Numerical Simulation For Effects Of Avenue Trees On Particulate Reduction Based On Growth Models

In this study,the biometric parameters?including tree height,branch height,crown width,leaf area index?and tree age of avenue trees are measured to establish the growth equation.Geometric models were established based on optimal growth equation of avenue trees,and effects of dynamic growth of avenue trees and normalized building height on PM₁₀concentration distribution in street canyons were investigated.A computational fluid dynamics?CFD?simulation was conducted with standard k-?and revised generalized drift models under three normalized building heights?H=9m,18m and 36m?and five common avenue tree species(Gingko biloba,Aesculus chinensis,Acer buergerianum Liriodendron chinense and Cedrus deodara in street canyons.Results demonstrated that:?1?In the urban street canyon,each parameter of avenue trees had a great correlation with the tree age,and its predicted value can be used to build a simulation model.Among the biological parameters of tree species,trees age was strongly correlated with height and crown diameter?R²?0.71?.The correlation between LAI and tree age was weak?R²?0.54?.The correlation between undershoot height and tree age was weak?R²?0.34?,but still increased gradually with tree age.Among the four regression equations selected,the logarithmic equation had a good fit in most cases.?2?At pedestrian level,the effects of avenue trees at different growth stage on the concentration and distribution of atmosphere PM₁₀ were significantly different.The decrease rate of the average PM₁₀ concentration varied greatly at different growth stages of avenue trees.The difference of removal ability between tree species increases with age increasing.As the tree age increased,the PM₁₀ concentration decreased significantly.With the increase of tree age,the vortexes gradually became weaker,and average reduction rate increased.When on a three-plate four-belt type.After the street trees reach adulthood,the absorbing capacity is ranked as G.biloba>L.chinense>A.chinensis>A.buergerianum?C.deodara.In the case of two-belt on a plate,the retention ability of street trees in adulthood is ranked according to the prediction equation:L.chinense>G.biloba>A.chinensis>C.deodara>A.buergerianum.?3?For pedestrian level,when H/W?0.9,the particle concentration increased with aspect ratio.When 0.9?H/W?1.8,the particle concentration decreased with the increase of the aspect ratio.Changes in the aspect ratio of buildings have different effects on the distribution of particulate matter for leeward streets and leeward streets.The concentration of windward streets increased with the increase of aspect ratio,while the concentration of leeward street increased first and then decreased.For vertical surface,concentration on the windward wall was greater than on the leeward wall.And as the aspect ratio increased,the vertical vortex gradually increased,and the vortex became larger.?4?In the three plate and four belt type,the vortex was larger than that in the one plate and two belt type,and the PM₁₀concentration was slightly higher than that in the one plate and two belt type.Under the condition of H/W=0.45,when the tree age was 5 years and 10years,the reduction ratio of the particulate concentration of the three-plate four-belt type was greater than that of the one-plate two-belt type,and when the tree grew to 30 years,one plate two belt type had a larger reduction ratio.Under the condition of H/W=0.90,the reduction ratio of PM₁₀ of the three-plate four-belt type was always greater than that of the one-plate two-belt type at three growth stages.?5?Tree height,crown diameter and crown volume in street canyon were primary influencing factors of PM₁₀ reduction ratio at the pedestrian level.The tree height and canopy volume of the avenue trees had the greatest impact on the PM₁₀ concentration reduction ration at pedestrian level?R²>0.84?.There was a strong correlation between the reduction rate of PM₁₀ concentration and tree height,crown width,LAI,and crown volume?R²>0.70?,but weak correlation with crown base height?R²=0.54?.The reduction ration increased with the height,crown base height and crown diameter of the tree.And it increased first and then decreased slightly,and gradually increased with the increase of LAI and crown volume.