基于CFD的砂石覆盖对近地表风场的影响

为了抑制由风蚀引起的土地荒漠化进程及促进农牧业生产,对西北贫瘠土地采取砂石覆盖、植被覆盖、作物留茬等多种保护措施,能够明显改善近地表风场、有效减小风蚀、保持土壤水分和减缓土地退化.针对砂石覆盖模式,基于CFD方法对砂石粒径为2.0~12.0 mm、风速为5,13 m/s的砂石覆盖近地表风场进行三维稳态模拟,并进行了现场观测.研究结果表明:距地面同一高度下,砂石覆盖对近地表风速的削弱度随粒径增大而增大,当粒径超过10.0 mm后削弱度基本不变;削弱度增幅随粒径增大而减小;同一粒径下,削弱度随地面高度的增大而减小;对比5,13 m/s这2种风速条件下,削弱度对风速的变化不敏感.通过现场观测结果发现,模拟所得削弱度较实测所得削弱度精度达89%以上.研究可为干旱区生态农业发展提供理论依据.

Effects of gravel coverage on CFD-based near-surface wind field

Wind erosion is one of the main reasons for land desertification in Northwest China. To su-ppress the desertification progress and promote both agricultural and livestock production, many protective measures, such as gravel and vegetation coverage, crop stubble and so on, have been applied in barren lands in Northwest China. In consequence, the near-surface wind field was improved significantly and the wind erosion has been reduced effectively, and the soil moisture has been maintained, eventually the land degradation has been slowed down. In the paper, the three-dimensional, steady near-surface wind fields around a series of gravel coverage were simulated by CFD method for 2.0 mm-12.0 mm gravel size at 5 m/s and 13 m/s wind speeds, respectively; meanwhile, field observations were conducted. The results show that at the same height above the ground the degree of reduction of near-surface wind velocity rises with increasing gravel size until the size reaches 10.0 mm; once the size is beyond that value, the degree doesn't change with gravel size basically. The increment in degree of reduction of wind velocity increases with gravel size; moreover, at the same gravel size, the degree of reduction decreases with height apart from the ground. It was found out that the degree of reduction of wind velocity is insensitive to change in wind velocity by comparing the results at 5 m/s and 13 m/s wind speeds. The predicted degree of reduction of wind speed matches the field observation as good as more than 89%. This study can provide a theoretical basis for development of ecological agriculture in an arid area.