Abstract: Narrow belt and small net shelterbelts play an important role in arid land vegetation construction. The study of windbreak effect of narrow belt and small net shelterbelts is of great significance to the research of spatial allocation and structure optimization of shelterbelts. In this research, we selected two typical types of narrow belt and small net shelterbelts as research objects and conducted wind tunnel simulation experiments on six superimposed shelterbelt nets based on wind velocity flow field. The result showed that: after imposing narrow belt and small net shelterbelts, wind velocity presented a decreasing tendency with the increase of the number of superimposed shelterbelt nets, and also tended to become stable in the middle of the whole shelterbelts. Wind velocity became stable in the third net of the shelterbelts composed of only trees, and became stable in the second net of the shelterbelts composed of bushes and trees. Wind velocity of both types of shelterbelts expressed normal distribution characteristics, and presented right skewness and leptokurtic distributions when wind velocity was stable. Under wind velocity of 16 m·s^-1, distribution range of windbreak efficiency of superimposed shelterbelts composed of only trees (0-252 cm) was from 16% to 74%, and overall, played a good windbreak effect within 60% of efficiency; distribution range of windbreak efficiency of superimposed shelterbelts composed of bushes and trees (0-252 cm) was from 15% to 89%, and overall, played a good windbreak effect within 70% of efficiency. Under wind velocity of 16 m·s^-1, the range of windspeed acceleration rate of superimposed shelterbelts composed of only trees (0-42H, H=6 cm) was from 0.25 to 0.94, and the range of windspeed acceleration rate of superimposed shelterbelts composed of bushes and trees (0-42H, H=6 cm) was from 0.10 to 0.94. Based on the characteristic of windspeed acceleration rate distribution, vertical wind velocity was divided into four different areas. The result also showed that bushes had significant impact on the wind flow nearby surface layer and also played an important role in reducing wind speed under crown height.

Key words: wind velocity flow field, narrow belt and small net shelterbelt, superimposed shelterbelt, windbreak efficiency, wind tunnel simulation