Three Dimensional Structure Model Of Costal Metasequoia Glyptostroboides And Populus Euramevicana Shelterbelts And Numerical Simulation Of Wind Field

In oder to better describe the shelterbelt structure and improve the simulation of boundary layer flows as influenced by that shelterbelt,we established the three-dimensional structure model of costal Metasequoia glyptostroboides shelterbelts and Populus euramevicana with tree DBH,height and canopy radius according to standard tree method.Meanwhile,based on the three-dimensional structure model,we calculated the aerodynamic parameter of both shelterbelt and simulated the wind filed by the software-FLUENT.According the simulation result,we analyzed the difference of wind filed feature between M.glyptostroboides shelterbelts and P.euramevicana shelterbelts.We also simulated two structure control measure,density regulate and construction of multi storied shelterbelt.Based on simulation result,we discussed the impact of different structure control measure on sheltering effect so as to provide a basis for designing and management of costal shelterbelt.The result showed that:(1)To M.glyptostroboides shelterbelt,the vegetative surface area density of ranged from 0.0012 to 3.4857 m2·m-3,and the volume density ranged from 0.000002 to 0.012397 m3·m-3.To P.euramevicana shelterbelt,the vegetative surface area density of ranged from 0.0070 to 7.9337m2·m-3,and the volume density ranged from 0.000008 to 0.008028m3·m-3.Overall,the surface area and volume of P.euramevicana shelterbelt was greater than M.glyptostroboides.The structure was heterogeneous in space: the diameters of trunk was reduced with height,so its surface area and volume was decreased in both M.glyptostroboides and P.euramevicana shelterbelt.The height under branch of M.glyptostroboides and P.euramevicana shelterbelt was 4m and 6m respectively,which resulted in big gap under shelterbelt crown.At crown area,the branches surface area and volume was first increased and decreased later.The peak value of braches surface area and volume appeared at middle of crown in M.glyptostroboides shelterbelt,but appeared at upper-middle of crown in P.euramevicana shelterbelt.The peak value and distribution trends of leaves and branches surface area and volume in M.glyptostroboides was largely consistent.But to P.euramevicana shelterbelt,the peak of leaves surface area and volume appeared at top of the crown.The surface area and volume proportion of each component had big difference: the order of surface area proportion in M.glyptostroboides shelterbelts was leaves(78.39%)>branches(16.04%)>trunks(5.57%),and to the P.euramevicana shelterbelts,the order was leaves(84.76%)>branches(12.13%)>trunks(3.11 %);The order of volume proportion in M.glyptostroboides shelterbelts was trunks(75.28%)>(20.85%)>leaves(3.87%),and to the P.euramevicana shelterbelts,the order was trunks(67.81%)>(26.34%)>leaves(5.85%).The order of surface area to volume ratio in M.glyptostroboides shelterbelts was leaves(20.23)>(0.77)>trunks(0.07),to P.euramevicana shelterbelt,the order was leaves(14.49)>(0.46)>trunks(0.05).(2)By contrasting wind filed simulation result of M.glyptostroboides and P.euramevicana shelterbelt,we concluded that: the changing tendency of airflow before both shelterbelt was extremely similar.The airflow suffered slightly influence at 4H~6H before shelterbelt and its velocity began to decrease.Then the airflow velocity was sharply decreased when the airflow reached to 2H before shelterbelt.But behind the shelterbelt,the airflow velocity had much difference.There was big gap under the crown,so the airflow velocity drop was smaller than airflow at crown height.And because of the relative higher density of branches and leaves,the airflow at crown showed separation and sank to the height under branches.The airflow near the ground was squeezed,so the airflow velocity accelerated at small rang,but decreased later owing to diffusion of the squeezed airflow and finally recovered.The airflow velocity drop at the crown height(0.5H,0.7H)was relative higher.But because of the diffusion of the squeezed airflow near the ground,there was fierce momentum exchange between airflow at crown height and under the crown,which caused the velocity at crown height was first sharply increased in a small range and slowly recovered later.Compared the wind filed of M.glyptostroboides and P.euramevicana shelterbelt,because of the higher overall density in P.euramevicana shelterbelt,the velocity drop was greater in most region behind the P.euramevicana shelterbelt,and the effective sheltering distance of Poplars shelterbelt was 12 H lager than M.glyptostroboides shelterbelt.So the sheltering effect of P.euramevicana shelterbelt was much better.(3)The simulation result of different plant spacing for M.glyptostroboides and P.euramevicana shelterbelt showed that: The changes of airflow velocity before the shelterbelt was very tiny among different plant spacing.Behind shelterbelt,the changing tendency of airflow was very similar.The drop of the airflow velocity was increased as the plant spacing narrowing at all height.For the M.glyptostroboides shelterbelt of 3m×2m and 2m×2m,the effective sheltering distance improved 2H to 4H,and for P.euramevicana shelterbelt,the effective sheltering distance improved 4H to 7H.But the plant spacing should not be further narrowed.To the M.glyptostroboides shelterbelt of 2m×2m,the velocity near ground was very close to zero,there would appear backflow if the planting space was further narrowed.Compared the P.euramevicana shelterbelt of 3m×2m with 2m×2m,the backflow area behind shelterbelt was larger,which location was closer to ground.Because the backflow could lead to plant lodging,it was harmful to the crop growth.In summary,the M.glyptostroboides shelterbelt which plant spacing was 2m×2m had the best shelter effect.But to the P.euramevicana,the shelterbelt which planting space was 2m×2m had the better shelter effect when the protective target height was relative lower.But if the protective target height had a higher height,the planting space would better set to 3m×2m.(4)In this study,we simulated multi storied shelterbelt by setting different rows of shrubs.According the simulation result,we found that: because of existence of the shrub,the gap under the crown was become smaller,the drop of the airflow velocity near the ground was significantly improved.And the velocity acceleration was greatly relieved owing to the reduced sank airflow form crown height.At crown height,the drop of the airflow velocity was increased but the momentum exchange was decreased,so the speed recovery became smooth at the range from 0H to 5H.At far location behind the shelterbelt,the difference of the airflow velocity was gradually diminishing,so that there was little difference between the shelter effects.But on the top of the crown,the sheltering distance was decreased behind the shelterbelt which planted two rows of shrubs.In summary,planting shrubs under the shelterbelt could effectively improve the shelter effect near the ground,but has little impact on airflow at crown height and might have negative influence.