Background The structural configuration of shelterbelt is crucial to the protective effect of shelterbelt. In the current research on the windbreak effect of farmland shelterbelt, field wind speed observations are mostly used, which is complicated and laborious to measure, and the differences in the windbreak effects of different configurations of shelterbelts are not studied enough. Based on the numerical simulation of the wind speed field of the shelterbelt, this study analyzed the windbreak effect of different configurations of shelterbelts and the distribution characteristics of the wind speed field around the shelterbelt.

Methods Four different configurations of shelterbelts (0.8H width shelterbelt, 0.2H width shelterbelt, the arbor-shrub mixed shelterbelt and shrub-free shelterbelt, H represents shelterbelt height) in the Ulan Buh Desert were used as study objects. The two-dimensional numerical simulation method was used to simulate the wind speed field around the shelterbelt, and verified with the wind speed measured in the field. The influence of different shelterbelt structures on the characteristics of the wind speed field around the shelterbelt, the horizontal wind speed at different heights, and the efficient protection distance of the shelterbelt was explored.

Results 1) When the airflow passed through four shelterbelts with different structures and configurations, different speed zones were produced around them, which were respectively the speed lifting zone above the shelterbelt, the weak wind zone behind the shelterbelt, the lower airflow acceleration zone, the reflux zone and the airflow recovery zone behind the shelterbelt. The airflow acceleration zone and the reflux zone were greatly affected by the structure of the shelterbelt.2) The impact on airflow under different shelterbelt widths mainly occured behind the shelterbelt.At a height of 0.1H near the ground, compared with the 0.2H width shelterbelt, the wind speed decreased by 90.8% within 1H behind the shelterbelt and the reflux intensity increased by 55.2% behind the shelterbelt for the 0.8H width shelterbelt, and the efficient protection distance was 17.8H and 15.5H for the two shelterbelts, respectively, which decreased by 2.3H compared with the efficientprotection distance for the 0.2H width shelterbelt. 3) At the height of 0.1H, the wind speed in the arbor-shrub mixed shelterbelt decreased to 0 within 0.7H after the shelterbelt, while the shrub-free shelterbelt showed a significant acceleration of airflow and reached the maximum wind speed at 1H after the shelterbelt, which was about 70.5% of the initial wind speed. Compared with the shrub-free shelterbelt, the wind speed decreased by 122.4% and the reflux intensity increased by 15.9% in the post-shelterbelt 1H range in the arbor-shrub mixed shelterbelt, and the efficient protection distance of the shelterbelt was 21.5H and 23.7H, respectively, which was reduced by 2.2H compared with the shrub-free shelterbelt.

Conclusions The wider shelterbelt and mixed shelterbelt of trees and shrubs can well improve the wind speed at the back edge of the shelterbelt and effectively suppress the acceleration of airflow near the ground, but also enhance the reflux behind the shelterbelt and shorten the efficient protection distance, so the shelterbelt configuration should be planned reasonably according to different locations.