Three-dimensional Canopy Resistance Charactistics And Reserch On Outdoor Particulate Matter Capture

With global warming,desertification in some semi-arid regions is becoming increasingly apparent.The dust storms brought by the desert have had a tremendous impact on humans and the ecological environment.The shelterbelt can be used to alleviate sand and dust,and its dense canopy layer forms wind resistance and reduces windstorms.The canopy structure parameters and canopy resistance coefficient are important parameters to measure its wind-proof effect.Exploring the relationship between the two can provide theoretical guidance for further research on sand control.In addition,small particles as the main culprit affecting indoor air quality,seriously affecting the health of the human body.The unique structure and biological characteristics of the leaf surface of the canopy layer can adsorb fine particles.Therefore,it is particularly urgent to study the factors affecting the collection efficiency of the canopy and the dry deposition rate.In order to deeply analyze the functional relationship between the internal structural parameters of the canopy,the functional relationship between the internal structure of the canopy and the canopy resistance,the factors affecting the capture efficiency of the canopy and the dry deposition rate,The main research contents and conclusions of this paper are as follows:(1)The leaf characteristic length Df and the aspect ratio a/b of common plants on the campus(octagonal gold plate,mulberry tree,privet,wood hibiscus,paulownia)were measured by experiments,and the morphological structure differences of different plant leaves were characterized from quantitative angles.(2)Based on the study of the morphological and structural characteristics of common plant leaves,the four canopy structure parameters of plant filling rate,leaf area index,fractal dimension and optical porosity were further explored.The results show that the crown filling rate is proportional to the leaf area index,and is exponentially related to the branch dimension and optical porosity,and the expressions between the morphological parameters of the five experimental species are given.(3)Based on the analysis of the morphological and structural parameters of common plant canopies on campus,the effects of canopy structure parameters on canopy flow resistance were further explored by wind tunnel test.According to the test results,the multivariate regression method is used to obtain the expression of the relationship between the flow resistance of the canopy and the optical porosity and wind speed.(4)Using the Computational Fluid Dynamics Software(CFD)to simulate the three-dimensional canopy layer by the additional source term method(UDF),numerically calculate the wind speed distribution around the canopy and the distribution of particulate matter,and study the inflow wind speed and particle size on the plant.The effects of capture efficiency and dry deposition rate,and comparison with relevant literature data,provide a simple simulation method for numerical study of canopy capture of particulate matter.On this basis,the relationship between the structure layout of the multiple trees,the planting density and the efficiency of the forest to the particulate matter collection was studied.