Numerical Research Of The Characteristics Of Wind Field Near The Windbreaks

Windbreaks play an important role in the conservation of water and soil,wind prevention and sand control and soil erosion.Therefore,it is very important to investigate the characteristics of wind field near the windbreaks for both theory and practice.At present,the major of the research of the characteristics of wind field near the windbreaks was field observation and experiments,but a part of the studies was numerical simulation,which mainly focus on the two-dimensional simulation.This paper discussed the relationship between the drag coefficient and its influence factors based on the previous research achievements,and the accuracy of the relationship was verified.At the same time,the influence of gaps between trees,gaps between rows,leaf area index,rows and settlements on the windbreak effect were studied.The primary coverage in this dissertation are as follows:1.The control equation of the wind field in the vegetation canopy was introduced and the derivation process was given in detail.On the basic of the time-average turbulent control equations,it was derived to utilize the space-average theory for the study of the wind field in the vegetation canopy.At the same time,the solving method and the value of the parameters of the model were discussed.2.The drag coefficient was regarded as a constant in the previous studies about the wind field in the vegetation canopy.However,the leaf area density along the height of the vegetation is different so that the wind resistance ability is obviously diverse,and the corresponding drag coefficient will change.Therefore,the theoretical model of the wind field in vegetation canopy was used to simulate the effects of wind speed and leaf area density on the drag coefficient,and the drag coefficient as a function of the leaf area density Cd=f(A)was obtained by means of curvefitting.The wind speed and turbulence intensity of flow entering the spruce forest were calculated by using the function of drag coefficient,and the simulation outcome was compared with the field observation data to verify the accuracy of the function.3.The influence of gaps between trees,gaps between rows,leaf area index,rows and settlements,width of canopy on the windbreak effect were simulated.With the increase of leaf area index,the windbreak effect enhanced.The smaller the gaps between trees were,the better the windbreak effect was.The greater the gaps between rows,the stronger the windbreak effect of the corresponding position on the same height of the leeward of the second row.The windbreak effect of two-rows of staggering windbreak was the best,which compared with two-rows arranged in parallel windbreak and one-row windbreak.In addition,the windbreak effect of two-rows arranged in parallel windbreak was better than one-row windbreak.Width of canopy had a significant effect on wind resistance of windbreak.The greater the maximum width of canopy was,the better the effect of wind resistance was.