库布齐沙漠含水率对风沙运动影响的风洞模拟

Effects of Moisture Content on Sand Flow in Hobq Desert:A Wind Tunnel Simulation

采用室内分析和风洞模拟试验的方法,研究了不同风速下库布齐沙漠沙丘沙含水率对粗糙度、风速廓线和风沙流结构变化的影响。根据风洞实际动力情况,确定试验进口风速为6,8,10,12,14,16m/s;除干沙外,人工配制了含水率为0.25%,0.5%,1.0%,1.5%,2.0%,2.5%6组不同湿度的沙样,分别开展了风洞模拟试验。结果表明,地表粗糙度随着风速的增加而增大,但随湿度的增加整体呈减小趋势;试验所包含的湿度范围内,其风速廓线均随高度呈对数分布,随风速的增大,风速廓线的对数规律越好,风速梯度逐渐减小;湿度越大输沙率随风速增加的绝对量变小,但相对量有所增加;随着湿度的增加输沙率呈整体下降趋势;不同湿度输沙率都出现随高度增加而减少的趋势,当湿度达到2.5%时,不管任何高度风蚀过程几乎停止;干沙输沙量80%集中于近地表5cm内,但随着湿度增加,5cm以上输沙率所占比重呈增加趋势,当湿度介于0.25%~1.5%时,地表5~8cm之间输沙量占总输沙率的30%以上。说明在地表含水率较高的库布齐沙漠,采用格状沙障等增加地表粗糙度的机械防沙措施能收到比西部沙漠和戈壁地区更为理想的效果,而且采用固沙措施的高度也应高于干沙地区。

In order to provide theoretical basis for scientific prevention and control of sand dune hazard,in this paper,lab analysis and wind tunnel simulation were used to study the effects of sand moisture content on surface roughness length,wind velocity profile and structure of drifting sand flux in the Hobq Desert.According to the real dynamics of wind tunnel,the inlet wind speeds were set to be 6,8,10,12,14,16m/s.In addition to dry sand,artificially mixed sand,of which the moisture content was 0.25%,0.5%,1%,1.5%,2%and 2.5%,was also used for the wind tunnel simulation experiment.The results showed that the surface roughness length increased with the increasing wind speed and overall showed a trend of decrease with the increasing moisture content.Wind velocity profile showed a logarithmic distribution with height.As the wind speed increased,the logarithmic rule of wind velocity profile became better,wind velocity gradient decreased.When the moisture content increased,the absolute sand transport rate with the increase of wind speed decreased,but the relative value increased.As a whole,sand transport rate decreased with increasing moisture content.Under all moisture conditions,sand transport rate decreased with increasing height;when the moisture content reached 2.5%,the wind erosion process almost stopped,regardless of the height.About 80% of dry sand transport occurred within the first 5cm near the surface,but when the moisture content increased,a higher proportion of sand transport occurred below 5cm;when the moisture content was between 0.25%and 1.5%,sand transport occurred in the 5cm to 8cm layer near the surface accounted for more than 30% of the total sand transport.Our results indicated that the mechanical sand prevention measures which can increase the surface roughness length should be used in Hobq Desert,and the height of the sand fixing measures should be higher than that in other deserts.