基于流体运动仿真的不同林冠形状抗风强度分析
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摘要
【目的】研究强风力扰动下不同林冠形状的森林内部风场分布情况,为防风林营造与种植过程中树种的选择提供理论依据。【方法】首先建立3种不同冠形林分模型(其中冠部为多孔介质模型),并根据冠形对应树种的消光系数确定多孔介质的孔隙率与叶面积指数(leaf area index, LAI)的关系;然后以k-ε湍流模型为基础,在动量方程中添加源项,建立三维树冠流计算模型,计算3种冠形在强风力下林分内部各处风速、风压与湍流动能强度。【结果】圆锥形林冠林内风速最小值(0.047 m/s)与圆台形林冠林内风速最小值(0.076 m/s)相差0.029 m/s。椭球形林冠林内风速最小值为0.940 m/s,且波动大于其他冠形。圆锥形林冠林内压差与湍流动能强度均最小,分别为30.22 Pa和0.17%。椭球形林冠林内压差最大,压差均值为62.14 Pa。圆台形林冠林内湍流强度最大,最大值为25.19%。【结论】结合湍流动能强度对树木抗风安全性的影响,以及风速的降低和压差减少作用,在构建防风林体系时,应选择与圆锥形林冠特点相似树冠的树种,使得防风林的抗风效果更强。
【Objective】 Studying the distribution of wind fields inside forests with different canopy shapes under strong wind disturbance can provide a theoretical basis for the selection of tree species in windbreak forest construction and planting.【Method】 First, we established three different forest models with different canopy shapes, in which the canopy structure was simulated using porous media. The relationship between the porosity of the medium and the leaf area index(LAI) was determined from the extinction coefficient of the corresponding tree species. Then, based on the k-ε equation turbulence model, we added source terms into the momentum equation to calculate wind velocity, pressure, and turbulent energy intensity of different canopy shapes under strong wind loads. 【Result】The difference between the minimum wind speed in the conical canopy forest(0.047 m/s) and the minimum wind speed in the truncated-conical canopy forest(0.076 m/s) was 0.029 m/s. The minimum wind speed in the ellipsoidal canopy was 0.940 m/s, and the fluctuation was greater than for other crowns. The conical canopy forest had the lowest difference in pressure(30.22 Pa) and turbulent kinetic energy(0.17%). The pressure difference in the ellipsoidal canopy forest was the largest(mean: 62.14 Pa). Turbulence intensity in the truncated-conical canopy forest was the largest, with a maximum of 25.19%.【Conclusion】The method proposed in this paper solved the problem that wind factors such as turbulent kinetic energy intensity and differential pressure at real time cannot obtain due to the complexity of the tree canopy. Because of the influence of turbulent energy intensity on the wind-resistant safety of trees and the reduction of wind speed and pressure difference, crowns with characteristics similar to the conical canopy should be selected when constructing a wind-proof forest system.
【Objective】 Studying the distribution of wind fields inside forests with different canopy shapes under strong wind disturbance can provide a theoretical basis for the selection of tree species in windbreak forest construction and planting.【Method】 First, we established three different forest models with different canopy shapes, in which the canopy structure was simulated using porous media. The relationship between the porosity of the medium and the leaf area index(LAI) was determined from the extinction coefficient of the corresponding tree species. Then, based on the k-ε equation turbulence model, we added source terms into the momentum equation to calculate wind velocity, pressure, and turbulent energy intensity of different canopy shapes under strong wind loads. 【Result】The difference between the minimum wind speed in the conical canopy forest(0.047 m/s) and the minimum wind speed in the truncated-conical canopy forest(0.076 m/s) was 0.029 m/s. The minimum wind speed in the ellipsoidal canopy was 0.940 m/s, and the fluctuation was greater than for other crowns. The conical canopy forest had the lowest difference in pressure(30.22 Pa) and turbulent kinetic energy(0.17%). The pressure difference in the ellipsoidal canopy forest was the largest(mean: 62.14 Pa). Turbulence intensity in the truncated-conical canopy forest was the largest, with a maximum of 25.19%.【Conclusion】The method proposed in this paper solved the problem that wind factors such as turbulent kinetic energy intensity and differential pressure at real time cannot obtain due to the complexity of the tree canopy. Because of the influence of turbulent energy intensity on the wind-resistant safety of trees and the reduction of wind speed and pressure difference, crowns with characteristics similar to the conical canopy should be selected when constructing a wind-proof forest system.
引文
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[16]PANFEROV O,SOGACHEV A.Influence of gap size on wind damage variables in a forest[J].Agricultural&Forest Meteorology,2008,148(11):1869-1881.
[17]KHAN Z,JOSHI J B.Comparison of k-ε,RSM and LES models for the prediction of flow pattern in jet loop reactor[J].Chemical Engineering Science,2015,127:323-333.DOI:10.1016/j.ces.2015.01.054.
[18]ANALYTIS G T.Implementation of the renormalization group(RNG)-turbulence model in GOTHIC/6.lb:solution methods and assessment[J].Annals of Nuclear Energy,2003,30(3):349-387.DOI:10.1016/S0306-4549(02)00061-0.
[19]徐进生,李登科,胡军然,等.障碍物对火焰结构影响的Realizable k-ε模型数值模拟[J].工业安全与环保,2014,40(4):40-42.DOI:10.3969/j.issn.1001-425X.2014.04.013.XU J S,LI D K,HU J R,et al.Realizable k-εmodel simulation on the structure of flame induced by an obstacle[J].Industrial Safety and Environmental Protection,2014,40(4):40-42.
[20]吴彤,倪绍祥,李云梅,等.由冠层孔隙度反演植被叶面积指数的算法比较[J].南京师大学报(自然科学版),2006,29(1):111-115.DOI:10.3969/j.issn.1001-4616.2006.01.026.WU T,NI S X,LI Y M,et al.A comparison on the algorithms for retrieval of LAI based on gap fraction of vegetation canopy[J].Journal of Nanjing Normal University(Natural Science Edition),2006,29(1):111-115.
[21]刘胜.黄土高原半干旱区人工林林分消光特性及辐射热量平衡研究[D].北京:北京林业大学,2006.LIU S.Study on extinction characteristics and heat balance of pantations in semi-arid region on Loess Plateau[D].Beijing:Beijing Forestry University,2016.
[22]杨春雨,冯锦东.小叶桉、木麻黄和橡胶树抗风能力比较研究[J].中国林业,2007(10):62.YANG C Y,FENG J D.Comparative study on wind resistance of Eucalyptus urophylla,casuarina and rubber tree[J].Forestry of China,2007(10):62.
[23]宋怡,安淇,皇甫苏婧,等.唐家岭防风林详细调查及改造[J].现代园艺,2015(14):25-26.DOI:10.14051/j.cnki.xdyy.2015.14.014.SONG Y,AN Q,HUANGFU S J,et al.Primary report of injecting with pine wilt disease immunity activator[J].Xiandai Horticulture,2015(14):25-26.
[24]周继磊.胶东沙质海岸防护林树种抗风评价及选择[D].青岛:山东农业大学,2010.ZHOU J L.Wind-resistant evaluation and selection of tree species in sandy coastal protection forest of eastern Shandaong[D].Qingdao:Shandong Agriculture University,2010.
[2]杨春雨.台风影响下的防风林和作物种植策略[J].防护林科技,2009(1):63-64.DOI:10.13601/j.issn.1005-5215.2009.01.026.YANG C Y.Windbreak and crop planting strategies under the influence of typhoon[J].Protection Forest Science and Technology,2009(1):63-64.
[3]AHRENDS A,HOLLINGSWORTH P M,ZIEGLER A D,et al.Current trends of rubber plantation expansion may threaten biodiversity and livelihoods[J].Global Environmental Change,2015,34:48-58.DOI:10.1016/j.gloenvcha.2015.06.002.
[4]罗冠勇,宋希强,杨冬华,等.海南10种园林乔木生物学特性与抗风性关联性分析[J].热带作物学报,2013,34(2):263-267.DOI:10.3969/j.issn.1000-2561.2013.02.012.LUO G Y,SONG X Q,YANG D H,et al.Correlation analysis on the relationship between the biological characteristic of ten ornamental tree species and the wind-resistance ability in Hainan island[J].Chinese Journal of Tropical Crops,2013,34(2):263-267.
[5]IWATA T,KIMURA A,MOCHIDA A,et al.Optimization of tree canopy model for CFD prediction of wind environment at pedestrian level[C]//National Symposium on Wind Engineering.Japan Association for Wind Engineering,2005.
[6]NORRIS B K,MULLARNEY J C,BRYAN K R,et al.The effect of pneumatophore density on turbulence:a field study in a sonneratia dominated mangrove forest,Vietnam[J].Continental Shelf Research,2017,147:36-45.DOI:10.1016/j.csr.2017.06.002.
[7]关德新,朱廷曜.树冠结构参数及附近风场特征的风洞模拟研究[J].应用生态学报,2000,11(2):202-204.DOI:10.13287/j.1001-9332.2000.0053.GUAN D X,ZHU T Y.Wind tunnel experiment on canopy structural parameters of isolated tree and wind velocity field characters nearby[J].Chinese Journal of Applied Ecology,2000,11(2):202-204.
[8]MOCHIDA A,TABATA Y,IWATA T,et al.Examining tree canopy models for CFD prediction of wind environment at pedestrian level[J].Journal of Wind Engineering&Industrial Aerodynamics,2008,96(10):1667-1677.DOI:10.1016/j.jweia.2008.02.055.
[9]VICKERS D,THOMAS C K.Some aspects of the turbulence kinetic energy and fluxes above and beneath a tall open pine forest canopy[J].Agricultural&Forest Meteorology,2013,181(21):143-151.DOI:10.1016/j.agrformet.2013.07.014.
[10]HIRAOKA H,OHASHI M.A(k-ε)turbulence closure model for plant canopy flows[J].Journal of Wind Engineering&Industrial Aerodynamics,2008,96(10/11):2139-2149.DOI:10.1016/j.jweia.2008.02.018.
[11]DIAS-J U'NIOR C Q,SL D A,FILHO E P M,et al.Turbulence regimes in the stable boundary layer above and within the Amazon forest[J].Agricultural&Forest Meteorology,2017,233:122-132.DOI:10.1016/j.agrformet.2016.11.001.
[12]DESMOND C J,WATSON S J,HANCOCKP E.Modelling the wind energy resources in complex terrain and atmospheres:numerical simulation and wind tunnel investigation of non-neutral forest canopy flows[J].Journal of Wind Engineering&Industrial Aerodynamics,2017,166:48-60.DOI:10.1016/j.jweia.2017.03.014.
[13]毛泽魁.多孔介质森林模型中流场分布特征的研究[D].兰州:兰州大学,2016.MAO Z K.Research of the characteristics of flow field in a porous medium forest mode[D].Lanzhou:Lanzhou University,2016.
[14]杨会,付海明.树冠流动阻力特性数值模拟与实验研究[J].中南大学学报(自然科学版),2016,47(12):4292-4300.DOI:10.11817/j.issn.1672-7207.2016.12.043.YANG H,FU H M.Numerical simulation and experimental study of canopy flow resistance characteristics[J].Journal of Central South University(Science and Technology),2016,47(12):4292-4300.
[15]GUAN D,ZHANG Y,ZHU T.A wind-tunnel study of windbreak drag[J].Agricultural&Forest Meteorology,2003,118(1):75-84.DOI:10.1016/S0168-1923(03)00069-8.
[16]PANFEROV O,SOGACHEV A.Influence of gap size on wind damage variables in a forest[J].Agricultural&Forest Meteorology,2008,148(11):1869-1881.
[17]KHAN Z,JOSHI J B.Comparison of k-ε,RSM and LES models for the prediction of flow pattern in jet loop reactor[J].Chemical Engineering Science,2015,127:323-333.DOI:10.1016/j.ces.2015.01.054.
[18]ANALYTIS G T.Implementation of the renormalization group(RNG)-turbulence model in GOTHIC/6.lb:solution methods and assessment[J].Annals of Nuclear Energy,2003,30(3):349-387.DOI:10.1016/S0306-4549(02)00061-0.
[19]徐进生,李登科,胡军然,等.障碍物对火焰结构影响的Realizable k-ε模型数值模拟[J].工业安全与环保,2014,40(4):40-42.DOI:10.3969/j.issn.1001-425X.2014.04.013.XU J S,LI D K,HU J R,et al.Realizable k-εmodel simulation on the structure of flame induced by an obstacle[J].Industrial Safety and Environmental Protection,2014,40(4):40-42.
[20]吴彤,倪绍祥,李云梅,等.由冠层孔隙度反演植被叶面积指数的算法比较[J].南京师大学报(自然科学版),2006,29(1):111-115.DOI:10.3969/j.issn.1001-4616.2006.01.026.WU T,NI S X,LI Y M,et al.A comparison on the algorithms for retrieval of LAI based on gap fraction of vegetation canopy[J].Journal of Nanjing Normal University(Natural Science Edition),2006,29(1):111-115.
[21]刘胜.黄土高原半干旱区人工林林分消光特性及辐射热量平衡研究[D].北京:北京林业大学,2006.LIU S.Study on extinction characteristics and heat balance of pantations in semi-arid region on Loess Plateau[D].Beijing:Beijing Forestry University,2016.
[22]杨春雨,冯锦东.小叶桉、木麻黄和橡胶树抗风能力比较研究[J].中国林业,2007(10):62.YANG C Y,FENG J D.Comparative study on wind resistance of Eucalyptus urophylla,casuarina and rubber tree[J].Forestry of China,2007(10):62.
[23]宋怡,安淇,皇甫苏婧,等.唐家岭防风林详细调查及改造[J].现代园艺,2015(14):25-26.DOI:10.14051/j.cnki.xdyy.2015.14.014.SONG Y,AN Q,HUANGFU S J,et al.Primary report of injecting with pine wilt disease immunity activator[J].Xiandai Horticulture,2015(14):25-26.
[24]周继磊.胶东沙质海岸防护林树种抗风评价及选择[D].青岛:山东农业大学,2010.ZHOU J L.Wind-resistant evaluation and selection of tree species in sandy coastal protection forest of eastern Shandaong[D].Qingdao:Shandong Agriculture University,2010.