飛砂移動機制之風洞試驗

Abstract

This study was to explore the mechanism of Aeolian sand wind erosion. By the wind tunnel experiment, we tried to find out the Aeolian sand characteristics including density, diameter, texture, water content, shape etc. and the relationships between wind erosion amount and primary specific site characteristics of sand diameter, wind speed and water content. The study sites located at the near coast area around Houlong, Yuanli, Da-an and Da-jia in the central part of Taiwan. The densities were in the range of 2.62 and 2.67 g/cm^3 and the particle size distribution mainly ranged in 0.25-0.42 mm. Since the sand content was over 96% of all the samples, the soil texture was recognized as sandy soil by USDA soil classification. The water contents of all the samples were less than 1%: the highest highest observation of 0.967% in Houlong and the lowest one of 0.282% in Da-jia. After the shape analysis, Da-an sample was identified as sphere, Da-jia as flat shape and the others were between. According to the results of wind tunnel, the starting wind speeds of erosion in different diameters were as follows: 5.5-7.0 m/s of 0.15-0.84 mm and 5.0 m/s of <0.15 mm. Furthermore, when the water content below 1.22%, we had the maximum amount of wind erosion. The further study showed Aeolian wind erosion amount would be decreased from 1.22% to 1.84% and the minimum amount was exhibited of 1.84%. This study not only to demonstrate the severe wind erosion in the area but also concluded and identified several important mechanism characteristics of Aeolian sand erosion. We hope the knowledge and the research method could help our government to the urgent preventive contingency process of Aeolian wind erosion.本試驗為瞭解砂粒之移動機制，因而利用風洞進行不同砂粒粒徑、風速及含水率之觀測，實驗用砂取自於後龍、苑裡、大安及大甲濱海地區。砂粒物性實驗結果：各樣區土壤之質地皆為砂土，其密度介於2.62~2.67g/立方公分之間；粒徑分布在0.25~0.42mm者最多；而土壤含水率皆在1%以下，其中後龍樣區0.967%最高，大甲樣區0.282%最低；再由形狀係數得知，大安樣區砂粒接近球形，而大甲樣區則較為扁平。至於風洞實驗結果：砂粒粒徑介於0.15~0.84mm時，其起始風速為5.5~7m/s，又粒徑在0.15mm以下之砂粒，其起始風速為5m/s；當砂粒含水率低於1.22%時，飛砂量達到最大值；含水率由1.24%遞增至1.84%時，飛砂量急遽遞減；而含水率達1.84%時，對砂粒起動之抑制作用達到最大值