aeronautical Science,1956,23(11):1007-1011.
[11]TOMINAGA Y,STATHOPOULOS T.Turbulent Schmidt numbers for CFD analysis with various types of flow field[J].Atmospheric Environment,2007,41(37):8091-8099.
[12]SHAH K B,FERZIGER J H.A fluid mechanicians view of wind engineering:large eddy simulation of flow past a cubic obstacle[J].Journal of Wind Engineering and Industrial Aerodynamics,1997,67/68:211-224.